Concrete Casting Basics 101: Making a foam letter relief concrete cast!
For specific details, search online for how to create concrete casting forms.
To cast concrete with lettering and a logo if desired, you need a form, concrete and letters.
The form can be on a flat surface, into which you can pour your concrete, or the form can be erect with a bottom, sides, a front and a back. Be sure to mix sufficient smooth concrete so that a spill or leak won't scuttle your casting pour. Stir and poke the concrete to reduce incidence of air pockets.
For the sake of simplicity, this article focuses on using a flat form or pan for making pavers.
After deciding on the form or pan shape and size, follow the basic preparation instructions.
|Reverse-cast metal letters with a 7-degree draft for casting|
Letters made to be reused are generally made of either rubber or metal. Rubber letters are flexible, and so can be compressed to remove from cured (hardened) concrete, and metal letters are made with a 7° draft, which allows them to be removed from the concrete.
The draft (slightly sloped sides of the letters) allows the hardened concrete to release the letters, as the fit is a very slight bit wider at the base of the letter as viewed from the side. Regardless of which you use, you will want to oil the letters once you're ready to pour concrete. The rubber and metal letters are made in reverse like a rubber stamp so that the resulting imprint in the concrete reads correctly.
See below for using single-use foam letters.
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What is the difference in how the letters work?
As far as the concrete is concerned, there's little discernible difference to the naked eye. The rubber letters are generally 1/8" to 1/4" [3.18mm to 6.35mm] deep, and so the resulting impression is not very deep. This is best for flat pavers, as water and dirt will not make a deep 'pool' on the surface. For a deeper casting, the metal letters we make are an average 3/4" to 1.5" [19mm-38mm] deep, depending on the letter height. These may be better for vertical concrete casting and deeper cast letter effects. Foam (single-use) letters can be 1/2" to 1-2" thick.
|Large-cell beaded foam is the most economical but leaves a texture.|
For a single casting (one side of one sign) it's not very cost-effective to buy letters made to be reused. You can use our very economical large beaded foam letters if the resulting letter "texture" is not a problem, or our smoother smooth-cell foam and gator foam materials. Letters in foam materials are removed or dissolved when removing from hardened concrete, and so are single use.
So if you were planning on a mixed-media sign like the one above, we would help you by determining what you need to cast it in concrete (the letters spelling "Sunflower" are embedded in concrete and the panel beneath is made of dimensional letters mounted to a panel shape, which in turn is mounted to the sign face) and to assemble your sign.
We have all the D.I.Y. products you need, made to order.
|Form for a hollow-center columnar cast.|
- Exact wording with the
- Size of letters (measured by letter height),
- The desired thickness of letters,
- Kind of material (foam, metal, rubber)
- Typestyle if any, otherwise a bold block like the letter "E" above will be used, and any
- size or space limitations if there are limits, like a 120-foot width and 40" overall sign height. For example, if your casting area is 24 by 60 inches and you have to make the letters fit, tell us the maximum width and height that the letters must fit within.
Article author Joe Giral is the founder and creative director of LetterBank and My DIY Signs. Your comments are welcome.