Waterproof membrane with marine plywood boat?

Epoxy has its place for sure, but it is toxic stuff. I have read about "poor man's fiberglass" but maybe there is another way which doesn't involve fiberglassing or canvas?

For example, has anyone tried something like this:

Loctite Purbond HB S 309 Polyurethane Glue (solvent free)
PURBOND HBS 309 Structural Grade Polyurethane Adhesive 800gm https://www.glueguru.co.nz/shop/BRANDS/LOCTITE/LOCTITE+PURBOND+HB+S+309+Polyurethane+Glue+800gm.html

with a non-toxic roofing waterproof membrane such as Neptune Coatings Wetsuit product:
Wetsuit ® Products - Neptune Coatings https://www.neptunecoatings.com/neptune-products/wetsuit-c-products

I appreciate this wouldn't protect at all against impacts e.g. with rocks but perhaps the skid design can help to reduce that risk for below and some form of protection for the sides such as fenders?

Other alternatives?

 

I don't know why you think epoxy is so toxic. However, you should first read the SDS on Purbond is category 4 (maximum) on acute toxicity and category 3 in Target organ systemic toxicant.

https://mk0vicashofi82akh3r8.kinstacdn.com/wp-content/uploads/2020/04/PURBOND-SDS.pdf

 

Oh, yes you are right.

Uncured epoxy on the skin gets absorbed into the skin and affects organs such as kidneys and liver. The effects won't be noticed for a while though... Also, sanding uncured epoxy (takes two weeks to fully cure) must not be breathed in (sticks to insides of lungs). Perhaps there is an easier, non-toxic practical alternative for a small wood boat aka jon boat type?

 

Oil based paint, although there is still toxicity.

 

So it would seem, and as bad as epoxy.

The waterproof membrane I mentioned above which is designed for roofing applications I admit, is a bituminous rubber type product. In terms of toxicity it is far less toxic although I have yet to establish how it would fare with seawater. I do know it has been applied to plywood rooves:

https://www.neptunecoatings.com/res...cc-sds-ghs-clp-17-ws-wetsuit-2-part-v340/file

The search for a non-toxic glue that doesn't mind being used in a marine application and will keep bits of wood attached to each other is proving to be much harder. Ideas?

 

So, for epoxy, use gloves and long sleeves. And an N95 when sanding.

done

Every now n then I sand no mask and it usually makes me gag.

 

You don't need to waterproof plywood, it's waterproof by itself. Of course the ability of plywood to resit rott depends on the wood it's made of, so you want to use a naturally rott resistant species, like sipo. Plenty if boats were constructed out of ply without a drop of epoxy or fiberglass, and are still here over 50 years later. Yes better ply is more expensive, but that fact is balanced out by not needing to buy epoxy and glass. Paint or varnish is needed in both cases, epoxy is not UV stable, and bare wood will become gray. Less toxic paints and varnishes need more frequent renewing, that's the tradeoff.

Without epoxy you need to use another form of construction, with mechanical fasteners and some form of sealing for the joints, and you need much better joinery skills. While the bedding compounds/glues are still toxic, you don't normally need to sand them. After all, even plywood itself is toxic, the glue contains phenol formaldehyde and the wood itself can be toxic. That's why ppropriate PPE is mandatory in boat construction.

 

Problem is people become sensitive over time to epoxy not toxicity. So wear appropriate PPE to avoid getting sensitized. Lots of suggestions here: Epoxy Sensitivity http://www.fram.nl/workshop/controlled_vacuum_infusion/allergy.htm

Safest way to handle epoxy is vacuum infusion with foam core. No fumes and no sanding.