A popular question that comes up every now and again has people wondering how they can make their own finish coat material for stucco. I never really thought that you would want to make the finish coat, but I guess in certain circumstances, it would make sense.
I guess if you don't have a stucco manufacturer close by or something similar then getting a finish material would be a challenge. A finish coat is not hard to make though, now that I think about it and I'm sure an article on how to make it would probably help a lot of people, so here goes!
Acrylic VS Traditional Stucco Finishes:
Now this tutorial is going to be about how to make a traditional stucco finish, only because the makeup of an acrylic finish is much harder to make, so for right now, let's just focus on traditional (cement based) finish coats.
I might do a tutorial in the future on how to make an acrylic stucco finish if enough interest is shown and will link to it in this article.
A Note On Bagged Mixes:
Usually, myself and the majority of other plasterers use a pre-bagged stucco finish material that has the cement, lime and sand mixed together. All we have to do is add the color (if applicable) and water to get the finish material mixed up and ready to go.
The makeup of these bags consists of white portland cement, lime and sand for the most part and more water is usually added to get a thinner mix, when compared to a stucco base coat material.
Let's Look At A Bag Of Material:
I wanted to take a look at a standard bag of stucco finish mix from LaHabra to get a better idea of what's in it and make a similar product...
The image shows the ingredients taken from LaHabra's Exterior Stucco Color Coat material and as you can see the main ingredients are: Portland cement, lime, aggregates (sand) and proprietary ingredients (not too important).
- Portland cement: They will use a white Portland cement or a grayish-white base for their colors. You can find white Portland cement at some supply stores but may be hard to find. You only need to use a white cement if you want a white or pigmented stucco color.
You can use a standard grey Portland cement if you plan on painting the finish or having the grey finished cement look. Color can be added to grey Portland cement but is not as prominent as it is with a white cement.
- Hydrated lime: Lime will also be needed and a hydrated Type-S is usually recommended. You can find lime at many places including larger hardware stores like Home Depot.
- Aggregates: Like I stated earlier, aggregate is just graded sand. Graded is just another term that represents the size of the sand. For instance, some manufacturers have finishes that are 16/20, 20/30, 30/30 and so on, which represents the size of the sand used.
The larger the number, the smaller the particles of sand are. You can find some of these sands at bigger stores but not all of them will be graded, so you are basically left with a fine, medium or coarse sand to use with your finish.
- Proprietary additives: I am not really sure what these proprietary ingredients are but for the simplicity of this tutorial and the fact that you really don't need them in most cases, we will skip their use for this tutorial.
The Basic Stucco Finish Formula:
The basic formula for a stucco finish coat mix will be very similar to that of a base coat recipe but more water will be added in order to thin out the material, seeing as how it is usually applied at a thickness of around 1/8".
- 1 part Portland cement
- 1 part hydrated lime
- 3 parts sand
- Water to thin out mix to a cake batter consistency
If you were to compare that to a standard 90 lb. bag of finish material that you would typically get from the manufacturer, that would roughly equate to:
- 18 lbs. of Portland cement
- 18 lbs. of hydrated lime
- 54 lbs. of sand