Adobe 101

What Happens:  The most common source of moisture in adobe walls is weather related. Adobe walls absorb moisture from the surrounding soils, similar to a dry paper towel soaking up water. After the walls get wet, a natural drying process occurs as moisture travels through an adobe wall (via capillary action) toward the surface and the surrounding dry air.  As the moisture travels through the adobe, naturally occurring soluble salts are leached out of the adobe dirt, eventually reaching the surface of the wall. When the salts reach the surface, they crystallize and the salt crystals form a crusty white residue on the exterior of the wall.

Okay… So, what?  Big deal… the wall has white crusty stuff on it, how does that cause any significant harm?  That’s just it.  Those little crystals are a big deal.  The crystallization process exerts a force of 8,000 pounds of pressure per square inch.  So that, little by little repeated drying cycles pulverize the previously hard surface of the adobe walls until eventually plaster and paint crack and fall off and the surface of the adobe wall turns to dust.

If you own an adobe building and you have white crusty stuff on the base of your walls, you are probably starting to freak out.  Am I right?

All buildings require various types of maintenance on a regular basis.  Adobe structures are no exception.  Let’s first take a look, at how the “old-timers” dealt with maintenance using the materials they had on hand.

Pre-Cement Era:  Prior to the ready availability of cement plaster, the same natural drying process occurred, of course.  The difference was that moisture could easily travel through the exterior coating of either lime or mud plaster because both types of plaster were permeable.

Regular Maintenance:  The white crusty stuff formed at the base of the walls, people noticed the damage, and they periodically scraped off the damaged parts and then reapplied a new coat of lime or mud plaster and with on-going maintenance, adobe buildings remained intact and in good condition for hundreds of years.

Cement Plaster: Fast forward a few hundred years later… cement plaster and elastomeric paints have become typical modern-day coverings for walls, because they are durable and are designed to be impermeable.  The impermeability feature protects the walls from moisture that could enter the wall from the surface. Unfortunately, adobe buildings regularly absorb moisture, through capillary action from dampness in the ground. The application of modern-day impermeable materials traps this moisture in adobe walls, which is accelerating the deterioration of the structural integrity of adobe structures.  Overtime, trapped moisture will degrade building materials (bricks, wood, cement, steel, sheetrock…) and adobe bricks are no exception.

More Cement, Please…  Did you know the modern day cure for damage caused by impermeable materials is to apply more impermeable materials?  Modern day fixes include covering up damage by applying another coat of cement plaster or elastomeric paint, pouring a “cement collar” along the base of adobe wall or building a concrete buttress to strengthen the damaged areas.  These solutions cover up the problems (temporarily), now the damage is hidden, but it continues to occur (and it gets worse over time).

Trapped Moisture: Here’s a good example of a very typical problem that occurs in adobe homes as a direct result of many years and multiple applications of cement plaster. Multiple applications of cement plaster, on the exterior of the east side of the Guadalupe House, created a 2 – 3 inches thick coating.  The thick impermeable layer blocked moisture from reaching dry air and exiting the walls during the natural drying process. In this case, the trapped moisture traveled horizontally into the base of the interior walls where it was able to evaporate at the surface.  Years of accumulated crystallization and the usual tell tale signs of moisture related damage are visible along the base of the interior walls in the front entryway.

Cheer Up!   Now that we are all thoroughly depressed about our soggy adobe walls and crusty white stuff, let’s talk about our options.

Simple Sensible Fixes

• Prevent moisture from getting into walls through leaks (in roof, around canales, from plumbing, etc.)
• Improve water drainage away from the building to prevent water from pooling next to the walls

Restore Permeability:  (Let Your Walls Breathe!)

• Apply a permeable coating along the base of the wall (using mud or non-hydraulic lime plaster) to create a place for moisture to exit the walls. Yes, you will need to do regular maintenance because you will still see the white crusty stuff left behind as your walls continually dry out, but at least you know your walls are able to dry out and with consistent maintenance the moisture is less likely to cause extensive structural damage.

List of References, Resources and Links:   http://mvpres.org/mvpres.org/Welcome.html