Infloor Radiant Heat

Susan_4

Building a 34' x 40' garage and have chosen infloor radiant heat for this project. Climate is Anchorage, Alaska. Have had several contractors bring up the subject of the concrete cracking if poured over blueboard material. I have been told to compact the foundation material til the surface is totally flat, wet the area down well, then compact the soil again after it has dried, then place your 2" thick blueboard in foundation, place your mesh material, tie down the pex and pour the concrete. I have also been told by various contractors to skip the blueboard and use sand as the concrete won't crack. Anyone out there with an opinion on this?

kevin coppinger_4

I would get ...

a different concrete contractor....If the soil is prepared PROPERLY compacted and flat you should have no problems due to that.You need to insulate 2" of polystyrene is a good start ,get the perimeter too w/ at least 1"> sand will not work to insulate,period. You could tack/staple to the styro instead. It siunds to me that they are not preparing the concrete well...kpc

Mark Eatherton1

The problem with cracking

also known as crazing is cause by excess moisture being held in the concrete during cure. Provisions should and can be made to allow this excess water to drain through the insulation by leaving small gaps between the insulation sheets. I've never had a problem with crazing.

ME

hot_rod

Concrete finishers

generally do not like pouring over foam or vapor barriers. As Mark mentioned it slows the cure time by not allowing some of the "waters of convience" to escape through the bottom.

As such, all the water must come to the top. This can extend the time it takes before the finishers can get on the slab for the final finish. Some finishers will add calcium to speed the setup time. They can also play with the amount of fly ash added.

That being said, there are a number of ways to work with this. The mix can be modified at the plant. Adddetives are available to speed or slow the cure time. Shrink reduction products, sealers and foggers may be needed, depending on weather conditions at time of pour. n

Find a concrete contractor that knows his trade. Concrete is poured over both foam, and vapor barriers on a daily basis. Sucessfully! Trust me, it can be done.

Keep in mind ALL concrete can crack regardless of the precautions taken. Cracks can be caused by shrinkage, too fast or too slow of a cure, settlement, external restraint, improper finish techniques, dozens of other causes. I have seen slabs crack 3 years after the pour! (my own shop)

If you absolutly, positively want a crack free floor for eternity, concrete may not be you best choice

When a crack appears, pros in the concrete business call this a "free control joint"!

Good luck finding "your guy". plenty of concrete websites to give you tips and pointers for problem free concrete slabs, also.

hot rod

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Susan_4

Information

Hey all,
Thanks for the information - I'll let you know how it turns out - will be doing the infloor radiant heat later this month (cross fingers) - the factory has advised that no insulation is needed inside the foundation wall but will take the suggestion and do a 2" strip with the 2" blue board on the bottom after making sure the fill is compacted well.

[Deleted User]

Skip the Blue Board

Skip the Blue Board, use Insul-Tarp. Works better, costs less, and easier to install... We use it all the time here in Iowa, and Anchorage doesn't get as cold as we do. I know, I lived in Alaska for 18 years....