Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

[pastorbud]

I am replacing the floor on my 1987 Bayliner 18.5' Trophy center console. The floor is out and all the interior hull components look good.

I've looked at the prices for marine plywood and found it not only expensive but hard to find.

A couple of DIY websites say that if you "glass" the pressure-treated it works fine, except that some types will corrode aluminum (mine's fiberglass).

For example, at:
Marine Grade Plywood Vs. Pressure Treated for a Boat Floor | DIY Guides

"There is no structural advantage to using marine-grade plywood in a boat?s floor. The solid laminate layers inside won?t make the floor significantly stronger, it will cost more initially and marine plywood is not resistant to decay. The woodworking skills needed to do the repair and installation are identical. You?ll likely be better served by using pressure-treated plywood."

And at: What Type of Plywood Is Used to Replace a Boat Floor? | eHow

"Pressure treated plywood is also used to replace boat flooring. This type of plywood is treated to be more resistant to weather damage. It typically has a greenish color due to the chemicals used in the treating processes. Pressure treated plywood is treated with mold growth retardant and the treating process is not water soluble, which reduces water adsorption in the wood."

BUT-- These are not boat repair forums, so I wanted to ask guys with more boat repair experience. All in all, I'm only looking at about $150 difference, so I'll get the marine plywood if it really matters. Just gotta drive quite a bit further to pick it up.

 

[jbcurt00]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

Use a good quality exterior (NON-PT) plywood. Aurauco (sp?) is a great exterior ply to use when you can find it. Menards carries it in a lot of locations in the upper mid-west, Lowes/HD stock it in some areas, it's hard for me to find. I will likely end up using ACX for most of my boat plywood needs.

PT wood is usually damp & heavy compared to non-pt wood. As it dries (you'll want it as dry as possible before you encapsulate it w/ fiberglass) it also tends to warp, often severely. You should still wrap it w/ resin & glass, that is the primary strength & waterproofing for the ply and is still necessary. Heavy, prone to warping, more expensive & doesn't save time or money over exterior grade ply, I think I'd rather not use it. Many current boat makers (tin & glass) use PT wood, but it is kiln dried, highly quality controlled and not easily sourced as a DIYer.

Take great care to encase the exterior ply (both sides & all edges) in poly resin & fiberglass before installation & after. Fill all penetrations to seal them. You'll get a very reasonable end product, and when taken care of it will out last your use of the boat.

 

[jigngrub]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

Pressure treated lumber that has been kiln dried after pressure treating works well, treated wood that has not been dried... not so good.

The typical PT lumber you buy at lumber yards and big box home centers will not be dried and will still contain a lot of moisture/PT soloution. This will adversely affect fiberglassing by not letting the resin penetrate the wood and will prevent the resin from setting and curing properly.

Kiln dried CCA pressure treated plywood is a very good boat building material... but is expensive and hard to find, but worth it if you can. It comes with a lifetime warranty and will never rot even if it gets wet.

Regular exterior grade plywood is the material of choice for the vast majority of members on this forum. It's cheaper and readily available at all lumber suppliers.

 

[pastorbud]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

You guys r da best. G'night.

 

[fishrdan]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

For example, at:
Marine Grade Plywood Vs. Pressure Treated for a Boat Floor | DIY Guides

"There is no structural advantage to using marine-grade plywood in a boat’s floor. The solid laminate layers inside won’t make the floor significantly stronger, it will cost more initially and marine plywood is not resistant to decay....

Not necessarily true, marine plywood has the ply's laid at 45* opposed to the 90* of most plywoods. The ply's laid at 45* makes it more rigid, a more solid deck. That said, I' don't suggest that you use it due to the higher cost. I would use 5-ply 1/2" plywood though, it's stronger than 3 ply 1/2" plywood.

 

[pastorbud]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

Any suggestions for how to join the pieces of plywood at the seams? Since the opening is about 6'X12', I won't be able to do this with a single piece of 4X8 plywood.

Should I just butt the pieces together and glass over them? Sounds weak.

My first instinct is to

1) pre-seal the pieces with resin
2) Gorrilla glue the seams and clamp the pieces together
3) after the glue cures, sand off the excess so the seams are flat
4) put down two layers of mat over the whole piece
5) put an extra layer of tape across the seams

 

[jbcurt00]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

Lay the pieces as 6'X4', you'll need 3 total sheets of plywood cut to 6' wide, running the width of the boat, starting from the transom headed towards the bow.

Plan the joints to fall on a bulkhead running port to starboard between the stringers. Or add a rip of plywood to the long side of the plywood as a doubler, creating a ledge for the next piece to lay onto. Use gorilla glue & screw the plywood down to the doubler, like this:

 

[jigngrub]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

This will be your strongest build with a rock solid deck:


You can either add stringers or bulkheads or cut your plywood back to the closest existing and make your filler piece larger.

 

[pastorbud]

Re: Pressure-treated vs. marine plywood in a 1987 Bayliner floor restoration

Don't know if it was the best way to go on this site, but I started a separate thread for the part I found under the deck. I've move pretty far afield from my original question. Thanks for all the help!

http://forums.iboats.com/boat-resto...-1987-bayliner-trophy-609524.html#post4247412