Our first mega-project was building concrete countertops for our kitchen. The baby blue laminate circa 1992 just wasn’t cuttin’ it any more. I used an article from the DIY network as my basis.
I’ll add my own wisdom on top of that. The article tells you to first and foremost build your molds. You need melamine to do this. It is white and smooth and the concrete won’t stick to it, however we oiled it prior to pouring. It comes in 4×8 sheets like plywood at Lowes. Don’t use Home Depot. Worthless. Build your template from luon. It also comes in large sheets and you’ll cut this into 2-3 inch strips. Its flexible and creates a great template. You’ll probably only need 1 sheet. Hot glue the pieces together and trim as needed with a chop saw/miter saw. The template gets built preferably with your old countertop off otherwise on top to get the angles, overhang, and measurements exact. You’ll need to determine where your seams will be also. Ours were easy to determine by size. We had 2 pieces, separate molds, on either side of the oven which we seamed behind the oven. The bar was one piece and the sink and dishwasher area were 3 extremely heavy pieces. If your cabinets were custom to the home they most likely will support the concrete, otherwise you’ll need to add a plywood top or some such other support. We were ok except the dishwasher area needed an extra vertical board drilled into the brick then supported by the cabinets. The template has to be FLIPPED before tracing it onto the melamine as the bottom of the mold is the top of the countertop. So hard to wrap my little brain around. We lost a day of work to this little error! Cut your traced piece of melamine with a table saw/jig saw/circular saw however you need to get the trace perfect. Once it’s cut you cut 2 3/4 in strips of melamine to form the sides of the mold. This allows for a 2 inch thick countertop as the melamine is 3/4 inch thick. Drill and screw the sides into the mold. Caulk the inside with 100% silicone black caulk so you can see it well. (long standing joke about me getting some black caulk!)
We used 2 Quikrete bottles of charcoal stain to 1 80 lb bag of Quikrete countertop mix. Also purchased at Lowe’s. We needed around 15 bags for our project. We rented a 8 bag cement mixer, but it was pretty hard to handle. You could get away with a smaller one and help keep all your mixtures the same color.
We used steel mesh from Lowe’s, cut to size and placed in molds at 2/3 full to get great strength. I never could figure out rebar. The consistency of the concrete is tricky. Wetter than Peanut butter, drier than pudding. We allowed the concrete to dry in our house for 14 days with plastic over the molds for the first few days to allow even drying. We were in January, though. The bag does not say to dry this long. I hired a consultant. He was helpful but a real jackass. He would have charged us $8000 to do the job! I think we ended up spending much less than $2000 and that includes a $400 sink!
Caulk the areas where the molds will lay and caulk the seams. After the molds are flipped and placed, you make a slurry mixture of Portland cement, water, and stain and this fills in all the holes and seams. Use gloves, it can cut your fingers. We did use electric sanders along the sides of the molds right after pouring to decrease air holes. The slurry mixture is fabulous! Allow this to dry for a day.
Prior to the epoxy, we sealed with a basic concrete sealer the consultant gave me. This is an important step. This dried for a day. The epoxy seal is extraordinary. You buy it at sherwin Williams. Its not cheap.. About $80 and we needed 2. It’s called envirotech 2 part epoxy. You mix it together and have a 15 min period before it becomes hard as a rock!! You dust and vacuum to perfection then apply with foam brushes. You use a heat gun to remove air bubbles. It was stressful. You make a tray to catch overflow so as not to get on cabinets and floors. We used cardboard and waxed paper. It was messy but controllable.
We used foam for the sink and faucet knockouts and wrapped the edges with packaging tape to give it a smooth edge and prevent the concrete from sticking. We cut the foam with a jigsaw. Our sink came with a template. It is undermount. The faucet knockouts must allow for a thicker countertop so you can screw the parts together. One more mistake we made.
5 men flipped for us. 25lbs per square ft I think is what it’ll weigh.
I hope I’ve not overwhelmed you. It’s doable. Other than pouring the concrete, it can be done in as long or short of a time frame as you want. My complaints are that it water spots, but the beauty of it compensates. Good luck and please post any questions and we’ll do our best to answer! -L & H