Thinning polyester resin for penetration

On my current canoe tri project, which I finally started, I'm looking at using several types of wood, and both marine and non-marine plywood depending on the location. Particularly in the case of non-marine plywood, I would like to seal it with polyester resin, thinned for penetration. I'm currently doing a test of poly resin on several scrap pieces of pine lumber thinned with various percentages of acetone. Sytrene is often recommended, but is not easily found....... at least not here. Dilution rates I'm playing with range from about 10% up to 50/50. This has no structural function, however I will probably be using T88 to bond pieces together that are resin sealed in some places. In other places edges will be tabbed to the hull with glass and normal polyester resin.

I'd appreciate any first hand accounts. This is a "budget operation", or I would be working entirely with marine ply and epoxy.

H.W.

 

Polyester resin isn't very waterproof on wood and the amount of penetration (regardless of resin type) into the substrate, has little bearing on the effectiveness of the waterproofness of the coating. These are well established tests and acknowledgments that have been performed independently and by industrial peers over the last few decades. You can do some research or take your chances, but there's little (tested and documented) to counter what I've just posted.

 

Adding any type of solvent to polyester resin will degrade it, the more you add the worse it gets.

 

There are resins designed for this purpose, but they use a different polyester chemistry to provide the very low viscosity

 

You can buy epoxy paint that will do a much better job.

 

Is this due to an absence of translucent fillers, or something else ?

 

To a point yes, but the actual resin base is different also.

Infusion resin works much better than laminating resin

 

So ply could be coated with the polyester infusion resin, and then glassed with laminating resin, with the expectation of better adhesion ?

 

Yes, infusion resin has a Viscosity of about 100 cps

 

Interesting, and the two types of resin cohere well ? Is there any indication of how much extra adhesion to timber it has ? A difficult question to answer accurately, I suppose, and depends on the wood too.

 

it's better to use a polyurethane resin as a primer , it protects the woods somewhat from acids in the polyester resin and make it way more durable, and improves the adhesion. Ask your supplier for the correct PU resin.

 

These aren't two different types of resin, the resin base can be identical for hand lamination and infusion, so they are 100% compatible, and as far as that goes, 99.9% of all polyester and VE resins are completely compatible, the chemistry of each works well with the others.

The difference between infusion resin and hand lamination resin is the products used to increase the viscosity so it doesn't sag and drain out of the laminate. Silica is typically added to increase the viscosity, once its been added you can't overcome its effects by just adding more styrene, its still there trying to do its job. Before adding silica the viscosity is very low, so at that point it could be used for infusion easily. And by adding more styrene you degrade the resin, which makes it less water resistant and typically even more brittle than a normal polyester resin.

There is no way to determine the increased adhesion or absorption, it would depend on each piece of wood, soft porous woods tend respond well to polyester sealers, harder to bond to woods, the dense and oily types, tend to do better with PU sealers.

The actual polyester or VE sealers used for wood or foam (any substrate) use a different chemistry which allows it to be much lower in viscosity than an infusion resin, but they are still compatible with typical polyesters and VEs

 

So, if I'm understanding this correctly, a "thin" resin is available to seal timber first, that is more penetrating than either infusion or laminating resin ? I've never heard of it, or noticed it in product lines, but I'll certainly be on the lookout in future.

 

Here's a sample of the products.

They're used on CNC cut MDF plugs, molds and tooling board too.
http://duratec1.com/pdf/FLYER CLEAR PE TOPCOATS WEB.pdf

 

The amount of penetration a resin has into a substrate, has little to do in regard to its effectiveness as a waterproof coating. It's the physical qualities of the resin itself that determine a coating's suitability as a waterproof coating.

Non-reactive viscosity modifiers (fillers and chemicals) are what's used in most formulations.