Concrete Countertop

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Introduction: Concrete Countertop

About: mechanical engineer, DIY hobbyist.

My wife and I were having a butlers pantry (bar) installed into our house but wanted to save a few $$$ by doing some of the work ourselves. Do to the high cost of quartz, granite, and marble we wanted something different. Although a butcher block wood counter was a possible choice, the poor material properties (chips, dents, scratches, durability, water and heat stains) pushed us away from that idea. Wood requires high maintenance. If these countertops are not resealed regularly (about every six months), mold and bacteria can take over, and the countertop will need to be replaced. To add our own flair to the kitchen and to keep price down, we opted for concrete!

Since these countertops are custom-poured, homeowners can add everything from unique stones to embedded glass or tile, incorporating a piece of themselves into their kitchen design. Sturdy and resistant to chipping and scratching, concrete countertops do crack, but the cracks are easy to fix precisely because more concrete can be mixed up and poured in. Though there are some drawbacks; concrete has to cure, which means you'll have to wait a while before you can use your counters. If you want something that can be installed in a day, steer clear! Concrete is also porous, which means these counters can stain easily and require regular resealing.

Step 1: Materials

Counter Materials

  • 4'x8' sheet of melamine for the concrete form ($30) - Melamine
  • (2) Quikrete Profinish Crack Resistant 80-lb High Strength concrete Mix ($6.50per) (yields 0.6 cu ft) - concrete
  • 1/2" thick polystyrene ($15) - Polystyrene
  • concrete sealer ($30) - sealer

  • Black Silicone caulk ($6.50) - caulk

  • metal wire mesh ($10)
  • Liquid Nails ($3)

Total Cost: $107.50 (excluding tools)

Tools

  • concrete mixing tool for drill ($12) - mixer
  • 60, 80, 400 grit sandpaper - Sandpaper
  • orbital sander
  • drill
  • Concrete trowel
  • drill bits
  • 1-5/8" wood or drywall screws
  • Wax, olive oil, bees wax, canola/vegetable/peanut oil, candle wax,WD-40
  • table saw or circular saw
  • caulk corner tool
  • hammer or rubber mallet
  • exacto-knife or box cutter
  • plastic putty knife
  • mixing tub
  • gloves

Step 2: Building the Concrete Form

This will be the initial step and opportunity to be creative.

  1. This is the foundation for your concrete countertop. Given that I will be creating a countertop that is 54" long x 26" wide x 1.5" thick, I need to cut the large malamine sheet down to those dimensions using either a table saw (recommended) or circular saw.
  2. In order to achieve a 1.5" thick countertop appearance, we need to cut strips of malamine to go around the perimeter of the surface. The strips will be 2.25" thick (1.5" counter thickness + 0.75" melamine thickness). I'll be cutting (2) strips at 55.5" x 2.25" and another (5) at 27.5" x 2.25".
  3. Pre-drill the melamine perimeter for the screws. Using the 1-5/8" wood or drywall screws, secure the strip pieces around the outer edge of the surface piece.
  4. Using the olive oil or WD-40, rub the oil across the entire surface of the melamine sheet including the interior walls. DO NOT FORGET to apply into the corners where the strips meet the surface sheet.
  5. Apply a constant bead of black silicone caulk around the interior corners of the form. Using your finger or the caulk corner tool, run the tool (or finger) around the caulk to create a smooth rounded edge. Let silicone set for about 2hrs (check manufacturers recommendation).
  6. Once the silicone has set, peel the excess caulk from the interior perimeter. DO NOT peel the caulk from the corners as this will provide appealing smooth corners to the surface of your countertop.
  7. OPTIONAL CREATIVE STEP: Add and objects you would like to inlay into the form that will be shown once the counter has cured. Maybe use shells or wood etc. Make sure they are secured down since the concrete may shift them during the pouring & leveling process.

Pro Tip: Using painters tape or masking tape to tape over the tops of the screw heads. This will prevent concrete from going onto the screws which will allow them to be removed easier in later steps.

*(3) of the 27.5"x2.25" melamine strips will be used later on to help create a weight reducing cavity.

Step 3: Mix & Pour Concrete

*Pay close attention to the instructions on the concrete bags for proper water to concrete ratios.

QUIKRETE Crack Resistant Concrete Mix is a 4000psi (27.5 MPa) blend of properly proportioned stone or gravel, sand, Portland cement, special synthetic fibers and other ingredients approved for use in concrete. The synthetic fibers eliminate the need for wire mesh in slab-on-grade construction. We will add mesh anyway to strengthen the concrete.

IMPORTANT: Wear protective gloves when mixing concrete. The concrete coloring can stain your skin and clothing.

  1. Concrete Mix can be hand-mixed in a suitable mixing container, or machine mixed in a barrel-type concrete mixer or a mortar mixer. For this project we will need (2) 80-lb bags of mix.
  2. Plan to use approximately 3 quarts (2.8 L) of clean water for each bag of concrete.
  3. Add coloring to 1-2L of water and mix thoroughly.
  4. Add about 1L of water at a time. DO NOT add all the water at once (see Pro Tip). With the drill and mixing tool, begin adding the concrete to the bucket. Do not exceed a total volume of 1-gallon (3.8 L) of water per bag. If the material becomes too difficult to mix, sparingly add water until a workable mix is obtained. The consistency should be that of cake or brownie batter.
  5. Pour concrete mixture into the mold to approximately 1/2" thick.
  6. Insert the wire mesh (48"x18" in my case).
  7. Over the wire mesh with another 1/2" of concrete and smooth over.
  8. Using the hammer or rubber mallet, firmly tap the bottom of the form repeatedly to release air bubbles from the mixture. You may see the bubbles rise to the surface and pop. Some say that vibration is not needed for glass fiber reinforced concrete but i prefer to do this step regardless. Do this for a good 15-20 minutes.

Pro Tip: it is always easier to add water t the mix than it is to remove water. Be careful how much water you use. The more water that is used = the weaker the concrete strength will be.

Step 4: Add Insert and Increase Counter Thickness

Based on the size of the concrete countertop I am looking to make (54"x26"x1.5"), the weight can easily exceed 176-lbs! We will be using the 1/2" foam board to create a cavity to reduce the weight down to approximately 136-lbs! Savings of 40-lbs!

  1. We will be using the 1/2" thick foam board. Using a exacto-knife or box cutter, cut the foam board to so that its profile is 3" away from every interior wall. In my case that will be 48"x20".
  2. Place the foam board on top of the wet concrete 3" from all interior walls.
    • Pro Tip: add painters tape around the edges of the foam board and overlap onto the faces. Use wax or light amounts of oil across all surfaces that will contact the concrete prior to placing it onto the wet concrete. This will help ease the removal of the foam board after concrete has cured.
  3. Using the remaining (3) strip of melamine board, place those over the top of the foam board and secure them to the concrete form. These will act as braces to hold the foam board into place.
  4. Pour the remaining concrete mixture around the foam board. Make sure to fill the spaces underneath the brace strips between the form and foam. Pour to the top of the wood form.
  5. Use a concrete trowel or smooth edge to smooth out the surface of the concrete The smoother you can make it now, the less abrasive sanding you will have to do later.
  6. Proper curing increases the strength and durability of concrete. Curing should be started as soon as possible and should continue for a period of 5 days in warm weather at 70 F (21 C) or higher or 7 days in colder weather at 50-70 F (10-21 C).

    • If you live in a cold climate; protect concrete from freezing during the first 48 hours. Plastic sheeting and insulation blankets should be used if temperatures are expected to fall below 32 o F (0 o C).

Step 5: The Big Reveal

Now that you have allowed the concrete to cure for a week, the BIG REVEAL is ready to happen! Some say that you can begin the next steps within 24hrs (36hrs if temperature is under 70F) but I prefer to say on the safer side and allow the concrete to fully cure 3-5 days for substantial strength.

  1. Remove the tape that we used to cover the screw holes on the form. Remove the screws from the form and top strips over the foam insert.
  2. Pull the form side pieces away from the surface. If needed, use a rubber mallet and lightly tap the edges to separate from the concrete. BE CAREFUL not to chip the concrete.
  3. With all of the side pieces removed, try moving the slab of concrete. I was lucky that mine moved freely. If yours has some adhesion to the melamine, use a plastic putty knife and wedge it between the form surface and the face of the concrete to separate.
  4. Remove and tear out the foam insert in the concrete.
  5. Flip over and REVEAL the final product.

Step 6: Finishing

With the molding and curing finished, we can now clean-up and seal the final product for aesthetics.

  1. As you can see from previous pictures, my countertop was a bit porous. Using remaining concrete dry mixture, create a thin slurry and apply to the surface. This will help fill in any holes or pores.
  2. If the top surface of the counter is rough to the touch, use the orbital sander and 220 grit paper to smooth down the surface. Switch to 400 grit and,with water, wet sand the top surface till very smooth.
  3. Use a hand-block to round out the edges and sides of the counter.
  4. Flip the counter over to the underside and use heavy 60-80 grit sandpaper to help remove the uneven bottom side. This will help get a smooth contact surface when mounting. A diamond grinding wheel may be needed if texture is too rough.
  5. Flip the counter back over. Using a rag, apply multiple coats of concrete sealer. Use the manufacturers instructions for more precise detail.
  6. Once sealing is complete, install the new counter in your applied situation. Liquid nails is a preferred choice for securing concrete counters to a cabinet base.

Annual concrete sealing is recommended

ENJOY

Step 7: Lessons Learned

This was my first time ever making a concrete countertop, let alone any concrete project. Here is a compilation of things I learned:

  • If the concrete slab is going into a confined area (my butler's pantry was confined by 3 walls), measure 2x,cut 1x. Then check the melamine surface in the space to ensure it fits. Its easier to make alterations to the form that it is the finished concrete. MUCH lighter too!
  • Save a cup or 2 of dry concrete mixture for repairs later on. You may need some to fill pores or voids that may have formed.
  • Make a large bucket of colored water. Separate your powdered concrete into smaller batches and blend. Added the smaller blended batches to the tub and then mix together thoroughly. I had a VERY difficult time mixing (2) 80-lb bags of mix together in the tub. EXHAUSTING. My drill batteries died from working the mixer too hard so I had to mix it all by hand. The coloring did not come out as uniform as I would have liked.
  • Vibrate the mold for at least a good 30-45 minutes to get any bubbles out. Cavities and pores can be seen in the surface of my slab due to insufficient vibrating.
  • For the 3-5 days that you allow the concrete to hydrate/cure, keep the concrete moist by spraying or wiping water on it. This will increase the strength.
  • Do any sanding or grinding outside in the open air. The dust can be overwhelming.
  • USE A DUST MASK AND GLOVES.
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5 Tips

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Use a corded drill for big jobs like this.

We flipped over our slabs while they were still in the molds. The melamine added a bit of extra support during this critical moment. Once flipped, we removed the mold and the slabs remained in place and continued to cure throughout the grinding & polishing process.

Almost a mandatory tip for concrete countertop making is Fu-Tung Cheng's book (some would say 'bible' ;-) Concrete Countertops. It covers all the pitfalls you may run into (like "Hey these things are REALLY heavy...make sure you have enough people, and room for them to move to install it!")

Borrow or rent a grinder-polisher with diamond discs, and use LOTS of water. (These tools often have a built-in water jet that you hook up to a hose.) It's super messy -- prepare to ruin some clothes -- but it's way better than the dust cloud you get from dry sanding, and you'll end up with a silky smooth surface.

Nice work here. one comment on the caulk and the tear out it looks like you got at the edges. The DAP caulk in the picture is acrylic latex caulk with silicone -- it will stick to the concrete and cause the tear out like you got. The 100% silicone caulk you linked to (GE brand) is the stuff you should use -- it would eliminate the edge issues you had. Nice write up though, and the end product looks good :)

1 Questions

I love it and it looks like the ones from the Scandinavian inspired homes and so affordable. My question is, do you need to do any external coating? Since concrete do adsorb liquids.

1

Hi! I did do multiple coats of the Cheng's concrete sealer (Step 6 - Finishing: Task 5). This brand seems to be used a lot on other projects and has high reviews on Amazon. It's kind of expensive but i only used like 1/4 of the bottle for this size slab. The instructions request that for each coat you apply to increase the sealant portion of the water to sealant ratio until you do a 100% all sealant coat.

This is also not a polished concrete. Polishing requires hardener and a wet polishing tool as well as much higher grit sandpaper I believe. I enjoy this project a little more on the 'rustic' side.

5 Comments

I have not heard that idea before. I assume the excessive water for polishing was not too much for the hydration/curing process. Its good to keep some moisture on the concrete to cure, just have not heard whether there is a limit to how much moisture...

We did the polishing after curing for about a week under plastic. By that time, the grinding/polishing water should not have made any difference to the cure. It worked out fine.

I will definitely have to check out that book before the next one. "Hey these things are REALLY heavy." YUP! Luckily I found the tip for the foam insert cavity which paid dividends on my back.

Thanks for the tip! I had planned to buy the GE silicone caulk and realized I had some DAP laying around. Now it makes sense why the edges look a little bit rougher. Luckily we were going for a little more 'rustic' look. This would have been a mistake if we were looking to polish the slab.