New Shop Building

Put lots of rebar in the floor. I used the fiber, and don't think it did anything except lighten my wallet. It certainly didn't stop cracking...Paul

Neither will rebar, if you don't also cut some control joints (unless very small, any slab will crack - you simply want to tell it where it's OK with you that it should crack). I have both rebar and fiber in my slab, and there are cracks running out from the ends of the control joints (where the saw couldn't cut right up to the wall). No cracks on the face of the slab (so far anyway), so I assume that the contol joints have done what they are supposed to do.

You didn't say what part of the country you're in. If you're north of the Mason Dixon line, put hydronic heat tubing in the floor, even if you don't plan to use it now. Installing just the tubing is very inexpensive and leaves open your option for the best heating system their is. Unless you put insulation under the floor, this would only be a supplemental heat.

Karl

The plans call for control joints every 12 feet but the concrete guy suggested going to joints every 10 feet. They are going to be sawcut to a depth of about three inches. The slab and footing will be poured in one flat monolithic pour. The concrete guy also suggested using wire mesh reinforcing in the floor in addition to the fiber additive.

The most important part seems to be to get a good compacted base that won't settle or expand with moisture to place the concrete on.

Thanks for your comments.

Bob

The base material thickness, prep, and compostition are CRITICAL to a good slab. It will depend a lot on your soil and frost condtions but the amount you need will scare you. My clay soil and 4' of frost needs 12" for a small slab and 24" for a larger one. And it needs to be compacted down in layers using a vibrator packer.

Be sure they use a 4mil (or more) plastic sheet under the c> The plans call for control joints every 12 feet but the concrete guy

Karl,

Mason Dixon line, put hydronic heat tubing in the floor, even if you don't

while your at it put down some insulation around the outside edges

cracking...Paul

The beauty of rebar is even if you get cracking (and you will), it prevents the slab from shifting. My shop floor is a full 6-1/4" thick, 6 sack mix, with rebar on 12" centers two ways. Instead of cutting the floor, the guy that finished it used a bull float and scored lines approximately 12' apart, then finished over the score lines. That provides a weaker zone for the crete to crack where you want it to. It works, and you don't get a big line that fills up with crud like you get from saw cutting. I have cracking, but only where he had scored and finished, so it's very narrow, and there has been absolutely NO shifting of the crete. The floor is now 5 years old. I highly recommend rebar, although it does take a lot of time and money to install it. If you do it yourself, it's not all that bad. In my opinion, it's worth it. Cheap insurance when you consider the cost of the job overall. I fully agree with a properly prepared base, too. Ours was compacted well as the fill was installed, then it sat through a full season of winter rain in Western Washington. We used rock for fill, 3/8"- with fines. Worked out great.

Harold

My shop has just such a heating system. I fully agree. Not only is it comfortable, but the overall environment is much dryer, thanks to the heated concrete. The typical shop floor can have 3/8" diameter tubing in 200' runs on 18" centers and do a great job. I used the rebar I mentioned in my other post (above) to tie the tubing in place. In my case, the tubing wasn't cheap, though. Heatway, which is now Watts Heatway, uses a rubber tubing (hose) instead of plastic. They have it made especially for heating. It's three ply, with one of the layers an oxygen barrier. It's important that closed hydronic heating systems do not absorb oxygen. The system has been running for 4 years now and has worked flawlessly once I got it balanced.

Harold

Not just the outside edges. Code calls for an R10 under the slab when you heat hydronically in slab. It may cost a little to install the insulation, but it will pay for itself in short order, especially with energy prices headed higher and higher. If you plan to run a fork lift in the shop, or install some very heavy machinery, the insulation comes in grades, up to 100 PSI. The typical stuff you see at the lumber yard is usually either 15 or

25 PSI. I used 40 for my shop, which appears to be more than adequate. I have a fork lift that weighs just under 10,000 lbs, and it can pick three tons. I've hauled one piece inside that taxed the capacity and got no cracking or settling. I did do one thing to help prevent edge cracking, though. I have rebar on 6" centers in the door ways, in a couple feet or so, where you might get edge cracking. A few bucks spent before the crete is poured can save a lot of heartache later.

Harold

After vacuuming up the dust from my sawcuts, and squeezing in 2-1/2 tubes of caulk, I don't have any big lines that fill up with crud, either. These cuts are only 1/8 inch wide, so it's not like you're going to drop a wheel in them..

I certainly thought it was pretty reasonable in the overall cost scheme of the project, but I did install my own. You simply cannot go back later and put the stuff in.

I also put extra steel (both bar and mesh) in the at doorways.