The Quick Step By Step
1. Silicone 1/2" mason board to cabinets making cutout for sink and faucet. The circular saw works best for cutting this and you will need the proper hole saw for the faucet.
2. Cut Z-Forms (with a miter saw) and screw down using zinc covered screws to prevent from rust coming through. Cut a piece of wood for the oven knockouts and screw to cabinet.
3. Silicone edges of Z-Forms except corners tape those on the outside edge.
4. Cut steel mesh to size and dry fit.
5. Mix and pour concrete. WET MASON BOARD BEFORE APPLYING CONCRETE. This is definitely a two person job one should mix and the other should be smoothing, hitting the sides of the forms with a mallet, and installing steel mesh. Pour half the depth then put in steel mesh. Pour second half and smooth with Magnesium Float.
6. Once cured take of edges.
7. Go back with wetter concrete mix and fill in any gaps you have.
8. Wet countertops and sand. Start with a low grit and work your way up until smooth.
9. Rinse and vacuum all of the dust.
10. Seal with Aquathane.
The step by step with explanation
When quarantine began I had no where to go like the rest of us so my Fiance and I decided to redo our kitchen! We tour out the floors, put the new ones in, cabinets, open shelving for the uppers and then I get to the countertops...... The whole kitchen took a month until I got to the countertops which is why I wanted to write this.
We knew we wanted to do concrete countertops but there's no really good step by step guide. What do you use for the base? What about the form should you do pour in place or do it outside and carry them in? What do you use for steel mesh? What do you seal them with? As you can see I had a million questions and either too few or too many answers. So I'm just going to go through this as I did it.
Pour in place method vs making your own form. My Fiances Uncle had done this before and told us to go with the pour in place method which I'm glad we did. I have lifted countertops before and it's backbreaking and with concrete it could crack. Plus you could build it outside then put it in place and it's not level.
So the pour in place method:
1. Make or buy a form.
2. Use mason board for a base.
3. Make a knock out for the sink and faucet.
4. Wet mason board before laying concrete down.
5. Pour half of concrete
6. Place in steel mesh. (Precut and fit with bolt cutters)
7. Pour second half and smooth with a float. We used a Magnesium float.
The forms that we used were prefabbed and buy Z-Form. Z-form was not cheap but the product was amazing and shipped to me in a few days. They are also a one stop shop for everything except I bought the mason board and concrete at Lowes.
So for the side buy the oven I screwed a flat piece of wood into the side level with the tops of the other forms. This part was actually hard because I had to fab the piece of wood on my table saw. Our cabinets had notches on the side that I had to cut slots in the wood for. If your cabinets are flat on the sides it will be much easier.
NOTE: Duck tape the outer corners and silicone the screws and seams where the form meets the mason board. This will prevent leaking from the water.
I have some experience with concrete. When I mixed it I used my Drill and mixing tool and the batteries lasted about 20 minutes Lol. Then I used a piece of wood and mixed between two five gallon buckets. Dumping between the two buckets helped get all the clumps out. I would definitely get a mixer next time. You can do it with buckets but it's tough. AS YOU ARE POURING AND SMOOTHING CONCRETE: you need to be hitting the sides of the forms with a rubber mallet or hammer a ton to get the air bubbles out. Otherwise you will have a lot of holes in your countertops from the air bubbles. It was hard to get the concrete really smooth especially with how tired we were. But we did a pretty good job!
Sanding and Smoothing
So the countertops came out pretty good there were divots near the back edge and were really rough to touch. So professionals would use a wet grinder but I didn't want to shoot water all over my new kitchen. SO THE ALTERNATIVE: Amazon sells these sanding pads that attach to an orbital sander you just have to really wet the surface down before sanding. Concrete Sanding Pad Link
If you have gaps or holes in your countertops from air bubbles make some wetter concrete mix and apply with a putty knife and smooth with a sponge. I had to do this along the sink edge and countertop edges. Then you can sand all this smooth.
So originally we used a concrete sealer which made liquids bead up. However they were still eventually absorbing into the concrete and staining it. In addition whenever you touched the countertops you would get dust all over you.
We ended back up at the Z-forms website and bought Aquathane. You just roll it on with a fine roller 2-4 coats and thats it! It provided a shiny coating and did a great job. It now has a great seal on it and nothing absorbs into the countertops anymore and you can clean them like any other countertop.
The Finished Product