How to Make a Concrete Countertop

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Introduction: How to Make a Concrete Countertop

About: I'm a woodworker/maker on YouTube

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!

2 People Made This Project!

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129 Comments

Awesome! Really neat countertop. You used silicone which can be tricky to work with - sticky. Would acrylic which is so much easier to work with do the same? That is smoothed easily with a finger. Or would it stick to the concrete?

you lost me in the first sentence... what is Melamine? is that a brand of some common material?

1 reply

ah ha! here's what I get when I search for it at Lowes (our only local building supply store)

temp_272393385.jpg

For getting a smooth round over on the silicone I use a tool designed for the purpose. Do a search for "caulking smoothing tool" and look at the pictures. It is tool with a special plastic that will not stick to silicone or caulking and a radius on the end. They give a nice even curve for those of us who are "challenged" at such things.

3 replies

Ah that'd be amazing, the stickiness is the worst part of the process. Thanks for the tip!

Use oil based modeling clay instead of silicone. Make a custom tool out of sheet metal or plastic for shaping it: basically a rectangle with one face against the mold edge nad one face on the mold bottom, with the radius cut between them. Roughly press the clay into place, and drag the tool along, firmly against the mold, as the excess clay is removed.

moldtool.jpg

you can find another great tool in many hardware stores for this purpose - it is a little handheld silicone square, about the size of a credit card - each corner has a different edge profile.

They typically look similar to this:

http://www.aok.org/images/calk-master.JPG

easy application, and easy cleanup

This is so tempting. I wonder, is it possible to dye concrete? not something weird like red or orange, but a marbled black? That would soooooo be my house! Great job, Robin! I'll keep your 'ible in case I ever get the other, more pressing things finished!

3 replies

Google acid staining of concrete. There are many commercial stains out there, but there are some people that developed DIY methods.

Only, make sure you pour several smaller pieces to experiment with, before applying it to the large slab.

Good advise. Thank you, FlorinJ :)

Hi Teresa!

In my meager experience molding concrete I've learned that concrete die comes in two flavors, very fine powder or syrupy liquid. Both require more than usual mixing to get the color consistent. To get a marbled finish I had to mix 2 batches (one colored) and pour them right after each other and gently stir it just a little bit with a nail. I haven't had much luck with it but the stuff I mold is pretty small, 1" or so.

I haven't tried this on something the size of a paver yet but that would be my next step so I could get some experience with it before I committed to a counter top.

For my .02 I think I would mix the batch a little on the wet side too. The bubbles come out a lot easier. I also use a palm sander to vibrate the table since it only takes about a minute.

You said you used a 25% mix of sealant.

What sealant did you use and what did you cut t with?

Thank you.

You made me see I can do this now :)

Thanks :)

3 replies

I think you can also rub in hot beeswax. I've read other people had a good experience with tung oil.

Hey Sherylin, thanks for the comment. The sealer is water based (it's used for pavers, but I think you can get a food-safe product specifically for countertops) so it was cut using water. If you used a solvent based sealer than you'd cut it with some form of spirit (thinners, turpentine, etc)

Aha ok thank you. Wasn't 100% sure what you used so just wanted to be sure.

Thanks for a rapid reply :)

Great project! Thank u for sharing!

awesome project. you might want to use self leveling concrete mix for this project. and also chicken wire , or another form of mesh wire to reinforce the concrete to help prevent cracking.

I love it. I am making one for my kitchen next month. Thank you.

1 reply

No problem, hope it all goes smoothly

The look of concrete is beautiful...thanks for sharing this!