control/expansion joints in radiant heat floor slabs

catarondack

I'm installing radiant heat in a concrete slab and will be putting control/expansion joints in the concrete floor. I'll then be tiling or staining the concrete (depends on the room use). What's the best way to run the pex tubing? A) under the joints (out of the concrete slab and back into it) OR B) Right through the joints.

My concern is that when the slab cracks or shifts, won't the tubing get torn up?

One more question please...when installing pex tubing for a water system, the guidelines I've heard all say to have pleanty of slack in the piping to allow for expansion and contraction...OK, that makes sense...what about pex tubing embedded in a concrete slab...isn't that also expanding and contracting, at a different rate than the concrete slab?

Hey, if I'm thinking of it now, someone must already have thought about it already. I'd appreciate any help. thanks...Mike

hr

Control or expansion joint

These days most concrete installers score the slab with a saw cut @ 1/3 the depth of the slab. Ihis is considered a control joint to stop any cracks from traveling across the entire slab. Sometimes it works, sometimes not. Although a crack is a "free' control joint

An expansion joint is usually a seperation of the slab with a piece of expansion material. A cold joint, really. This type of joint would allow the slabs to move independantly. Rarely see these in radiant slab jobs anymore. Typically only where the drive way apron connects to the heated slab.

Inside the heated space, you really should not have slab movement up and down. This would indicate a poor subgrade prep job!

I have poured radiant slabs up to 20,000 square feet without expansion joints.

It would be wise to expect some small "haze" or drying cracks. Typically the small "road map" looking cracks. These are generally caused by the curing process and the weather conditions. Sealers or foggers will help prevent this if a slab is poured in hot, windy, or dry weather conditions.

Your concrete supplier should be able to advise you on proper mix and additives for your local conditions.

hot rod

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jjacobsnyc

Hot Rod, Thanks for the information about radiant heat floors and expansion joints. We just put a concrete floor with radiant heat in a small addition (10'x17'). It was poured last April. Our contractor told us to expect hairline cracks, as we don't have any expansion joints (except at the perimeter). All was great until yesterday morning my husband heard a loud pop from the next room. There is now a crack down the entire center of the floor, and it looks like there are cracks which are beginning to radiate from that crack. I'm heartbroken and very nervous about what might happen to the rest of the floor. Any advice? Thanks.

Jamie Hall

Can't comment on your specific situation, jjacobsnyc, except to extend some sympathy...

Nor really on the problem of PEX in the slab. However, from the standpoint of concrete slabs in general and cracks (and I've been involved in a fair number of big ones in a past life), I always spec'd three things: a "breaker" layer of sand beneath the slab if it was on grade; mesh reinforcement throughout the slab; and fiber (preferably kinked steel in indoor applications, glass fiber in outdoor or moisture exposed) reinforcement throughout the mix. All in addition to whatever structural reinforcing steel might have been needed. I've also seen post-tensioned slabs in large tanks -- but that's overkill for what we're looking at here.