Gelcoat and Lacquer/Acetone

For some time I have seen remarks about problems with using lacquer thinner on Gelcoat. I have completed an unscientific test on an old Gelcoated wing tip. It has been soaking for weeks and there has been no degrading of the surface. I wonder if this is one of the old folklore stories.... Urban legend. RE Gaines,

Acetone is anathama to gelcoat. The DG website has a brief article on Gelcoat care and cautions to never, never use acetone (among other solvents) on your gelcoat covered glider. Schempp-Hirth recommends the same in the literature that accompanies their new gliders. Now that you've bathed the piece, put it out in the sun for a while next to a piece untouched by solvents, then watch what happens. From experience I can tell you that acetone will shorten the life of the gelcoat by half (at least).

When I'm not flying gliders, I'm responsible for providing educational and certification programs to gel coat manufacturers and composites molders.

Here are the technical facts: Aromatic solvents, such as acetone and lacquer thinner, or petroleum distillates, such as mineral spirits, have little or no affect on gel coat. In fact it is possible to store acetone in a gel coat lined vessel. There is absolutely no problem wiping down gel coat with either one. There is no documented association between wiping a cured gel coat with acetone and discoloration. (There is an issue with thinning liquid gel coat with acetone during application, that produces a known set of performance problems).

I think the glider pilot folklore comes from wiping lacquer-based paint stripes with either acetone or lacquer thinner. People see the 'paint' coming off and assume it could affect the gel coat in the same way.

In terms of solvents the only really bad actors with gel coat are methylene chloride, dibasic ester (DBE), and propylene carbonate (PC). Methylene chloride or DBE are the base products in most paint removers, and PC is an industrial solvent not readily available to the general public. Occasionally some of the tape residue removers use these solvents.

The composites industry in general routinely uses acetone for gel coat surface clean-up. I use acetone or lacquer thinner as needed on my glider.

Bob Lacovara - 2BT

<<<<Acetone is anathama to gelcoat. The DG website has a brief article on Gelcoat care and cautions to never, never use acetone (among other solvents) on your gelcoat covered glider. Schempp-Hirth recommends the same in the literature that accompanies their new gliders. Now that you've bathed the piece, put it out in the sun for a while next to a piece untouched by solvents, then watch what happens. From experience I can tell you that acetone will shorten the life of the gelcoat by half (at least).

Bob, thanks for your thoughtful and informed reply. I know an 'old hand' who uses kerosene to remove mylar seals and tape residue. It works well, as long as you are patient. I assume that kerosene falls into the petroleum distilates category and is also safe?

We have a mixed bag in DG's statement: They are correct that 'a further enemy of gel coat is chlorinated hydrocarbon cleaning solvents.' Earlier I referred to methylene chloride and being a no-no with gel coat. So is trichlor, but to a lesser extent.

However, the misinformation in the DG statement is including the ketone solvents, (i.e. acetone and MEK) in a true statement about chlorinated solvents. There are several possibilities to consider: 1) any solvent a manufacturer recommends *will* be abused by someone and they will complain that they damaged their finish; 2) they consider a solvent a solvent and are not technically discriminating the properties.

The areas you mention as being the first to show signs of failure are the areas that get some extra treatment at the factory's finishing shop. When this work is first carried out it blends well with the general gelcoat finish. However in time it shows discoloration or cracking long before other areas. The reason (I believe) is that the gelcoat is over catalysed and excess thinner is used to help speed up the process. Other areas include the top of the fuselage and the leading edge of the vertical stabiliser. I run a repair shop and see this type of failure quite often. I also see the same failure on old repairs (and some not so old repairs) where the gelcoat was mixed incorrectly. In the workshop we use acetone on a regular basis to clean adhesive residue and around areas to be repaired. No bad effects have ever been observed and some of the ships have been coming to us for many years.

Tom Gilbert

I stated that Schempp gives the same warning. I recieved a printed page with my delivery paperwork that recommended agains the use of acetone due to long term damage, and warned that petrol product could be used, but should be removed as quickly as possible.

I think I'll stick to my safe position and be wary of solvents in general... convenience should always be suspect. But I'll do some experimenting of my own. Bob, I want to simulate long term effects in a relatively short time; is it appropriate to take identical pieces of gelcoated fiberglass, expose them to sunlight for a prolonged period (months), wiping one down with acetone each morning while cleaning the other with a water-dampened cloth?

I want to simulate long term effects in a relatively short time;

The acetone will pull off wax, inclding any UV protector in the wax, while the water will not. Maybe rewax after each try? Just trying to get a good controlled experiment here!

I use the 3m adhesive remover for most uses covered here. Any comments from the experts about this product?

John Cochrane

Good post, Bob. So what should we be using to thin gel goat for spraying?

I've been told by an engineer at Simtec to use acetone because it was so volatile that it would evaporate after leaving the gun and probably before it hit the work. Also, what are the known performance problems?

Wondering in Placerville, JJ Sinclair

On another, but similar, front...

What about taking the yellowish old tape residue off of wood and fabric. Specifically at the wing root of a K-6? Any recommendations for getting this stuff off safely?

Ryan Wubben Chapel Hill, NC