In this video, This Old House host Kevin O'Connor learns how to create concrete kitchen counters.
1. Make a template of the existing countertops out of 2½-inch-wide strips of ¼-inch plywood.
2. Adhere the plywood strips together using hot-melt glue. Label each template to identify its position on the cabinets.
3. Build a form out of melamine-faced particleboard. Rip 2-inch-wide strips of particleboard on the table saw, then crosscut them to length with a miter saw.
4. Place the template upside down on top of a sheet of melamine-faced particleboard.
5. Hot-glue the 2-inch-wide strips around the perimeter of the template.
6. Miter-cut the strips at inside corners and seal the joint with silicone sealant.
7. Remove the template, then wipe beeswax around the inside of the form.
8. Apply a bead of silicone sealant along all inside corners and perimeter edges of the form.
9. Smooth the silicone with a length of ⅜-inch-diameter plastic dowel.
10. Once the silicone has cured, peel off the excess.
11. Use a ½-inch electric drill with mixing paddle to blend together sand, cement, liquid polymer and powdered pigment to create the concrete for the countertop.
12. Vacuum the form clean, then wipe it down with a clean rag dampened with acetone.
13. Use an air-powered sprayer to spray a ¼-inch-thick layer of concrete into the countertop form.
14. Sprinkle a contrasting-color stone aggregate into the wet concrete.
15. Mix a second batch of concrete, but this time, add glass fibers to increase the strength of the countertop.
16. Carefully pour some concrete into the form, then smooth it out by hand to about ⅜ inch thick.
17. Compact the concrete with a hand roller. Add another ⅜ inch of concrete and compact it again.
18. Cut 1-inch-thick rigid polystyrene foam board 3 inches smaller than the inside of the form.
19. Lay the polystyrene foam on top of the wet concrete.
20. Screw 1x3s across the form to hold down the polystyrene foam.
21. Pour concrete around the perimeter of the polystyrene, filling it flush with the top of the particleboard form.
22. Allow the concrete to cure for three days.
23. Unscrew and remove the 1x3s.
24. Smooth the concrete using an angle grinder equipped with a diamond-impregnated cut wheel.
25. Pry off the polystyrene foam board with a flat bar. Vacuum the surface clean.
26. Use a hammer and chisel to remove the particleboard form from around the perimeter of the countertop.
27. Round over the sharp countertop edges with a sanding block.
28. Tap a wide-blade putty knife underneath the countertop, then insert a wood shim. Repeat in several places around the perimeter until the countertop breaks free from the particleboard form.
29. Flip over the countertop.
30. Lightly grind the top surface with a wet grinder and diamond pad. Continue grinding until you've exposed the aggregate.
31. Mix together cement, polymer and pigment to create a slurry. Hand-rub the slurry into the entire countertop.
32. Wait for the slurry to harden, then smooth the entire counter—top surface and edges—with a random-orbit sander fitted with an 80-grit abrasive disk.
33. Switch to 100-grit abrasive and sand the surfaces again. Switch to 220-grit abrasive and smooth the countertop one last time.
34. Use a steel-wool pad to apply concrete sealer to the countertop. Let dry for 10 minutes, then apply a second coat. Repeat until you've applied eight coats of sealer.
35. Set the finished countertops on top of the cabinets.
36. Lift the countertops and apply a bead of construction adhesive along the tops of the cabinets. Set the counters back into place.