Fiberglass prep

Kristian · Post by **Kristian** » Sun Dec 16, 2007 4:23 pm

As I prepare to apply fairing compound (west epoxy+407 filler) to our keel, I thought it would be a good time to ask the experts hereabout prep, specifically chemical cleaning of the surface.

I used to use acetone until someone pointed out that it takes the sanding scratches out of polyester, then I started using the 3m prep wash as thats what west recommends.

What do you use? I'm always on the lookout for something better, and definitely don't want to do this job ever again!

Rachel · Post by **Rachel** » Sun Dec 16, 2007 4:56 pm

Hmmm, I didn't know that about acetone (great, something else to worry about! <laugh>). Folks here use either acetone or denatured alcohol, or sometimes Solvent Wash 202. I'll be interested to hear the input on this one.

Rachel

Post by **Tim** » Mon Dec 17, 2007 7:39 am

Kristian wrote:I used to use acetone until someone pointed out that it takes the sanding scratches out of polyester...

No, not really, and certainly not in a wipe-down, general usage, cleaning capacity. But then a lot of people still think the tiniest bit of acetone will dissolve their whole boat, enter their bloodstream, and all sorts of horrible things; few products have more urban myths in the boating world, it seems. Acetone will immediately affect certain materials or surfaces, particularly enamels, bottom paint, and some other paints; it is a strong solvent after all. I'm not recommending ignoring the real hazards associated with acetone or other solvents, of course, but acetone, used properly, is a safe and effective solvent and wipe down material when used in an appropriately moderate manner.

I don't know what 3M Prep Wash is, but you can rarely go wrong using the product specifically recommended by the paint or epoxy manufacturer, of course.

I use acetone when I can because it's a very refined, clean solvent that evaporates quickly and cleans well. You can use just about any solvent for fiberglass surface prep, though: paint thinner, alcohol, what have you. Some solvents have more chance of leaving minor contaminants behind, particularly low grade paint thinner. Sometimes this matters more than others.