How to Treat CMU Buildings With Stucco

Prepare the surface of the wall by first inspecting it for holes, cracks or other defects. Powerwash the surface and remove old paint, mold or dirt. Sandblasting is sometimes necessary to eliminate all the impurities that could prevent bonding of the stucco.

Fasten strips of 3/8-inch wood lath (screed) to the top and bottom of the wall using masonry nails. Additional strips may be added to the middle of a tall wall.

Mix the base coat in the mortar mixer by first calculating how much water will be needed. Water weighs 7.8 pounds per gallon; the water should weigh 1/2 the weight of the lime and cement combined. The consistency should be about the same as soft butter.

Moisten the wall with a sprayer or mister before applying the stucco. Use the hawk to load stucco onto the trowel. Start applying the stucco with the trowel held at a 45-degree angle, gradually moving it to a 30-degree angle. Spread the base coat in a sweeping motion across the wall, about 3/8-inch thick. Wait a few minutes.

Level the surface with a straightedge. Put the edges of the level along the screeds that were attached to the wall in Step 3, and move it in an up-and-down motion to smooth the stucco out to a 3/8-inch thickness and remove excess stucco from the wall.

Remove the screeds with a nail puller and hammer without marring the stucco.

Reduce the amount of shrinkage and cracking in the stucco by wiping the wall with a mason’s wooden float in a circular motion. This helps consolidate the stucco as it cures but must be done after the sheen is gone and before it hardens completely.

Mix another batch and apply it the next day for the final coat. The procedure is similar to applying the base coat without the use of screeds since it will only be 1/4-inch thick or less.

Finish the wall by texturing the surface using a trowel, sponge float or other tool. There are many possible textures, so make sure to have an idea what you’d like before beginning the process.