It was a large multi building apartment complex in central Florida. Only about 6 years old, and the owner wanted a new paint job to freshen up the buildings. It was a typical painting/sealants job to clean, prime, seal and paint. A minimum one primer and one finish coat using a high build water-based elastomeric paint system. A consultant was hired to develop the specifications and provide quality control and assurance. Bids were solicited, and a qualified painting contractor was selected. After a few months, the buildings were all painted and ready for turnover and final payment. All was fine, until, damage begins to appear!
Within a few months of completion, the property management noticed areas where paint was deteriorated or missing in areas of the wall surfaces. Spots, about a half dollar in size, were scattered about the wall surface in random locations. The spots indicated that the tan colored top coat was largely gone, leaving only the white primer exposed. It was isolated and primarily in the lower five to six feet of the exterior wall. Very minor areas of the damage occurred higher up, but always below the second floor accent band. It was a peculiar phenomenon. The most peculiar aspect of this case was that there were no paint chips on the ground below the damaged areas.
Where we saw paint spots were deteriorated or missing, we always noticed something extra. Small, dark, tube-shaped objects stuck to the surface of the wall. At times as many as ten to fifteen of these objects within a square foot area. They were stuck to the painted wall over perfectly painted surfaces. Many were curiously pigmented the same color as the paint. They were very small, so we pulled out our pocket microscopes and loops to get a closer look. Now, hold your breath.
Could snails be depositing pigment-laden waste to the walls adjacent to the damaged areas? This stuff was full of undigested paint pigment. It was completely embedded within the excrement of snails that had traveled across these walls, stopping only for a meal, and to relieve themselves along the way.
Something about this paint was attracting the snails, so we began to research the composition to see what secrets it held. What was the delicious ingredient that this paint contained? It turned out to be Calcium Carbonate, CaCO3. The paint from the bucket contained 33% by wet weight measurement, and upon drying contained up to 54% by dry weight measurement. This simple compound, CaCO3, responsible for so many things on our planet, is also the building block for the shells of these guys, which they call home. Snails typically eat soil and vegetation to get the calcium carbonate they need, but in this case the paint was much more tasty!
Our friends had atypical appetites. These guys were like a kid in a candy store with grandma’s coin purse. They could get everything they needed to build their home–without leaving home–simply by devouring the new paint on the walls. Time to issue an eviction notice!
These guys had clearly overstayed their welcome. So what was the solution? Simple enough: Iron Phosphate, a non-toxic snail bait recommended by the local Extension Office to “evict” the unwanted guests. This material would be applied around the perimeters of the buildings as often as needed, essentially acting as both a barrier and a poison to the creatures. That was the first step. Then, time to repaint.
Only the lower portions of the buildings needed repainting. (The horizontal accent band was heroically acting to deter the snails from climbing any higher up the wall.) And maybe we should try a not-so-delicious paint this time. With the track record here, we selected something that contained none of the goodies responsible for this mess. No Calcium compounds to tempt any stubborn snails that might remain after the Iron Phosphate attackiii.
In Building Science, we sometimes need to dig deeper, and to think outside the box. One of the most important lessons we have learned in our field is to always ask questions. Why were these little black objects stuck to the wall where we were seeing the paint “failures”? How did the paint pigment get into them? Was this an isolated incident? Or could it be responsible for other paint failure cases? Should the coatings industry now take note and look at alternate formulations for their exterior paints? Further investigation is needed, but at least for our particular client, we answered their pressing question of: “What is causing the paint deterioration on our freshly painted walls?”