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moisture trapped in gypcrete floor

moisture trapped in gypcrete floor

moisture trapped in gypcrete floor

I have a floor system that consists of (from top down): laminate flooring with moisture barrier + 1.25-inch thick gypcrete + 1/2-inch diameter PEX radiant floor heat tubing + (2)- 3/4-inch plywood panels over wood floor joists spaced at approximately 16 inch centers.

Problem: laminat flooring replaced after water leak. laminate floor is buckling when pex floor heating is turned on. could heat from PEX tube floor heating be causing trapped moisture in gypcrete to rise above and buckle the floorboards? Seems reasonable to me but I am looking for additional thoughts.

RE: moisture trapped in gypcrete floor

Is it possible the laminate floor was cut too tight at it's ends and it doesn't allow for standard expansion and contraction?

RE: moisture trapped in gypcrete floor

@jayrod12: I would say no since the flooring has been replaced multiple times and the buckling is occurring as soon as the radiant floor heating (PEX) is turned on.

RE: moisture trapped in gypcrete floor

My point still stands. If it has been cut too tight to the walls at each end then when the in-floor heat comes on and the laminate tries to expand outwards it's restrained and the only place to go is upward to relieve the expansion stresses.

It's the same as vinyl siding installed tight to the corner mouldings in cold weather, buckles outward in the warm weather because there's no where else for it to expand.

RE: moisture trapped in gypcrete floor

psuengineer1...what is the moisture content of the gyp fill? Check that.

What you are describing can occur without regard to the restraint at the ends as jayrod12 notes. If the area of the flooring is large, the friction restraint at the sides of the individual pieces creates a lot of cumulative restraint, thus buckling can occur.

The material to which the surfacing is bonded is essentially a finely divided paper product. This absorbes moisture and causes differential expansion.

RE: moisture trapped in gypcrete floor

I find it hard to believe that it is buckling due to moisture in the gypcrete, especially if it has been replaced multiple times. I have a similar system at my home but it is engineered wood floor glued to gypcrete (no moisture barrier). My problem is drying during the winter months. I see cupping (shrinkage of the real wood portion on top). It was installed during the summer months. The sheets were installed tight to each other. (sorry really help with this statement)

Would the floor actually expand that much due to thermal change? Would the temperature really get that high? I mean more so than the temperature in the summer?


RE: moisture trapped in gypcrete floor

The gypcrete and everything below your laminate flooring must be absolutely dry. You must allow the gypcrete to completely cure and dry. And, I believe there should also be a moisture vapor barrier under the flooring. I suspect your problem is primarily caused by a difference in moisture btwn. the top and the bottom of the laminate flooring. You’ve got dry A/C or heating on the top side, and some moisture on the underside. You’ve got moisture drive upward, from the gypcrete into the room. This is notorious for causing buckling of this type of flooring. This same thing can happen with solid flooring, slightly different with the (because of the) laminated materials. I’ve seen this same thing happen with flooring over a crawl space which was not insulated and conditioned. The flooring should also be brought inside some time before installation, and allowed to acclimate properly. Then, of course, you can have the other normal expansion and contraction issues too.

RE: moisture trapped in gypcrete floor

I did a lot of work at my dad's flooring store - this sounds like the flooring was installed poorly without room for expansion/contraction.

-Peel off some baseboards and check to see how tight the laminate is to the baseplates. There should be at least a 1/4" to 1/2" gap in the cold condition to allow for expansion (along all walls)
-If there are no baseboards and the laminate is tight to the wall this is 100% an expansion issue.

Three options for remedy:
-Trim the end runs, if it is a square room this is easy - if it isn't... well - have fun. Appropriate baseboards are installed to hide this gap.
-Remove & reinstall the laminate. Keep the floor heat on and unbox the laminate. Let it sit for AT LEAST 2 weeks in the room, in contact with the floor heat to allow the laminate to expand to final size prior to install. This will be vulnerable to contraction if the floor heat is left off for any period of time.
-If the floor heat is going to be sporadic (lots of on/off cycles) switch to an engineered hardwood with low contraction.

RE: moisture trapped in gypcrete floor


I have seen what you are experiencing too. If you have the money / inclination to fix the issue their are purpose built humidifier / barometers made by Mercier (hard wood mfcr out of Montreal) to take care of this.

RE: moisture trapped in gypcrete floor

What is the space under the floor ?

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