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Blister Fix: Finding a Cause and Solution to a Common Defect

A D+D Online Feature published October 18, 2010

More items for Good Technical Practice

by Jayson L. Helsel

Coatings applied to concrete and masonry substrates can exhibit a number of defects related to moisture. One such defect—blistering—is examined here, in a review of a case encountered in a major commercial building....
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Tagged categories: Blistering; Concrete coatings and treatments; Paint defects

Comment from Walter Rexing, (10/19/2010, 11:30 AM)

No chain is stronger than its weekest link. The underlying PVA based coating will continue to provide challenges and Jason's recommendation for annual maintenance unfortunately will likely be required. Therefore, saving some on the newly applied topcoat for touch-up is recommended. Jason's recomnendation to stay with 100% acrylic is right on the money.

Comment from John Ahern, (10/21/2010, 5:42 AM)

No mention of adhesion testing done prior to coating. This would save a ton of headaches. It sounds like moisture was trapped which can be a problem with the thicker coatings. Many contractors make the mistake of painting too soon after power washing or not taking a moisture reading. I do have issue with the final recommendation for a complete total recoat after spot repairs.In our past successess and failures with moisture issues is that adding another coat only exacerbates the problem and does not provide a long-term solution. The blisters will eventually come back in random areas, sooner than later, unfortunately. They are better served providing minimally touched areas (the less paint the better) and when ready to truly fix the problem and make successive paint applications easier is for a dry removal or minimal water use method of the existing coating followed by a coat of Masonry Conditioner prior to ANY topcoats.

Comment from Jay Helsel, (10/27/2010, 6:16 AM)

The investigation of the coating problem did evaluate adhesion using the tape test (per ASTM D3359, Method A) and by subjectively probing the coatings with a utility knife. The adhesion was poor immediately surrounding locations where blisters were present, but fair to good in locations where the coating system was intact. Further adhesion testing would be recommended when performing coating repairs to ensure that poorly adhered coatings are removed. Dealing with moisture problems can be challenging and one of the key determinations is the source of moisture. In this case, the evidence showed that the moisture was coming from the outside environment. Since the scope of the failure/blistering was relatively small (1% of surface area), there did not appear to be a widespread problem with water penetrating the coating system. Rather, the problem appeared limited to locations where the coating did not adequately protect the substrate due to pinholes or gaps in the coating system. If the source of the moisture was from the interior of the walls, it would be unwise to try to salvage the system as the PVA block filler would continue to be affected, leading to more blistering over time.

Comment from Manuel Contero, (11/4/2010, 8:37 AM)

Information about both, composition of the concrete tilt-up panels and the surface preparation/paint application carried out ,could also help us in determining the problem. Suppose the following scenario : The surface was cleaned by means of high pressure fresh water.This type of panels has tendency to absorb water.Insufficient drying.No moisture reading were taken.The weather conditions during the application were not good(air condensation ) .If coating application was progressing with this scenario , could we assure that the cause of the blistering is "the result of water or moisture from the surrounding environment absorbing through the coating film".?The laboratory analysis doesn't say anything about the film formation of the taken samples and the report say "There were numerous pinholes or gaps visible in the textured coating, which did not necessarily correlate with blistered areas" and "there were also many areas with pinholes where the coating remained intact with good adhesion ". Think about it.

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