STUCCO NEWS.NET

Several years ago my wife & I began building a small vacation home in Honduras.

I read your website recommendation against concrete glue as a bonding agent. Although I didnt use form oil, need I rough-up the face of poured concrete to get a good bond ?

Altho I can buy good portland cement, un-screened river sand & lime in Honduras, specialty materials (admix, trim etc) are not available. I must ship down everything else I will need, which requires advance knowledge of my needs. To this end, I will appreciate and recommendations you can provide me.

This is part one: Bonding stucco to concrete using portland cement No need to rough up the concrete, as long as it is clean. An excellent method of bonding cement mortar to concrete is an Acrylic additive such as Flex-con (what we use) or Acryl-60. I want to explain another method which works, however old-fashioned and only requires portland cement. This may be a lot more practical considering the effort and expense required transporting Additives to the Island.

First of all, don't even dream of putting cement mortar directly on concrete because it won't permanently bond. It may stay there 2 or three months but will eventually fail.

A method that I learned from an old plasterer is this: Mix a portland cement paste in a bucket, with no sand and no lime. It should be stiff enough to paint on with a paint brush. Wet your concrete and when enough water runs off or soaks in, you can paint on the paste.

You need to mix up some paste in a bucket (we have used a cup for patch work) and have some portland sand mortar mixed and ready. You paint on the paste with a stiff brush or broom leaving the surface rough. You will notice the paste sets hard immediately after touching the concrete. The paste then starts to dry quickly because the concrete sucks the water out of the mix.

THIS IS IMPORTANT: You want to put mortar on the paste BEFORE it dries.

This could be done with two people, one painting and the other scratching on mortar, or one person, working in small sections, applying mortar before the paste dries out.

Scarify your scratch coat good and let it set at least over night, better 2 days, before applying the brown coat. If your concrete is nice and flat you may get by with just a scratch coat, evened out and roughed up with a float, a brush, or a wood straight edge.

Does this work ? Swimming pools were plastered this way for years before acrylics were invented. This is still done a lot in Latin America on concrete. I saw this method of cement paste used when I was in Mexico on exterior ceilings. Just think about it when you walk under ceilings on office buildings in Mexico that 3/4" of stucco is bonded using cement paste. If a piece of that ceiling falls off it could kill somebody.