Question about fairing compound . . .

Greetings,

I am nearing completion of my fiberglass extension bracket, which is fiberglass over
Coosa construction (see my thread on the subject if desired). I will need to do a layer of fairing compound to smooth out any irregularities before applying the gelcoat.

I see that most pre-mixed fairing compounds are epoxy-based. I'm concerned about epoxy vs. polyester gelcoat and the related adhesion problems that can happen with applying poly over epoxy.

I thought I would get some fairing filler and use some of my VE resin to make a fairing compound. I have also noticed that some firing compounds/fillers are not for use below the water line and some are.

Help me out in getting a better understanding of all this. Ideally, I'd like to have something VE-based that can be used below and above the waterline. What product(s) would be best.?

Thanks in advance.

 

Found something . . .

940 Vinylester Fairing Compound – LBI Fiberglass Products https://www.lbifiberglass.com/product/940-vinylester-fairing-compound/

I was just at LBI last week.

 

You really want to stir things up with controversial topics.

The short answer is, if you want to use gel coat stick with VE, if you know you want to use paint go with epoxy, but you can easily paint either one.

Any VE will work for this, but knowing which one sands easier or is stronger is a little tougher, but there are many options.

If you need a little strength you can use milled fibers in it, but they make the putty more difficult to work with, it won't smooth out as well when being applied.

Don't ever use epoxy with micro balloons in it if you want to bond VE or polyester to it, it doesn’t hold up well. Although just putting a layer of straight epoxy over it will solve the problem. But I still recommend not mixing and matching resin types because you need to do quite a few things right to get a good bond, and it still may fail below the waterline.

 

Thanks @ondarvr . . . Yes, it seems like I ask controversial questions . . . . sometimes.

 

You got the best contributor (sme) on the forum to reply. I have nothing to add.

 

Use a vinyl ester (VE) based fairing compound, either a commercial VE filler or a mix of your VE resin with suitable fillers rated for above and below the waterline. This ensures compatibility with your VE gelcoat and avoids adhesion problems.