Slab

I guess it all started when I got the home test for Radon. I opened up the container and set it in the basement near the crawl space opening. After 3 days of exposure, I covered it up and sent it to the lab. It cost $15 for the test. A week later it came back with a level of 8 Pico-Curies. The instructions said that level was on the high end of average, and also to re-test. Now I had the opportunity and reason to get the slab down. The floor was open in the family room where the mantle was going and I still had an un-nailed plywood panel in the new bathroom for access. There are also 2 small 1"x6" vent windows on the west side of the family room that could be removed to bring in materials. To reduce the radon level, the first activity is to cap off any interior that is open ground with a vapor barrier and a cement slab. Only a thin slab or rat slab is needed. If I was going that far, I reasoned that I might as well go all the way and use the opportunity to use the slab as thermal storage.

I was just starting to tune into converting the house from forced hot air to hot water radiant and the thermal storage slab idea fit in great. Parallel water tubing loops would run inside the slab to transfer the heat either into or out of the concrete mass. To prepare for the concrete pour here is what had to be done:

1. Level out the uneven ground as best as possible.

Since digging out the high areas was right out, I elected to fill in the low spots. I had 5 tons of 3/8" pea gravel delivered from the Millington Quarry and dumped past the end of the driveway. The total cost was around $110. I later had 1 yard of sand delivered and over the course of 2 Saturdays hiring outside help moved all 8,000 pounds into the crawl space.

This also served to bury a water tubing circuit to be later used for heat rejection in the summer.

In the summer, if I could cool water down to 50 or 60 degrees it can be circulated through the slab and the rest or the radiant tubing, it would cool the house almost for free.

2. Lay down a vapor barrier. I bought a 1,000 ft² roll of 6 mil (0.006") plastic sheeting. We covered the ground with this.

3. Insulate- I bought 40 2'x8'x2" panels of extruded polystyrene panels. We tiled the ground and the exterior side walls with it. The cracks were sealed with expanding canned foam.

4. Lay down the wire reinforcing mesh. It comes in a roll that is 100' long and 5' wide with #10 steel wire welded in a 6"x 6" pattern. We cut 25' pieces, re-rolled them and unrolled them on top of the insulation. It still wanted to curl, so I bought some #4 re-bar and tied it in.

5. Install the water tubing. From Radiantec, a radiant heating mail order supplier I bought tubing and a slab distribution manifold. In speaking with their technical support, about the design and they recommended for my 500 ft² slab, 3 parallel 200 ft loops of 7/8" PEC (partially cross linked polyethylene) tubing. It had to be secured to the wire mesh to keep it from floating around in the concrete pour. To test it I applied compressed air at 40 PSI which had to hold for 2 hours. Stan from work helped me out.

6. Install ground vents through the slab. I cut a piece of 3" PVC piping and put it in a hole through the insulation and plastic. In the future if the Radon level remains high, I can attach an exhaust fan to the piping stubbed out from the slab.

The pour was scheduled for Saturday, 2/27. The masonry contractor, Asen Kuprov was going to supply 4 workers, I was to supply 2, and we were going to bring in 6 yards of cement in 5 gallon buckets. That's a lot of buckets. Counting everything, the labor was going to cost $700 and take 6 hours to move the cement in. the work was cancelled because there was not any plant making cement that day. Weekends in the winter are slow for the plants, if they don't have 70 yards on order, they don't open up. While I was calling around, I tried giving some cement pumping guys a call. To have the cement pumped in it would cost about $950. A bit more than buckets, but I wouldn't have a team of guys hauling buckets of cement through the house all day, instead it would only take 1 hour. The upgrade was to pour 10 yards instead of the originally planned 6 for an additional $350 ($888 total) 10 yards wasn't possible using buckets. This would give me a 27,000 pound concrete thermal storage bed.

After last minute scheduling changes by Rich-Wall (the cement pump service) I rescheduled the masons and called Weldon Concrete Co. to get the cement delivered. They couldn't deliver until after lunch on Thursday, while everybody else was going to be there first thing. I called Rich-Wall back with the news, they were not happy either, but they were willing to help. Since they do a lot of business with Weldon, they had a contact on the inside to help me out. I called the person at Weldon and he was so nice to me, he even saved me $200 bucks off the price the other guy quoted me.

It was a crappy morning, cold rain and snow. The party would go on, rain or shine was stipulated. The Pump showed up 1 hour before the cement to set up, at 7:30 AM.

They ran a 3 1/2 inch metal pipe from the truck, up the stairs and to the front door. Here they transitioned down to a 2 1/2 inch rubber hose,

I think it took almost 1 1/2 hours to complete. The masons poured and floated that front and back section and saved the middle section for last. I think that there was over 10 yards delivered. In some places the slab is 10 inches thick.

It was a money day, almost $2,000. We were done by 10:30 AM.

Later that night I belly crawled on the slab cleaning up the float marks the mason left in the cement with a trowel. The slab was 75 degrees and the crawl space had 100% humidity from the curing cement. I was soaking wet with sweat. When I felt the wetness in my pants, I knew that it was a love relationship with this slab- my baby. 27,000 pounds of thermal storage. PEX tubing, rebar, re-mesh, 2 inch insulation, 10 yards of pump mix 3/8 gravel- OH- OH-OH. The inside of all the windows in the house were dripping with water. The relative humidity in the house was above 60% for 3 days and it smelled like wet cement. "I LOVE THE SMELL OF CEMENT IN THE MORNING, SMELLS LIKE........VICTORY" Bill Nichols 3/4/1999.