Pouring the Slab

The Slab got poured!

Unfortunately, I wasn’t there to see it happen. Luckily, my wife would be home, and I asked her to take some photos.

I left for work first thing in the morning (still dark outside) and wouldn’t be back until again after dark. In the mean time, the masons would be hard at work pouring the concrete.

When I finally did get home, I was able to take a look at the finished slab by the light of the moon and my car’s headlights. The concrete apron in front of the garage was even poured. I hadn’t expected that to happen until later, so I hadn’t even specified anything. For example, the man-door would need some sort of a step in front of it. Already done was a nice semi-circle sweeping from the man-door to the garage door. Overall, it looked really good!

Uh-oh. In a pile off to the side, I found that the tips of my angled foam had been cut off! All that hard work to make the fancy bevel, and the mason simply cut it off!

The next morning, the mason returned to mark chalk lines and then run the saw into the slab. This makes the relief cuts into the concrete so that the material has a place to pull from as it cures and shrinks a tiny bit. Should the concrete ever crack, it should crack on these controlled lines instead of randomly. I was assured that the cut is less than an inch deep, and my Pex tubing is on the very bottom of the slab, and on the other side of metal reinforcing wire.

I asked the mason about the bevel of the foam being cut off. As I thought, he said that the concrete would be too thin at that point, and would simply crack there. The pour was first thing in the morning and the trucks were all lined up, so the most timely thing to so was simply cut the bevel. That means that my 5-inch thick slab is only insulated on the perimeter for about 3 inches, and the top 2 inches are uninsulated, running all the way to the wall. When I spoke to the mason the last time before the slab was poured, I told him what I wanted to do with the insulation, but we were both in a little bit of a time crunch right then, and perhaps I wasn’t as clear as I could have been.

Looking back at this now, I would have just run the 2-inch insulation all the way up and square, have the concrete get poured, then trim away any extra and just later figure out how I would want to cover that 2 inch perimeter all the way around the slab.

Oh well. Live and learn. The upside is that the perimeter insulation is completely covered and protected. No worries about the foam getting damaged, being exposed to UV radiation in sunlight, or getting water or debris in there.

Speaking of water, I realized that where the Pex goes through the plastic bend into the concrete is unprotected from the weather. We’ve had some great weather lately, but there’s a chance in the forecast for some rain followed by freezing weather. I used a can of Great Stuff expanding foam to fill the inside of the channel into the concrete. This will prevent water from getting inside the concrete and freezing, and it also just insulates the Pex tubing.

On the next sunny day, I also thought to film some thermal video. Of course, the slab isn’t heated yet, but it would be interesting to see what’s going on with temperatures while the sun was shining directly on the concrete. The main thing that I noticed was that any VERTICAL surfaces (such as the north stem wall) REALLY soaked up the sunlight. Much of that concrete was 75 degrees F. On the other hand, the horizontal concrete slab itself didn’t seem to suck up much heat. The sun was just too low in the sky.

When I had the thermal camera in one certain position by the wall, I COULD see where the two inch perimeter insulation was. There was just enough of a temperature difference for it to show up. In this case, the concrete was being heated from the outside in, so the concrete in that last two inches was thinner (only 2 inches thick, instead of 5) and absorbed the heat faster. When I do eventually hook up the heat in the slab, it will be interesting to see how this outside two inches looks on a thermal scan.

As it is right now, the concrete is solid and slowly going from a dark gray to a light gray as it cures. I’m told I can park a car on it after about a week. In the mean time, I did just lay down on the concrete to soak up the sun for a bit. In my area, November is NORMALLY the cloudiest month of the year and usually depressingly dark, dank, and gray. It’s been nice to have a sunny and warm November.

My work schedule is beginning to calm down, and I hope to be able to start the real work of building the walls soon.

As always, I’ll keep you updated as the project advances!

-Ben

 

Tagged as: concrete, heat, insulation, radiant, slab