Tue. May 21st, 2024

Alex’s mom is visiting this weekend, but we stole a few hours for ourselves and made some serious progress.

In the couple of hours we had before dinner on Saturday, we build our mold.


During our major Home Depot trip last week, we bought melamine and had the pieces cut to the width we needed (since we don’t have a table saw). Every blog I read about building concrete countertops said to use melamine. It’s great because the sides are completely smooth, which means the concrete will also be smooth.

Building the Mold

We first figured out how long to cut the melamine strips. We want the hearth to be the exact width of our fireplace, so we used the edge of the brick and our backer board (which was cut perfectly to size) as our guide. 

Once the strips were the right length, it was time to construct the mold. Since we haven’t installed the floors yet, we had the luxury of attaching the melamine strips directly to the subfloor. However, since melamine will split, you MUST pre-drill the holes first. We didn’t have any splitting, but I read a lot of blogs of people who did…

Our floor isn’t level and despite our incessant sanding last weekend, it’s still not even close. We want to make sure that when we install the floor, the same thickness of concrete is seen all around it. We decided that since we’re (eventually) going to have a wood stove sit on this thing, that it had to be level. So, we’ll just deal with the uneven floor when we get there (by shimming the new subfloor, likely). 

To make the melamine strips sit level, we had to shim the left side of the hearth, since this side sits significantly lower (maybe a full inch) than the right side. We simply used cedar shims and a level to make sure that everything sat at the right height. Leveling and get the right shim combination took a while. But it was worth it.

After pre-drilling the holes, we screwed screws (specifically wood screws) into the melamine, through the shim and into the subfloor. This step actually worked quite well and was fairly easy. We screwed the strips every 6-8 inches.

Gus supervised.

Once all the sides were in place,  it looked like this:

Important Tip: It’s important to put tape over the mold screws or the concrete will fill into the screw head and you’ll never get the mold off. 


After the melamine strips are in place, it’s important to caulk the space between the backer board and the melamine with silicone caulk. We used DAP’s Alex Plus, which was pretty cheap and easy to find. I’m not entirely sure why it’s so important; it might be to fill the gaps or to allow the mold to pull away easily once removed. But I’m not sure. Yet.

We don’t have any photos of this. It didn’t go well – mostly because we first tried to do it half drunk at 11pm – so we weren’t in a picture-taking mood.

Marking the Non-Mold

Figuring out the height of the concrete will be easy in the mold. But the firebox is a different story. I’m not a huge fan of eyeballing, plus I want a nice clean edge inside the fireplace as well. So we had to mask the brick with tape.

For this task, I used dental floss and my level. The front of the fireplace brick was very easy. I simply took a string of dental floss and taped it to the top of the side pieces of melamine. I then had a nice, level line across the front. I simply took my tape and followed the floss to create my mask.

The inside of the firebox was a bit more challenging. I took the dental floss again and taped it to the top of the front melamine strip and dragged it across to the back of the firebox. I had to eyeball it and keep adjusting the height of the floss until it was level. This was pretty tedious, mostly because the old dirty brick isn’t very tape-friendly.

I then used the reference points I created to make a straight tape line across the back and then the sides. It really wasn’t overly fun and the constant adjustments were a bit annoying. But I’m glad I did it and it really didn’t take all that long (maybe 30 minutes).

The final markups were surprisingly accurate.

The extra melamine piece (pictured above) is something I’m particularly proud of. During the screeding process, I’ll need something to help manage the large 2×4 that will pack down the concrete. This extra piece of melamine is going to help me do that. You’ll see… 

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