possible mold under hardwood floor

[Megunticook]

My kitchen has 3" birch flooring that was installed in 2003. It's fastened to wooden sleepers over a concrete slab. Some years ago our kitchen sink drain leaked and it ended up dampening a portion of the slab below. Fixed the leak and dried things out with fans best I could. Floor didn't buckle but I suspect we may have developed some mold on the bottom side of the flooring near the sink area--getting a faint off smell, not the classic mold smell but I can definitely detect something a little odd. I notice it particularly sometimes when I go away for a few days and come back. There's no visible mold anywhere.

I'm thinking about removing the flooring to see what's going on under there but not exactly sure how to go about it. I can't access the last course because it runs beneath the cabinets (see photos below). Situation is further complicated because the flooring also runs beneath an island. Should I cut out one of the pieces and inspect for starters? What's the best technique to do this?

Also, the finish on the floor has gotten pretty worn (I used Osmo Hardwax Oil which penetrates the wood and can be reapplied without sanding). I refinished it once but it's worn off now. I'm wondering if maybe water splashed onto the floor (you should see what happens when my 16-year-old is asked to do the dishes!) is now just soaking into the wood and maybe "re-activating" any mold that might be under there. Thinking I should refinish the floor so it stays dry, then rip out a piece and inspect the bottom for any sign of mold (refinishing is pretty easy--you just clean the floor then brush on a thin coat of the hardwax oil).

Finally, noticing some significant gaps in the past year--and a couple of the boards are feeling a little loose now--near the sink area. Wondering if water splashing on the unfinished floor is causing some extra swelling/shrinkage and creating more movement? We heat with a woodstove so it can get very dry in the house during winter.

Thanks for any advice. Here's some photos:

 

[C.J.]

As far as inspecting what’s going on underneath, how about an inspection cam. Drill a small hole and snake the cam through it to see what’s going on underneath. Or you can remove the island, pop a couple boards up to inspect. When you put the island back you’ll never know you took up a couple boards.

You need to wax that floor. Wax is super easy and you don’t need to sand before reapplication. The downside is it needs to be done more frequently. Once a year? Couple times a year? Get your daughter to help and tell her it’s because she’s sloppy when she does dishes.

Funny thing about wood, floors or countertops, is they need to be maintained frequently. I’ll finish a wood countertop for somebody with multiple coats of oil and a wax popper for that shine. They love it until they ask me how long until they need to reapply oil or wax. I’ll tell them a few months and they always give me the same look. Kinda like buying a black corvette, you’re gonna have to maintain it if you wanna keep it looking nice.

 

[Megunticook]

As far as inspecting what’s going on underneath, how about an inspection cam. Drill a small hole and snake the cam through it to see what’s going on underneath. Or you can remove the island, pop a couple boards up to inspect. When you put the island back you’ll never know you took up a couple boards.

You need to wax that floor. Wax is super easy and you don’t need to sand before reapplication. The downside is it needs to be done more frequently. Once a year? Couple times a year? Get your daughter to help and tell her it’s because she’s sloppy when she does dishes.

Funny thing about wood, floors or countertops, is they need to be maintained frequently. I’ll finish a wood countertop for somebody with multiple coats of oil and a wax popper for that shine. They love it until they ask me how long until they need to reapply oil or wax. I’ll tell them a few months and they always give me the same look. Kinda like buying a black corvette, you’re gonna have to maintain it if you wanna keep it looking nice.

Thanks for your advice. Inspection cam is a good idea--had considered that. Removing the island would be a significant project but could be done.

Let's say I do find mold underneath the flooring. Can I remove the mold and re-use the old flooring? Would something like borax solution work?

Hate to throw away all that beautiful wood. I pulled out the old receipt (sawn by a local mill), paid $500 and the current quote I got was $1300 to replace it. Has flooring really almost tripled in cost over 20 years? Hate to be building a house now....

 

[Floorist]

Thanks for your advice. Inspection cam is a good idea--had considered that. Removing the island would be a significant project but could be done.

Let's say I do find mold underneath the flooring. Can I remove the mold and re-use the old flooring? Would something like borax solution work?

Hate to throw away all that beautiful wood. I pulled out the old receipt (sawn by a local mill), paid $500 and the current quote I got was $1300 to replace it. Has flooring really almost tripled in cost over 20 years? Hate to be building a house now....

All wood has tripled in cost.

 

[C.J.]

The cost of everything has skyrocketed. One thing to consider is that mold needs moisture to grow. If you’ve cured the moisture problem then the mold will go dormant. Problem solved.

 

[Floorist]

The cost of everything has skyrocketed. One thing to consider is that mold needs moisture to grow. If you’ve cured the moisture problem then the mold will go dormant. Problem solved.

Yep and black mold is only dangerous if you are allergic to it.

 

[Megunticook]

The cost of everything has skyrocketed. One thing to consider is that mold needs moisture to grow. If you’ve cured the moisture problem then the mold will go dormant. Problem solved.

True. Glad we built our house back in 2003 because we probably couldn't afford to do it today!

So that point about the mold being a non-issue as long as the wood stays dry is something I've been thinking about a lot. The leak was fixed but it seems like sometimes I still smell something. If the relative humidity gets high enough, I wonder if that can "reawaken" the mold? Or if you don't keep your floor maintained with a coating (guilty!) maybe water on the surface can penetrate and do the same.

The other thing--I really wish we had put a layer of Advantech on top of the concrete instead of sleepers. That was the original plan. We ended up going with the wooden sleepers and I wonder if when it's hot whether moisture could possibly be condensing on the cool concrete. But there's definitely something going on in the kitchen.

 

[C.J.]

Have you looked around the exterior of your house. Is the ground properly sloped away from the foundation. Gutters properly draining away from the foundation. How about a minor dishwasher leak or something else that could be introduc

I’m just tryin to think of all the simple stupid things that it could be before you have to rip up flooring.

How about getting a moisture meter and poking several boards throughout your kitchen. Maybe you’ll find an area that is high and that will save you from having to rip up the entire floor.

 

[Megunticook]

Have you looked around the exterior of your house. Is the ground properly sloped away from the foundation. Gutters properly draining away from the foundation. How about a minor dishwasher leak or something else that could be introduc

I’m just tryin to think of all the simple stupid things that it could be before you have to rip up flooring.

How about getting a moisture meter and poking several boards throughout your kitchen. Maybe you’ll find an area that is high and that will save you from having to rip up the entire floor.

Don't think any moisture is coming in from outside--grade slopes away from house, there's drainage tile around the foundation footings, the foundation walls are waterproofed, and the slab was poured over a layer of thick poly.

I pulled the dishwasher out last week to check, didn't see any leaks or any signs of recent or old moisture.

I ordered a moisture meter and will check the boards. Seems like they would be swelled, or cupped, and I wouldn't have those gaps showing either. The only moisture sources I can see would be the sink leak which was fixed quite a while back and water splashed on the floor when people wash dishes.

Beginning to think installing a wood floor in the kitchen was a dumb idea. If I had it to do over again I would do tile.

 

[C.J.]

So you already know water gets slopped on the floor when doing dishes. Wouldn’t it be crazy if all you had to do was wax the floor? I don’t necessarily think that is the source of your problem but if you’re not waxing your floor (regularly needed maintenance), what else aren’t you paying attention to.

 

[Megunticook]

Yes I've been very negligent in caring for that floor. Am going to refinish in the next few days and then once a year (or sooner if it looks like it needs it) I'll apply some maintenance wax. I'd be delighted if that's all it takes to resolve the issue.

I cut out the bottom of the cabinet under the sink so I could access the concrete slab directly when the leak happened and I regularly check under there. Have never seen any further signs of moisture or any visible mold under there. Also checked the dishwasher.

I used to sort of snicker at the Rockefellers who live across the road and have 2 full-time maintenance people busy all the time (plus the usual parade of contractors). Now I don't laugh--it's not easy keeping up on everything along with work, family, etc. I definitely struggle on that front. But clearly floor care needs to get bumped up on the priority list.

 

[JPfloor]

If you’re spilling that much water when doing dishes perhaps a throw rug in front of the sink would help? Wet unfinished wood is not good… It will rot out eventually. Or just get your 16 year old to spill less water…

 

[Megunticook]

Agreed, I did start throwing a big towel down by the sink and asked him to please be careful. Also asked him to wipe up any spills immediately. Of course we all know that 16-year-olds all obediently follow their parents' advice unfailingly...

 

[C.J.]

Yes I've been very negligent in caring for that floor. Am going to refinish in the next few days and then once a year (or sooner if it looks like it needs it) I'll apply some maintenance wax. I'd be delighted if that's all it takes to resolve the issue.

I cut out the bottom of the cabinet under the sink so I could access the concrete slab directly when the leak happened and I regularly check under there. Have never seen any further signs of moisture or any visible mold under there. Also checked the dishwasher.

I used to sort of snicker at the Rockefellers who live across the road and have 2 full-time maintenance people busy all the time (plus the usual parade of contractors). Now I don't laugh--it's not easy keeping up on everything along with work, family, etc. I definitely struggle on that front. But clearly floor care needs to get bumped up on the priority list.

I wonder if cutting out the bottom of the kitchen sink cabinet is what is allowing the occasional musty smell into your living space. Prolly a good idea that you cut it out for inspection but now it allows some of that stale musty air out whereas before it would have just been contained to underneath your floor. How easy would it be for you to cut an insert and slip it back into the opening yet still remain removable for future inspections.

Maintenance on a home or a vehicle is a bitch at times. My buddy asked me why my wife n I always have small houses. Same reason I don’t drive an Audi, BMW or Porsche, the maintenance alone will kill you.

 

[Megunticook]

I wonder if cutting out the bottom of the kitchen sink cabinet is what is allowing the occasional musty smell into your living space. Prolly a good idea that you cut it out for inspection but now it allows some of that stale musty air out whereas before it would have just been contained to underneath your floor. How easy would it be for you to cut an insert and slip it back into the opening yet still remain removable for future inspections.

Maintenance on a home or a vehicle is a bitch at times. My buddy asked me why my wife n I always have small houses. Same reason I don’t drive an Audi, BMW or Porsche, the maintenance alone will kill you.

I did replace the bottom of the cabinet with a removable piece of plywood for exactly that reason. Unfortunately that didn't solve the issue.

Speaking of cars, I got so sick of paying money to have my vehicles repaired by "professionals" who did crappy work that I ended up just doing it all myself so I can make sure it's done right. But of course that just adds another bunch of ongoing tasks to my full plate. More than once careless mechanics have left their tools in my engine compartment--tells you a lot. One time I nearly lost an engine after a water pump replacement when the engine overheated. We now have an electric though so far less maintenance time.

 

[Tile Tom]

If it's on sleeper's there's definitely some moisture issues going on. If nobody is sick and it's not bothering anyone then it might be best to just leave it alone

 

[Megunticook]

If it's on sleeper's there's definitely some moisture issues going on. If nobody is sick and it's not bothering anyone then it might be best to just leave it alone

Condensation on the cool concrete?

So would a proper installation have been vapor barrier over concrete, then Advantech subfloor, then finish floor?

One day I may rip up the whole thing and do it right. It's what I wanted in the first place but I was overuled by SHMBO.

Nobody's sick but I like a fresh-smelling kitchen. And who knows if there might be some low-grade effects.

 

[C.J.]

SHMBO. Lol. Never heard that one before.

 

[Megunticook]

Guessing you deciphered it?

 

[C.J.]

Had to google it. Still chuckling.