Recoating the hull gell coat...

[wetass]

Thinning exclusively with acetone will promote a 'weaker' gelcoat ... and with acetone you need to 'stand back' further to allow better 'flash off' of the acetone .... or you get 'pin holes' if the acetone 'flashes off' IN the spray deposited gel. The further you need to stand back to allow the acetone to flash the more gel gets carried away by wind/air and the 'rougher' the sprayed surface will result. Not a major problem, just be aware.

What I have found is that acetone seems to thin it better - meaning it sprays easier and will have fewer runs, but Styrene definitely makes for a harder/durable and more shiny gelcoat - Can be good and bad I guess - I can only see the gelcoat repairs on my boat that I thinned with Styrene-only because they stay shiny longer then the rest of the hull. The areas I thinned with Acetone-Styrene mix blend in perfectly along with the rest of the hull as the season progresses. Blending the two seems to work - I get some of the benefits of Acetone not creating sags and almost the same shiny finish of the styrene.

 

[JohnS]

So, what are the arguments against recoating the whole hull in gelcoat? Is it more expensive than paint? I imagine to do the whole hull you would have to mix the catalyst in batches. I imagine you could do sections at a time as long as you're drawing from a large supply of gelcoat all mixed together to guarantee an even color.

 

[25yearslater]

There is much to be said both pro and con for either method. Gelcoat thinned with Duratec High Gloss Additive yields a sprayable mix that air cures to a hard glossy surface. It must be catalyzed at 2% to achieve proper cure so using MEKP-9 is a must. MEK is used to clean your equipment. The biggest problem with gelcoat is the post cure finishing. Don't even think about using power sanders to cut down the inevitable orange peel. Even open coat sandpapers will wear out quickly as most sanders are just too fast. Maine Sail's sponge and paper setup is the ticket. I have affixed a sponge to my sanding board and just finished the starboard side. 4 evenings work. This is the downside to gelcoat, it is labor intensive. If a thinner mix is desired Duratec thinner is the preferred thinner. I have just completed my Oday 27 sprayup and have experienced no problems. This mix can be thin coated but yields a translucent finish that will not hide repairs and other previous colors. The solution I used was to spray thinned gelcoat only, to hide, then apply the mixed gelcoat/Duratec to finish and cure. It is up to the individual as to how much work they are willing to perform as to the selection of finish. Good luck either way you go.

 

[JohnS]

Assuming that a well done sprayed on gel coat finish is almost as durable as the factory finish (bad assumption?), it seems to me the question becomes one of a lot of work now for a finish that, if maintained, won't have to be redone for a couple decades, versus a bit less work for a job that will need to be repeated in a couple years. Correct?

 

[RichH]

So, what are the arguments against recoating the whole hull in gelcoat? Is it more expensive than paint? I imagine to do the whole hull you would have to mix the catalyst in batches. I imagine you could do sections at a time as long as you're drawing from a large supply of gelcoat all mixed together to guarantee an even color.

The real problem is that generally marinas are not going to let you DIY spray gelcoat, especially for large areas because of the 'drift' of 'overspray' ... and all the EPA, etc. regulations and liability issues because the components are 'chemicals'.

Gelcoating an entire hull is quite expensive, and can be quite laborious ... but is better lasting and not as 'fragile' as 'paint' and most importantly does not 'lift' when the surface is subject to long term water immersion which is the downside of ALL topside 'paints'. With very close 'color matching' only the 'problem areas' need to be restored not the entire hull, no so with 'paint'. OEM gelcoat is usually quite thick and can usually be quite deeply sanded down to 'good' gelcoat. Even if you mistakenly sand into the matting layer, the gel is still easier to apply than 'painting an entire topsides'. Once you paint topsides, etc. you will be continuously painting the topsides, etc. forever more.
The downside of gelcoating is that it has a HIGH learning curve ... good gelcoating as well as spray painting is a finely developed 'art' but can be learned if you are 'fastidious' and not timid.

 

[Steve Dion]

Here is some additional information.

http://bertram31.com/proj/tips/re-gelcoating.htm

This does not take nito account anything to do with color matching which is the difficult part of this job.

 

[25yearslater]

Those are excellent points Rich. I am basically someone who should never be allowed to touch spray equipment. The only reason I could spray an entire boat was have it moved to my yard. The overspray can carry quite a distance as my truck was parked 75 feet away and has a lovely speckled finish. Glad it's a rolling wreck. Someone with a high dollar yacht or even their pride and joy might be a bit upset. Were I more adept at spraying the work of sanding would have been considerably less. Notice the orange peel in photo one and the after sanding in photo two. This took approximately 15 hours to achieve. I also had the benefit of considerable coaching by two expert bodyshop technicians and numerous discussions with the product manufacturers and distributors. The total cost will well exceed 1500.00 in materials only. Some overlooked items are a compressor with enough volume to operate an HVLP sprayer as well as the gun(s) along with the sandpaper both before and after. Tape alone and masking paper will run up to 100.00 for a boat this size. Gelcoating is a huge, expensive, labor and time consuming job. The end result is incomparable but, and here's the rub, know your limitations before you start. Also thanks Maine Sail your step by step is turning out pretty good although I am using the Aqua Buff.