Moisture damage at the bottom of interior walls

Team, do we have any “logical” explanation for the typical paint bubbling and damages that we always see at the bottom 20 cm or so on painted concrete walls?
Here are some facts:

  1. Not in ground floor so no wicking of moisture option
  2. No bathroom at the back of the wall - i.e. no plumbing leak or water on the floor
  3. What it ONLY happens at the bottom? Never see it extending to the top

Any thoughts? These are concrete block wall with cement mortar troweled on top and a finish paint coats


What is supporting these interior concrete walls? My assumption is a footing so why is wicking not an option?


Because it is an apartment in the 3rd. floor. Not at ground level

That’s good info to know in order for people to help diagnose this.

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Is it possible the concrete near the floor was not fully dry when the top coats were applied?

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There are many possibilities. Air movement, drying to the inside, mortar mixture etc. This may be helpful.

Here is a snippit:

First: There must be water-soluble salts present
somewhere in the wall.
• Second: There must be sufficient moisture in the wall to
render the salts into a soluble solution.
• Third: There must be a path for the soluble salts to migrate
through to the surface where the moisture can evaporate,
thus depositing the salts which then crystallize and cause

612.pdf (261.8 KB)


Good point, the block will typically be wetted prior to plaster application.

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Hi, Ryan
The building is 2 years old and they repaired these areas like three time but it keeps happening again and again. Also, why alway “only” at the bottom of the wall? Why not in the middle or at the top? Same condition applies throughout the wall

Brian, why only at ghe bottom part of the wall where the mortar, drying time, etc is the same throughout the entire wall?

Where are you located, Ehab?

I am a Building Science Thermographer, and this is the work I do.
More information and testing is required, but at this point you should consider that there are only three sources of building moisture, building envelope leakage (air or water), plumbing, and condensation.
You seem to have excluded plumbing. Take a stab at the other two.

Construction practices, blueprints, etc will help with building envelope. What is really happening inside the wall. Fiber optics may be needed to see what you can’t see. Walls must be waterproof, but must be allowed to drain and ventilate to dry. But this is not foolproof either. After the big Nashville, Tn flood, I found several “flooded” houses where the source of water was the weep holes (improperly placed, and in excessive number required by code).
Moisture inside the wall should be determined. We really can not exclude capillary action going on here.

Condensation is always a fun one for me. After the process of elimination is done and excludes plumbing and wall leaks, I turn to condensation. It takes persuasion to get the facility engineer of the other two however…). Condensation requires specific conditions to occur, and these can be measured. Psycrometrics tell you what you need to know.

Note: HVAC design can play a large part in this (depending on where you’re at, which is why I asked). Air stratification can play a large role in this, as air distribution can put the condensation thing over the top. This can be an Air Leak turned water problem. Check building pressure. Air leakage can not occur w/o a pressure differential.

I noticed in your third pic that there is the same damage in adjacent rooms. You stated this is happening everywhere and on the 3rd floor. This problem has a wide scope, beyond an isolated air/water leak.

If this is just a Home Inspection, you may never know the answer…


It will never be the same.

Also note that solar exposure drives moisture inward. The wall floor density stays cooler longer and may condense the water vapor from the wall above. Interior A/C keeps this area colder, longer.

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@dandersen is now on this post, which is a good thing for you. I will defer to him.

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Hi David, this is in Dubai. Hot and moist air in the summer. Almost no rain occurs here. I checked leakage with blower door and smoke test, as well as thermal imaging. There are some un caulked through penetration and some air leak from around windows panels. Nothing significant though. However, if condensation is the issue, the question why only appears at the bottom part of the wall, consistently?

Concerning your blower door test, air leakage/transmittance may be occurring within the CMU wall, not to the interior.

Hot and moist weather requires air conditioning. It is always cooler at the floor than at the ceiling.

The first course of concrete block is generally not constructed the same as the blocks above in the same wall, producing greater mass. Mass effects temperature conductance rates.

It is quite plausible that high temperature air within the wall during the day (which contains greater amounts of moisture than cold air) will condense as the wall cools in the evening, helped along with the air conditioner. Condensed water (or just saturated air) will fall towards the bottom of the wall and remain in that state because the mass prevents the temperature to rise to a point that it will evaporate. The air conditioner dehumidifies in order to lower the temperature inside the building… This causes moisture within the wall to move towards the interior damaging the interior wall on the way. (Greater vapor pressure).

I live in a hot humid zone and visually, your photographs look very similar to concrete buildings I work in. It is unlikely for me to find water in the damaged areas, rather a constant movement of moisture laden air infiltrating towards the interior air-conditioned space.

I’d be interested in looking at any thermal scan and you may have of the wall. Radiometric scans would be best. I have written several isotherms to deal with moisture intrusion problems of buildings. I may see something helpful.


What was the cause of the damage needing the obvious repairs to the base of the wall?
That isn’t just ‘fresh paint’ applied.

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Thanks for the insight David. So let me phrase it the way I understood.
Air leak from outside cause a moist and hot walls. When AC is turned on, cold air with hot and moist walls cause water condensation, which naturally falls to the bottom of the wall, and hence the major damage is happening at the bottom part of the wall?

No getting what you mean, Jeff?

You only mention ‘bubbling paint’. That damage is obviously not just ‘bubbling paint’ repairs. Looks like plaster from Minnesota.

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Seems unlikely in this case but something to keep in the back of your mind with lower wall damage is cat pee. I always stick my nose right down to it and am surprised how often that’s what it is.

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It is possible that the wall is heated from above? If the 3rd floor is the top floor (you didn’t say it was, but just assuming), is it possible that the block wall is getting heated during the day from the attic area, or maybe humid air is getting within the block (if hollow) from outside.

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