Protecting Plywood with Polyester Resin

This is just a question for the wood floor (the wood on top of stringers) of my 14' Fiberglass fishing boat. The boat will be mostly trailered and covered when not used.

I am planning on using untreated plywood to floor the bottom of the boat. I have read that treating the wood with resin (using Polyester Resin) will protect the wood againist the effects of water. I have also read that using Treated Plywood(e.g. marine or exterier) is not good becasue, "Polyester Resin cannot enter the wood grain in order to gain a proper grip on treated, wet, oiled, waxed, or painted wood. When fiberglass resin is applied to any of the fore mentioned plywood, de-lamination will occur" Source: http://www.capndsboatshed.com/


So can I just use untreated plywood and coat with Polyester Resin?

After that, Should I just fiberglass over the resin treated wood on the edges to protect the volnirble corners, or should I enclose the whole plywood floor in Fiberglass?? If I do either one of the above solutions, should I put another piece of resin treated on top for extra protection? And if i do that do i need to glass any of the second piece of plywood or just fit and carpet?

 

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Jimbo

 

Thanks for the simplest answer...I am not going to use Epoxy...sorry to go aganist the majority here.

 

About the only reason I can think of NOT to use epoxy is if you are allergic to it. Are you allergic or just a contrarian?




Jimbo

 

Would you believe that I am allergic and being a contrarian?

 

asianbandit

Polyester resins are not necessarily the best choice for waterproofing plywood, marine or otherwise. Epoxy is a much better, but more expensive, option. How and what to glass depends on the span the plywood will gap and the amount of flex you're willing to accept. If the span is short and you only want to protect the edges then taping them should be good enough. If the span is large you should consider glassing the entire panel, both sides, to gain strength.

You should test your materials to see how well they're going to work, if the resin will adhere to the wood, if it'll soak through, etc. Then again there are other materials available, "King Starboard" etc. that can provide a one step solution. If you're planning on keeping your boat for awhile then the investment in marine ply and epoxy are worth it. If not, use the cheapest materials (porch paint works @$40/gal) you can get and ditch the boat after a year or two.

Good luck with your project.

Rick

 

Marine grade plywood means the glue which bonds the layers is water resistant which is not the same as pressure treated wood (or plywood) which has a preservative added to the wood under pressure. You should always use marine grade when water is present. No doubt epoxy is better but consodering that the floor is not always under water I would think polyester would be fine. In the north east marine grade plywood coated with polyester resin is commonly used for bulkheads. It may not be the best but it should last for quite a while.

 

Polyester resin doesn't last, isn't completely water proof and doesn't hold onto wood very well (nor much else, including itself) This is the reason epoxy is the common choice. Starboard, should never be considered for a sole (decking) as it isn't a structural material and can break under it's own weight, let alone a person standing on it. Starboard is great for instrument panels, ice box lids and cutting boards, but can't be glued, doesn't hold fasteners well, is non-structural and no polyethylene manufacture, nor reputable designer would spec it's use for decking, except as a decorative inlay over a substantial substrate. Sorry to be so negative about Starboard, it has it's place, but as a decking material, it just doesn't work, except as mentioned.

I sympathize with your sensitivity, I know many that are. Some brands of epoxy are less likely to cause reactions, depending on your allergic requirements. If you have issues with most highly alkaline products (like ammonia), then you may want to try a sample pack of non blushing type of epoxy.

If you're bent on not using epoxy, I'd recommend using vinylester resin, rather then polyester. Its water tight properties are much better and it sticks to wood better too, not as well as epoxy, but pretty good, particularly on a trailer boat, that will receive good care (clean, dry and covered).

If you drop me an email, I can provide a list of a few manufactures that you can get sample kits from, to text you reaction (and gooing skills). These epoxy manufactures use different hardener formulations, which aren't as bad as others. Some have a very low reaction with all but the most sensitive.

 

Epoxy is the better product, but polyester will work, but you can't just paint it on, it has very little strength and will just crack and peel off. You need at least one layer of glass to hold it together and stay water tight. If a small trailer boat is kept covered and dry, then even a bare plywood floor wood last for a few years, add some good paint and it will last a little longer. If there are unsealed holes or screws in the plywood then it makes no difference what you use, the water will get in and rot the wood.

 

You can also thin polyester resin with acetone so that it will penetrate the timber well and use 2-3 coats.

 

My plans

Thanks for all the info guys. I belive i am going with Vinyl Ester Resin for the project. I did not know that Epoxy could not be used with all Fiberglass Mat, that is what I am planning on doing my repair work with. I am going to make a new post with detail on what i plan on doing...Please take a look, i will post pictures and outline what i want to do....Please take a look and let me know what you think..It will be titled, Plans for 14 foot fiberglass

 

I just tried using vinyl resin on a plywood cockpit roof project. What a fiasco! Experimentally confirmed: the stuff is no good for anything that has to do with wood. The joints never cure. Throwing it all out and starting over with epoxy. Donating the gallon of vinyl crap to whoever wants it at the marina (but who would want it?)

 

The problem you're experiencing has nothing to do with the wood or resin if the joints aren't curing. The resin in some types of wood can slow the cure of polyesters, including VE, but its normally only on the knot holes.

If the joints aren't curing its a different issue, lack of catalyst, poor mixing, old resin, an odd type of filler in the joint. If the entire lay up isn't curing then its back to catalyst level.

 

Epoxy needs protection against IR, didn't see anyone mention that. I don't know if the same is true of VE. If you're using (relatively) cheap ply and it gets to dry out frequently, why not use a good quality exterior stain? It's cheap, easy and quick, looks great, won't scratch and colors are available that will hide the treated ply's color.

 

I agree with Terry, especially on a trailer boat. I used Behr High Solids stain on some homemade picket fence that has been exposed to New England weather for over 10 years with no ill effects. I am sure there are even better brands out there.