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concrete countertops

How To Make Concrete Countertops

Jun 13, 2020 by Liz Brumer

Homeowners setting out on a home improvement project are always looking for ways to get the most bang for their buck while upgrading the home to accommodate lasting trends. Concrete countertops can be a stylish and durable option for your kitchen remodel or home office that can be created with little or no experience at a relatively low cost, making concrete a wonderful countertop choice.

Learn how to make concrete countertops for your next DIY project, including all the necessary tools, in six steps.

Necessary tools and materials

There are several tools required for this project. If you don’t already have these tools and materials, you’ll want to purchase them before you begin.

  1. Tape measure.
  2. Sawhorses.
  3. Lumber.
  4. Medium-density fiberboard (MDF).
  5. Saw.
  6. Power drill and drill bits.
  7. Wood screws.
  8. Caulk guns and caulk.
  9. Rebar and re-mesh.
  10. Bolt cutters.
  11. Cement.
  12. Colorants (optional).
  13. Concrete mixer.
  14. Mixing tub.
  15. Gloves.
  16. Power sander and sandpaper.
  17. Plastic sheet.
  18. Putty knife.
  19. Shims.
  20. Respirator mask and eye protection.
  21. Microfiber cloths.
  22. Sealer.

Step 1: Create a mold

The first step to making concrete countertops is creating a mold of the countertops. Measure your base cabinets, adding an additional ¾ inch for an overhang, or measure your existing countertop. Take a piece of MDF that is larger than your intended slab and lay it on top of the sawhorses. Trace, then cut the exact dimensions of your measurements for the base. Then cut side pieces to the depth of your countertop, plus enough additional height to account for the MDF depth.

Next, attach the side pieces to the mold base using screws every 6 inches. Concrete is heavy; if the mold is weak or flimsy, you will end up with warping, so don't skimp on screws. Don't forget any cutouts for a sink or stovetop. It's a good idea to double check the interior measurements of the mold and make sure that it is level and square before moving on.

Step 2: Finish the frame and prepare reinforcement

Due to the weight of concrete, sometimes the sides can warp or the middle can bow, especially with larger slabs. Combat this by placing several sturdy lumber boards running lengthwise underneath the mold for additional support. Vacuum out any sawdust or debris from inside the mold, then run a bead of caulk along all the seams, smoothing it with a wet finger.

Any imperfections in the mold or caulk will show up in the concrete, so take your time with this step. Cut your rebar and re-mesh to size for the mold, giving 2 inches of space between the rebar and the edge, then set it aside for later. Allow the caulk to dry for 24 hours before proceeding.

Step 3: Mix and pour the concrete

Following the package instructions, mix the cement with water in a tub or container. If you’re using a colorant, now is the time to add it.

Concrete cures quickly, so it’s important to work efficiently and in small batches. It can be very helpful to have one person mixing and another person pouring to prevent curing before the project is complete. Wearing gloves, fill the mold and press the concrete into the corners. When it's halfway full, add the rebar and re-mesh, making sure they don't touch the edges of the mold. Continue filling the mold until the concrete is slightly higher than the top edge. Try not to apply too much pressure at this point or you may unintentionally press the rebar down, which could expose it to the countertop surface.

Step 4: Remove bubbles and wait

Smooth the surface using a float or a 2x4 to draw out any aggregates. Next, run a sander, with no sandpaper, along the outside edges of the mold. This will help release any air bubbles that are trapped in the concrete. Smooth the surface again, then repeat sanding and smoothing until no more bubbles appear on the surface.

Not only can bubbles cause imperfections in the final product, but they can also weaken the countertop, so be thorough here. Once satisfied, loosely cover the slab with a plastic sheet to keep debris from falling in it while the form cures. This can take four to seven days, depending on the size of the slab, the level of humidity, and the temperature of the room.

Step 5: Remove the form

Next, you’ll need to remove the form. Unscrew the mold sideboards. It’s fairly common for the boards to stick to the form, and if that's the case, gently insert a putty knife between the board and the form and, if needed, tap the putty knife with a hammer. Just be careful, as this process can cause cracks to form.

At this point, you'll want to bring in someone, or several people, to assist you in flipping the slab over and placing it back on the sawhorses. To remove the base of the mold, use the same method of inserting the putty knife and tapping, but as you work, insert shims between the slab and the MDF to help lift the MDF off the concrete.

Step 6: Finish the countertop

The final step is finishing your countertops. Put on your respirator and eye protection, as this step gets very dusty. Start sanding the concrete to remove imperfections, starting with 80 grit sandpaper and gradually working your way to 220 grit paper for a smooth finish. Unless working on a very small countertop, you will likely run through a lot of sandpaper, so make sure to have extra on hand so you don't have to stop and run to the store.

Vacuum up any dust or debris, then wipe the surface with a wet microfiber cloth and allow it to dry. Finally, the countertops should be sealed just like granite, since concrete is a porous surface. If your countertops are in a kitchen, make sure to use a food-grade sealer.

While this may seem like a complicated project at first, creating concrete countertops is an achievable task for a dedicated or experienced DIY homeowner. To help get the hang of the process, it can be a good idea to try a few small practice forms before starting in on your main project so that you can figure out the best cement consistency, how to remove the air bubbles, and how to remove the slab from the form without cracking it. While just about anyone can accomplish this project, it will take some time to complete, especially if it's your first time. Thorough preparation and allowing ample work time -- which can stretch over several weekends, depending on the time you have available -- will all help this project go that much smoother.

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