plywood choices for floor and transom

[baconaneggs]

KJ, upon giving it a little more thought, the whole idea of encapsulating the wood is to prevent it from absorbing water. So using a piece of treated pw that has been in a warehouse drying seems like a good idea. However it is pressure treated, so it does tend to squirm around during the treatment process as the different veneers absorb fluid at different rates and move in different directions, leading to a sheet that is not totally straight or dimensioned properly. Is it as strong as it once was? I don't know. Marine plywood conforms to a much higher standard than regular plywood. It has waterproof glues and decay resistant wood species. You have to know in the back of your mind that if you used marine pw, you would never have to worry about the quality of your work. But everytime you saw a thread about stringers or transoms, there would be a twinge of doubt! What ever you use, just pay attention to any cuts, limber holes, and chase ways. ultimately it is the penatrations through the encapsulating cover that leads to the downfall. I'm ripping apart a 73 center console right now to replace the floor and stringers. I can't wait to see whats underneath!

[RidgeRunner]

Regular pressure treated plywood is a NO-NO. It will be so wet you will never have proper adhesion. Most treated plywood is Southern Yellow Pine which is not the best plywood to use in the first place. Pressure Treated Marine Plywood that has been Kiln Dried After Treatment is dry and will work. Marine Plywood is FIR and has a better grade of interior plies.(Less Voids) It is available with or without the pressure treatment.
All of the plywood of BC grade or better has a finish too smooth for my liking. I like to rough them up before laminating with resin. I do not know if the glue is different from regular exterior grade plywood. Most all of the delamination issues come into play due to lack of proper glue in the manufacture of the plywood. There are numerous brands and species. I wouldn't use a cabinet grade plywood for core on a boat. I would make certain that whatever I used it had Exterior Grade Glue. Look for the X on the end of the grade. (CDX, BCX, etc.) If you don't want to invest in the Marine Grade Plywood, at least go with Exterior Grade Fir. Okume is very nice but expensive. Happy hunting..

[Kracker Jack]

I just built a storage box for our duck decoys on my buddys Chincoteague scow. And we used salt treated he had laying around and the hollows in the layers and the soft plyable wood makes me nervous to use in structual applications such as a trannsom. And also resins and wet treated wood is like mixing oil and water. This salt treated plywood he had had been in his garage for like 6 monthes and it was all we had so we made due. As for the v20 im not wanting to put junk wood in my transom, but i am looking for functional money saving material that will serve my purpose. Thank you for all the info so far guys.

[spareparts]

I've used what I've been told is forming grade plywood with good luck, its the stuff with the red paint around the edges. Its not marine ply, but it doesn't cost like marine ply. resin seems to stick good to it, I redid the compartments on my Mitchell a few years back, that boat has been thru three owners since then, been used like a government mule. the work I did on it is still holding up last time I saw it

[Kracker Jack]

I know where theres a couple sheets of that form plywood at, but they slapped diesel fuel on it a couple times to reuse for concrete forms and keep the crete from sticking to it. I looked into some at my Grandaddys house after reading one of your thread responses.


Back to this "hot coat" technique one of you guys posted on here about treating a cdx with raw resin and letting it soak in and then putting a Hardener/resin batch over that then sanding then applying to transom. Is this true? this sounds fairly plausible to me. Im probably gonna go with marine ply. But just curious about materials that some backyard builders use and are sucessful with.

[spareparts]

I don't like the idea of having resin without any catalyst under cured resin. I don't think the under coating will ever kick, I could be wrong as I've never tried it. I usually lay down a thinned coating of resin with catalyst, thinned with acetone, (you have to add more catalyst when you thin with acetone), the thinned resin gets into the wood pretty good. Don't thin more than 10% as it won't kick

[RidgeRunner]

Yep, That is a hot coat. With Vinylester it helps to penetrate into the wood and gives it some bite. Essential on Kiln Dried PT Plywood IMO. With PT plywood the cells of the plywood that would ordinarily be open for penetration are actually full of preservative, metals like chromium copper and arsenic. It can give a case hardened effect making penetration difficult, that is why I recommended you grind it with some 40/60 grit before laminating with glass.(It helps the mechanical bond) Always wear Personal Protective Equipment when working with PT or any time you grind or sand on glass.
If you seal any type of plywood properly it will work for a long long time. I do not consider Wellcraft's glasswork to be that outstanding. My hull had lots of voids and buggers once the foam was removed.
ACX Fir seems to be a lower cost alternative to Marine Plywood and is available at most of the Box Stores. You need dry and without contaminants.

I have always mixed the hardener in with the resin. I'm like Spare, how does the resin underneath harden. I try to keep the ratios of hardener to resin consistent at the low end of the scale so I can have the most potlife and work on larger areas. (Mind you I glass in 95 degree weather) I threw out more kicked up in the bucket resin than I care to admit trying to find balance.

[Kracker Jack]

Well after 2.5 hours of research on this plywood i have decide this Aruaco plywood is the material im gonna use for my transom and floor repair. This plywoods only down fall is alot of guys say its very thirsty when it comes to treating it with a hotcoat. everyone says its very solid with no voids and is put together with a good grade exterior glue. I read some negatives also but most of the negatives came from the purists or the old school workboat builders(which means alot because these are our wise men) they simply didnt like it due to more use of resin and some inpurfections in the thickness of the plys which they consider make the panel not as strong, when i seen the material at Lowes today all the plys were very consistent with each other in my opinion. Alot of the guys on other forums have put samples of this plywood in there diswashers to do the BOIL TEST and the plywood has passed the test with flying colors all claiming no delaminisation what so ever. One guy even put it as his base floor in his pontoon boat like 4 years ago and the integrety of the plywood still remains the same. im gonna be bringing my v20 home this weekend after my morning deer hunt on saturday so I will make a new build thread and start documenting my demo and rebuild with plenty of pics. Thanks for all the help guys Im sure im gonna need alot more of before this is all said and done.

[RidgeRunner]

Good choice. The price is right. We pressure treat plywood on a regular basis. Arauco plywood is one hard plywood to treat. It has interior plys that are so dense we simply have trouble. The interior plys are also allowed to be hardwood which cannot be penetrated effectively by the pressure treatment process.
On the other hand, Radiata Pine boards and fence picketts are like a sponge. Due to the fast growth of the tree, the growth rings are not very close together so there is a lot of sapwood that is easy to penetrate with preservative.
I don't think you will have any issues. It has a great track record. Keep us posted.. Pictures too..

[inaforty]

Very interesting research.
The front deck of our V is soft and will need recoring at some point.

I used Coosa board to recore the cockpit hatches on the Bertram last winter but the Coosa was pretty $$$.