I want to put a concrete floor in my shop. I would like to incorporate radiant heating. What type of concrete and how thick would it have to be in order to be a crack free floor? Where can I find plans for designing the radiant heating system to put inside the floor? This will be used for automotive repair and a machine shop with large equipment.

The addition of radiant heat should not have a huge effect on the type and thickness of the concrete.
I would incorporate insulation board under the concrete to isolate the slab from the ground below and direct the heat upward. In my area of the country, the garage you described would have at least a 6" slab of 3000 PSI concrete with wire reinforcement. These specs will vary by region, so I would check with local pros and, of course, if you have codes people to deal with, they will have the final say so, so you might as well ask them first.

Might want to add some footings for a lift while you're at it so you don't drill anchors through a tube.

Sean

I've been told there is no such thing as a crack free concrete floor. You might get close using double plastic over foam underneath, glass/plastic fibers, 5% MgO and post stressing. Or just let it crack at well placed expansion joints.

My neighbor is a foreman for a bridgebuilding company and when I poured my slab he advised me to mist it with water everyday for five days and try to keep it around 5 degrees C for a slow cure. Turned out really well with no cracks yet, although it's still pretty new. I did the same with my garage slab 10 years ago and there is only a couple of hairline cracks, very minor. Also he said make sure they don't add any "High Easy" or extra water, makes it easier to spread and cures faster causing problems.

Sean

For the loads that a heavy machine or automotive shop would impose, I would specify a 6 inch slab. A good way to go for radiant slabs is to use the EZ-Floor system. It is insulation, vapor barrier, and mounts for your radiant tubes all in one easy to use sheet. You just lay them down and they interlock. If you plan on an epoxy coating, the vapor barrier is critical. Ditto for any conditioned space above a slab. Shop slabs tend to see quite a lot of impacts from dropped tools, parts, steel, etc. so I would advise a 4,000 psi mix with a blend of fibers. The fibers will serve to increase impact resistance and to mitigate cracking. Try to get 1.5 inch rock in the mix. This will lower the cement factor and reduce curling and cracking as well. 15% fly ash with a mid-range water reducer will also help, because the fly ash will increase workability and densify the slab. The water reducer will allow the concrete to be placed at a 6 inch slump, with no water added. Adding water to increase slump will increase shrinkage and cracking. We do quite a few shop floors with Shrinkage Reducing Admixtures. Both Grace and Master Builders have them, so your local ready mix producer will know what they are. The producer may also recommend a good flatwork contractor who does quality work and can put a nice hard trowel burn finish down for you. With proper practices, mixes and the SRAs, we have produced 30 by 30 floors with no joints or cracks. If you don't use a SRA, be sure to follow ACI jointing layouts. A joint is just a pre-planned crack. Joints need to be 1/4 the depth of the slab. Your bridge buddy is correct on the curing and the accelerators. Ponded water is the best and most economical for curing, but it can be a pain. Membrane cure and seal products are easy to roll on the next day and will keep moisture in your slab. This moisture is needed for proper cement hydration and strength development. The sealer will help keep the slab easier to clean. If you are planning an epoxy coating, be sure any curing product you use will be compatable or you will have to sandblast it off before doing the coating.

Posted By Alton on 10 Mar 2010 03:07 PM

Cracks in concrete can be limited by using the correct water to cement ratio, by installing expansion joints at critical locations and by using good finishing techniques applicable to the local weather. 

And by proper curing.

Posted By shijimi on 09 Mar 2010 09:10 PM
I want to put a concrete floor in my shop. I would like to incorporate radiant heating. What type of concrete and how thick would it have to be in order to be a crack free floor? Where can I find plans for designing the radiant heating system to put inside the floor? This will be used for automotive repair and a machine shop with large equipment.

Assuming a hygronic system I guess you would need to run antifreeze unless you were sure you would keep the heat on when necessary.

Re "What type of concrete and how thick would it have to be in order to be a crack free floor? " The thickness of concrete is not necessarily a foolproof crack deterrent. I have seen 20" think concrete crack several times. I will say that you are not going to be able to get radiant heating tubes in 4" of concrete though.

Another important aspect to crack free concrete is proper substrate preparation. It needs to be very firm and any irregularities in bearing capacity will create the potential for cracks. Rebar in the footings help too.

Is this a frost protected shallow footing slab, a monolithic slab, or what? One thing I don't think you told us is what area (climate) you live in. This is an important consideration.

Radiant tubing in a 4" slab is no problem. There are basements all over the US with radiant tubing in 4" slabs.

Last fall I put a radiant slab in my garage. I found this link helpful http://www.radiantcompany.com/details/grade.shtml in planning for the tubing and insulation. I had a contractor do the actual pour, but I put down the instulation and did the tubing laytout and tied it to the wire mesh. Get your contractor involved early if you plan to do the prep work yourself to make sure you don't have to redo anything. Heated slabs are very nice! Good luck!