Concrete Countertops Finished!

Well I actually finished them a while ago but I’m just now getting around to posting my pics. Yes, the concrete countertops are finished. I’d say the whole process took 2 months or so. It was a lot harder than I expected - getting that much concrete poured, shoveled, and vibrated in the form is hard work - not to mention lifting the behemoth and installing it!

Read on to see more pictures !

Here are some more pictures of the finished countertop, which has been sealed and waxed (please pay no attention to the rest of the kitchen, especially the cabinets, because we are refacing them - this is our next project):

And here are some pictures of the pour (actually just before the pour):

I spent quite a bit of time building the mold, which is made mostly out of melamine covered MDF. The mold has to be exactly the right size and all details, including the location of the sink and faucets, etc. The seams are caulked to retain water and to make a smooth edge.

Rebar was bent to fit inside the mold. I welded the rebar and remesh to make a strong cage that fit perfectly into the mold. The cage had to be suspended midway in the mold during the pour so it is tied to the sides of the mold with wire, which was clipped and the wires pushed down into the mold after the concrete had cured slightly.

There were two molds to make two sections of countertop that were joined at a single seam. We rented a large capacity mixer from Home Depot so that we could do the pour into both molds at the same time so that the color would be uniform. This was a big mistake, though as the concrete sets up so quickly. Normally concrete does not set up as fast, but we used the cheng products that include water reducers, which makes everything set up in about 30 minutes. We should have poured one batch and then mixed and poured the other. Consequently, the concrete poured into the second form had set up a good bit and was very difficult to vibrate properly. Once we released the molds, the concrete had quite a few holes in it.

Fortunately, the cheng company makes a slurry that can be used to fill the holes - it is applied much like grout in tile work. It is also color matched very well. I applied two coats of slurry and once everything dried it looked good. The slurried holes actually give it some character which I like.

The installation was tough! I estimated that each piece of the concrete weighed about 300 to 350 pounds with a total weight of about 650 to 700 pounds. My dad and a friend helped me lift and place the countertops but it wasn’t easy! I read about a few different ways to attach the contertops. Some sources said they don’t eve attach them as the weight of the countertop seems reasonably sufficient to hold the ginormeous slab in place. Others glue the coutnertop down using silicone caulk. I chose to simply install tapcon concrete screws through the bottom of the countertop.

I reinforced my existing cabinets by adding 3/4 inch plywood to the backs of the countertops and attaching the cabinet backs to the wall studs behind other portions of the cabinets. 3/4 plywood was also added to top of the cabinets to create a table for the slabs to sit on. This also serves to distribute the weight evenly. Since the bottom of the slab wasn’t completely flat compared to the plywood (the mold is created upside-down so the top of the mold is the bottom of the countertop and is merely smoothed flat by hand with a trowel), I used wood shims around the edges to make contact and add support.

Now we are on to the next project - renovatting the rest of the kitchen. We’ve already replaced most of the appliances, but we’re also refacing the cabinets and re-painting the cabinets and walls. There is still a lot of work ahead!