Stucco is very popular for the siding of houses and even businesses depending on the area you live in. To apply the cement stucco base, you should know that there are three layers for the base coat which are the scratch coat, brown coat, and finishing coat. Applied in that order.
Please be sure to follow the instructions below to correctly apply all three layers.
- Building paper for walls not made of concrete or bricks
- Metal meshing
- Weep screed for the bottom of the wall
- Control joints
- Galvanized nails
- Mixing barrel
- Trowel with notches for scratch coat and long trowel for base coat
- Finishing trowel for finishing coat and float for texture if used
- Cement, lime, sand, and water (these are the ingredients for the base coat)
Stucco application techniques
Step 1: First you need to make sure to prepare your walls. You will want to ensure that they are clean and clear of any debris.
If your wall is not made of bricks or concrete you want to put building/waterproof paper on it so that the edges cover at least 4 inches of the other paper.
You will want to apply metal reinforcing on top of paper before you try applying any stucco. This will help ensure the stucco bonds better to the wall. Install weep screed on the bottom of the wall and install the metal reinforcing on top of that. Make sure it runs horizontally the whole length of the wall with your tool of choice (laser is easy to get these days).
How to stucco a concrete wall is pretty much the same process as brick and board walls. If you have a brick or concrete walls, you can skip the metal reinforcing if you like, but I’d still do it. If for some reason the stucco won’t adhere well, the metal will keep it in place for years.
I’ve probably fixed near 100 walls and thousands of holes on the stucco where there was no metal reinforcement and it usually starts with one patch falling and water starts to eat the surface around the hole in stucco. If you patch it, it will usually pop out or crack as it’s different strength from the surrounding material.
So the metal reinforcement can save you some time if there comes time for repairs.
Note: Poured concrete walls need to be ground, sand-washed, or acid-washed so that the stucco will adhere well. That is another common reason why stucco cracks and needs to be repaired before its time.
Step 2: Now if you need to install reinforcement of any kind, make sure that the metal is galvanized (rust-resistant). The installing of reinforcement materials will help the stucco get a better bond like stated before and helps strengthen the structure. The weep screed is there to let the water escape so install it well.
If you use control joints, they are meant for dividing the wall and crack control. Try to place them as square as possible and aesthetic so your wall won’t look mismatched. Also, place them where two different walls meet as that is the usual cracking point.
Now there is one important thing to remember, depending on the type of reinforcement. If it’s galvanized net, the stucco needs to get behind it a little so it will stick to it and the wall behind it. Also, follow the reinforcement nets installing instructions so you have it attached well to the wall and one attachment point doesn’t have to carry too much weight.
Ideally the net won’t be carrying the stucco, but if it with time has to, all of it won’t come down.
Step 3: For the scratch coat you will mix one part cement, ¼ part lime, and three to five parts sand. Mixtures change from place to place and you should be able to get ready mixed bags as well. Add enough water to make this a workable mixture, keeping in mind that you will be applying this coat in a ½ inch layer.
Before applying you will want to dampen the wall with a spray of water to help this layer bond better. Don’t soak it, just let a nice spray so the bricks or concrete is moist, but won’t be dripping wet.
This should completely cover the metal reinforcement material. While you are applying this layer be sure to use your notched trowel so that you are leaving horizontal lines on the surface. The grooves will help the brown coat bond more successfully. Allow your scratch coat to dry for several hours.
Alternatively, if you’re using a hopper gun for spraying stucco, you can leave it at the spray surface. It is rough enough for the next layer to adhere to. This is actually how I do it usually if I have big surfaces to do.
Step 4: After the scratch coat is dry after 24 to 48 hours, you will make the same mixture as in the step above for your brown coat. Be sure to dampen the scratch coat before you start applying the next layer for better adherence. Now with the brown coat, you need to ensure that it is being evenly troweled on to 3/8 of an inch thick and smooth.
Depending on the wall, how level it is, and are you using control joints, you might have to do this twice to get a level surface. Without control joints, I usually do one layer horizontally where I use a long screed or long finishing trowel (24 inches at least) to finish the surface.
I let the first layer dry and sand the high trowel marks away. Then I’ll do the second coat that I finish vertically. This way brown coats will be level and there will be little “waves” on the surface as it’s done like a cross.
Another way is to do “benches” and let them dry or make them with plywood and fill the middle with stucco. It doesn’t have to be this complicated, but I’ve met some walls during my career that had to be done the hard way. Usually old brick walls.
Step 5: Now that your cement base coat layers are done, you are ready to apply your finish coat. Just remember that before you can do the finish coat, you need to allow several days of drying time for the base layers and moisture them every day.
You don’t want to pour them with water, just gentle spray that the surface will get moisture. This will help the curing process of cement.
When you’re doing the finishing layer, you can do it with hopper gun to get texture or finishing trowel and float. It’s a matter of taste here.
Hopper gun is the easiest as it is just sprayed and let dry. When you spread it with a trowel and float, depending on the float you might need a little skill. Some ready-made finishing coats are easy to apply with plastic float and the layer is very thin and might need a paint coat below it.
I hope this answered how to make a stucco exterior wall. It can be a little bit confusing and sometimes better left to professionals. On the other hand, if you have manageable wall sizes it isn’t that hard and can be even fun to do it yourself.
Working with stucco is all about preparation. You have to have your wall ready for doing the coats and no interruptions. Have the stucco materials and water near so you won’t have to run around to get them. When you can just make stucco and apply it to the wall, it will be easy.