Sealing plywood

Humblefish · Nov 30, 2017

Long story short, I am stacking quarantine tanks on these: https://www.lowes.com/pd/Gladiator-72-in-H-x-77-in-W-x-24-in-D-Steel-Freestanding-Shelving-Unit/1000003004?

However, I’m not comfortable putting the tanks directly on the metal grating so I plan to use 3/4” plywood all the way across to more evenly distribute the weight.

Obviously, the bare plywood will not last long if it comes into contact with saltwater; so I’m looking for a cost effective sealer to use on it. I like using this varnish on my “good stands”, but it will get kinda expensive using it on plywood: https://www.homedepot.com/p/Rust-Ol...-Gloss-Spar-Varnish-Coatings-207008/202520882

Humblefish · Nov 30, 2017

Based upon my calculations, I could seal 2 sheets of plywood using the marine varnish I linked above.

Covers up to 125 sq. ft. per quart

4X8 sheet of plywood = 32 sq ft X 2 (both sides) = 64 sq ft (or 128 sq ft for 2 sheets)

At $13.57 per quart, it would cost me $6.78 to seal a $32 sheet of plywood if I went this route. Just curious to know if there are more cost effective options to consider. TIA

Sycoticrealm · Nov 30, 2017

Why not use some of that pond shield stuff they use for making plywood tanks?
Any good brand enamel paint should work.

JDowns · Nov 30, 2017

You could use melamine instead. While the surfaces are waterproof the edges are not.

Get water based wood glue and thin it so it's runny but no more than 5% water. It doesn't take much. Use a rag to soak into the edges. Sand between coats to a smooth finish. Seal with paint or varnish. Much easier than sealing sheets of plywood.

JDowns · Nov 30, 2017

Little extra tip to make things easy. You can use a bottle like the BRS reef chili to mix the glue. Squeeze a line down the middle and use a squeegee for window tint to press into the seam. Capillary action will pull the glue into the wood. Have a wet rag ready to wipe down the melamine sides of any drips. Should only take two or three coats and the glue dries fast.

Any varnish or epoxy can be used as a final sealer.

Works well on mdf also.

cracker · Nov 30, 2017

I would recommend a 2 prt marine epoxy. However it would be a little pricey.

Big G · Nov 30, 2017

JDowns said:
You could use melamine instead. While the surfaces are waterproof the edges are not.

Get water based wood glue and thin it so it's runny but no more than 5% water. It doesn't take much. Use a rag to soak into the edges. Sand between coats to a smooth finish. Seal with paint or varnish. Much easier than sealing sheets of plywood.

+1
https://www.homedepot.com/p/Melamin...ctual-750-in-x-49-in-x-97-in-461877/100070209
They make edging tape that comes in rolls that is pre-glued for you to iron on. But I like using 1/4" x 3/4" wood screen moulding. Glue and nail it to cover exposed edges after you have painted or sealed the moulding. Makes a very durable edge.

chipmunkofdoom2 · Nov 30, 2017

For what it's worth, my tank sits directly on a piece of 3/4" ply that tops my DIY stand. I painted everything black with a spray paint, a Krylon semigloss. Other than that, I didn't treat or seal the wood at all. It seems to be holding up really well to more than occasional splashes.

If paint that is not really designed to protect wood from water does a decent job doing so, I think most sealants and epoxies should offer pretty good protection.

Humblefish · Nov 30, 2017

Thanks everyone, these are some awesome suggestions. :)

don_chuwish · Dec 1, 2017

Start with exterior grade plywood - that alone will make a big difference.
https://www.andersonplywood.com/389/exterior-plywood/
Then honestly a good paint job would be enough.