STUCCO NEWS.NET

It seems of critical importance that I expand on my writings on bonding mortar because the danger of stucco falling off and causing injury. Of course, it is also important to make sure the work stays on the wall, that is, do it once and do it right.

A lot of our work is repairing old stucco. The old stucco sometimes fails from water damage, due to lack of flashing or other reasons. We find a lot of stucco fails from lack of bond. I say the word bond, not "stick". Bond means a permanent attachment of mortar. Stick means it stays there, but maybe not for long. For example, stucco over cast concrete will usually stay on the wall 6 months or so before it shows evidence of coming loose. This is because the concrete usually has a few pits and holes for the mortar to hang on. Also, the concrete has a tiny amount of suction. Suction means the fact that a surface absorbs water, meaning mortar can be absorbed into the pores. This suction isn't adequate for a permanent bond.

In our travels, we have found stucco put on painted block, which will fail. Sometimes the mortar hangs on the holes and pits of the block for years, but the stucco can be scraped off easily.

Another reason for failure on block is the blocks were painted with link. Link is a very weak bonding agent which never worked well. There is a myth that blocks need to be painted with link or covered with metal lath. This is another absurd myth. Blocks, concrete blocks known as CMU were invented for a plaster base. Tearing the mortar off the block usually takes parts of the block with it. Blocks are rough and very porous, meaning blocks absorb water rapidly. This means mortar is absorbed into the block. I have found stucco failure from link where the application of stucco was done over 50 years ago, but the mortar can be scraped off easily. Just because it hung on the wall 50 years doesn;t mean it is worth a damn. I have found bluish link under the block many times, showing how old the myth is of painting the blocks with link first. The link seals the pores and prevents a good bond, doing more harm than good.

Years ago, when I patched a lot of plaster, I found plaster coming loose many times where old ceilings were skimmed up over link. Link is identifiable by it's bluish white color. Plaster weld, or Euco weld would fail if it got wet. Plaster weld is identifiable by it's pink color. Plaster weld failure on the inside can be found in areas prone to leak, such as chimneys or basements. This probably is mainly due to repairing the plaster before fixing the leak.

When you see stucco falling off and the wall is pink underneath, this is due to someone using Plaster Weld on the exterior, which is a complete no-no. When the wall is blue underneath, this is Weld-Crete. When the wall is bluish white, this is link.

I don't use Weld Crete at all. It is a good product if used under certain conditions, but my preference is to use an acrylic bonding admixture. First of all, Weld Crete should never be used over a painted surface, because it will eventually fall off. Weld Crete and stucco failure has been a subject of stucco failure in Florida. Weld Crete works the best over unpainted concrete, using a thick scratch coat. One of the reasons for Weld Crete failure is that a thin coat of mortar over the Weld Crete will dry out before it sets. The scratch coat turns into a powdery mush that will not support permanently the next coat. This is kind of like painting over a dusty window sill. You can pull the paint off with your fingers. Other reasons for Weld Crete failure are painting on Weld Crete with a wet brush or roller, form release on cast concrete, product old or has been frozen, applying mortar before the Weld Crete has dried enough, etc.

One great advantage of acrylic bonding admixtures is the mortar retains liquid in the mix so the mortar doesn't dry before it sets up. That way, your brown coat, or next coat will have something solid to bond to. If you continue to read my chapter on bonding, or visit my site frequently, you'll see we mix Flex-con, or what ever brand of bonder we are using, half and half with water. A paint on bonding agent can be made by mixing pure bonder, (no water) and portland cement with no sand. This can be painted on with a brush, leaving the surface rough. This mixture sets fast, allowing coating the same day.