Damaged paint on mamposteria or block walls.

There has been lots of discussion lately on expat forums, about the damage that occurs to paint coatings in the Yucatan. This damage can usually be seen in the bottom 1/3 of the walls. Peeling paint, plaster falling off or even fungus or mould growing are all symptoms of the same issue, water in the walls. When talking about mamposteria or block walls, they both have one thing in common, a binding cement that holds the rock or block together. Now there are newer waterproof cements, but almost all of the homes in question were built with older cements that absorb water, like a wick. There are three basic ways water can get in a wall – from the outside on unprotected surfaces, from the top down filtering through cracks or exposed surfaces and from the bottom up. The first two are pretty easy to fix, a good exterior paint on the outside walls and a impermeable coating on the roof and other topside surfaces. The hard part is stopping moisture from wicking up the wall from the ground, after the wall is made. I am sure a method probably exists to waterproof a foundation after the fact, but I do not have any experience with it.

Lets look at the composition of a typical foundation on an older home here in the Yucatan. Most of the Colonial era homes were build on a foundation of limestone rock and a limestone based cement. This is where the issue actually starts, as limestone is porous and can absorb moisture from the ground. Even new homes here are build on a limestone foundation, for the most part. On new buildings it is easy to put a vapour barrier of plastic, damp course, or a tar coating on the concrete top edge of the foundation, to prevent water from wicking. But that was not done on most older homes in the Yucatan. So when the rains come, water starts wicking into the walls at the foundation level. As the moisture gets drawn in to the dryer higher part of the wall, it brings various ground salts with it. And as it rises it also starts to evaporate, but since the inside walls of a house are usually coated with some form of plaster and paint, the water is trapped and eventually causes the coating to fail, this is why the damage is usually restricted to the bottom of walls. The trapping of moisture can also create problems with mould and fungus growth. You may also notice a very fine soft crystalline formation coming out of your paint or wall coating, that is usually Calcium Hydrate being brought to the surface as the moisture (acid) in the walls slowly bleeds it from the limestone and cement. The technical term for this is Efflorescence. Eventually, after many many years, the binding cement may fail, which can be seen on many old neglected structures in Merida, where the cement in the walls just seems to crumble.

The question is how do you stop this from ruining the paint on your walls. The answer is, it is not easy at all.  If you buy an older home, traditionally vapour barriers were not used. You can put sealers on the walls, but you run the risk of trapping the moisture in the walls and maybe make a good breeding ground for mould or the moisture may build to a level where the wall coating fails anyhow. There are also coatings on the market, that open up the pours in the paints to allow the moisture to evaporate quicker, thus saving the paint. I have also heard of people drilling holes into the walls near the ground to let moisture escape, but I have no experience with this process. There is no easy answer other than prevention in new homes.

There are a few things you can do to make life a little easier however. Paint the lower part of the wall a different colour. This means you do not have to paint the entire wall when the time comes. Some people put a pattern on the lower part of the wall, to hide the effects as well. Then of course there is alway wainscotting to hide problems as well. If the exterior of the particular wall is uncoated consider a coating to prevent excess water penetration from the outside to the inside.

Or accept the fact, that it is just part of life in the Yucatan.