Door Stop

• Choose a font: “Impact” is used in this example because it’s bold and thick. The concrete won’t be very strong if it’s less than 1″ wide, and even then it will be easy to break, so take this into consideration when determining the size and shape of the letters.
• If you don’t have a program like Photoshop or Illustrator, just use a program like Word. Re-size the font until it takes up most of the 8.5″ x 11″ page.
  •    Print the template out full-scale.
  •    Cut the paper template out with scissors.
  •    Trace around the template on the foam with a permanent marker.
• You can also sketch straight onto the foam and cut out any shape you want; just make sure the thinnest parts are at least 1″ wide.

Step 2 – Cut Out the Letters

• This step might be easier with a laser cutter or a hot wire, but a coping saw, jigsaw, or utility knife will work just fine.
• Make sure the blade is vertical.
• Gently clamp the foam over the edge of a work table.
• Drill a hole so the blade of the jigsaw has a place to start.
• Cut out the negative space first, like the middle parts of the letters O and P. Cutting them out first will be easier and safer than trying to do it later.
• Then cut out the rest of the letters, following the traced lines. Leave some room so you can sand it to the exact size.
• After the shape is cut out, sand the inside of the foam by hand with 120- or 220-grit sandpaper. The smoother you can sand it, the smoother the sides of the finished concrete piece will be.

Step 3 – Glue the Foam to a Baseboard

• Place the foam on the board and trace around the inside and outside with a pencil.
• Put the negative spaces in place, like the centers of the O and P. Trace around them.
• Spray one side of the foam with spray adhesive, holding the can at least 12″ away from the foam because the aerosol can melt the foam. You can also use silicone caulk, which will provide a better seal against bleed-out, but it takes time to cure.
• Use the pencil lines as a guide and press the foam down firmly to the baseboard. To get the best seal, follow the instructions on the spray adhesive and spray a little bit on the baseboard too.
• The spray adhesive and silicone will leave some texture on the concrete unless you clean it off the baseboard with denatured alcohol.
• Pour the form soon after it has been glued down with spray adhesive. The spray adhesive won’t stick as well the next day and this can cause problems if the concrete bleeds through and forces the foam up.
• If you’re using silicone to hold the foam down, wait for it to fully cure before pouring (3+ hours in the sun). Unlike spray adhesive, you could pour a silicone-sealed form a week later with good results.

Step 4 – Mix and Cast Concrete

• The finished weight of this example is 5 lbs. Because this is a small project, we can mix the concrete in a 4-quart bucket. Check out the Mixing Concrete By Hand Guide for additional tips.
• Take a handful of concrete and drop it into the form, being careful about damaging the foam.
• Work the concrete into the corners and fill it to the top.
• Vibrate the form using drop compaction (pick up one side of the baseboard a few inches and repeatedly drop it to help the air bubbles rise to the surface).
• Top off the form with concrete and smooth the top flat with a trowel, always being careful about the foam.
• After the piece is cast, cover it with plastic to keep the humidity inside while curing. Leave it somewhere in the shade, never in freezing weather or direct sunlight while curing.

Step 5 – Remove the Foam

• Wait 4+ days before demolding. If your piece is very thin, wait a few extra days and be extra careful when removing it from the foam mold, or it will crack.
• Slide the piece sideways to break the seal to the baseboard.
• Break the foam away with your hands and a plastic putty knife.

Step 6 – Continue Removing the Foam

• Try not to gouge the concrete or bend the piece, because it can break at the thinner points.
• Scrub away the foam left on the surface with a bristle brush or an old tooth brush. You could dissolve any residue with denatured alcohol or acetone, but it’s not necessary.

Step 7 – Sand Rough Edges

• Knock down any rough edges with diamond hand sanding pads.