fairing compound

[rxcomposite]

I agree with Gonzo. Bondo is fine. I use it most the time. Others say it falls off. Only when it is applied as globs. I apply a thin coat first. and apply it with a firm pressure. Then add some more.

Bondo is basically polyester with micro balloons filler and BPO catalyst. I suspect it does not adhere well to epoxy based boats. I think that is the problem thats why others are not so sold with it.

On larger surfaces, bondo becomes relatively expensive. I switch to the basics. Mix resin, mix filler, long time to dry, lots of sanding. But still cheap.

If it is Epoxy boats I use west system, if polyester, i use polyester based resin or bondo.

[HWL]

Originally Posted by rxcomposite

When you coat gel coat (or resin) as an outer finishing surface it foes not cure as completely as it does when sprayed on the mold as an inner layer.

It cures somewhat but has that "tacky feel" that adheres to the sandpaper when you have to fine sand it. The trick is to add liquid wax solution to the gel coat in the range of 5 to 10%. Its available from resin suppliers.

Resin is hygroscopic, meaning it absorbs moisture in the air. The outer surface exposed to the air does not cure completely or rather takes several days to cure. Did you notice that tacky feel on the last layer everytime you laminate even though it has cured? The inner surface that is in contact with the mold cured completely because it was not in contact with the air.

Wax solution, suspended in the resin, floats to the surface as it cures and seals the resin from contact with the air. The result is a surface that is completely cured or tack free.

Try to experiment with it on a small panel to be comfortable with the effect. Try coating one panel with wax solution and the other without.

Just dont use it on the inner layers when laminating. You will get delamination on every ply.

I suspect Bondo has a wax solution. There is that waxy feel when it dries.

rxcomposite
thanks a bunch for the info. that is very interesting, i will try it

[daredevil69]

Couple things.
On the fairing compound, Upol makes a product called Fibral that works very well on polyester or vinylester repairs.
The wax can also be sprayed onto the repair after the gelcoat has been applied. I use pva (poly vinyl alchohol or mold release wax) in a cheap paint gun. It cleans up with water. After the repair cures use a spray bottle of water to clean the pva off.

[yokebutt]

3M Q-cell mixed with whatever resin system you're using, (maybe with some silica to keep it from sagging) sands quite easily.

Happy spooging,
Yokebutt.