Floor Joists advice...

Hello. I recently purchased my home, (November of '09). I was actually renting this place before I purchased it. Anyway, when I was still leasing the house, I striped old caulking from the master bath shower (because it was quite ineffective, and had intrusion issues), allowed the shower to dry out, (by using the common bath in the hallway) and recaulked to seal the shower. I have decided to remodel the master bath. I am in the first stages of demolition and was curious to see just what the damage really was. The sub-floor was rotting just under the shower pan curb, some of the sub-floor under the framed walls is rotten also. I have inspected the joists that are directly under the bad sub-floor where the curb was. I removed some of the sub-floor, about a 4'x2' space, and have a pretty good visual on the joists. On the sides, the joists are dark in colour from where moisture came through the sub-floor. I took a screwdriver and poked around the joist and aside from the discolouration on the sides, they are solid. However, it is a different story on the top of the joist. There seems to be some sort of mildew or mold on top of the joist, where it was in contact with the rotten sub-floor. This area is white on the surface and spongy to roughly 1/16" to 1/8" deep. I knew that this was going to be a problem area, because our house inspector informed us of the possible damage. He said that the sub-floor might need to be removed and joist treated with Timbor. Before I treat it with Timbor, do I need to remove any of the mold or surface wood? If remove all the surface wood, do I even need to treat it with Timbor? Or is the wood hopeless and needs to be removed altogether and replaced? Is just slicing away the bad surface sufficient according to building codes (I'm in California). Are there any other treatments that I can use on the wood after scraping off the surface? Any help on this matter would be greatly appreciated. Thanks!

Some pics would help

If the wood seems solid you are fine. Just let it dry out, maybe put a fan on it to speed it up.

For the mold use a water and bleach mix in a spray bottle and kill the mold with that. Spray on and let sit most of the black will go away apply a couple of times if needed.

You colud always sister the joist in question, if you can get them in there.

Good Luck

I agree with the previous post that simply sistering the damaged joist will provide a strong solid nailing surface to fasten the new subflooring to.

Another option would be to simply nail a 1X2 about 5 inches below the top of the joist (or 6 1/2 inches above the bottom of the joist) and to cut off the top 1/8 inch of joist with a circular saw. Then, have a piece of fir 2X4 ripped to 1/8 inch thick on a table saw and glue it in place with a very strong glue like LePage's PL Premium. Screw or clamp the piece down to the joist while the glue cures to ensure that you have a minimum of glue thickness for a fit that's flush at the top of the joist.

(the house inspector) said that the sub-floor might need to be removed and joist treated with Timbor.

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Your house inspector is misinformed about the appropriate use of borates. Timbor is a borate based wood preservative. It's effective at preventing wood rot, but like all borate based wood preservatives, it's highly soluble in water.

Timbor Wood Preservation, Timbor® Wood Treatment

So, externally treating the joists with Timbor stands right next to not treating them at all. The reason why is that if you ever have any futher water leaks onto that Timbor treated joist, the water is just going to wash the Timbor off the joist and effectively render it "untreated". You'd be much better off to use a wood preservative that isn't soluble in water, like a copper naphthalate based end cut preservative. And, after applying the end cut preservative once, keep in mind that allowing the mineral spirits to evaporate completely from the wood before treating the joist a SECOND time with the end cut preservative allows the wood to absorb MORE copper naphthalate for more protection. (If it wuz me, I'd probably start treating any wood that may get dripped on with end cut preservative now so that you can muster as many as possible treatments before you have to install the subfloor and no longer have good access to the joists. And, I'd treat the subfloor with end cut preservative too. Then, I'd nail the untreated underlayment down to the treated subfloor and glue your new bathroom flooring to the underlayment. (I'd be concerned that the end cut preservative would interfere with the glue bond holding the flooring down.)

Hey Brain and Nestor,
That's some good advice. I actually do not think that sistering the joists will be necessary. They are completely solid (of course with the exception of the top 1/8
" that is a bit spongy).

Nestor, you wrote, "Another option would be to simply nail a 1X2 about 5 inches below the top of the joist (or 6 1/2 inches above the bottom of the joist) and to cut off the top 1/8 inch of joist with a circular saw. Then, have a piece of fir 2X4 ripped to 1/8 inch thick on a table saw and glue it in place with a very strong glue like LePage's PL Premium. Screw or clamp the piece down to the joist while the glue cures to ensure that you have a minimum of glue thickness for a fit that's flush at the top of the joist."

Just a question about that, is it with in code? Is this an acceptable repair if I were to have it inspected later on? This was actually the method I was considering, but was not sure if it was acceptable.

Thanks.

Username said:

Hey Brain and Nestor,
Just a question about that, is it with in code? Is this an acceptable repair if I were to have it inspected later on? This was actually the method I was considering, but was not sure if it was acceptable. Thanks.

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I'm not a building contractor, but I don't think this kind of a repair would "meet the code". But, that's not because it's not a good repair; it's because it's not until relatively recently that we've had glues that could be applied in the field that would form a bond as strong as the original wood. So, as in so many other cases, good ways of doing things don't meet the building code because the building code doesn't keep up with technology.

Your floor joists were sized with a significant safety factor built in so that your house doesn't collapse if you drill a hole or cut a notch into a joist. The damaged joist would still be plenty strong enough to support the weight that it will be required to carry even without your doing anything. But, I would go ahead and glue that shim in because by glueing it in rather than simply nailing a shim into place to avoid height problems on the floor, you make that piece
you put in STRUCTURAL. That is, it helps support the weight of the floor. And, that, in my books is better than simply nailing a shim into place.

I have a background in engineering. I graduated from the U of Manitoba in Mechanical Engineering in 1978. You CAN add wood to a joist to make it stronger, and the only requirements are:

1. The wood you add is as strong or stronger than the wood the joist is made of, and

2. The glue joint is as strong or stronger than the wood the joist is made of.

By doing that, neither the wood you add nor the glue bond holding that wood in place will be the weakest link in the chain. The joist wood will break or crack before the added wood will because both that new wood and that glue are stonger. It's only within the past 10 years or so, however, that super strong construction adhesives like LePage's PL Premium that will form a bond stronger than the original wood, and can be applied in the field, have been available.

Anyhow, no building inspector is going to smile on that repair because I think he'd want you to sister that part of the joist. However, he'd realize that by glueing a piece of clear fir (or even hardwood) in with PL Premium to replace the rotted wood, the joist should be as strong or stronger than it was before the wood rot occured. So, I'd do it in my own building.