How Would You Replace Rotted Subflooring?

[Adamsta]

So noticed some rot in the plywood so I decided to gut it....

Original design:
Steel subframe
Layer of thin aluminum or steel
1/2" plywood
Then outdoor carpet

The aluminum sheet has taken a beating and looks like.it was shot with a 12 gauge with bird shot.... so my thoughts are

1. Call around to sheet metal shop and have one cut and then adhere to new piece of ply wood and recover with carpet.

2. Replace with old sheet of tin and smooth and seal with roof sealant/tar and new sheet of pt ply wood. Then recarpet....

[Lt Dan]

That looks like oriented strand board (OSB) and not true plywood. OSB is a very cheap substitute that does not hold up to water very well. I would use 5/8-3/4 inch marine grade plywood then undercoat the bottom with a good sealer. With that, you may not need the metal underneath which was originally there to keep out the moisture. You would also want to lay a good bead of sealant around the framework when you put the plywood in.

[keymastr]

I agree, no OSB should ever be used. It swells when wet and then the glue lets go so it turns to mush. Marine plywood with 2 coats of waterproofing would be permanent. Standard exterior plywood with the same sealer would still last longer than you will probably keep it.

[Chargerman]

Another thought is to wire brush and apply 2 coats of POR 15 to all of the metal. A great product to stop and prevent rust.

[gvette85]

OSB is never supposed to be exposed to moisture,if it gets wet as said it disintegrates.Marine plywood is the best option in my opinion.Like Chargerman said POR15 is great for the exposed metal.I have used it on rusty metal and it encapsulates the rust and stops it. A word of caution,wear gloves if you use it .If it gets on your skin you have to wear it off ,its tough !!

[Chargerman]

Good catch gvette85. Must wet gloves and long sleeves is also recommended. Impossible to remove if it gets on skin.

[grindstone01]

The problem with the metal pan and plywood being used together is that moisture gets inbetween the two materials and the plywood does not get a chance to dry out, expediting the rot process.
I agree with a marine grade plywood, caulk the edges and no metal pan (let the plywood breathe).

[Chargerman]

I think I would consider priming the marine plywood and then apply rubberized undercoat to the bottom side once installed. What do you guys think of this?

[MRUSA14]

Originally Posted by Chargerman

I think I would consider priming the marine plywood and then apply rubberized undercoat to the bottom side once installed. What do you guys think of this?

I don’t like it. As soon as the undercoat develops a crack or a pinhole, water will seep between it and the plywood and be trapped there.

[Chargerman]

Good thought. Would you put anything on the bottom side of the plywood? Seems kind of strange to leave it exposed

[bldrbob]

The difference between exterior and marine grade plywood is the layers. Marine has all layers solid while exterior nay have small gaps in the layers which would not be good in a boat but will not hurt the floor.The other difference is price.

[Winemaker2]

Originally Posted by Chargerman

Good thought. Would you put anything on the bottom side of the plywood? Seems kind of strange to leave it exposed

A couple of coats of 2 part resin... either epoxy or polyester like used in fiberglass layup.
Be sure to cover the edges as well. If any voids in the plywood edge you can thicken the mix (talc will work for small qty) and apply w a putty knife

[Adamsta]

Well project made good progress.

Used 1/2 ext ply wood
Then used 4x8 sheet of shower wall material.
Liquid nails and screwed the two together.

Wire brushed frame and then re shot with rust resistant paint.

Slid them back in and screwed to frame

Primed all the wood for carpet glue

Going to:
Reseal the gaps when temps get above 40 or so
Glue carpet
And just check on last finishing touches

Hope it works...

[Adamsta]

Pictures