Introduction: How to Make a Concrete Countertop
I was amazed at how easy it is to create a concrete counter top. I've never done this before and I have little experience using concrete, but the result was amazing! Let me show you how to make your own.
Step 1: Make the Form
It all starts with cutting a mould out of melamine to the size of the slab you want. The 2 main things to consider here are thickness and over hang. In my case I went with 45 millimetres thick and an over hang on the front of 30 millimetres. There were numbers that T decided on from my own research so as someone with little to no experience with concrete I felt safest using someone else’s experience. I’m sure you could go thinner if you wanted but the mix would need something like fibergalss added.
I then measured the inside length of the mould, which would be the total length of the counter top and lined up the strips I cut earlier.
I clamped these down and screwed them to the base making sure to pre drill each hole because you don’t want the melamine to expand from the screw. Also make sure to counter sink the holes, this’ll make sense later.
Covering the screw holes with tape makes sure that if any concrete ends up in there, and it will, you don’t have problems getting the screws out.
Step 2: Add Silicone Caulk to All the Corners
Once all the sides have been screwed into place it's time for caulking. I’m terrible with silicone but the method I find works is to use soapy water and a lot of rags. This will be the round over on the top so find an object that reflects that edge. In my case I used a rounded pen lid. You also want to make sure that where the silicone meets the melamine there is a feathered edge. You cannot believe how precise the concrete shows absolutely every lump and bump.
After the silicone dries (24 hours is normally enough) wipe the inside surface of the form with olive oil. This will help release the concrete later.
Step 3: Mix and Pour Concrete
Then it was finally time to mix the concrete. I used a high strength mix from my local hardware store. All the videos I've watched either used Quickrete, which I don’t think we have in Australia, or it’s not mentioned. I get the feeling that any concrete, besides quick set, would work fine.
Make sure to mix the concrete as dry as possible. Using excess water reduces it’s strength.
You really want to force the first layer on concrete into the corners of the form. Because you’ve mixed it dry it won’t run as much you think.
After the first layer I vibrated using a rubber mallet.
Step 4: Add Rebar and Vibrate
Now I added the rebar. I wish I had used a sheet of mesh instead of strips of tracks. I also researched how concrete uses rebar as strength and this helped to explain where it should be placed in the mix. Have a watch of this video, it helped me out a lot.
Then I vibrated for about an hour. You can use all kinds of methods for this but I found using the rubber mallet worked ok. Just make sure you tap the entire form. As you hit the form you’ll see bubbles rise to the surface and then pop. As it pops the hole fills with concrete, this is what you're looking for. Once this stops happening you’re done vibrating.
Step 5: Cover the Form and Keep Moist
I then covered the concrete in plastic to keep the moisture in and the humidity high.
Make sure to keep the concrete moist for about 4 days. You don’t need to cure it for any longer than that. Do a bit of reading up on curing if you’re unsure, it’s really interesting stuff.
Step 6: Remove the Form and Flip the Countertop
After 4 days I removed the mould. It should come away easily because of the olive oil.
I found once I had broken the water seal underneath the concrete (the side is down at this stage) using a metal spatula I was able to move the top. At 120 kilograms it wasn’t light but the water was creating a slight suction.
Then a friend came around and after lots of discussion and planning we flipped it over. Don’t he a hero, get someone to help out.
Step 7: Seal the Concrete
I let the concrete dry for the next 4 days. Before sealing you need it to be properly dry and to test this you place a piece of rubber on top. If there is a wet spot underneath after 2 hours, it needs to dry for longer.
I used 6 coats of water based sealer starting the first coat at 25% strength then moving up to 100% on the last 2 coats. Thinning the first few layers helps the sealer to sink deeper into the concrete, improving it's ability to repel spills.
Step 8: Set the Countertop in Place
Then the counter top was finished and needed to be installed. Any questions? Feel free to get in touch. Make sure to plan the whole process out from start to finish and have an understanding of each step.
But most of all, give it a go!
If I can, YOU CAN!