STUCCO APPLICATION PROCESS

By Jon Humble on 14 November, 2014

Once the walls have been prepared with flashing, paper and rainscreen (when called for), stucco stop bead and weep/drain facility is installed at all horizontal drain points. High performance metal lath is then installed over the entire area that is to receive the stucco, along with metal structural corners.

A base coat of stucco mortar is then applied over the wire lath at a depth of 3/8". The lath becomes embedded in the base coat and acts as a reinforcement mechanism. It is then scratched horizontally to facilitate a mechanical bond for the following coat of stucco. This 1st base coat of stucco is unsurprisingly known as the "scratch coat". The mix ratio for the scratch coat is adjusted so that it very hard and tough when cured . The scratch coat is left to set and cure for a minimum period of 7 days at 4 degrees centigrade or above.

The 2nd coat of stucco is then applied over the scratch coat and is leveled and floated to a flat plane. The mix ratio for this coat is designed to enable it to flex slightly with the stresses of expansion and contraction which minimises the potential for cracking. The brown coat is left to set and cure for a minimum of 7 days at 4 degrees centigrade or above in preparation fpor the final coat of stucco. This second coat is surprisingly known as the "brown coat" (surprising because it is not brown at all but grey).

Just to clear this up - the origin of the seemingly odd term "brown coat" dates back to Victorian Britain where the material for the leveling coat of interior plasterwork was called "browning" and was actually the colour brown.

There are several types of finish stucco material that can be applied over the brown coat. California stucco finish can be applied in a variety of textures; it is a more traditional type of stucco in as much that it is similar to types of mortar that has been used for literally hundreds of years. It can be tinted to different colours but these days it tends to just get painted after installation due to the nature of the challenges involved in maintaining colour consistency. The more modern equivalent, acrylic stucco finish is the new kid on the block and comes in every colour imaginable.

Improvements have recently been made to be able to more extensively texture this type of stucco material to match the larger pattern capabilities of California stucco. Colour consistency is also way more stable. Acrylic stucco is basically a high performing type of acrylic, paint like material that has different grades of sand added to it, to effect different grades of texture. Temperature and humidity provisions are less flexible with this type of material but none the less it has proved to be a very material.

If a rock dash or slop dash (also known as roughcast) is called for the second leveling brown coat of the stucco process a third coat is not necessary.

If a rock dash is to be installed, after the brown coat is applied, rocks are cast on with a trowel whilst the mortar is still wet. If a slop dash type of stucco is to be installed it is cast directly onto the brown coat with a special type of trowel.

Whatever the finish is that is to be applied an overall measurement of 3/4" will be the final depth.