polyester resin for undercoat/end grain sealing

[pohukai]

Has anyone used this as an alternative to Henry's asphalt goop for sealing the underside and plywood end grain sealing?

This is a polyester resin so the fumes are pretty nasty, but not as expensive as an epoxy resin. It's not being use for structural strength but for encapsulation.

http://www.homedepot.com/h_d1/N-5yc1v/R-202077791/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=fiberglass+resin&storeId=10051

JimG

[Tom Kurth]

According to a canoe-building book or website (I no longer remember which particular one), polyester resin hardens to a surface with tiny pinholes in it due to the use of thinners. (That's why epoxy should never be thinned if it is to be waterproof, but the thinners are necessary to the chemical reaction that causes polyester to harden.) Because of the pinholes water can permiate the polyester coating causing delamination.

Best,
Tom

[Oldragbaggers]

According to a canoe-building book or website (I no longer remember which particular one), polyester resin hardens to a surface with tiny pinholes in it due to the use of thinners. (That's why epoxy should never be thinned if it is to be waterproof, but the thinners are necessary to the chemical reaction that causes polyester to harden.) Because of the pinholes water can permiate the polyester coating causing delamination.

Best,
Tom

I have a different perspective on this. What you say is true, but it must be taken in context.

Not too many years ago the fiberglass boatbuilding industry was using polyester resin in boat construction. I think we can all agree that the boats were (and MANY of them still are) sound, waterproof and still out there plying the waterways of the world. But, after years of these hulls sitting in water some did develop blisters due to the osmosis you are talking about. Faulty layup practices have been cited. There are many old polyester fiberglass hulls out there that have never developed blisters at all. And for the ones that did, we're talking about most of them being submerged 24/7/365 for years before this occurred.

I would not think that the water exposure of the underside of a teardrop will rise anywhere near to the level that it would take for water to migrate through the polyester resin. If it were me, and if that is what I had on hand, I would not hesitate to use it.

[PcHistorian]

some of the guys on other topics here are using a 50/50 thinner(mineral spirits/turpentine) and oil based polyurathane to coat wood with for sealing. The philosophy is that the thinner makes it more viscous and soaks in easier, then the poly hardens to seal it. maybe two coats for some, just to make sure. Now realize, you are not going for a poly fine, finish here, just to seal the wood. oh and before you lay it down and do your floor build. my skepticism has been with the edges of the plywood, so I am using a putty knife and caulk on the edges. But for the center area surface the 50/50 seems to be doing a good job. I'll have to test some pieces and let you know. :-)