Thread: Thinning Poxy

The advice is to stop thinning it. It isn't going to go in any further and can only go in as far as the first ply anyway (but it won't). Second, by bunging all that thinners in the poxy, you are NOT making the ply waterproof. The thinners evaporates and leaves the epoxy porous ie, water gets through it.

If you are using the poxy as a sanding sealer, ie, not trying to put on a waterproof coat, you can get specially blended poxy's for the job that have the right thinners in the right ratio and you don't get the porous finish, but it's still not a proper waterproof layer and doesn't give the scratch protection that full strength poxy will.

Use unthickend and like Mik always says, wet on wet (lay the next layer on while the first is still tacky). Use a roller and it goes a loooonnnnngggg way (it amazed me, changed my earlier attitudes to the job I can tell you) and put on three layers - the first will have dry spots as the poxy soaks in, the second will probably be a good coverage by may still have dry spots, the third will seal the lot properly.

The alternative is not to use any poxy and paint with oil based enamels. These last well but, according to Mik (I haven't had a boat long enough to disagree), you'll be repainting more often and, as I can testify to, the enamels need touching up all the time.

Richard

Thanks Daddles

I'm only working off the instructions given in the plan set, the boat gaboon ply. It states to coat the outside of the hulls with two coats of thinned epoxy of a watery consistency. It also states the underside of the decks (which are 4mm gaboon ply) should be coated with two thinned coats of epoxy (leaving a bit between coats for the thinners to evaporate) before fitting. On the inside of the hulls before the hulls were pushed into the deck jig it states to apply a coat of thinned epoxy, and then before the fitting of frames etc.. a coat of undiluted epoxy.:confused: The two coats of watery consistency on the outside will be directly under a 2pak epoxy undercoat, followed by 2pak top coats.

Epoxy laminating resin can be thinned with metho and/or MEK solvent.

I've used this thinning system when sheathing plywood decks and cabintops on many ocassions. Only need about 10-15%, just takes a bit of the glugginess out of the resin and also helps stop the tackiness when using a roller, making matt/cloth easier to wet out.
Wouldn't recommend acetone, as stated in previous post, acetone vapourises too much and gives you a porous looking finish. If you use acetone to disolve the binder from CSMatt you may need to apply an additional fillercoat to fill any pin holes caused by vapourisation of acetone.

Cheers

Howdy,

If you thin epoxy with any evaporative thinner you end up with porous epoxy - water can get through the layers much like it can when using paint.

So you lose the main advantage of using epoxy in the first place - that water will find it hard to get in and add weight to the structure of the cat.

There is more detail on
http://members.ozemail.com.au/~store...ervative2.html

Of particular note is the graph of real life testing from WEST showing the different water absorbtion amounts for different coatings.

Certainly you don't want to add too much weight to a cat structure - so to thin epoxy a better solution is are the TPRDA (that's the name that Bote Cote use) type thinners that most of the epoxy producers make. Basically they don't evaporate from the epoxy matrix - so the porosity is not changed. But they do allow you to spread the epoxy out much further.

I wouldn't be too worried about it if you have gone through the process already catbuilder - it sounds like everyone else will be doing it too - but it is not best practice if the intention is to keep water out of the structure.

Best Regards
Michael