Exterior plywood with resin

[parratt1]

Hey all sorry if this has been beat to death. The search button pulls up HUNDREDS of hits. I have been researching a lot for my build for my plywood floor and casting deck and apparently you can save a lot by using exterior grade plywood and then painting it with epoxy resin. What kind of plywood do I need? I looked online and there are sooooo many options. Will a lumber yard in my area carry what I need? Seems that HD and Lowes carry CDX which is not what I am looking for? I have a friend that has done some of the resin, but I just need to know about the plywood.
Thank you!!

 

[lugoismad]

Hey all sorry if this has been beat to death. The search button pulls up HUNDREDS of hits. I have been researching a lot for my build and apparently you can save a lot by using exterior grade plywood and then painting it with fiberglass resin. What kind of plywood do I need? I looked online and there are sooooo many options. Will a lumber yard in my area carry what I need? Seems that HD and Lowes carry CDX which is not what I am looking for? I have a friend that has done some of the resin, but I just need to know about the plywood.
Thank you!!

I was in the same boat (haha, get it, boat? cause its a boating forum?....I'll show myself out...) as you when I redid my transom. I read several people that said they used pressure treated wood and coated it in urethane and it went years with no issues. So thats what I did. Cut a new transom insert out of a PT 2x10 and then coated it in 5 coats of spar urethane. However, its only been in about a week, so I can't really tell you how it holds up.

 

[lckstckn2smknbrls]

Never use pressure treated wood!!!

 

[lckstckn2smknbrls]

Exterior grade plywood will have an "X" in the grading ABX, BCX, CDX.
As for resin you want epoxy resin unless you plan on using fiberglass cloth then polyester resin is used.

 

[Skiffing]

Personally I'd use BC exterior 3/4" and laminate the C sides together to make up 1 1/2"

 

[lckstckn2smknbrls]

Personally I'd use BC exterior 3/4" and laminate the C sides together to make up 1 1/2"

The thickness he needs will depend on the original transom other wise I agree.

 

[parratt1]

Guys im not making a transom. I'm looking for flooring and casting decks. Poster #2 is talking about transoms. I am interested in 5/8 to 3/4.

 

[parratt1]

Exterior grade plywood will have an "X" in the grading ABX, BCX, CDX.
As for resin you want epoxy resin unless you plan on using fiberglass cloth then polyester resin is used.

I meant epoxy resin not fiberglass. Great catch!! I fixed it in my post.

 

[Skiffing]

Guys im not making a transom. I'm looking for flooring and casting decks. Poster #2 is talking about transoms. I am interested in 5/8 to 3/4.

Sorry - I misread..........

I'd still use BCX w/ the B side up.

3/4" will span 24" supports w/o noticeable deflection. If your supports are closer 5/8" should be fine. Be aware that some 5/8" is only three laminations though. You want five.

I would NOT use epoxy. It does not tolerate UV and shouldn't be exposed to sunlight. I would use polyester resin and thin it out pretty good to get penetration into the plywood edges. Multiple coats. all sides.

I'd use tongue and groove so any unsupported edge is keyed into the adjacent panel and use construction adhesive before mating them together.

Once polyester cures fully you need to use a primer before additional coats are applied.

For finishing off you can coat with polyester that is tinted to your color and broadcast fine silica on it then use a short nap roller to bed it in.

 

[parratt1]

Guys im not making a transom. I'm looking for flooring and casting decks. Poster #2 is talking about transoms. I am interested in 5/8 to 3/4.

Sorry - I misread..........

I'd still use BCX w/ the B side up.

3/4" will span 24" supports w/o noticeable deflection. If your supports are closer 5/8" should be fine. Be aware that some 5/8" is only three laminations though. You want five.

I would NOT use epoxy. It does not tolerate UV and shouldn't be exposed to sunlight. I would use polyester resin and thin it out pretty good to get penetration into the plywood edges. Multiple coats. all sides.

I'd use tongue and groove so any unsupported edge is keyed into the adjacent panel and use construction adhesive before mating them together.

Once polyester cures fully you need to use a primer before additional coats are applied.

For finishing off you can coat with polyester that is tinted to your color and broadcast fine silica on it then use a short nap roller to bed it in.

Great info. So how about if I plan to cover with either vinyl, carpet or something like hydroturf? Same advice on the polyester?

 

[Skiffing]

^^^^

Yes.

Although expoy is stronger I'd only use epoxy that is encapsulated in other material and /or not exposed. You don't need strength - you need penetration into the wood.

When you apply your finish floor material you *may* have to rough up the polyester a little before applying your adhesive.

Polyester is essentially gelcoat - like on a fiberglass boat. Any marine flooring can be used per manufacturer installation instructions.

 

[minuteman62-64]

I've used two types for decking/seating. Both have worked out well.

5/8" ABX for replacing some seats. 1/2" MDO for some bow decking. Both saturated with a penetrating epoxy and painted with a quality oil based exterior paint.

 

[rabbit]

I used 1/2" BCX for my rear deck and put two coats of poxy with green powder tint on top and a clear coat of poxy on the underside. I thinned the first coat 20% with acetone. Two years and the ply has checked (cracked) along with the poxy. If I did it again I'd use 3/8", coat the bottom with poxy and glass the top. As it stands I'll have to glass the top if I want it to last. I'll probably try polyester as suggested above. The deck is laid on stringers approx 22" centers and doesn't have noticeable flex but it's only 40" wide and about 66" across.
Coat the holes the fasteners go through.
3/4" ply is heavy and I think the suggestion to use 5/8" is a good idea, maybe even 1/2". Powdered tints are available online. Certainly the best floor material would be aluminum.
I'd be interested in knowing what the thinnest ply you could get away with. I've carried a thousand or more sheets of 3/4" and it probably weighs 50 lbs a sheet.
https://forum.tinboats.net/download/file.php?id=44702&mode=view/Grizzly%2016.jpg

 

[surfman]

1/2" is plenty thick enough and much lighter too.

 

[parratt1]

What thickness of aluminum Sheet would a guy need assuming those same 2x2x.125 angles on 2foot centers?

 

[riverbud55]

What thickness of aluminum Sheet would a guy need assuming those same 2x2x.125 angles on 2foot centers?

.120 but imo need more support 16'' oc,, .020 if you can get foam behind it for support,,,,,,,,,

For Plywood I would use MDO ,,, just cut to size then treat/seal the cut edges with resin, with maybe a good coat of oil base primer and paint

'' Medium Density Overlay (MDO)
The primary use of MDO plywood is for road signs. Its other names are "lusterboard" and "signboard." MDO is a high quality exterior veneer with a bonded resin overlay. It is weather resistant, even outperforming metal products when used for outdoor signage. The surface is very smooth and flat with a paint-grabbing finish. MDO is also used for cabinetry and concrete forms''. ,,,,, Read more : https://www.ehow.com/list_7591348_kinds-exterior-plywood.html

 

[rabbit]

Pretty sure my floor is .10" like the rest of the hull. It's laid on ribs 12" on center. 2' centers is a bit wide for that material. Might lay aluminum or even 3/4" hardwood stringers at 12" o.c., then the aluminum floor.
My deck is on poplar poxy coated stringers. The poplar hasn't checked. I have wood and the tools so that's what I used. I'm happy with the weight of the 1/2" ply but the checking bothers me. With 3/8" plus the glass I think it would work good but I haven't tried it so I can't vouch for it.
The MDO idea could work quite well also. I like the idea of using paint instead of poxy/poly.

 

[rabbit]

Have to ammend my previous post. Had the deck off to do some work and it's 3/8" not 1/2". Plenty strong.