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Picture of DIY CONCRETE:: Door Stop
This Instructable will show you how to make a concrete door stop using a piece of 2" thick insulating foam. You'll print out a template, trace it onto foam, cut it out, glue it down to a base board, and then fill it with concrete.

Materials + Supplies:
Tools:
  • Jig Saw
  • Sandpaper (120, 220 grit)
Concrete Mixing:
  • Bucket / Wheelbarrow
  • Shovel / Trowel
  • Particle Mask
  • Rubber Gloves
Concrete Finishing:
  • Diamond Hand Sanding Pads (optional)
 
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Step 1: Print out the Template

Picture of Print out the Template
If you don't have a program like Photoshop or Illustrator, just use a program like Word. Choose a bold, thick font, and re-size it until it takes up most of the page. Or you can skip the following steps and sketch straight on the foam.

  • Print out the template.
  • Cut out the template with scissors.
  • Trace around the template on the foam with a permanent marker.
Choosing a font:
The font you use should be bold and thick, like Impact in this example. The concrete won't be very strong if it's less than 1" thick, and even then it will be easy to break, so take that into consideration when determining the size of the letters.


Step 2: Cut out the Letters

Picture of Cut out the Letters
This step would be easier with a laser cutter or a hot wire. A coping saw or a jig saw will work just fine - the trick is to make sure the blade is vertical. You could also use a utility knife for cutting out very simple shapes.

  • Gently clamp the foam over the edge of a work table.
  • Drill a hole so the blade of the jig saw has a place to start.
  • Cut out the negative space first, like the middle part of the letter O and the 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.
What kind of foam?
DOW makes a rigid polystyrene insulating foam that works well for projects like this and is available in 2" thickness from most hardware stores or places that sell building supplies. Owens Corning makes a pink insulating foam has the same qualities and will work as well, but you don't usually see it over 1" thick. White styrofoam will also work, but it's not as dense and doesn't sand as well as blue foam. Experiment with what you can find in the dumpster. Anything more rigid is unnecessary, and anything with an open core won't really work.

Step 3: Glue to the Base Board

Picture of Glue to the Base Board
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In this example, the foam is glued down backwards, so the front of the word STOP will have a cast finish from the melamine baseboard. If you don't glue it down backwards, you will want to trowel the top of the concrete smooth after casting to get an even surface.

  • Place the foam on the base board and trace around the inside and outside with a pencil.
  • Put the negative spaces in place, like the center of the O and P. Trace around them.
  • Spray one side of the foam with spray adhesive, hold 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 takes a few hours to cure.
  • Use the pencil lines as a guide and press the foam down firmly to the base board. To get the best seal, follow the instructions on the spray adhesive and spray a little bit of foam on the base board too.
  • The spray adhesive and silicone will leave some texture on the concrete unless you clean it off the base board with denatured alcohol.
When to Pour:
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, wait for it to fully cure before pouring (3+ hours). The silicone will bond just as well over time, so you could pour the silicone-sealed form a week later and still get good results.

Step 4: Mix + Pour Concrete

Picture of Mix + Pour Concrete
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The finished weight of this example is 5 lbs. Make sure to mix up enough concrete for your project. Because this is a small project, we can mix the concrete in a 4 quart bucket. The most common mistake when mixing concrete is to add too much water to the mix. Add water gradually.

For more tips on mixing concrete, check out the How-To-Mix Concrete Instructable.
  • Add the dry materials to the bucket (Concrete Mix and any Pigment or Admixtures like CHENG Pro-Formula).
  • Blend the dry materials together until the color is consistent. Break apart any clumps of concrete or throw them out.
  • Add 3/4 of the recommended water to the mix.
  • Scrape around the walls and the bottom of the bucket with a trowel.
  • Gradually add the remaining water.
  • 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 base board 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.
  • Cover the concrete with plastic to keep the humidity inside while the piece cures. It should cure somewhere in the shade, never in freezing weather or direct sunlight.

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 base board.
  • Break the foam away with your hands and a plastic putty knife.
  • 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.
  • Sand any rough edges with diamond hand pads.
That's it. Hopefully this project inspires you to experiment with using scrap foam as a mold for concrete. Thanks for following!
splatman1 year ago
The blue foam by Dow is Styrofoam. It's usually printed right on the material.
Creativeman2 years ago
Thanks for this instructable. It did inspire me to make a variation of the doorstop. See:http://www.instructables.com/id/Make-A-Variation-Of-The-Concrete-Doorstop/. I enjoy working in concrete and instead of telling you how to "improve" your creation (as numerous other commenters do), I actually made my version. Thanks again.
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CHENG Concrete (author)  Creativeman2 years ago
Very very nice, thanks for sharing! I like how you improved the process, made it more robust, and used two different colors. Here's a picture of some two-colored house numbers I made using a similar technique (except using gasket rubber instead of foam for the cutout). It's tricky to fill just the numbers without having the red bleed into the grey. Nice work!
house_numbers_colored_1.jpg
Yes, I like this...may try a few to solve that bleeding issue. Maybe just let the letters set up (a few hours) then pour the base. Adherence shouldn't be a problem I think. I have poured just numbers on an acrylic sheet, then removed them. They could then be glued onto a base.
jack85592 years ago
If it were me, I'd put in about 2 thirds of the concrete, vibrate it, add some steel wire to make it keep from cracking as easily, then add the remaining concrete to fill the form. I'd also paint some diesel fuel on the form itself before adding the concrete assuming that it didn't eat the form up as a release agent. You could cut the form out with a slight bevel (about 10 degrees) to it so as to make the piece come out of the form easier as well and possibly re-use the form. Just a thought....
CHENG Concrete (author)  jack85592 years ago
Diesel fuel will most definitely melt the foam. No mold release is necessary because a foam mold like this won't be re-usable. In order to re-use it, you could try lining the inside of the foam with clear packing tape, but that's really tedious. The tape will keep the concrete from locking into the microscopic pores in the foam, and it might slide out if there's enough draft. The clear packing tape will also give the concrete a smooth and shiny texture. A wire cage for reinforcement is a good idea, and when I try this again, I'll make a frame from wire coat hangers and suspend it in the form. At least if it breaks, the wire will help hold it together.
Right on.
Eh Lie Us!2 years ago
Question: Imagine that! I was wondering if a metal (wire/rebar) frame is recommended for this if people will be stepping on it or you'll be moving it around. Not sure how strong the concrete will hold.
Horef2 years ago
Very good job! i love the simple technique and elegance of it :)
jack85592 years ago
If it were me, I'd put in about 2 thirds of the concrete, vibrate it, add some steel wire to make it keep from cracking as easily, then add the remaining concrete to fill the form. I'd also paint some diesel fuel on the form itself before adding the concrete assuming that it didn't eat the form up as a release agent. You could cut the form out with a slight bevel (about 10 degrees) to it so as to make the piece come out of the form easier as well and possibly re-use the form. Just a thought....
granthams2 years ago
Neat instructable. We use 2 coats of rubber cement to bond styrofoam, etc. Put rubber cement on both surfaces, let dry and apply a second coat. Allow to dry for 10 - 15 minutes before bonding. We also use a hot wire cutter for cutting.
racoontnn2 years ago
Funny thing - put a vertically just inside the door garden gate!
lime3D2 years ago
What about using some sort of release agent (like Pam cooking spray, silicone spray, etc.) to make it easier de-mold it?
Phiske2 years ago
Very well done. Turned out super crisp. Simple technique but effective. Great job!
Kiteman2 years ago
This will, of course, work with any brand of concrete, not just that promoted by the author.
CHENG Concrete (author)  Kiteman2 years ago
You're absolutely right. This project can be done with any type of concrete (or styrofoam), but a 5000 psi. concrete mix will achieve greater strength and this helps cut down on the curing time. Sakrete 5000+ in particular is formulated to be free of fly ash and other fillers which can have a negative effect on color when the concrete is being pigmented. But of course you can use whatever concrete mix is available at the local hardware store. Thanks for the comment.