Cement Stucco Foundation Finish
DEAR TIM: My home has two types of foundation: concrete block and poured concrete. They look horrible because of the different colors and textures. How can I make them look uniform? I have seen other homes where the foundations have been covered with a stucco material. Is it too late to do this? How was the stucco successfully applied to my neighbors' foundations? Lori B., Bright, IN
DEAR LORI: I couldn't agree more with you with respect to the contrasting colors and textures of concrete block vs. poured concrete. There is simply something about the horizontal and vertical lines in the concrete block that clashes with the monolithic appearance of poured concrete. Making the two different foundations appear as if they are one is going to be fairly easy. Masonry walls have been stuccoed for thousands of years and some still retain their stucco.
High quality ingredients to make stucco are probably close at hand. Visit a building supply material business or a brick dealer and you should find bags of Portland cement, hydrated lime and different sands. The Portland cement made today when mixed with clean sand and a little hydrated lime will produce a stucco that is easy to apply and will last hundreds of years. The best part is the cost: You can probably purchase the needed materials for the entire job for less than $100.00. That is a bargain when you think about the longevity of the finished product.
The first thing you need to do is clean the foundation surfaces. This is one of the few instances where I advocate the use of a pressure washer. Often rainfall causes dirt and silt to splash up onto a foundation. If you live in an area with clay soil, very fine clay silts can get deeply embedded in the pores of both the poured concrete and especially the concrete block. Pressure washers quickly and efficiently remove this silt.
Squirting the dirty masonry with a regular garden hose and a nozzle will not remove all of the dirt. A stiff scrub brush with soap will work, but that method involves considerable work. Once you have cleaned the walls, rinse them with clear water making sure they are perfectly clean.
Next I suggest you buy one or two pieces of one-half inch thick cement board. It typically comes with one side slightly rough and one side smooth. Tack this cement board with the rough side facing out to an existing wall surface so that it does not flex. If you have to build a small temporary wood stud wall, do so. This surface is going to be your stucco simulator practice area.
Mixing stucco is easy. I suggest you blend three parts medium sand, one part Portland cement, and one-half part hydrated lime. Mix the dry or damp sand with the cement and lime until you have a uniform color and texture. It is now time to slowly add clean water to the mix. Blend the water, sand, cement and lime until the final texture and consistency resembles bricklaying mortar. When the correct amount of water is added, the stucco mix can be formed into a ball that is fairly plastic and will hold its shape if set on a flat surface.
The next step is to mix some cement paint. This is the most critical aspect of the application of the stucco. The cement paint is made by mixing pure water with some Portland cement powder. Mix enough water so the powdered cement turns into a slurry that resembles paint. Mist the cement board with a little water to get it damp, brush on some cement paint and immediately apply some stucco. Do not allow the cement paint to dry before it is covered with stucco.
The stucco thickness should not exceed one-quarter inch. Use a regular steel trowel to apply it with curved strokes. The stucco should magically stick to the cement board without falling off. If it does fall off, the stucco mixture may be too dry. The hydrated lime in the mix makes the stucco sticky and improves the workability of it.
Now comes the fun part. There are an infinite number of designs, techniques, tools and textures you can create. For example, you can use a stiff brush and stipple the stucco. You draw a brush across the stucco to create random brushed texture. The steel trowel can be dabbed randomly into the stucco to create a different texture. Small angular colored stones can be cast into the wet stucco. The only thing holding you back is your imagination.
Be sure to stand back 20 or 30 feet to look at the practice stucco simulation. This is what people will see from the road or your yard. Looking at the stucco up close will give you a false impression of the real look you will see once the job is complete.
The best time to install stucco, in my opinion, is cool to slightly warm weather. Working on an overcast day with little or no threat of rain is best. Sunny, hot and breezy days are the worst as the stucco can dry too quickly. You want the stucco to dry slowly. Try to follow the sun, meaning work on a wall surface after the sun has moved and is not directly striking the foundation wall
Once the stucco has hardened to the touch, keep it slightly damp with very light misting of water. If possible, try to do this for two to three days. This added water allows the cement in the stucco to cure allowing millions of microscopic crystals to grow into the poured concrete and concrete block surfaces. These crystals are the glue that permanently bond the stucco to the masonry surfaces.