Selected Answers

From Jeff Donius of Premier Veneers on March 5, 2015:
I have success with clear coatings over concrete f ...read more I have success with clear coatings over concrete floors as long as the moisture content is under 5% using a Tramex Moisture Encounter II. I expect the same level would be acceptable on walls.

From Rodney White of Independent Consultant on March 4, 2015:
The best source to determine the level of moisture ...read more The best source to determine the level of moisture the coating will tolerate would be to consult with the manufacturer of the coating to be used. Measuring the moisture is a different matter. I agree with William that there is a marked difference in painting a concrete structure above grade when only MVT (moisture vapor transmission) is the issue. Acrylic coatings generally handle this well. Concrete surfaces at or below grade subject to osmotic pressure create a much different issue. Coatings subjected to osmotic pressure must be able to bond  into the concrete matrix well enough to resist the pressure, and acrylic systems generally will not perform to this level. At best, testing methods to determine moisture in concrete are iffy. Regardless of the method, the measurement will determine the amount of moisture at that spot at that time, and since concrete in non-homogenous, that value could swing significantly from spot to spot.

From john schultz of o-gee paint co on March 3, 2015:
I would not recommend painting a surface that meas ...read more I would not recommend painting a surface that measures above 110 on my Protimeter Aquant in 4 out of 10 samples. Environmental variables also need to be accounted for, but, if it looks dry in Miami, it will get painted and typically successfully. Most waterborne, thin film, acrylic wall paints will tolerate moisture in a wall that is dry to the touch, and the worry is usually wetting after application. In my experience, a replenishing or active source of moisture from a leaking pipe or saturated surface will cause a coating to fail around the point the of moisture migration .

From William Slama of International Paint/Ceilcote Products on March 2, 2015:
We require passing the plastic sheet test (ASTM D4 ...read more We require passing the plastic sheet test (ASTM D4263). That ensures that the moisture won't interfere with the wetting or curing of the primer. However, later external water pressure from behind the concrete (on grade or below grade) is a more complicated issue. The ability to withstand the water pressure is related to the adhesion and modulus of elasticity and thickness of the lining system. These acrylic coatings do not usually withstand these (osmotic?) pressures.

From Warren Brand of Chicago Corrosion Group on February 27, 2015:
Ok. This has been hanging out here for several da ...read more Ok. This has been hanging out here for several days, with no response. So I'll open myself up to review. Here's my understanding. There are two issues: first, the moisture content of the concrete wall, and second,  emissivity, or, as I understand it, the ability or tendency of moisture to travel through the concrete. These are two very different types of issues. Moisture content, from our experience and understanding, is much easier for coatings to deal with , as there is no pressure against the coating after cure. The only issues, as with this questions, is if the concrete is dry enough so that when the polymer is applied, the moisture will not interfere with its curing mechanism. I would guess that the short answer would be less than 4% moisture content, but it is a guess. I'm all about learning and getting smarter (which, as my kids frequently remind me, is no easy thing to do as I'm not that bright to begin with), so I'm looking forward to additional comments.