Getting the first floor slab poured is one of the bigger milestones of the project. It has taken a lot of planning and preparation to get everything ready. It’s not the sort of thing we wanted to screw up, so we were being extra careful to make sure it went smoothly. Though it wasn’t made easier by the fact that we hadn’t worked on a job with an exposed concrete radiant thin slab, and neither had our installers, or really anyone we tried to get advice from.
We already had our perimeter trim installed 1 1/2″ tall by 2 1/2″ wide hemlock. So the basic plan would be to lay down 6 mil poly directly onto the plywood subfloor, tape over the hemlock trim, and run plastic about 36″ up the walls. The radiant tubing would go down onto the plastic as in a typical install.
The most tedious part of this was getting the plastic and tape set flat onto all the edges. One type of tape we used wasn’t working which we had to remove and re-tape. Eventually we got it right.
In all we had to install five 300 foot loops of radiant tubing, spaced 8″ apart.
To help control some of the inevitable cracking we added strips of hemlock trim at different places in the slab that would be flush with the floor surface.
It took us two days to go from plywood to ready for concrete. The logistics forced us to make a rush to prep everything in two days. Being mud season we had to ask permission from the road agent to get a concrete truck into the site on any given day. Since the road agent will only give permission a day or two ahead of time, we had to wait for the forecast to show favorable conditions, get the permission from the road agent, then scramble to get the floor prepped before the truck shows up. I’m glad we gave ourselves two days, I don’t think we could have done it any quicker.
The concrete pour went well, all done by Kearsarge Concrete. The spec was a standard concrete mix with 3/8″ pea stone, and the color dye that we selected.
After the slab had setup for a couple days we had to remove all the plastic, grind the edges, and scrape away the concrete that was over the floor trim. Because the floor had to be smoothed with a power trowel, the trim pieces that ran across the floor were covered with a very thin layer of concrete. In the end we decided to paint the trim pieces. The process of removing the concrete and the tape roughed up the hemlock quite a bit, which the grey paint helped to hide.
After the slab looked good and was cleaned up we started applying two layers of ‘Polyseal WB’. This would keep the slab protected from staining. The first coat we applied had some visible streaking after it was dry so we rented a floor sander/buffer and sanded out the streaking as best we could. Before the second coat we buffed the whole floor which made for a very smooth surface.
We’re very happy with how the floor turned out. It’s smooth, durable and will soak up the winter sun nicely.
Our wood fired cookstove was delivered on Friday. As soon as the slab was finished we set it in place. It’s made by Sopka. It weighs about 500 pounds, and seems to be pretty solid.