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Old 04-09-2011, 02:09 PM   #1
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What's Happening on my Slab?


Hi all. I am replacing the carpet in my master bedroom with laminate flooring. The house sits on a concrete slab, and when I pulled up the carpet the slab seemed to have some issues along the exterior walls.

Here is a picture of the exterior wall. There is an exterior concrete slab along this side of the house.


I removed the carpet last Saturday (2-Apr) and today (9-Apr) noticed fluffy white growths in the discolored area along the wall. Here is pic of what the growth looks like:


This wall was an exterior wall as well, but the previous owner built an addition along the back, so there is an "interior" slab poured along this wall, which is protected from the weather. It also shows discoloration along the wall, with lots of white crumbly stuff which I already cleaned-up up before taking the photo:


Here is the corner where the walls meet. The slab in the discolored area is not smooth, but rather is deteriorated and crumbly on the surface:


I was planning to smooth and seal the slab in the discolored areas with Henry 345 Premixed Patch n'Level Floor Patch and Smoothing Compound. I am also putting a underlayment under the laminate that will come up the wall. This should protect the laminate. However, a few questions:

1) What is the growth, do I need to treat the slab in some way.

2) This appears to be water intrusion. I am not sure if its recent, but there was a 2x4 bolted to the floor that served as the bottom of a stub wall for a closet. When I removed the board the concrete was dark near the wall like it was moist (the room addition is along this wall) and the bottom of the board seemed damp. Where would the water be coming from, perhaps between the old and new slabs? What else should I do?

3) It rained last night, but there are no sign of current water intrusion along the exterior wall. Is there any else I should do or be concerned about?

4) Any other recommendations?

Your help and comments are deeply appreciated.


Last edited by chew; 04-09-2011 at 02:12 PM. Reason: Typos and additional question.
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Old 04-09-2011, 07:04 PM   #2
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What's Happening on my Slab?


That looks like efflorescence to me------Moisture leaching chemicals out of the concrete----

You may want to have a flooring pro do a moisture test on that slab.


Laminate flooring fails very quickly on a damp slab-----Lets see what Rusty or one of the other flooring pros have to say about this.----Mike----

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Old 04-09-2011, 07:30 PM   #3
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What's Happening on my Slab?


You are right, Mike. The place to start is a moisture test. After you have that done, we can better help you.
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Old 04-09-2011, 08:46 PM   #4
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What's Happening on my Slab?


I'll concur.

What you are seeing is efflorescence. Efflorescence (in a nutshell) is caused by the rising of natural salts that occur in concrete products. Moisture migrates into the slab and activates the salts. The moisture then tries to evaporate reaching upward towards the warmer air and it brings the salts with it. If the salts are minimal there is usually only a whitish powder that forms on the surface of the concrete as the moisture dries out. If the salts are in abundance they then tend to blossom and bloom like is shown in your photo.

When the carpet was in place the moisture simply evaporated through the carpet and went unnoticed but I'll bet there was a musty smell.

The source of the moisture should be remedied before any other floor covering is installed. Keep in mind however that moisture can occur in all concrete and the seriousness of the occurrence depends on landscaping and proper gutters and downspouts and even a high water table underground.

What are the structural walls made of?

I should also mention that efflorescence (to my knowledge) is basically harmless while at the same time it can ruin some flooring products I suppose. Given enough moisture the efflorescence will one day play-out. But who can wait for that to happen?

Before anything else happens a moisture test is absolutely in order.
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Old 04-10-2011, 12:26 AM   #5
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What's Happening on my Slab?


Thank you all for your comments. I will look into getting the moisture test and update with the results.

The structural wall is wood frame construction with stucco siding.
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Old 04-10-2011, 05:39 AM   #6
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What's Happening on my Slab?


Real stucco or Dryvit over Styrofoam?


Here is a bit of bad news about Dryvit--Is Dryvit Dead???? - General Discussion - Contractor Talk - Professional Construction and Remodeling Forum
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Old 04-10-2011, 12:11 PM   #7
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What's Happening on my Slab?


In the meantime...
There doesn't appear to be any moisture wicking into the wallboard-that's good!

This doesn't necessarily mean there is no moisture in the structural framing however.

How about the exterior landscaping? Is it designed so that water can move away from the dwelling rapidly when it rains? Are there suitable rain gutters and downspouts directing water away from the house? Is there decorative vegetation near the house that requires frequent watering?

Just throwing out a few ideas of things to look for.

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