solving wood floor over slab difficulty
Hi,
Some of you may recall my post during the worst of last summer’s hot, sticky weather regarding some 3/4 x 3″ ash t&g flooring installed over a slab. Beginning in July, after a spate of extraordinary humidity, the wood expanded like crazy and started buckling near a couple walls and door sills where it ran out of room to expand. It’s shrunk back up now, and I’m trying to figure out a permanent solution (actually, I’m hoping like hell that there IS a permanent solution).
Details:
- flooring is installed on wood sleepers over concrete slab–3/4″ expansion gap around perimeter (except at door sills)
- flooring was stored in rooms where installed for 4-6 weeks before installation–humidity was very low (Jan.-February, wood stove heat)
- slab is insulated with blueboard sides and bottom, vapor barrier also sides and bottom
- slab had cured 6 months before I installed flooring–tested slab multiple areas for excess moisture before beginning installation, was dry
- 90% sure moisture source is condensation on surface of cool concrete when warm, moist air entered house (witnessed this one evening in previous autumn before flooring was installed–slab became damp when it got very rainy and warm following a cold night (this was before the house was insulated).
- identical flooring upstairs installed on Advantech sheathing is fine
- flooring in kitchen had much larger expansion gap (hidden beneath cabinets) and was fine, although moved well over an inch.
- slab has pex tubing embedded, but in-floor heating system not operational yet
If I had it to do over again I would have done a differnent installation so that warm moist air could not come in contact with the concrete (what’s the best way to do that, by the way?). I read quite a bit and consulted a couple of architects, but got lots of different answers on that one.
So the question now is, can I fix things now so that the floors don’t buckle come July and if so, how? Again, the problem is restricted to places where the flooring has no expansion room (doorsills) or where the 3/4″ expansion gap proved to be too little (I’m still actually amazed that the flooring would expand that much–the living room’s only 18 feet wide or so and I used a spline in the center so the tongues are pointing in opposite directions on either side).
Should I just pull off the baseboard, yank the final flooring board and rip it down some? How about the door sills? And how do I fasten down areas of the floor that buckled up and pulled their fasteners up out of the sleepers?
Thanks,
Ed
Replies
Can you reduce humidity? If you dehumidify, the conditions that cause the problem might go away.
Ed:
The way I look at it you must give the floor room to expand. By chance is this below grade? Drainage problems from the outside? Expound more on these door sills. Is there any way the flooring can slide underneath. There are ways of doing so without placing ugly thresholds in the area. This amaizes me it could move so much in such a small area.
Ken Fisher
http://www.hardwoodinstaller.com
reducing the humidity would be the easiest...............but if you can't, figure the amount of expansion at peak (think you said 1"?) pull the boards at the buckle, rip them down and cover the gap by attaching quarter round to the base.......around the door sills? don't know, but there's always a way........just whatever you do make it look like you planned it............this means you gotta do the 1/4 round in the whole room etc......................all that moisture may in-time f up the underside of your flooring though?
Ed,
Is the floor "finished" now? I ask because maybe if it isn't having some kind of oilpolywhatever finish you chose might help? But I'm thinking it already is as it sounds like its been down a while.
I have 3/4" oak in my lower floor, slab-on-grade and I'm in Florida and haven't had any trouble with mine. I do have AC however that allows me to control the humidty to a certain point.
Did you have any kind of vapor barrier between the slab and sleepers or sleepers and flooring?
Mike
Thanks for the replies all. To address your questions:
reducing humidity--a few people last summer suggested running a dehumidifier during the summer. I'm sure that would help, but the downstairs is pretty open and I think it would take a monster unit to do the job. Not sure I could handle that racket all the time, plus we'd have to keep the house closed up at night--and we don't have AC--our cooling system is to open 'er up sundown to sunup (works great, by the way).
The slab is above grade. I'm virtually certain that the moisture source is condensation on the surface, not moisture from the ground. The site is well drained, plus we threw in a perimeter drainage tile around the frost wall footing.
The sills (interior only) are simply 3/4 red oak ripped to the width of the door jamb. Flooring butts against the sill to create a perfectly flat threshold. I'm not a big fan of the toe-trippers, but now I'm wishing I had designed it so the flooring could expand beneath the sill.
The floor is finished--used "OS Hardwax Oil" which is a breatheable penetrating finish, very different than poly.
There's no vapor barrier between the slab and the flooring (there is between the slab and earth, however). That's something I debated for a long time, since NOFMA and other industry folks say a v.b. is a must. I talked with 2 different architects about that, and they both agreed that poly was pointless since the fasteners puncture it thoroughly. Mastic might have worked, but I'm not sure that would've solved the condensation problem, since presumable the mastic would be the same (cool) temperature as the slab and the warm moist air would still condense on it.
Using Advantech as a subfloor probably would've solved it, and was my original choice, since it would've acted as a thermal break from the cool concrete, but my wife was concerned about the PF offgassing, especially with the radiant heat, so we went with sleepers.
My wife interestingly suggests heating the slab slightly during the really humid weather to prevent condensation, which is an interesting idea. But I kind of hate the thought of turning on the heat in the dog days of August!
The corner round at the foot of the baseboards is a good solution to the potential gap problem. How do I refasten the buckled boards without pulling them all up (I was hoping just to yank the last row)? Or should I pull everything that isn't still securely nailed down and renail it? Damn, I was afraid you' say that.
Ed,
I honestly think your problem is from a lack of vaopr barrier between the flooring and slab. All the moist air has no where to go but up through the wood.
You are correct in the fasteners would have penetrated the vapor barrier but the opening area from just the nail would have been less than the whole open void space. I used 30lb felt as I thought it might be more "self-sealing" around the nails. Mine also has 3/4" ply below the flooring.
Good luck with it!
Mike
You probably answered your own question by replying to several questions asked.
You like how well the house cools down at night with the windows open.
This doesn't mean the humidity level is dropping at the same time.
The huge slab area is a condenscing surface, especially with it able to make more free contact with the air due to the sleepers you used for the flooring.
With this situation, I am not sure if a vapor barrier will solve the problem. Condensation may still form on the top of the vapor barrier.
I hope others concur, but this is just my observation based on info provided.
Many folks face similar situations when cooling down a house in the evening with the windows open for fresh air/etc, especially in basements.
Dehumidifier is a necessity in many cases.
One plus is the heat generated by the dehumidifer also raises the temp above the dew point, which brings back your wife's suggestion.
You may be able to run the in-floor heating loop at much lower temps, just to bring the temp above the required level ?
Yeah, I think if the problem recurs this summer after I take some time right now to rip down some of the perimeter boards, redo the doors, etc. then using a very moderate amount of radiant heat just to keep the slab close to the air temp. should solve the condensation problem.
Interestingly, we're now into the second half of Feb., probably the driest the house is all year, and I notice that while the buckled areas have settled down largely, the flooring has not shrunk completely back to where it was when I installed it last Feb. Not sure why--but I figure I'm looking at max. shrinkage right now, and come March and April things will slowly start swelling up again.
There are some very experienced and "high-end" architects in my town here that I spoke with casually about the vapor barrier question before installing the flooring. They say they have never dared put wood flooring over a slab. (and they also said the vapor barrier wasn't going to help in my case).
As far as the dehumidifier, I realize closing up the house tight and cranking the thing (or having central air) during the dog days would probably solve the whole problem, but that's just not our cup of tea. One of our biggest design goals was low-energy use, for one thing, and for another we love to have fresh outdoor air in the house as much as possible. I spent a few months in Houston once and didn't really care for the AC lifestyle--the only time people go outdoors in the summer is walking from an air conditioned building to their air conditioned car.
Edited 2/18/2004 10:58:21 AM ET by MONSIEUR_ED
Edited 2/18/2004 10:58:42 AM ET by MONSIEUR_ED
I am all too familiar with Houston weather, having lived in Humble for two years in the early 80s.
I still remember the funky odor that was a combination of exhaust, industrial and wetlands outgassing plus the humidity.
The humidity was what got to me more then the heat.
Sunny one minute, then a downpour with cars gurgling their exhaust at intersections.
Then suddenly sunshine again.
I think Terratzo or stained concrete with radiant loop would be perfect in Houston.
It's the perfect market for expensive throw rugs.
My impression is there are a lot of tiles in living spaces.
Mostly slab-on-grade and a basement would be an oddity.