Non-marine plywood prep

[zachduckworth]

Hi all,
I have a 1.5” drilled hole to plug in my cockpit deck. I was going to use marine plywood to make a plug, then epoxy/glass it in top and bottom with a chamfer on each side.

I called a local plywood place and the guy who I spoke with said that for this I’m be better off buying an off-cut of normal plywood, cutting the plug, and then prepping it with epoxy prior to epoxying it into the hole, chamfering, etc.

Obviously this is a lot cheaper, and he explained that the use and technique probably doesn’t call for marine ply. It would also save me about $190.

I’d prefer to go this route over marine ply. Does snyone have advice on how to prep the plywood for this application? Should I just hit it with epoxy until it won’t absorb anymore, then fit it in? I’ll be sanding and epoxying the walls of the hole of course as well.
thanks!

Btw, I have penetrating epoxy as well as regular, should I hit the plywood with that? Any benefit there?

[Bowdrie]

Originally Posted by zachduckworth

Btw, I have penetrating epoxy as well as regular, should I hit the plywood with that? Any benefit there?

For that kind of application, a high-grade marine plywood is not necessary.
Cut your plug a bit smaller than the hole it is to go in.
You have penetrating epoxy, "Smiths?".
Anyway, make a little dish out aluminum foil, or use a "Tupperware" kind of dish.
Put your plug in the dish and just pour your penetrant over it, letting it soak in for as long as you want/need.
After removing it from the penetrant, let it cure, then proceed as usual, using your epoxy with some filler to glue the plug in with "Thickened Epoxy".

[zachduckworth]

Sounds good, thanks for info.
The epoxy is West Marine’s penetrating epoxy.
Looking forward to getting this done…

[tkeithlu]

Nice set of directions, Bowdrie.

[smj]

The guy I worked for years ago would coat the plywood plug with 3 coats of epoxy, scratch the surface then epoxy in place.
You could fill with thickened epoxy then grind a dish/taper in each side and glass in.

[RaymondR]

Thee are interior and exterior grades of "normal" plywood. Exterior grade plywood uses the same glue as marine and should not fall apart if water intrusion occurs. Cut a small piece off and boil it for half an hour, non exterior will generally fall apart through glue line failure.

[Ballsnall]

It's a 1.5" plug that will be encapsulated with epoxy when you glue it in. Soak a little straight epoxy into the edges before you glue it in any will be fine.

[Rumrace]

Plywood was designed to eventually separate. It was a massive mistake using it inside glass. Marine plywood is made in thinner layers uses a better horse glue but it truly is and antique material.
A plug as in a mould? Marine plywood will hold a better curve offer more strength, less warping, simply make a better mould. To plug a hole with plywood and epoxy plastic attached to fibreglass is not a marriage made in heaven. Kevlar, or carbon fibre roving with epoxy is. The biggest problem with them is getting resin in them. Vacuum bagging consumes up to 40% waste. Even triaxial 12oz is stronger plywood. I’ve seen a repair like your hole is the worst spot on textured surface. You can buy non slip moulds for just about every year brand of boats but this fella made his own using a latex mould.

[Fore and Aft]

Zachduckworth if you have some old resin and glass laying around you could always laminate up a 1.5" plug. Probably use a disposable coffee cup etc as the mold. Lots of ways to skin a cat with this project.
Rumrace I am right now sitting in a six year old plywood yacht and there is nothing antique about our yacht. Just click on the link below and see how sweet a plywood yacht is.
Cheers
https://www.rm-yachts.com/en/home/

[RaymondR]

The risk you have is that a plug in a cylindrical hole is easy to punch out. The easiest way to prevent this is to use a rebating bit to form a step in the hole with a matching step in the plug. An alternative is to use two pieces of half thickness plywood to make the plug.

[pcmm]

Originally Posted by Rumrace

Plywood was designed to eventually separate. It was a massive mistake using it inside glass. Marine plywood is made in thinner layers uses a better horse glue but it truly is and antique material.
A plug as in a mould? Marine plywood will hold a better curve offer more strength, less warping, simply make a better mould. To plug a hole with plywood and epoxy plastic attached to fibreglass is not a marriage made in heaven. Kevlar, or carbon fibre roving with epoxy is. The biggest problem with them is getting resin in them. Vacuum bagging consumes up to 40% waste. Even triaxial 12oz is stronger plywood. I’ve seen a repair like your hole is the worst spot on textured surface. You can buy non slip moulds for just about every year brand of boats but this fella made his own using a latex mould.

What a load of BS... What makes you think "Plywood was designed to eventually separate."?? The bulkheads of my 44 year old Morgan are Exterior Grade ACX plywood and are still intact. When do they "Eventually seperate"??

The OP is filling a small hole, a plywood pulg will be OK in this application. Best to cut a rebate so that the plug has a shoulder for support and then glass over both sides once bonded in.

[fourlyons]

Originally Posted by Fore and Aft

Zachduckworth if you have some old resin and glass laying around you could always laminate up a 1.5" plug. Probably use a disposable coffee cup etc as the mold. Lots of ways to skin a cat with this project.
Rumrace I am right now sitting in a six year old plywood yacht and there is nothing antique about our yacht. Just click on the link below and see how sweet a plywood yacht is.
Cheers
https://www.rm-yachts.com/en/home/

Thanks for the link ForeandAft! I didn't know about RM yachts, they are doing some cool boats in plywood. I really envy the boat building innovation and diversity going on in France especially, and Europe more broadly. The boat building is a little boring here in the US these days.

[capt jgw]

"Marine" plywood is overrated. It uses the same adhesive as Exterior grade so is no more resistant to delamination. It does have more, thinner plies and no voids to allow more even bending over a mold, but that's only useful if you're building a whole plywood hull or other curved structure. The standards don't even address wood species or rot resistance which you would think would be the number one criteria but it's not even considered. Some of the so-called Marine plywoods have very poor rot resistance and will turn black and rot away to nothing if they ever get wet. So for most uses a higher quality exterior grade pine or fir plywood is fine and probably superior. Just pick one with more plies per thickness to resist warping. Some of the cheaper grades have only three plies, they will not stay flat in a larger panel. For a tiny repair like the OP has described just about anything will work as long as it is well encapsulated and bonded in with epoxy.

[RaymondR]

I decked my dingy using so called "marine plywood" and within three years it started to rot and fell apart and I was obliged to redo the decking. To rebuild it I used "bracing ply" which is manufactured from Australian hardwoods and uses a resorcinol glue line and is rated as an exterior ply.

[wholybee]

For a 1.5 inch hole in a floor (not a structural component), why use plywood at all? Why not just fill it with thickened epoxy? Tape the bottom of the hole. Fill with epoxy. After it cures add whatever paint or non-skid over it as needed to make it invisible.