# Is "light sanding" really needed for bottom paint?



## TakeFive (Oct 22, 2009)

Time for me to a ask a question that's been bugging me for the last year or so: Is "light sanding" really needed before applying new bottom paint?

_Breakin' Away_ is due for fresh bottom paint this year. I keep her in a DIY yard and will do the job myself before launching. Last year I bought her with a virtually paint-free (heavily sanded) bottom, and the yard put one coat of single season ablative on before launch. The finish is very smooth, with absolutely no loose spots that I can see. After a 14 hour trip to her winter storage (which looks to have sloughed off all the slime), the boat came out of the water almost perfectly clean. I didn't even bother to pressure wash like I normally do - I just scrubbed a slight scum line off last fall. There are some thin spots that definitely need new paint, so I plan to re-coat the whole bottom with a multi-season ablative (either Hydrocoat or Ultima SR-40/PCA Gold).

I've checked the compatibility chart for these paints, and they all say a light sand is all that's needed. I know from having done this job three times before on my prior boat that sanding is the most disgusting, toxic, dangerous part of the whole job. I have a pretty nice vacuum system that pulls 95% of the dust into a Shop-Vac, but it still really sucks.

I've read on a few sites that the main purpose of light sand is just to clean and identify any loose spots. With temps heading into the mid-60s this weekend, I am tempted to pull out my really nice pressure washer and use it to go over the bottom to remove any last traces of slime stain. In my experience, 3100 psi water does a pretty good job at exposing any loose spots.

Pressure washing is ergonomically superior to getting under the boat and sanding, and given that my bottom has no heavy accumulation of paint after having been stripped last year, it might be good enough.

Do any of you have comments from your own personal experiences?


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## Ajax_MD (Nov 24, 2009)

I say stick a dry wall sanding pad on the end of a pole and "scratch her belly." It takes 15 minutes and provides a surface with a bit of "tooth" for the fresh paint to adhere to.


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## Wes (Mar 27, 2016)

Not to sound snarky or whatever but what do the directions on the can of paint say to do? I'd be tempted to follow them...

I've never not sanded a bottom...


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## MarkofSeaLife (Nov 7, 2010)

I thought the light sand was to provide a mechanical bond for the new paint to attach to the old paint.


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## TakeFive (Oct 22, 2009)

Wes said:


> Not to sound snarky or whatever but what do the directions on the can of paint say to do?


As I said in my original message, it says light sand.



Wes said:


> I've never not sanded a bottom...


If you ever do, you'll know why I'm trying find alternatives ways to get a clean surface to adhere to. [Disregard - My response was wrong because I misread his message.]



MarkofSeaLife said:


> I thought the light sand was to provide a mechanical bond for the new paint to attach to the old paint.


That's one of several reasons that many people give, and perhaps the only reason that pressure washing does not address.

Here's the reason I'm skeptical of the mechanical bond argument: You sand and apply your first coat. 24-72 hours later everyone goes back and applies a second coat without sanding. Yet the second coat adheres just fine. So why wouldn't the first coat also adhere without sanding?

I can envision one other reason why sanding might be needed: Over time, orange peel may build up on the paint, and that texture could telegraph through subsequent coats and become even greater. This is especially a concern for those who want a racing finish, which is why racers often do roll-and-tip technique. In my case, the one coat is thin enough that I don't have significant orange peel, so this time around I don't need to sand it off. In fact, I think brushing the bottom in the water a couple times a season will also keep orange peel sufficiently low for cruisers.


Ajax_MD said:


> I say stick a dry wall sanding pad on the end of a pole and "scratch her belly." It takes 15 minutes and provides a surface with a bit of "tooth" for the fresh paint to adhere to.


Hmmm, food for thought. Perhaps my definition of light sand is a lot heavier than yours. I'll have to think about this, especially if it's only 15 minutes.


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## Ajax_MD (Nov 24, 2009)

Rick,

The 15 minute pad-on-a-pole job is all I did last April, and my bottom is in good shape. 
If your bottom is as good as you say it is, the quick job is all you'll need to do.

Buy the largest dry-wall pad you can find, and stick an aggressive sanding screen on it. You'll cover a lot area in a short period of time without breaking your back.


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## MarkofSeaLife (Nov 7, 2010)

ajax_md said:


> the 15 minute pad-on-a-pole job is all i did last april, and my bottom is in good shape.
> If your bottom is as good as you say it is, the quick job is all you'll need to do.


😂😂😂😂


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## Ajax_MD (Nov 24, 2009)

LOL...I know, too much idiom and innuendo.


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## Barquito (Dec 5, 2007)

You can put off scraping the built-up bottom paint for more years if you do a reasonable sanding each spring. Nothing more than a once-over with a gritty RA sander. Is a little bit of a back breaker, but, gets you in shape for sailing season!


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## Wes (Mar 27, 2016)

Maybe there's a compromise here...every other year, go at it with a DA to keep the build-up to a minimum and on the alternative years, do the drywall sanding pad technique.

I worked in yards for many a year and saw all kinds of stuff, but like I said, I have never NOT sanded a bottom.


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## TakeFive (Oct 22, 2009)

Wes said:


> Maybe there's a compromise here...every other year, go at it with a DA to keep the build-up to a minimum and on the alternative years, do the drywall sanding pad technique.
> 
> I worked in yards for many a year and saw all kinds of stuff, but like I said, I have never NOT sanded a bottom.


Oops, I misread your original message. Are you saying that you've never applied a second coat without sanding the first coat?

What is a DA?


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## Wes (Mar 27, 2016)

DA = dual action, similar to a random orbital sander. Sorry, wasn't clear, I've never just power washed and not sanded before applying the first coat. I've always adhered (pun intended) to the school of thought of providing "tooth" for the paint so it will adhere... Not sure whether it's recommended to "hot coat" the second coat (i.e. not sand between coats), that may depend on what paint you're using.

I DO agree, bottom sanding has a very low "fun quotient" but when you do it, where protection...I remember the years of grinding away in shorts and a t-shirt...ended up looking like a Blue Meany  Of course, we'd stop and take smoke breaks too...


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## TakeFive (Oct 22, 2009)

Wes said:


> DA = dual action, similar to a random orbital sander. Sorry, wasn't clear, I've never just power washed and not sanded before applying the first coat. I've always adhered (pun intended) to the school of thought of providing "tooth" for the paint so it will adhere... Not sure whether it's recommended to "hot coat" the second coat (i.e. not sand between coats), that may depend on what paint you're using.
> 
> I DO agree, bottom sanding has a very low "fun quotient" but when you do it, where protection...I remember the years of grinding away in shorts and a t-shirt...ended up looking like a Blue Meany  Of course, we'd stop and take smoke breaks too...


Whenever bottom sanding, I always wore full body tyvek with a hood, gloves, goggles, and dust respirator. Basically everything covered. When the vacuum system was working well I'd be able to gradually remove some stuff. At times when it wasn't working as well (filters blinding, etc), it would be a huge mess. I'm going to look into the pod/pole method in hopes that will get me further away from the nasty stuff.

I've spent my whole career formulating paints and inks, and I'm familiar with the term "hot coat." It generally applies to putting the next coat on before the previous one has cured. But the key word here is cure, so it only applies to enamels, epoxies, and 2K polyurethanes. If there is solvent present in the paint, you first allow it to flash off, but make sure to do your next coat before the curing is complete. The term "hot" refers to the fact that curing is an exothermic chemical reaction, as anyone who has ever mixed up too large a container of epoxy has witnessed. Hot coating is how you're supposed to do your 8 coats of barrier epoxy, or your 3 coats of polyurethane varnish.

But there's no such thing as hot coating bottom paint. Whether solvent- or water-based, it's a lacquer (not an enamel) which hardens by solvent drying with no curing. You have to let all the solvent/water flash off thoroughly before starting your next coat or severe orange peel will result when the partially dried paint is re-dissolved by the new paint. That's why the paint companies all tell you to allow at least 24 hours before the next coat. So for lacquers, it may make no difference whether the previous coat was done 24 hours or 24 months ago. In the special case of antifouling paints, the marine toxicant does oxidize over time, so if it's been several months you want to remove the top layer of paint first. For hard paints, this must be done by sanding. For ablatives, it can be done by sanding, but I believe it could also be done by pressure washing, which is why I started this topic.

Is there anyone here who sands the first coat of fresh paint before applying a second coat?


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## pdqaltair (Nov 14, 2008)

^^ The key question is what sort of dust mask:

* One of the white things with a pair of straps.
* A properly fitted (fit testing is required for industrial use) respirator with HEPA cartridges.

Dust masks are NOT OSHA approved for use with copper compounds.

---The tyvexs and hood are not the important thing.


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## MarkSF (Feb 21, 2011)

"Here's the reason I'm skeptical of the mechanical bond argument: You sand and apply your first coat. 24-72 hours later everyone goes back and applies a second coat without sanding. Yet the second coat adheres just fine. So why wouldn't the first coat also adhere without sanding?"

Because the first coat has not yet fully cured (it takes days, and maybe weeks), and by definition is the same type of paint as the second coat, so you get a chemical bond between them. The time window for re-coating that the paint manufacturer specifies is intended for just that purpose.


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## chef2sail (Nov 27, 2007)

Wes said:


> Maybe there's a compromise here...every other year, go at it with a DA to keep the build-up to a minimum and on the alternative years, do the drywall sanding pad technique.
> 
> I worked in yards for many a year and saw all kinds of stuff, but like I said, I have never NOT sanded a bottom.


Or buy a three year paint


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## DonScribner (Jan 9, 2011)

Use a ScotchBrite pad on a random orbit sander. It will do a heck of a job quickly. As far as the bottom paint goes, we've had good luck with HydroCoat hard ablative. It's a multiseason waterbased paint. Easy on, easy clean up, lasts for a couple of years.


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## chef2sail (Nov 27, 2007)

Nice thing about going the third year is that there is very little ablative left when hauled. Most barrier cost after power washing the last of the ablative off. 

I no longer do this project myself as like Take Five I found myself out of sorts for a few days after I prepped and painted now mater how much I had protected myself. 

To me paying someone to do that's money well spent. More than made up for the many other DYI projects we do.

We have always sanded before coat one.never had an issue by doing that. If that has worked well in the past why change the procedure and risk mucking it up. Unless of course you want to discuss all the permutations and possibilities. Chances are you will go back to the tried and proven way.

Tomorrow we are meeting one of our longest and youngest (lol) SN friends of many years for lunch with their beautiful young daughter. For us they are such a joy to be around and we are glad we met here. 

We are then going to wash our mainsail sail outside at home and hang it . Won't be long to sailing time now


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## Turnin Turtle (Jun 25, 2016)

There is no paint of any type that will adhere properly without appropriate surface prep.

Generally that means sanding off any loose paint, degreasing and often adding a primer.

Salt water bottom paint is designed for helping release barnacles and other stuff that will stick to your hull (especially for a boat kept in the water for months or years) and will have chemicals to make the hull less desirable to those growths. Its a relatively soft paint, so the paint will be more likely to scrape off with the barnacles rather than taking chunks of the hull.

Fail to sand and you are applying new paint on top of an old paint that is essentially designed to peel... That is pretty much asking for the new paint to fail.


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## TakeFive (Oct 22, 2009)

MarkSF said:


> Because the first coat has not yet fully cured (it takes days, and maybe weeks), and by definition is the same type of paint as the second coat, so you get a chemical bond between them. The time window for re-coating that the paint manufacturer specifies is intended for just that purpose.


As I posted before, bottom paint doesn't cure -- it's solvent evaporation only with no chemical reaction, aka lacquer. For this reason, time window on the can for recoat is a minumum only, no maximum. As further proof of no curing, take a brush that dried hard as a rock two years ago and put it in some thinner. You'll find that you can rejuvenate it just as if you had cleaned it without drying. You can't do that with curing paints, but you can do that with bottom paint or other lacquers.


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## sailingfool (Apr 17, 2000)

*Re: Is "light sanding" really needed for bottom paint?*

I use a multi season ablative Sea Hawk Cukote. My boat is power washed when hauled in October. The next spring I sand any leftover scum and damaged areas, and touch up any areas showing wear. Every other year I put a full coat on without any sanding, on the alternate years I just launch as is. The only risk when using a good ablative is putting too much paint on. Paint too thick will chip and flake, requiring that you remove the paint buildup and start over.


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## TakeFive (Oct 22, 2009)

pdqaltair said:


> ^^ The key question is what sort of dust mask:
> 
> * One of the white things with a pair of straps.
> * A properly fitted (fit testing is required for industrial use) respirator with HEPA cartridges.
> ...


It was not a cheapo felt four-pack like you get at Home Depot. Those are worthless. It was an industrial grade, NIOSH certified with HEPA filters for pigment dust protection, with soft rubber cushion all around nose and mouth to get a perfect seal. My former boss allowed employees to take PPE home from work to encourage safe practices at home, so that's where I got it. It was a paint/ink lab, so they were well equipped for this kind of stuff. I'll have to search for a replacement because I can't find it now, Home Depot only has junk, and I've moved on to a different company that's not as generous with PPE.

I've been fit tested before with the banana oil stuff, but that was for organic filters, not dust. I was not fit tested for personal use (OSHA rules don't apply strictly for DIY work), but I pre-tested by putting my palms over the filters and verifying positive seal. Obviously that does not guarantee that fine dust won't get through the filter media, but that becomes obvious if you end up with blue skin or blue snot under the mask. The nice thing about blue paint is that it serves as its own indicator. Last time, my mouth/nasal area were about the only things that didn't have blue on them.


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## TakeFive (Oct 22, 2009)

*Re: Is "light sanding" really needed for bottom paint?*



sailingfool said:


> I use a multi season ablative Sea Hawk Cukote. My boat is power washed when hauled in October. The next spring I sand any leftover scum and damaged areas, and touch up any areas showing wear. Every other year I put a full coat on without any sanding, on the alternate years I just launch as is. The only risk when using a good ablative is putting too much paint on. Paint too thick will chip and flake, requiring that you remove the paint buildup and start over.


Good points. My old boat had hard paint as a base, and PO had allowed it to build up too much, leading to chipping in places. I used ablative over it to prevent more buildup, but never got up the motivation to strip it all off. It worked OK.

My new boat is has a very even, thin coat, because PO had detailers strip the bottom essentially free of all paint. So there's just one coat of one-season ablative on there. I re-inspected this afternoon, and it's adhering very well, no chipping at all. Just needs freshening up. There's still paint everywhere, but some bare FG just barely starting to show through in certain areas. Based on your suggestion, I'm going to consider doing just one coat over top the current paint to freshen it up, then re-inspect next year and do a spot touch-up. I don't want to end up having too much paint leading to chipping like on my old boat.


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## pdqaltair (Nov 14, 2008)

TakeFive said:


> Whenever bottom sanding, I always wore full body tyvek with a hood, gloves, goggles, and dust respirator. Basically everything covered. When the vacuum system was working well I'd be able to gradually remove some stuff. At times when it wasn't working as well (filters blinding, etc), it would be a huge mess. I'm going to look into the pod/pole method in hopes that will get me further away from the nasty stuff.
> 
> I've spent my whole career formulating paints and inks, and I'm familiar with the term "hot coat." It generally applies to putting the next coat on before the previous one has cured. But the key word here is cure, so it only applies to enamels, epoxies, and 2K polyurethanes. If there is solvent present in the paint, you first allow it to flash off, but make sure to do your next coat before the curing is complete. The term "hot" refers to the fact that curing is an exothermic chemical reaction, as anyone who has ever mixed up too large a container of epoxy has witnessed. Hot coating is how you're supposed to do your 8 coats of barrier epoxy, or your 3 coats of polyurethane varnish.
> 
> ...





TakeFive said:


> It was not a cheapo felt four-pack like you get at Home Depot. Those are worthless. It was an industrial grade, NIOSH certified with HEPA filters for pigment dust protection, with soft rubber cushion all around nose and mouth to get a perfect seal. My former boss allowed employees to take PPE home from work to encourage safe practices at home, so that's where I got it. It was a paint/ink lab, so they were well equipped for this kind of stuff. I'll have to search for a replacement because I can't find it now, Home Depot only has junk, and I've moved on to a different company that's not as generous with PPE.
> 
> I've been fit tested before with the banana oil stuff, but that was for organic filters, not dust. I was not fit tested for personal use (OSHA rules don't apply strictly for DIY work), but I pre-tested by putting my palms over the filters and verifying positive seal. Obviously that does not guarantee that fine dust won't get through the filter media, but that becomes obvious if you end up with blue skin or blue snot under the mask. The nice thing about blue paint is that it serves as its own indicator. Last time, my mouth/nasal area were about the only things that didn't have blue on them.


Sounds good. There is only one fit test.

You can always shop at Grainger for better masks.

If you've got that much dust on your face you are doing something wrong with the sander. Check the dust hook up and the paper perfs. Maybe something is plugged.


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## TakeFive (Oct 22, 2009)

pdqaltair said:


> Sounds good. There is only one fit test.
> 
> You can always shop at Grainger for better masks.
> 
> If you've got that much dust on your face you are doing something wrong with the sander. Check the dust hook up and the paper perfs. Maybe something is plugged.


No, it wasn't the sander. As I mentioned in my prior post, the Shop-Vac's filter bag kept blinding, requiring me to open up the Shop-Vac and bang the dust off the bag with a stick. The puffs of dust from repeatedly opening the Shop-Vac were what got the dust all over me. It was the same filter bag that I had used in prior years (third one out of a pack of three), but both the paint and sandpaper were a little different. One of those two probably led to smaller dust particles which blinded the filter bag. I want to avoid that this time, hence my search for a different method.


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## chef2sail (Nov 27, 2007)

*Re: Is "light sanding" really needed for bottom paint?*



TakeFive said:


> Good points. My old boat had hard paint as a base, and PO had allowed it to build up too much, leading to chipping in places. I used ablative over it to prevent more buildup, but never got up the motivation to strip it all off. It worked OK.
> 
> My new boat is has a very even, thin coat, because PO had detailers strip the bottom essentially free of all paint. So there's just one coat of one-season ablative on there. I re-inspected this afternoon, and it's adhering very well, no chipping at all. Just needs freshening up. There's still paint everywhere, but some bare FG just barely starting to show through in certain areas. Based on your suggestion, I'm going to consider doing just one coat over top the current paint to freshen it up, then re-inspect next year and do a spot touch-up. I don't want to end up having too much paint leading to chipping like on my old boat.


If its down to the fiberglass it's a perfect time to strip all the paint off a put a barrier coat on to protect your fiberglass for years to come.


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## TakeFive (Oct 22, 2009)

I'm not going to make extra work that is unnecessary. My boat bottom does not have bare fiberglass anywhere - just tiny 1mm specks of white at the base of the orange peel texture in a few places. You can only see them if you look from a few inches away. They may have been there on day #1, since the yard only applied a single coat of paint. (This is one of the reasons they recommend two coats.) I would be tempted to just do touch-ups this year, except don't want to push it with a paint that was only designed for one season. The current coat of paint is adhering very well after the paint was stripped last year.

Hulls made with a properly designed vinylester layer don't blister, so barrier coat not needed. Some people apply barrier coat anyway, but most don't. Hauling out every winter, like I do, further reduces the risk of blisters. Aside from some flawed layups in the 1995-96 model years, I've never heard of a blister problem on a vinylester Catalina. Stripping the hull too many times runs the risk of penetrating the vinylester layup, so with a single coat that's fairly smooth, there's no pressing need to strip it again. I'll consider doing so if the paint buildup becomes too thick, uneven, or starts to chip. But not this year.


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## chef2sail (Nov 27, 2007)

TakeFive said:


> I'm not going to make extra work that is unnecessary. My boat bottom does not have bare fiberglass anywhere - just tiny 1mm specks of white at the base of the orange peel texture in a few places. You can only see them if you look from a few inches away. They may have been there on day #1, since the yard only applied a single coat of paint. (This is one of the reasons they recommend two coats.) I would be tempted to just do touch-ups this year, except don't want to push it with a paint that was only designed for one season. The current coat of paint is adhering very well after the paint was stripped last year.
> 
> Hulls made with a properly designed vinylester layer don't blister, so barrier coat not needed. Some people apply barrier coat anyway, but most don't. Hauling out every winter, like I do, further reduces the risk of blisters. Aside from some flawed layups in the 1995-96 model years, I've never heard of a blister problem on a vinylester Catalina. Stripping the hull too many times runs the risk of penetrating the vinylester layup, so with a single coat that's fairly smooth, there's no pressing need to strip it again. I'll consider doing so if the paint buildup becomes too thick, uneven, or starts to chip. But not this year.


Many people do have barrier coat. Not just because they had blisters,but to prevent them. Of course there were some years certain boats had issues inherent in the fiberglass that almost required it. Keeping the boat in the water at least 2 out of three years, sometimes three years in a row, it made sense to barrier coat Haleakula years ago as a prevtative / protective measure. C&C were not known to blister either. Actually many new boats are barrier coated. It's good preventative measure.

I guess it's a matter of preference , just like hauling every year is. It's why we do a little extra preventative stuff like barrier coating and 3 year bottom paint. That's why we coated...not because we were prevalent having blisters. We knew how we were going to use our boat and protected her accordingly.

It's a choice we all make. I don't like to paint every year...waste of time and money. I'd rather be sailing then gowning up every year to touch up paint.

Part of a successful program for us is also to have a diver wipe her down twice a year at $75 a shot. It's mostly for the Prop/ shaft as the Ultima 60 has proved itself a good defense.

For us we prefer not to see our boat picked out of the water , rolled up a hill, put in stands, with the added possibility of damaging her. . For me it is a MAJOR added expense to pay for winter storage when my slip fee covers year round usage. For me I'd rather have my boat transfer the wind energy into the water and roll, then sit in jackstands and vibrate . I like it supported by the water rather than 8 points of contact on the hull by a jack stand. For us It's much easier to work on her in the slip than climbing a ladder, which as I age is a big deal. There are no issues of taking batteries home when she stays in her slip. The small extra expense years ago of the barrier coat when we did it, is added peace of mind because of how we keep our boat in the winter. To us it's a waste of good money to have her lifted out every year. It also mean most years when the weather breaks we can just unwinterize, hook on the sails, and go sailing. We don't wait for a yard to get delayed dropping us in the water as they are backed up or I am blocked in by rows of boats because of bad weather. Every year we hear these stories about friends delayed getting in the water because the marina is behind in launching. One of the criteria in choosing keeping the boat where we do is the weather is not horrible in the winter and our marina provides us bubblers free of charge even though we own our own now. In our group of friends we are usually one of the first out sailing. Also the last to quit sailing on our own schedule not a marinas haul out edicts.

The money we can save year after year lets us take an extra sailing vacation chartering elsewhere or traveling somewhere else. More sailing equals a happy Captain and Admiral.


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## colemj (Jul 10, 2003)

Pressure washing now will accomplish little because any slime has hardened beyond being removed by a blast of water that wouldn't also remove paint and gelcoat. The time for pressure washing is when the boat is first lifted and still wet.

All I've ever done for painting (besides always aggressively pressure washing when first lifted) is a drywall sand pad on a stick using 80grit screens like previously mentioned. Use screens, not paper. The whole mask/suit smurf face thing mostly goes away since you are standing a long way away from the very little paint that is being removed. 15 minutes would be speedy indeed, but the whole thing shouldn't take more than an 1hr.

My understanding of light sanding is it is designed to remove any loose surface stuff (like a bit of dried slime, salt, grass clippings from the yard mower or ground splatter from rain) and provide a bit of tooth for the first coat.

My understanding of not needing to sand between coats (other than to be as smooth as possible) is that the solvents from the wet overcoat resolvate the surface layer of the dried undercoat, which ties the two layers together chemically.

Mark


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## Sailormon6 (May 9, 2002)

At my age I need to conserve my energy, so I simplify my spring boat prep. I stripped the bottom ten years ago, and have used a good quality ablative paint since then. At that time I strictly followed all the manufacturer's recommendations for application, to be sure the base coats were well bonded. I started with 3 coats of antifouling, with blue for the first indicator coat. Now, at end-of-season haul out, I have the bottom pressure washed. In the spring I hand wash the bottom to remove dirt accumulated during the winter, and let it dry thoroughly. I don't sand at all, unless there's a spot that especially needs it. Then I tape the waterline and apply one fresh coat for the season, or two coats if the blue indicator coat starts to show through. I have never had a problem with adhesion, and most of the one coat ablates during the season, so the coats of antifouling aren't accumulating, except near the waterline, and that can be wetsanded down fairly easily if it eventually becomes a concern. I don't think I'll ever need to strip it all again.


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## TakeFive (Oct 22, 2009)

colemj said:


> Pressure washing now will accomplish little because any slime has hardened beyond being removed by a blast of water that wouldn't also remove paint and gelcoat. The time for pressure washing is when the boat is first lifted and still wet...


As I've mentioned before, the 14 hour trip to winter storage appeared to have removed all slime except for a scum line which was easily scrubbed off. (Either that, or the cheap ProGuard paint is the best thing ever created.) I had my pressure washer with me at haulout, but it wasn't worth putting gas in it because the bottom was so clean. That's why I didn't pressure wash at the time.

My thoughts about pressure washing now are simply to remove any stale toxicants which have oxidized over the winter. Don't want those embedded under the layers of fresh paint, as they might create adhesion problems.


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## sailingfool (Apr 17, 2000)

*Re: Is "light sanding" really needed for bottom paint?*



chef2sail said:


> If its down to the fiberglass it's a perfect time to strip all the paint off a put a barrier coat on to protect your fiberglass for years to come.


I have to point out that if the hull of a 20-40 year old boat has not previously developed blisters, than a barrier coat is a complete waste of time. If you are changing the sailing venue, such as going into tropical water, that maybe a cause for caution and making the effort.


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## travlin-easy (Dec 24, 2010)

I only use the drywall screen for sanding the boat's bottom, and after the first coat was applied, a second was applied the following day without sanding - never had a problem doing this on many, many boats. The great thing about dryway screen is that you can dip it in water, no dust to worry about and it does a far better job than any sander I have ever used.

Good luck,

Gary


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## chef2sail (Nov 27, 2007)

*Re: Is "light sanding" really needed for bottom paint?*



sailingfool said:


> I have to point out that if the hull of a 20-40 year old boat has not previously developed blisters, than a barrier coat is a complete waste of time. If you are changing the sailing venue, such as going into tropical water, that maybe a cause for caution and making the effort.


I have to point out the barrier coat was done when the boat was only 15 years old. There were no issues then with blistering and I was determining not to have any in the future asi intended keeping Haleakala many more years and never wanted blisters to occur. Blister do not just occur because of the resins or new vinylester process , the can occur through water intrusion. This can take place also at points the fiberglass is pierced also.

At the point 18 years ago when Haleakula was barrier coated it was after a winter on the hard when we had the hull stripped down to the bare fiberglass and removed all the excess paint. It seemed like a good time to put the relatively simple process of putting the barrier coat on before we went to bottom paint her.

I have to disagree with you . An ounce of prevention here is worth more than the expense or aggregation that could potentially happen with blisters , so I don't agree with your advice for all.

Here is a technical article by the inventor of the process. I thought it interesting not to prove any ones points but to give a very thorough explaination.

The Real Story of Osmosis Blistering

To me it was not a waste of time at all for us to barrier coat a 15 year boat. We have complete confidence in it. To smugly say it wasn't necessary because it hadn't developed blisters at the 20 year mark or that no other boats of your brand had issues with it belies the fact the many boats develop blisters or problems the barrier coat coukd have prevented well after the 20 year mark.

It is likely a boat pampered by taking it out of the water and drying it out every year has much less chance of blisters, but our boat was not that type as we leave ours in extensively many years in a row. The barrier coat seems like cheap protection.

Many of our friends who use the boats extensively or live on them also gave their boats barrier coated even though there is no history of their boats brands or resins being subject to the pox. I look at it like the preventative protection we put on our sumbrella every year or the scotch guarding of our cushions. An ounce of prevention is worth a pound a cure as a wise man once said ( might even be Gary..lol)


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## Jeff_H (Feb 26, 2000)

There are three reasons to lightly sand ablative paint before repainting. The first is to remove contaminants and oxidzed bottom paint, the second is to create some tooth for the new paint, and the third is reduce paint thickness to avoid paint sickness. As much as sanding bottom paint is miserable it is in your future.

Jeff


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## TakeFive (Oct 22, 2009)

Dave, nobody is questioning whether it was a waste of effort for you to barrier coat your boat. I regret if my wording implied that. For any boat of Haleakala's vintage, barrier coat is a must. Blisters were bound to happen eventually on all polyester boats, because the chemistry allowed for water intrusion.

The introduction of vinyl esters was a step-change improvement in water barrier properties, and blisters are much less of a problem as long as the layup was done properly. Ironically, with the introduction of the vinyl ester resins, many boat builders upped their hull warranties, but specifically prohibited sanding, advising a sandless primer instead. Since sanding is an inherent part of the barrier coating process, buyers of post-1990 boats are faced with the irony of voiding their warranty and using 1970's technology to fix a problem that was largely fixed by 1990's technology anyway. As they say, "your boat your choice." But in your case, you made the correct choice for your boat.

Of course, my boat's warranty is expired, but the science behind the various chemistries is unchanged even after the warranty has expired.


sailingfool said:


> I have to point out that if the hull of a 20-40 year old boat has not previously developed blisters, than a barrier coat is a complete waste of time. If you are changing the sailing venue, such as going into tropical water, that maybe a cause for caution and making the effort.


This is great advice, especially about a significant change in sailing venue. I'd add a change to all-year storage in fresh water to your examples of high-risk venues, since the osmotic pressure difference is so much greater with fresh water outside the hull. I can easily see that high-risk areas might need a belt-and-suspenders approach.


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## davidpm (Oct 22, 2007)

I've used a drywall sponge sander block and water.

It works pretty good to feather things in a little if you have a few coats on.

It only takes a few minutes and you don't make a mess that can blow around and get you in trouble with the folks varnishing.


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## jerryrlitton (Oct 14, 2002)

Several people here swear that adding a couple of large handfuls of red or black pepper to your bottom paint will keep things like oysters and the like from attaching themselves to your boat by 80%. I am fixen to try this.


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## SHNOOL (Jun 7, 2007)

TakeFive, for the record, I use my RO sander, and throw a 220 grit on it, and give very little weight behind my sand... and I follow up with a hand rub behind my sanded spots for "smooth."

I'm using a hard racing bottom of course, but the premise is the same.

As for safety, all I used was a canister style mast rated for organic vapor, the 3m 5000 model. Given that I just did a light sand this time and not a removal, I hope it was enough. However, I will admit it was all I used when I did a complete bottom job with my Capri 25, and that was a total ablative removal, and new barrier coat, then 6 coats of VC17m.

Just did the bottom on my Wavelength 24, but it was already done in VC17m, and only needed bite for more paint. There was some hardened paint, and oxidized a bit, plus dried on gunk from last year. So 220 all around, then 3 coats of VC17m.
Before:








After sanding with 220.








After painting









By the way that last picture the VC17m was still drying and I still had another coat to do after that. I'll get final/final pictures when I get the boat outside.


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## Fstbttms (Feb 25, 2003)

jerryrlitton said:


> Several people here swear that adding a couple of large handfuls of red or black pepper to your bottom paint will keep things like oysters and the like from attaching themselves to your boat by 80%. I am fixen to try this.


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## bacinmass (Jan 31, 2009)

My new-to-me boat has a coat of ablative paint from last season in good condition. I'm considering the option of using the drywall screen sanding approach to lightly apply some "tooth" for the New of paint. What do you guys think of this tool to get that job done?

WEN
5 Amp Corded Variable Speed Drywall Sander with 15 ft. Hose
http://www.homedepot.com/catalog/productImages/1000/50/505b0679-f52b-40a8-8008-abc6ac9735c2_1000.jpg

I apologize in advance, I tried to copy/paste a photo, but it just wouldn't work.
Thanks for your thoughts!


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## Ajax_MD (Nov 24, 2009)

bacinmass said:


> My new-to-me boat has a coat of ablative paint from last season in good condition. I'm considering the option of using the drywall screen sanding approach to lightly apply some "tooth" for the New of paint. What do you guys think of this tool to get that job done?
> 
> WEN
> 5 Amp Corded Variable Speed Drywall Sander with 15 ft. Hose
> ...


Not all paints are compatible with each other.

If you know what the last coat of paint was, then investigate its compatibility with the new paint that you plan to apply. For example, Interlux provides a list of inter-compatible anti-fouling paints on their website.

If you're just painting with more of the same kind of paint and the bottom is in decent shape like you say, then yes, you can opt for the sanding screen and pole method.


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## Tanski (May 28, 2015)

My standard answer to this type of question regardless of the subject.
If YOU don't follow the instructions and it fails/breaks/doesn't work right, who are YOU going to blame?


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## Minnewaska (Feb 21, 2010)

I'm sure the surface is more contaminated than it appears, even after a power wash. Why would a paint manufacturer intentionally suggest their product is harder to apply than necessary? It would sell better, if they could say...... no sanding required.

At worst, with an ablative, I would wet scrub with a course scotchbrite pad. That would significantly cut down on the toxic dust. Although, your yard may not approve of the runoff.

I've found the paint manufacturers to be pretty good about answer questions over the years. I've inquired about compatibility and once had to trouble shoot a clear coating that wasn't taking properly.


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## JimMcGee (Jun 23, 2005)

I'm yet another fan of the sanding screen on a pole sander and dipping it in a 5 gallon bucket of water to prevent clogging.

After my bottom is pressure washed by the yard I can still see discoloration (surface contamination) along the waterline so I assume the manufacturer wants you to sand to remove any contaminants that could affect adhesion. 

Rick, just curious have you tried asking the question on Pettit's web site (assuming you're still looking at Hydrocoat)? It would be interesting to hear their response.

Jim


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## MastUndSchotbruch (Nov 26, 2010)

JimMcGee said:


> I'm yet another fan of the sanding screen on a pole sander and dipping it in a 5 gallon bucket of water to prevent clogging.
> 
> After my bottom is pressure washed by the yard I can still see discoloration (surface contamination) along the waterline so I assume the manufacturer wants you to sand to remove any contaminants that could affect adhesion.
> 
> ...


'My' marina offers (for a price) to 'doodle-bug' https://www.grainger.com/product/3U...3077!&ef_id=WKt2dQAABCuGl7fC:20170220230644:s the bottom right after power washing when they haul the boat in the fall. They claim that this corresponds to sanding with an 80grit. I have had them do this the last years and it seems to work well. And of course it means no work for me, and there is no problem with waste disposal since the run-off is all handled with the power wash water. (actually, a very impressive high-tech solution).


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