Mold on treated subflooring?

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Old 09-07-08, 07:41 AM
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Mold on treated subflooring?

About 4 months ago, I bought several 8x4 sheets of treated subflooring to put down in my bathroom. I stood them up and stacked them up against a wall in my garage, and stacked some OSB non-treated flooring in front of them. I finally got around to putting in the flooring this weekend. The OSB boards were fine, but all of the treated flooring looks like it is covered in a filmy brown substance from where the boards were resting against each other. I am not positive, but it looks very much like mold.

Does anyone know what this stuff could be, and why it would have gotten on the treated boards and not the OSB? And if treated boards can mold, why would I use them in my subfloor? I plan to put down two layers of subflooring. I don't want to do that if the act of touching each other caused mold to grow.

I've never really worked with treated wood before, but I did notice that the boards felt very damp when I bought them. Could they have had too much treatment on them or something? Thanks for any help.
 
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Old 09-07-08, 11:34 AM
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Pressure treated wood is wet. You stacked it with other wood over it and placed it in the dark. Viola! mold. It won't hurt anything, but if you feel better, you can spray the pt with a weak solution of bleach and water. It will kill the mold.
 
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Old 09-07-08, 11:46 AM
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Next time (saw this in a magazine), just put some spacer blocks between the top edges at each end of the sheets. They showed little 1x blocks stapled to a piece of nylon or leather strap.

Takes up more room, but lets the air circulate.
 
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Old 09-07-08, 02:50 PM
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Thanks guys. I guess I just assumed that because it was pressure treated, it was waterproof. Especially since the wood in the store was stacked on top of each other. So the actual wood is not damaged right, just mold growing on the top that I can bleach off? And when I lay it down on my floors and stack two layers on top of each other (the wood is 3/4" thick and I have heard my subfloor needs to be at least 1.25" thick for slate tile), it won't grow any additional mold?
 
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Old 09-07-08, 03:59 PM
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It's not waterproof, just rot and insect resistant (can't bring myself to say "proof", no matter what the makers say). Spray it with the dilute bleach (I like to scrub that kinda stuff after 5 min or so) then rinse and let it dry.

In the store it's a relatively controlled environment, and it moves out so fast, they don't worry about it.

Mold won't grow unless it has moisture.
 
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Old 09-08-08, 05:17 PM
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How did mold grow on it in the first place if it was stored in a garage the entire time? Is it because of the moisture that was on it from the treatment? If I just lay all the pieces out in my back yard in the sun for a day or so will the wood be dry?
 
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Old 09-08-08, 05:46 PM
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Yep, the stuff is wet as he11 when it comes in. We had plywood delivered from the plant that was too hot to handle during the storm seasons.

The mold spores are there when you bought it, just the right conditions allowed growth.

It will prob take more than a day. Don't lay them flat. Air circulation is important. Don't be surprised if they twist on ya.
 
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Old 09-14-08, 02:46 PM
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I'm planning on laying them up against my house and spacing them out. If they twist, are they ruined? They were somewhat warped when I bought them but the guy at the store told me they'd flatten out as soon as you screwed them down.
 
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Old 09-14-08, 02:55 PM
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You'll be putting screws every few inches, so it should be fine.

Plywood twists if you don't put it down as soon as it comes off the hack.
 
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Old 09-18-08, 04:24 AM
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I have some ? are you laying the tile? If not ask the person who is what they want. I don't understand the reason for treated plywood. are you puting the treated down first and then a layer of 1/2" over that. are you sure you need 1 1/4" of subfloor that will raise your bath floor up to at least 2" with finished tile on it that is to me an unsafe tripping problem unless you are going to knotch your floor joist 1 1/4" then you weaken your joist I've been doing this kindof work for a long time never heard of 1 1/4" of sub floor.If you just heard that this is what you need you might want to find out fist if that is true.
 
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Old 09-18-08, 03:30 PM
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PT Wood & Tile = BAD BAD....................................

1 1/4" subfloor is required for natural stone installations.
 
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Old 09-20-08, 04:25 PM
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Originally Posted by HotinOKC View Post
PT Wood & Tile = BAD BAD....................................

1 1/4" subfloor is required for natural stone installations.
I got the idea to use PT flywood from this forum:

http://forum.doityourself.com/showthread.php?t=342155

I was told to use "exterior grade plywood," which I assumed meant "pressure treated." I think I also bought it because I walked into Lowes and the only plywood I saw that was specifically labeled as "subfloor" was pressure treated. Should I use something else instead? The carpenter at my office said to get some tongue and groove OSB, since that's what they use in new houses, but I am positive that every site I saw said to absolutely not use OSB for a subfloor. Will just any 3/4" plywood at Lowes be okay, whether it is labeled as "subfloor" or not? Last time I went they had this stuff called "Plytanium plywood that I liked because it was very level and smooth, but I thought I couldn't use it since it was labeled as "siding" and not subfloor.

I absolutely know however that I was told, in several sites I visited (including the thread above), that if I'm going to put down slate, I had to have a minimum of 1 1/4" subfloor for stone tile. I was going to lay down two 3/4" sheets, then hardibacker board on top of it, then the tile. But actually, I just measured, and if I want it to be level with the floors in the adjoining room, I only have 1 5/8" space from the top of the joists. I don't mind a small raise in the floor, but would rather have no more than 1/2." Can I just put down 3/4" of plywood, then the 1/4" hardibacker, then the tile? Or maybe even 3/4" plywood, then 1/2" plywood, then the hardibacker? I actually haven't decided what type of tile I'm using, so if it means reducing the raise in my floor, I can use ceramic tile instead of stone.

Lastly, that PT plywood didn't warp badly at all, and I hate to throw it away. Can I put that down in my attic after I clean it?

Thanks for the advice. I'd hate to screw this up and find out I used the wrong type of floor after I laid down the tile!
 
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Old 09-21-08, 08:26 AM
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PT (Pressure Treated) and exterior grade plywood are not the same.
Exterior grade uses water resistant glue between the plys. It will be labeled as Exterior, AC or BC rated.
PT plywood warps and expands ALOT when it dries, which is bad for tile.
If you want the installation to last, I would install 3/4" T&G ply over the joists, then a layer of 5/8" ply over that. Then you would add your 1/4" Hardiebacker. Hardiebacker is not rated nor tested for strength, so you can't consider it's thickness into the subfloor calculations.
 
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