So many opinions...what paint?

Beautiful boat fluffflinger.

Can this Quantum 99 or other Polyurethane topcoats also be used in a mold with vacuum infusion? E.g. paint on the release agent then lay up fiberglass and foam and infuse? So your part comes out completely finished without the need for additional steps (except antifouling)

 

With epoxy laminate ?

 

Yeah epoxy.

 

ondarvr's opinion on that would be interesting, but I'd reckon there would be at least one snag with that idea.

 

not

Paint is very thin which would create lots of problems in the bag. Bumping or abrading the say 5 mi surface...

Why would you paint before fairing?

 

Hmm. Well with a sufficiently good mold I wouldn't need to fair afterwards either.

If I understand vacuum infusion correctly, first you wax the mold with release agent, spray gelcoat, then lay up fiberglass and foam and more fiberglass then bag it and infuse. Hull comes out faired like the hull is with no need for further treatment. Right? Or do you mean where you join parts of a hull together and need to repair the laminate and then paint?

So if the trend goes towards replacing gelcoat, can you do the same with the replacement?

How thick is gelcoat? Like 0.3 to 1.5mm? That's quite a bit of weight, but maybe it needs to be that thick in order to survive vacuum infusion or bagging.

 

Using paint as an in-mold coating would be a bit tricky.

Paints tend to have very low viscosities, and are affected by surface contamination a great deal. In a mold you’re trying to apply it over a wax or other type of mold release, so it will tend to fisheye.

Then you are looking for a product (epoxy) that is compatible and will bond great with the paint.

Thin paint may not stay in place on the mold while loading the glass and other rough handling.

People do use epoxy primer as an in-mold coating sometimes.

There are epoxy compatible polyester coatings that can be used in-mold like a gel coat, but they can be applied much thinner, saving weight.

 

Thanks! So the gelcoat is made relatively thick in order to work in a mold. I'm beginning to understand this better now.

Oh, I just realized that's why they are selling this "EP-Gelcoat" for. It's not UV stable but it replaces the gelcoat and protects the fiberglass from water. It's like a barrier coat.

So would a "polyurethane gelcoat" be a good way to go? Something like 0.3mm in the mold, then epoxy infusion. Assuming you can find "PU Gelcoat" and you can bond epoxy to the it, you get a UV protected part with a nice finish directly out of the mold.

Sorry for asking so many questions, I've read quite a number of guides and videos but there are so many applications, intricacies and evolution of the processes and materials it makes me want to study chemistry. Just trying to figure out if there is a way to build a boat that avoids the most amount of work. Especially sanding (I know, sacrilege).

 

You could keep spraying more coats of the PU finish till it looks like a heavy coverage, but I'm not sure how your bond would be, and if any outgassing from the PU as it cures could get locked in and cause problems, because it can't escape.

 

I guess you'd use a high-solids, low VOC polyurethane. From what I read polyurethane does bond to epoxy, so I would guess epoxy also stick to polyurethane since it's the stronger adhesive. At least when it's stick tacky / not fully cured.

I assume high-solids, low VOC also means that polyurethane can be a battier against water similar to how epoxy has no microscopic pores and prevents osmosis.

Searching for "polyurethane gelcoat mold" I didn't find any mention of using PU as a gelcoat.

Is polyurethane as a resin just too expensive to use as a gelcoat? Or is it just that no manufacturer made a special formulation for use in a mold?

 

You do detest sanding ! Can't say I blame you, you might be able to run some small scale tests to trial your options.

 

There have been some hybrid gel coats, the performance in the field was fabulous, but the cost and hassle factor was high. The down fall was the isocyanates, your average fiberglass shop is not set up to spray them

 

So an occupational safety matter ?

 

Yes

 

Inconceivable! A little cyanide never killed anybody!

I guess isocyanate the principal of the two components for foam or paint. This pdf actually explains the chemistry quite nicely. I wish I had paid more attention in school!