Parging an Adobe Wall

Español

Traditionally the walls of adobe houses in Honduras have been parged with a thin layer of fine clay and painted with a mixture of lime. The advantages of this method of parging are that it can be done with no purchased materials and it requires no special skills. The disadvantages are that the clay layer is not very water resistant and the lime tends to dust off on anything that brushes up against it. 

When they can afford it, many people will parge the walls with a mixture of Portland cement and sand. This makes the walls more resistant to water damage, and the dried cement mix can be painted with either latex-based or oil-based paint. The parging with cement usually is done in much the same way as the parging with clay, in a very thin layer that dries before the cement has properly cured.

The disadvantage of parging in this way is that the cement does not bond well with the clay of the adobes, and the parging layer often separates from the adobe and falls off, exposing the adobes beneath.
 

 

To keep the parging layer from falling off, a common practice is to make holes in the adobes so that the parging will cling to the wall. This helps to some degree, but the cement "pegs" that are formed can still pull out of the holes, allowing a piece of parging to fall.

Parging an Adobe Wall
ar

Parging an Adobe Wall

ging an Adobe Wall

 

 

 One solution to the problem that has worked very well for us is to drive 2½-inch drywall screws into the adobes at intervals of 8-10 inches, leaving ½ inch of the screws exposed. Over the protruding screws we hang 1-inch chicken wire, stretched so that remains flat about ½ inch off the adobe.




  



There is no need to tie the chicken wire to the screws. If stretched tightly, the chicken wire will remain in the desired position, and the subsequent parging will bond it to the screws.

After moistening the adobes with a spray of water, we parge with a stiff mix of 4 parts of sand to one part of Portland cement. The mix is applied by forcefully throwing trowelfuls of mix against the wall so that it penetrates all the irregularities, gradually building up the layer to a 1-inch thickness before troweling it flat. As we go, we pull the chicken wire out from the wall with a bent wire hook so that it remains roughly in the middle of the parge layer.

  









At the corners and where we join two pieces of chicken wire, we overlap the chicken wire pieces about 4 inches to minimize cracking of the parging. 











Once the parging has hardened, it must be sprayed with water several times a day to keep it continually moist for at least 7 days to allow the concrete to cure properly. A common error here is to treat the cement parging the same way as the clay parging, assuming that drying is what makes it harden. While cement parging that has dried quickly will appear hard, it will never reach its maximum resistance unless the chemical process of hardening has been allowed to progress--a process that requires water. 

If a fine finish is desired, a thin layer of a 3:1 mixture of very fine sand and Portland cement should be trowelled over the first layer while it is still moist (preferably the day following the application of the first layer). The two layers are then cured together.