Test for Moisture when Installing Hardwood Flooring

"Acclimating" flooring in the house before nailing down is not a sure-fire precaution. You should also provide a vapor barrier, and test the flooring, subflooring and slab for proper moisture content. December 26, 2006

I'm asking this question for a client of mine. She is having someone put in hardwood flooring. Shouldn't the guy put it in the house 2 weeks prior to installation for it to acclimate? She said he is going to install it and then wait 2 weeks before he finishes it. This doesn't sound right to me. I will be doing the base moulding and she wants me to put it in after the flooring is in. She doesn't like the shoe moulding that covers the gap between the base and the floor. Should I be wary of cupping that may push on the moulding, or other worries? We typically only do cabinetry but are starting to get into mouldings. Any advice is appreciated.

Forum Responses
(Architectural Woodworking Forum)
From contributor A:
I've heard even longer, like a month. But consider that most houses are built with the air conditioning off. I don't think most builders wait 2 weeks with the air conditioning on in a spec house to acclimatize the hardwood flooring.

(Finishing Forum)
From contributor B:
I need to know more about the job and more about the flooring material. Is the sub-floor concrete or wood, and glue down or nail? Either way, it should acclimate in the house before the install. Time could be 2 days or 2 weeks depending on climate and site conditions.

From contributor C:
I've done quite a bit of flooring over the years with both unfinished and finished. Many times everybody is in a rush and that flooring gets nailed down as soon as it gets into the house. I have a problem with people saying you need to let it sit in a new house for a while before it gets installed. There is so much moisture in a new house from drywall/lumber that I don't want the hardwood absorbing that. As long as the hardwood has been in a climate controlled warehouse before entering the home then I think you'll be ok.

From Gene Wengert, technical advisor Sawing and Drying Forum:
I think I hear more complaints about moisture in flooring and tables than any other products. I agree with contributors B and C that 2 weeks is not really a good guideline, especially if the flooring is not at the right moisture when it arrives. It would be prudent for the flooring installer to use a moisture meter to check quite a few of the pieces before installation. The cost of a meter ($200, no less) is certainly worth it. But the real questions are "What is the correct MC?" and "What is the correct RH for a storage warehouse?" In much of the USA and Canada, the answers are 7.0% MC and 38% RH. We might also ask "What is the RH going to be in the house when it is done?" In many cases, 37% RH average is typical. In summary, the flooring installer needs to have lots of experience and then also be responsible enough to want to do it right.

From contributor C:
There is more than the MC of the flooring in play here. The sub floor and, if over a crawl space, the ground beneath the floor also needs to be tested. A Quantitative Anhydrous Calcium Chloride Test to determine moisture in the concrete, if the sub floor is concrete, is absolutely necessary. The original poster didn't mention the words "new construction" but if (that little word again) the HVAC hasn't been turned on or if the concrete has cured for less than 60 days...etc. We don't really know if the wood is solid, engineered, or a laminate. More information is needed or we guess.

From Gene Wengert, technical advisor Sawing and Drying Forum:
Contributor B makes a very good point that I support. Concrete emits moisture for at least 60 days as it cures. I have seen a test used - I cannot testify that it is perfect - but it involves putting a piece of clear plastic (2' square perhaps) on the new concrete floor and then putting a piece of wood on top of it to hold it down. After a day, look for moisture under the plastic. No moisture signs indicates that the floor is ready. Any comments?

From contributor B:
Right. A simple test that seems excellent although lacks scientific confirmation to my knowledge is to tape (duct tape works) a 24 to 30 inch square piece of 6mil polyethylene directly to the concrete for 24 to 36 hours. If the bottom side of the polyethylene has droplets of moisture formed there is most likely a problem and a professional moisture test of the slab should be done. That's where the calcium chloride test will prove its worth. Most hard surface flooring pros (installers) can and will perform the testing.

From the original questioner:
The house was built in the late 70s and is in southern California. It has a concrete slab that the flooring will be built onto. I believe they are laying 3/4" subfloor (probably above some sort of moisture barrier) and then nailing the hardwood to it. So it's not a new home, but with the humidity and such here I am a little concerned for them.

From contributor B:
No red flags here. That said, take the usual precautions and the prudent testing, and you should be ok.

From contributor C:
Bottom line - contact the manufacturer and follow their recommended procedure. If a problem presents itself after installation that was done to their specs, it is not your responsibility.