# Dry or wet sand gel coat?



## rbyham (Dec 25, 2012)

I have a 1078 Bombay pilot.all gel coat is pretty dull. I have wet sanded previous boats followed by polish and wax but I saw a video recently where a dull gel coat was brought back by dry sanding. Guy used a random orbital with like 800. Being able to use a sander would be much easier than the hand sanding involved in wet sanding. So is dry acceptable? I'd love to hear voice of experience here...


----------



## SHNOOL (Jun 7, 2007)

On my Capri 22, I wet sanded, started with 400, went to 800, but it wasn't a real bad gelcoat... 

on my present boat (S2 7.9) I started with 300 dry sand, then did 600 wet, and it worked ok, with compound, polish, wax.

I still have some real issues with my gelcoat, but it's unrelated to this (prior repair to port side due to impact with gas station pumps).


----------



## RichH (Jul 10, 2000)

rbyham said:


> I have a 1078 Bombay pilot.all gel coat is pretty dull. I have wet sanded previous boats followed by polish and wax but I saw a video recently where a dull gel coat was brought back by dry sanding. Guy used a random orbital with like 800. Being able to use a sander would be much easier than the hand sanding involved in wet sanding. So is dry acceptable? I'd love to hear voice of experience here...


Dry sanding is possible; however, the paper will clog extremely fast requiring minute to minute change out. 
Probably why dry sanding clogs the paper so fast with paint and gel coat, etc. is because the 'dry' action causes strong electro-static (van der Waals) forces to build up at the molecular level and which firmly traps the particles 'between' the peaks of the grit. The smaller the grit the worse (stronger) the effect. 
For dry sanding you really need an 'open coat' paper (large empty spaces between the grit peaks) which isnt available finer than in about 100 - 200 grit. 
Buy LOTS and LOTS and LOTS of paper if you dry sand.

Wet sanding is preferred for the finer and extremely fine grits because when the water has a wee bit of detergent in it it takes a relatively long time to clog the paper - the grit usually wears out (comes loose and falls off) rather than becoming clogged.


----------



## SloopJonB (Jun 6, 2011)

I've never seen dry sanding used to bring out a finish in the car, furniture or boat world.

Bite the bullet and use wet paper - it's not that hard.


----------



## aloof (Dec 21, 2014)

Get weaker glasses. Go sailing. If the boat was built properly there will not be enough gelcoat to sand. Go lightly.


----------



## Skipper Jer (Aug 26, 2008)

Air driven sander then you can safely wet sand. Whats wrong with rubbing compound and a buffer?


----------



## sulli (Mar 9, 2013)

I rolled and tipped new gel coat on my Pearson 30, 4 coats.
I then dry sanded to get it smoother,with 180, then used wet sanding progressive grits up to 1800 in a 4" sq. electric block sander, looks almost new.
Just don't spray water on the sander and use a cheap one $21.99 at Harbor freight, no problem.


----------



## mike dryver (May 13, 2006)

Go to the archives Look for MaineSails Tutorial! If you can't find it here go to Cruisers forum. He gives you the whole process step by step!


----------



## Rhapsody-NS27 (Apr 8, 2012)

I did dry sanding a bit on my boat and it does clog up the paper. I did that because I didn't have a source of water near the boat while it's on the hard. For higher grits, I used a bucket of water and a spray bottle to keep things wet. That worked out really well. By now, likely need to do it again and then wax it this time.


----------



## RichH (Jul 10, 2000)

SloopJonB said:


> I've never seen dry sanding used to bring out a finish in the car, furniture or boat world.
> 
> Bite the bullet and use wet paper - it's not that hard.


The old fashioned way was to use 'just the grit' desired, and a very fine (either oil or water wetted) cloth was dipped into the grit (finely ground pumice, graded rotten-stone, etc.) to pick up the grit. This was the technique before modern sandpaper and can still be used to produce extremely flat and brilliant surface finishes - called hand rubbing. Such technique is still done on 'prime' musical instruments and very high value (museum grade) furniture, etc. 
In the old days, such was called '_finishing_' the coating, and the workers were called '_finishers_'. Ive seen it done in auto body shops that do '_concours d' elegance_' restoration work - and you can still buy the desired grits in _Maguires_ auto paint care products. 3M sells similar products for gel coated 'boats': _Finese-it™ and Perfect-it™_


----------



## SloopJonB (Jun 6, 2011)

That old fashioned way you refer to sounds like French polishing - it produces the finish on pianos.


----------



## deniseO30 (Nov 27, 2006)

There are air powered water sanding DA's available for the connoisseur of great and famous tools in most of us.... jus sayin...









Harbor fright sells a knock off


----------



## rbyham (Dec 25, 2012)

Thanks all... using a cheapo Harbor freight unit and spray bottle with water and dish soap sounds worth a try. Will update back here. I am assuming I have older thicker gelcoat but will be cautious...


----------



## PorFin (Sep 10, 2007)

Can it work? You bet.

I watched a neighbor's boat (A nice F-P catamaran) get some repair work done a few weeks ago, and I picked the worker's brain a bit.

His technique was to prep and spray the gelcoat and let it cure. After that, he put on guide coat (which is a dry, black graphite-looking powder that gets into and stays in the pin holes and low spots -- Google it). Used an electric 6" D-A orbital at low speed hooked up to a vacuum with 600 Abranet discs until the guide coat was gone. Repeated the process with 1000 grit. Followed that up with compound and polish.

The guide coat was the epiphany for me -- I'll give a shot myself when I do my cabin top next.


----------



## hellosailor (Apr 11, 2006)

Do as a bpdy shop does:
Wet sand, use pneumatic sander. For this kind of "once upon a time" use, I'd even say to buy a cheap compressor & sander from Horror Freight. Or you can rent the compressor at any rental or hardware store, for the weekend.

I would use 3M or other top-name paper though, never the cheap stuff. If you think 800 grit is nice, wait till you work up to 1000 and 1200 and 2000.(G)


----------



## miatapaul (Dec 15, 2006)

I would start no heavier than 800 grit wet sand. Even with 800 grit you may wind up going through the gel coat or making it transparent. If that happens the only way to fix woudl be to paint or re-coat.


----------



## SloopJonB (Jun 6, 2011)

You can't use air sanders on a small compressor - they are major air hogs. I have a Speedaire with 15 amp motor on a twenty gallon tank - too big to use on most boatyard circuits as it takes all 15 amps to start, even with dual capacitors.

A D/A will suck it dry in seconds. It won't even turn an air file on.

If you want to use air sanders in a boatyard you will either have to rent time on the yard compressor or have a truck mounted gas compressor.


----------



## RichH (Jul 10, 2000)

SloopJonB said:


> That old fashioned way you refer to sounds like French polishing - it produces the finish on pianos.


French polishing uses no 'grit'. Just shellac, alcohol, balls/pad of cotton fluff with a wee bit of oil, ...... the _finish_ is wiped, filled and burnished during 'constant' motion of the pad. Most brilliant gloss finish is produced this way, the development of iridescent glow (_chatoyancy_) of surface wood cells is absolutely unparalleled. 
The downside: easily destroyed by 'any' contact with water.

The closest one can come to french polishing for concours level interior work on a boat/airplane/firearm stocks, etc. etc. is 'hard' varnish, that is applied in thin layers, then flat sanded, then (bare) 'hand rubbed' with rotten stone, etc. to a dazzling gloss. I prefer using McCloskey's "Tung Seal", a mix of 'hard' varnish and tung oil, plus 'tinting dyes'.

https://en.wikipedia.org/wiki/French_polish


----------



## SloopJonB (Jun 6, 2011)

That's interesting - the furniture finisher who told me about French polishing was obviously talking about the other hand rubbed finish because she referred to rottenstone in a "bag" of cheesecloth


----------



## JimMcGee (Jun 23, 2005)

French polishing?????????????

Sheesh, c'mon guys it's a friggin' boat ! You don't see that shine when you're sailing.

Get a 6" random orbit polisher, a mix of pads, 3M compound, polish and wax and have at it.

Hell by the time I went over the hull twice with compound, then polish then wax I'd burned up _enough_ hours. Yeah there are some imperfections I could see on the hard, but you don't see them from the dock when the boat's in the water and you don't notice them from the dinghy. I've even gotten a couple of comments on how nice the boat looks this season.

Get the boat in the water, go sailing, crack a beer. There's such a thing as overkill.

:2 boat:


----------



## RobGallagher (Aug 22, 2001)

JimMcGee said:


> French polishing?????????????
> 
> Sheesh, c'mon guys it's a friggin' boat ! You don't see that shine when you're sailing.
> 
> ...


Some guys would rather french polish the dolphin then sail the pink canoe.

Sail on...


----------



## SloopJonB (Jun 6, 2011)

Don't youse guys recognize thread drift when you see it?

French polish a hull - yeah right.....well, there WAS that bright finished mahogany hull......


----------



## MarkSF (Feb 21, 2011)

Just been through this, restoring the gelcoat in the cockpit. My suggestion would be to skip the sanding altogether, and try the gelcoat compound with the more aggressive pad. You might find that it does an adequate job of removing the oxidisation on its own - that is what it is designed to do, after all.


----------



## newhaul (Feb 19, 2010)

I use 400 grit wet dipped in a bucket of water and to finish I use a Mr clean magic eraser. Melamine foam is approx equivalent to about 3 k grit buffing compound do it wet same as the sand paper then just wax and buff. Its what I do for all customer gel repairs. For large area gel restoration I start with oxalic acid bath then buff and wax.


----------

