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Unread 03-18-2019, 06:46 PM   #1
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Black Mold Remediation, from underneath (OSB subflooring)

Greetings, all! I have been here numerous times and benefitted tremendously and today was encouraged to post by an old clay target shooting bud, Dave (“Its' hell to gits' old”) Taylor (cue up the golf tournament applause ... fade ...)

Since this is not tile-related I thought The Mud Box to be the most appropriate forum to approach the braintrust, herein; and, Out of respect for everyone’s time, I did attempt a search (search term, ‘mold’) but, that turned out to be too general (brought up every mention of molding, etc.)

So, here goes!
Our situation: we have an area of black mold in sub flooring under a toilet that apparently the wax ring originally installed developed a hairline crack and started leaking just a little bit - at some unknown point between when the house was built 10 years ago and now. Leak was discovered 3 weeks ago and we got the toilet pulled and wax ring replaced pronto.

The problem is (our “challenge” remains) killing the black mold that is within the subflooring (osb board). Replacing the subflooring is not an option - it is NOT “just” a matter of “matching tile stones” but rather the subflooring runs under two separate walls forming a load bearing corner in the house (stone tile on bath side, hardwood floors on the other two sides) so, trying to replace the subfloor would amount to a major, major construction project.

Luckily, the underside of the bathroom floor is the “ceiling” in our semi-unfinished basement. We are talking an area of about twice the size of a tennis racket on one side of the engineered joist bisecting the area and about the size of a baseball cap on the other.

I am having some success at killing the black mold by getting up my 10’ ladder (subfloor is 11’ off unfinished basement floor) and using a spray bottle to dampen the area with various mold-killing liquids. I was reminded quickly that bleach is NOT an effective mold killer on porous surfaces, at all! Some success was found with mixing baking soda into vinegar (which ARE effective on porous surfaces) but, hands down, BEST has been straight household 3% hydrogen peroxide sprayed onto the area and allowed to dry ... but, so far, there are spots where the mold is returning.

I posted my situation on a fellow shooters forum and found out about Concrobium Mold Killer, went to Home Depot, got a spray bottle and applied that this afternoon. Checked again this evening and there are still large black blotches that appear to be much more than just “staining.”

SO, MY QUESTION IS THIS: has anyone had any success using any type of either:

1) atomizer / ionizer / ozone generator; or,

2) ultraviolet or other form of light?

I was pinning some hope on the ozone generator route but, I haven’t been able to find a whole lot of confirmation that they work on a localized mold colony (just “the air” enclosed spaces). Our basement is a relatively huge space, area wise (we’re talking 1,100 sf easy, with 11 foot ceilings ...)

I’ll say Thanks In Advance, Y’all! and add ...

Here’s what the area in question looked like the day we discovered the leak ... and 2nd pic shows progress after multiple sprays with different mixtures (settling on the Concrobium now) ...
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Unread 03-19-2019, 07:49 PM   #2
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Welcome, Thor.

You might wanna look in our Liberry under Mold. Couple good articles there as I recall. A bit dated, perhaps, but I don't think mold has changed much in the past 20 years. Or 20 thousand, for that matter.

My opinion; worth price charged.

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Unread 03-20-2019, 06:31 AM   #3
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Hi Thor,

I'd squirt it with laundry bleach diluted with water -- about a cut of bleach to a gallon of water. Let it dry and cover it up.

Hope the mold police don't get me.
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Unread 03-20-2019, 09:31 PM   #4
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Pool shock. Use pool shock instead of bleach. Set a dehumidifier in there an let it dry out. No more water=no more mold.
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Unread 03-27-2019, 02:21 AM   #5
Dave Taylor
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Hi Thor........

Folks herebouts' take a bit more practical view of handling mold issues than the brain trust on a shooter's site..... and I agrees' wif' em'.

Good luck to you.
Dave T (DIY'er)
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Last edited by Dave Taylor; 03-27-2019 at 02:47 AM.
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