HOW TO MAKE A CONCRETE COUNTERTOP & SINK
Basic DIY Steps, in 3 parts: Set-up, Pouring, and Finishing.Please note that the instructions listed here include products that we offer for sale at Expressions-LTD, but there are many products available that can be used as substitutes as well, so feel free to experiment and find out what works best for you and your needs!
- Here is a video overview of all the steps outlined on this page:
- Build a form to contain the concrete. This form can be made of various materials, and should be water-tight.
- Most forms are built from Melamine- particle board that has been coated with a thin coating of plastic, usually white. Melamine is what most cabinet shelves are made of, and can be bought at most hardware stores or lumber yards. We will use melamine as the form material for these instructions.
- Other options for forms are Formica, Plexiglas, Glass, Plywood, Rough Wood Planks, etc.
- Draw your measurements onto the melamine with a pencil. Remember to draw your countertop upside down, since you will pour the concrete countertop with the top down, and flip it over later.
- Place form boards around the edges of your drawn lines. Form edges can be made from whatever you want, but we recommend either cutting strips of your melamine down with a table saw, or using our PVC Countertop Edges -Sold Here- (available in 1-1/2" and 2" sizes).
- If you want an edge profile on the concrete, place a Rubber Edge Form Liner -SOLD HERE- in the form. You may need to adjust your measurements to compensate for the thickness of the Rubber Edge material.
- When making a countertop piece that has a sink in it, a knockout is needed to make a void in the concrete for the sink to fit in. There are 3 types of sinks:
- Drop-In Sinks: The sink is placed into the countertop from on top, and rests on the concrete. The hole in the concrete for this type of sink can be made out of anything in your form, since the concrete hole will be completely hidden by the sink. Use foam (sold in sheets of various thicknesses from your hardware store) so that you can remove it later from the concrete easily, and not stress or crack the new concrete countertop.
- Under-Mount Sinks: The sink is mounted under the countertop, or directly to the bottom of the concrete. The hole in the concrete will be visible, so making a nice knockout is required. Using dense insulating foam (usually blue or pink colored) from your hardware store, cut with a scroll saw or jig saw, and sand smooth to your sinks' shape. Wrap the foam with Form Tape -Sold Here- for a smooth finish on the concrete.
- Concrete Integral Sink: Using a Sink Mold -Sold Here-, you can place the mold as part of your form work, and pour the sink as part of the countertop. This is a great option for overall strength of the concrete. Making a large hole (as in the above 2 sink options) greatly increases the overall weakness of the concrete piece, and stress cracks are common around sinks. A countertop with a concrete sink in it will be heavier, but much stronger, and in most cases much better looking!
- Use a Mold Release Wax -Sold Here- and lightly wax all corner area surfaces of your forms. This wax will make the next step, siliconing, much easier to cleanup.
- Once your edges and form is secured (screwed in place), run a bead of silicone around all corners. Try to use GE Silicone Type II, which is easier to clean up than regular silicone, has a resealable cap, and comes in various colors (black stands out on the white melamine for easy cleanup later). As you apply the silicone, work only a few feet at a time so the silicone doesn't become tacky before you can smooth it. Run a Caulking Ball Tool -Sold Here- over the silicone. This will create a smooth corner bead, and push the excess silicone into a ridge on either side of the Caulking Tool. Allow the silicone to dry a few hours (until no longer 'gummy') and you can peel off the excess silicone ridges.
- Place any Faucet Hole Knockouts -Sold Here- as needed, or any other holes (such as a hole for passing cords and wires through).
- Apply a Form Release -Sold Here- to any parts of your form that need it. Generally melamine will not need release on it, but any rubber edges, fiberglass sink molds, or other types of form materials should be both waxed and then coated with the form release.
- Concrete can either be poured the traditional way, or GFRC can be sprayed and hand placed, rolled out to compact it. GFRC stands for Glass Fiber Reinforced Concrete, and is very similar to making things out of fiberglass, just replacing the fiberglass resin with cement and sand. Please look at our Concrete and GFRC Recipe Page Here. Our concrete recipes also show how much concrete you will need, based on how thick your countertop will be.
- We will explain using the traditional concrete pouring process here, following the Supreme Concrete mix recipe (as outlined at the link above). Feel free to use your own mix, recipe variations, or different products, but always plan on making a test piece before a 'real' piece anytime you chance a concrete recipe.
- Concrete should be mixed in a mixer to ensure thorough mixing of all ingredients.
- When possible, mix all dry ingredients together first (Concrete Bag Mix, extra Portland Cement, VCAS, Chopped Fibers). Mix them in a mixer, with something covering the opening to keep dust from getting out. Always wear a mask when working with any cement products that produce dust.
- Mix all liquid ingredients together with a small amount of water. About 1/2 gallon of water in a 5-gallon bucket, and then add the Riteks SP7000 Plasticizer, and Polyplex.
- While mixer is turning with dry ingredients, add the water mix. Add small amounts of water at a time, allowing 15 seconds or so after each addition for the water to work its way through. Normally you will want the concrete to look like thick oatmeal.
- Drier concrete will create more voids in the finished concrete, which is a common method used called 'dry packing'. The voids in the concrete are later filled with a different colored slurry, creating a veined look.
- Wetter concrete will flow better into hard to get into areas (such as a vessel sink mold). Wetter concrete will be weaker in the end though, so always strive to use the least amount of water possible.
- If using a color that is designed to be mixed into the concrete, add it slowly while the mixer is turning.
- Liquid Colors -Sold Here-
- Powder Colors -Sold Here-
- Stains are applied after the concrete is made, so will be described below in the Finishing stage.
- Mix for 4-5 minutes in most cases. If color was added, you may want to mix a few extra minutes to ensure even color distribution. Once mixed, you can take a spoonful of the concrete and spread it out on a board to dry it out quickly with a hair dryer or heat gun, so you can get a good idea what color the concrete will dry to.
- Mixed concrete can be placed in buckets or a wheelbarrow and moved close to your forms. A large flour scoop makes scooping the concrete into the form a little easier than a shovel.
- Most concrete mixers can mix 2 80lb bags of concrete at a time with ease. For a larger countertop, you may want to leave the first batch in a wheelbarrow until the next batch is mixing and ready to go. This will keep the first batch from setting up in the form before you have enough concrete in it to allow you to effectively vibrate it.
- Try to place the concrete from each batch that you mix at a time over the full form area. Don't pile it all at one end and then go mix some more. This will help keep the appearance of the finished concrete even across the whole countertop.
- Mix quickly for additional concrete needed (2 or more people is nice, and almost required for a large project with lots of bags needing to be mixed non-stop.
- Once you have about 1" of concrete or more in the form, vibrate the concrete. This can be done by tapping the sides and underneath the forms with rubber mallets, palm sanders (without sandpaper on them), sawsall (without a saw blade in it....), or the best way- a Concrete Vibrator -Sold Here-. Vibrators are available in electric or air (pneumatic) versions. Unless you have a large air compressor, running on 220V AC, you should stay away from the pneumatic versions.
- If the vibration in working, you will see small air bubbles rising up and popping (like cooking a pancake).
- Vibrating each area about 30 seconds should be plenty. Over-vibrating can be bad as it can sink all your heavy sand/gravel to the bottom of the form. Under-vibrating will leave most voids in the concrete making it potentially weaker, and making more holes for you to have to try and fill later with slurry.
- If adding Fiberglass Scrim, or Rebar reinforcement, you can lay it in the form now.
- Continue filling the form with concrete, and level it off with a wood or Magnesium (Mag) Trowel -Sold Here-.
Make sure the bottom of the countertop is very nice and flat. Uneven concrete will not sit flat on the cabinets when installed. A good practice is to come back and smooth the concrete again after about 45 minutes, and again after 2 hours.
- You shouldn't need to vibrate the concrete again, but if you choose to, don't do it very long if you have rebar in the form. Pressing the rebar down or vibrating it can cause it to consolidate the sand under it, which can leave a 'ghost' image of the rebar in the surface of your finished concrete.
- If using a Sink Mold, you will need to have built a box form that you place over the form, and around the Sink Mold to contain the concrete and hold it around the sink. This process is shown in the video at the very top of this page. If doing a Dry Pack method for the concrete, you can usually just hand-pack the concrete onto the Sink Mold, and not use a box. If using the Sink Mold, continue filling the form around the Mold with concrete, vibrating the box as you go (but avoid vibrating the main countertop when possible if rebar is in it). Using your fingers as you fill up the sink will help pop air bubble and consolidate the concrete as well.
- Most concrete can be left to cure for 2-3 days now. NEVER let it freeze. ideal conditions should be 60-70 degrees, out of the sun. Very hot temperatures may want to cover the concrete with plastic to retain the moisture so it can cure, rather than dehydrate. Wet curing is a good way to make the concrete stronger. Cover the concrete after about 3 hours from pouring it, and then each day pour a small amount of water around on the concrete, under the plastic.
- After 2-3 days, you should note a slight separation of the concrete from the edges of the form. This slight shrinking of the concrete and pulling away from the form is a good indication it should be ready to de-mold and flip over. It may be ready to de-mold much sooner, or later, so test and experience will play a role in knowing when to de-mold. An easy test is to see if you can make a mark in the concrete with your fingernail. If you cannot, it's most likely ready. If you can mark it at all, it should cure longer.
- Remove the edge forms. Peel any rubber edge form liners away from the concrete slowly, starting and one end and working your way across. The concrete piece will usually be stuck to the melamine board by suction, so removing the silicone caulking first will help. Try to lift the concrete piece up and flip it over. Multiple people will make it easier.
- The concrete piece can also be 'twisted' just a bit on the melamine- using 2 people, one will pull the concrete towards them at one end, and the other person will push the concrete away from them, breaking the bond to the melamine. Careful to not slide the concrete across dried concrete or sand on the melamine, since it will scratch the underside of the concrete (your eventual finished surface of your countertop).
- If the concrete piece cannot be lifted off the melamine bottom form, you may want to flip the concrete piece over with the melamine still stuck to it, and then left the melamine up and off the concrete.
- Once flipped over, place the concrete on some foam pieces, or wood blocks. Foam is nice because it has some give to it, and the concrete should be babied since it is still green and curing- getting stronger by the day.
- Depending on the hardness of the concrete surface, you may want to let it continue to cure a day before continuing to the Finishing stages. The surface of the concrete will be a bit softer than the bottom of the concrete that has been exposed to the air for the last few days. When it doubt, just wait a day.
- Any slight imperfections can be carefully sanded down. Common spots are the corners and edges where there was silicone caulk. These will often get tiny 'ridges' that a Diamond Sanding Pad -Sold Here- will quickly remove.
- Polishing the concrete to expose the aggregate is often done. Using Polishing Tools -Sold Here- and Diamond Polishing Pads -Sold Here- will grind and polish the concrete surface. Polishing Pads come in either Wet or Dry styles. Wet polishing will work best, and provide the longest lifespan of the Polishing Pads, but in cases where water use isn't possible or practical, Dry Pads are used.
- Even well vibrated concrete will have small pinholes that need to be filled with slurry. Many of these voids will be buried under a paper-thin layer of cement on the surface of your new countertop. Exposing these voids now makes filling them easy. Leaving them alone will often mean they will become exposed months later, after the countertop is finished and installed- making a fix much less convenient.
- Expose the voids by lightly sanding with 200 grit sandpaper on a palm sander. You may need to change the sandpaper out a few times.
- Use an air compressor to blow off all the dust and expose the pinholes.
- Mix up a Cement Slurry. You can use straight Portland Cement, but cement doesn't bond to just cement with much strength, and you don't want to use any sand in the slurry because it won't go into most of the small pinholes. When possible, mix Cenospheres -Sold Here- with the cement, or one of our pre-made slurry mixes available in Gray or White Slurry -Sold Here-.
- For best results, mix a few drops of Riteks SP7000 Plasticizer and a spoonful of Polyplex into 1/2 cup of water, and use that water to mix with the slurry until it looks like a peanut butter consistency.
- If a liquid or powder color was added to the concrete mix, the color will need to be added to the slurry as well. Colors are based on the amount of cement in the concrete, not the rocks and sand. If using the Supreme Concrete Recipe, there will be around 20lbs of Cement per bag of mix. If you used 1 cup of color, then you would use 1/20th of a cup of color with 1lb of Slurry to get the same result. It's best to mix the slurry with the color, and dry a small bit of it and compare to the color of the countertop. Add more color, or more slurry, to adjust the color until you have a good match.
- Spray a mist of water over the surface of the concrete as you work. Avoid standing water- just keep it damp.
- Work the slurry into the pinholes with your fingers or a plastic putty knife.
- Wait 10 minutes or so, and scrape of excess slurry with a plastic putty knife.
- After about an hour, sand the slurry with 200 grit sandpaper on a palm sander.
- Let the slurry cure for a few more hours, and them carefully sweep of blow off the dust, and evaluate the surface. Larger voids will usually require a second (sometimes third) coat of slurry to fill them so they are flat and smooth.
- Staining the concrete can be done to add a variety of colors and appearance. The amount of moisture in the concrete will affect the color of the stain. Most stain manufacturers suggest the concrete is fully cured before staining, which is 28 days for outdoor concrete, and bout 14 days for most concrete countertops (that are thinner and are flipped over and have air above and below them while curing). Many people chose to stain their concrete after 5-7 days. Just be prepared for varying results. Generally speaking, the more moisture in the concrete, the darker the stain coloring ends up being. If making multiple pieces that have to match each other, it's VITAL that they are stained with the same amount of moisture in them at the time of the staining, or they won't be a good match.
- There are 3 choices for staining. Acid staining is the most popular:
Acid Stains -Sold Here- can create limitless styles in coloring the concrete. Most well known for creating a mottled or antique 'marbled' look in concrete. If they are puddled, the coloring will be dramatic. If sprayed and brushed evenly, they create a much more uniform color. Multiple acid stain colors can be used and allowed to puddle up next to each other for even more variation. Acid Stains require a good amount of cleanup, involving neutralizing the stain with ammonia, and a lot of washing to remove all residue.
- Acetone Stains -Sold Here- Compliment the Acid Stain coloring, but generally apply with a more consistent, even coloring of the concrete. Acetone Stains are good for staining areas where Acid Stains were unable to react/color well- such as old concrete. Acetone Stains are also good for indoor use where cleaning up Acid Stains with lots of water isn't practical. Acetone Stains don't require cleaning up the concrete afterwards- it can just proceed to sealing the concrete.
- Water Based Stains -Sold Here- are generally applied by spraying so they go on even, and do not require clean-up (concrete can just be sealed afterwards). Water Based Stains come in traditional earth tones, as well as some very vibrant colors that you can't get in Acid or Acetone Stains.
- If any washing with water is done to the concrete, it must be allowed to fully dry before proceeding to the final step, Sealing the Concrete. Almost all problems with sealers and concrete are because the concrete wasn't dry enough, or it wasn't clean enough. Any dust, loose slurry powder, or acid stain residue that wasn't cleaned properly can cause major problems with a sealer. If the concrete is not dry, or has contaminant on/in it, the sealer can pull this out and into the sealer- resulting in discolored areas of the sealer, cloudy/whitish looking spots, and ultimately sealer failure since it will peel up, chip off in areas.
- Most sealers need the concrete to be sanded/polished to around a 200 grit surface so the sealer can bond properly. Surfaces polished smoother than 200 can cause the sealer to not bond as well (see below for sealers that work with highly polished concrete). Concrete polished rougher than 200 grit may still show the rough marks from the polishing after it's sealed. If honed to 200 grit, the sealer will fill in any of the fine 'scratches' in the concrete, and the finished countertop will look totally smooth.
- Sealer options include:
Concrete Expressions FDA Approved Sealer -Sold Here-: Waterbourne sealer (so it CAN freeze if shipped during the winter months by any means other than Overnight Air). Very simple to apply, great for novices. Meets FDA food preparation requirements. Can be rolled or sprayed, and dries to a nice satin finish. Not as hard and durable as other sealers (below), but great for lower use areas such as bathroom countertops. Can be waxed with Concrete Countertop Wax -Sold Here- to further help protect and prolong the life of the sealer. Most kitchens will want to use one of the next two options for durability.
Amperseal Sealer -Sold Here-: Two part solvent coating. Mix part A with part B right before applying. Very durable, and applied thinly (unlike an epoxy coating that is thick and makes the concrete look like it's coated in plastic). Professional coating (practice needed to be able to apply this correctly). Available in a Flat, Satin, or Gloss finish.
Rocktop CT Sealer -Sold Here-: Single part solvent sealer- no mixing required. Very durable, and also a professional grade coating that requires practice to apply properly. Rocktop Primer is also available for even better bonding abilities- great for areas under water such as fountains, concrete bathtubs, etc. Available in a Satin or Gloss finish.
- Penetrating Sealers: Available in No Sheen -Sold Here- and High Gloss -Sold Here-: Penetrating sealers soak into the concrete (or stone) surface, and do not provide a 'topical' layer. Pentrating sealers can be applied any concrete surface, even smooth highly polished concrete, granite, etc. Should be supplemented with a routine application of Concrete Countertop Wax -Sold Here- to help protect the against staining.
- This Video shows Nano1000 Sealer- but similar to any Penetrating Sealer:
- Once sealed, the sealer needs to dry enough time to be hard enough that you can safely move the countertop without marring the sealer surface. This time varies by sealer- anywhere from a few hours, to 72 hours. Care should be taken for the first 2 weeks even after the countertop is installed- sealers continue to harden and cure for a few weeks, so tread lightly while they harden.
So have fun, PRACTICE, and if you find yourself itching to demold the concrete about 8 hours after you poured it, to see just how cool it looks... then you're headed down the road to a very fun and profitable profession!