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Old 08-12-2011, 11:27 AM   #1
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sistering moldy joists with PT?


In one part of my basement, the joists are moldy/mildewed (basically they're now a light gray color). Some of the drain holes cut through the joists also are out of spec (boring 3 inches in a 2x8, even a 2x6 sitting on a shim, notched and essentially a 2x4 now). I'm going to be laying tile down on the floor, so I can't have any stupid things like that that might compromise the tile joints.

The current 2x8s sit directly on the foundation (no sill plate). If I sistered PT to these, would the PT be able to resist any mold/mildew that is currently on the joists? How's the strength of PT as joists anyways? I could upsize to 2x10s and just notch the bearing ends, if that would work even better. Of course I'm going to shoot myself with the electrical and such that is already going through there, but whatever :\
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Old 08-12-2011, 11:32 AM   #2
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sistering moldy joists with PT?


The pressure treated lumber won't be effected by the mold (not mildew), but that doesn't really solve the primary issue which is why there is mold on anything in the first place. You need to discover what the moisture issue is that's causing the mold problem. Sooner or later, if not already, the high moisture will affect the sub floor and any other wooden components.
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Old 08-12-2011, 12:04 PM   #3
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sistering moldy joists with PT?


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The pressure treated lumber won't be effected by the mold (not mildew), but that doesn't really solve the primary issue which is why there is mold on anything in the first place. You need to discover what the moisture issue is that's causing the mold problem. Sooner or later, if not already, the high moisture will affect the sub floor and any other wooden components.
was caused by 9 inches of water in there for a week when the sump pump failed. Thats all
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Old 08-12-2011, 12:26 PM   #4
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sistering moldy joists with PT?


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was caused by 9 inches of water in there for a week when the sump pump failed. Thats all
I would clean and dry the joists so the issue is removed. Then frame with regular wood.
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Old 08-12-2011, 12:32 PM   #5
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sistering moldy joists with PT?


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I would clean and dry the joists so the issue is removed. Then frame with regular wood.
I recall being told that once mold is in wood, it's there to stay. is that not true?
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Old 08-12-2011, 12:58 PM   #6
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sistering moldy joists with PT?


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I recall being told that once mold is in wood, it's there to stay. is that not true?
Check this out:

http://www.inspectapedia.com/sickhouse/cleanmold1.htm
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Old 08-12-2011, 02:07 PM   #7
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sistering moldy joists with PT?


Mold per se is a surface agent. There are various insects and complicated organisms such as lichen and a few protozoa that can live inside wood, however once the tree is cut and dried, and used as framing timber, in my experience mold is on the outside and can be effectively eliminated by standard techniques such as use of bleach. Of course, if you have not solved the water issue, the mold is going to come back, since there are always mold spores floating around, and mold is very opportunistic, all it needs is substrate, water, and temperatures above freezing, voila mold appears.

As for the strength of PT lumber, it depends on the species and grade used. Very often southern pine is used, and so far as I am aware, there is no strength reduction required simply because it has been pressure treated. PT lumber is rarely used inside because of cost, and some folks are concerned about the nasty chemicals commonly used to prepare the lumber.
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Old 08-12-2011, 03:04 PM   #8
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sistering moldy joists with PT?


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I recall being told that once mold is in wood, it's there to stay. is that not true?
In your case you have little to be concerned about. It was a one time water event which will not likely re-occur (hopefully). Mold can and will send microscopic hyphae into porous materials such as wood. These will regrow a mold organism if and when conditions become ideal. Hyphae are difficult to completely eliminate. Hence the idea that you can't get them out of wood. Much depends on how long the mold was allowed to thrive. In your case, I would imagine it wasn't very long. Wipe the joists down with a cleaner, then a fungicide, such as 10% bleach solution, then get them dry. Apply a sealer to lock down any stray mold fragments and proceed with the sistering. Forget about spores and magic mold killing solutions and almost everything else you read about "deadly mold". Any mold that remains will go dormant even if you don't completely kill it. The sealer will help to keep it in check. Common molds need three things to thrive, an organic food source, temperatures of 40-110 degrees and 60% or greater moisture content, but less than 100%.
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