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sorethumb61 01-10-2011 06:04 PM

New plank hardwood floor cupping
I've been told it's a humidity problem under the house. I have visqueen and insulation already installed. Humidity reading was 23%. How do I lower the humidity, preferribly to 10%?

bob22 01-10-2011 07:28 PM

You'll have to move to the desert for ambient (room) humidity to be low. Most houses are around 30% or higher. If the wood was 23% moisture, then it was never properly dried. Which are you measuring?

Floor Doc 01-11-2011 04:02 AM

You don't want to lower the RH. You're to low as it is .
Ideal RH for Humans is 35 - 55% at a temp of 68 - 72 degrees.

Was the wood installed the same day it was delivered ? where temp, RH , and MC readings taken of the wood and substrate to make sure the wood was acclimated ?

A moisture differential within individual pieces of flooring, usually
excessive moisture on the underside of the flooring. More subtle cupping can be caused by lack of
proper acclimation (this is generally permanent cupping).

there can be a few reasons why it is cupped . One is the floor was installed wet , the wood looses moisture at the edges first .

You really need a on site inspection by a independent inspector . one that don't have a dog in the fight. you can Pm or post where you are located, i will recommend a good one for you .

rocks911 02-03-2011 04:06 PM

Lots of considerations.

I really doubt that you need to lower the relative humidity in your home as most homes in the U.S. are like deserts as it is. Most lumber is sold kiln dried at about 7.5 % moisture content. The assumption used for this is that most U.S. homes are 72 degrees at 40 relative humidity (RH) and the wood is at stasis in that environment and will neither expand nor contract.

Cupping is caused by excessive moisture exposure on the underside of the board. That can include relative moisture, which is to say that if the environment in your home is very dry the exposed top side of the board is less moist than the bottom side. If anything you should increase the RH in your home.

How long has the floor been installed? What type of wood? Have you ruled out absolutely every source of water intrusion? Cupping can be caused by many things, even from a long distance, for example poor flashing on your
chimney/roofing, or a tiny water leak.

I know these things because I have a floor that is cupping and have yet to figure out my own problem. I have narrowed it down significantly though and next plan to tear into a wall near where plumbing is located to see whats up.

Good luck to you

Floor Doc 02-03-2011 04:33 PM

How long has your wood been down rocks ?

rocks911 02-03-2011 05:09 PM

My floor is 4" red oak been down 2 1/2 years. I have ruled out a fresh water leak. I paid for a new chimney cap as my chimney did not have one when I purchased the house and the flooring is near my fireplace, though the old timer that installed the cap said he doubted that it was related to the fireplace as my home is a 2 story and he said it is improbable that that much water was getting in from a lack of a proper chimney cap, so I continue to try to figure this out.

I've had roofers, the chimney guy, and several friends level a guess and still have no sure culprit.

The floor is installed over a concrete slab. The installer first put down a heavy mil plastic, then felt, then sheets of plywood with 20 nails per sheet into the slab, then more felt and the flooring laid perpendicular to the plywood.

I hope that I get into the wall and have an ah-ha moment, otherwise it's maddening trying to pin it down.

It's close to impossible to find someone who can walk into your house look at the floor and say "that right there is what is causing the problem" so it's pretty frustrating.

By the way I'm in the Dallas area and it's been awfully dry this winter.

woodman58 02-03-2011 05:27 PM

Big ? what is the width of the planks. 2 1/4, 3, 4, 5? We really need a little more info. What room is the wood in? Are you reading moisture at the wood or in the room. If the moisture reading was taken at the wood then you have a leak. If your relitive humidity(RH) in your house is only 23% you need to put moisture back in the house. Get a humidifier or just keep a pot of water on the stove with low heat. If you don't have a moisture meter to read moisture at the wood you can get a cheep one at Home Depot for about $25.

rocks911 02-03-2011 06:16 PM


Do you happen to know the make/model of the HD moisture meter?

LIHR 02-03-2011 06:26 PM

"You really need a on site inspection by a independent inspector" I'm with Floor Doc on this one.

You can go back and forth all day long on every variable as to the causes and still be just as confused. Most installers have not a clue on the proper installation of flooring, but "Luck-out" with the basic fundamentals of installation procedures only because the physcial sciences at play are in their favor on the day of install.

There are too many variables that are involved without a professional on-site inspection.

Floor Doc 02-03-2011 07:55 PM

Rocks , Making a sandwich with the plywood is a no no. :eek:
You need a on site inspection by a Hardwood flooring inspector , and possibly some destructive testing [Removal of a few boards]. to see what is going on underneath.

You say the installer put poly and felt down , then punctured it nailing the plywood . then sandwiched it with felt which is a retarder , not a barrier .

There would be a lot of questions i would be asking if i were to inspect the floor .

rocks911 02-03-2011 08:33 PM

Floor Doc,

I didnt mean to hijack this guy's thread so I'll start my own.


woodman58 02-03-2011 08:54 PM


Originally Posted by rocks911 (Post 584177)

Do you happen to know the make/model of the HD moisture meter?

It's a General. I did not have my Wagner one day so I bought it. It is within 1% of my wagner

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