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Need a Good Solution for Protecting PT Plywood Subfloor During Deck Installation

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Forum topic by wilschroter posted 07-07-2020 11:57 PM 436 views 0 times favorited 6 replies Add to Favorites Watch
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wilschroter

144 posts in 1330 days


07-07-2020 11:57 PM

I’m working on a 600 sq ft deck that will be tile on top and 3/4” pressure treated plywood below. I’d like to be able to set the plywood subfloor so I can work on the rest of the deck, but I’m concerned about how badly pressure-treated wood (or any wood) warps with rain exposure.

What do you guys recommend to keep the sub-floor somewhat protected from rain? Or should I even be worrying about this? I’m worried the wood will warp creating a horribly uneven subfloor for my tile install later.

However, putting down something like plastic could be a challenge because it will become slippery and may be difficult to work on top of without tearing constantly.

I’m sure you guys who build/frame houses deal with this all the time so was hoping I could get your pro opinion.


6 replies so far

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John Smith

2511 posts in 968 days


#1 posted 07-08-2020 12:14 AM

you really need to do some research on Laying Tile on Exterior Surfaces.
concrete backerboard & underlayment was invented for a reason.
I have laid a lot of tile on patios and backyard porches that had a concrete pad.
never on exterior plywood. it just sounds like an ongoing expensive nightmare to me.

.

-- there is no educational alternative to having a front row seat in the School of Hard Knocks. --

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Dajur

36 posts in 65 days


#2 posted 07-08-2020 12:21 AM

I am a home inspector and I can tell you that just about all of the decks I have ever seen that used a plywood underlayment have had rot and damage issues after just a few years.

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wilschroter

144 posts in 1330 days


#3 posted 07-08-2020 12:30 AM

John I will be using 1/2” cement board, 2 layers of thinsey and 3/8” tile. So this is just a question of how to best protect the plywood until the backer board and tile go down.


you really need to do some research on Laying Tile on Exterior Surfaces.
concrete backerboard & underlayment was invented for a reason.
I have laid a lot of tile on patios and backyard porches that had a concrete pad.
never on exterior plywood. it just sounds like an ongoing expensive nightmare to me.

.

- John Smith


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John Smith

2511 posts in 968 days


#4 posted 07-08-2020 01:35 AM

What do you guys recommend to keep the sub-floor somewhat protected from rain?
Or should I even be worrying about this?
I m worried the wood will warp creating a horribly uneven subfloor for my tile install later.
- wilschroter

What do you guys recommend to keep the sub-floor somewhat protected from rain:
4 mil plastic sheeting

Or should I even be worrying about this:
most definitely – you should worry

I m worried the wood will warp creating a horribly uneven subfloor for my tile install later:
your concerns are well founded

.

-- there is no educational alternative to having a front row seat in the School of Hard Knocks. --

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xedos

60 posts in 105 days


#5 posted 07-08-2020 01:36 AM


John I will be using 1/2” cement board, 2 layers of thinsey and 3/8” tile. So this is just a question of how to best protect the plywood until the backer board and tile go down.

you really need to do some research on Laying Tile on Exterior Surfaces.
concrete backerboard & underlayment was invented for a reason.
I have laid a lot of tile on patios and backyard porches that had a concrete pad.
never on exterior plywood. it just sounds like an ongoing expensive nightmare to me.
.- John Smith wilschroter

You’d best listen to John – as you and this deck are destined for failure. It’s just a matter of how quickly. PT ply might just be the worst surface for a tile substrate. Why are you considering that over say Advantec or similar ?

I’d suggest you head over to the John Bridge tile forum and pose your question for an education. But wear your kevlar underpants because they don’t hold back on questionable practices.

The crib sheet is : you’re not going to protect it now or after the tile goes in. You’ve got to figure out how to manage the moisture / water that WILL find its way into the assembly.

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wilschroter

144 posts in 1330 days


#6 posted 07-08-2020 11:03 AM

@xedos I wasn’t set on PT ply – I was just assuming since the rest of my deck was PT that I would use that for the subfloor, but certainly open to suggestions as I haven’t laid anything.

I’ll head over to those forums to see what I can learn and appreciate the advice.

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