Slab on grade radiant heating tubing... OK above WWM? 2

[atrizzy]

My first instinct is that the tubing should be placed below the WWM to reduce potential for cracking on top of the exposed slab on grade.
I've heard some say that this is crazy and that it always goes on top of the WWM.

Am I wrong? And if so, what can be done to mitigate cracking?

 

[dik]

I've generally seen hydronic heating tubes tied to the top of WWF... as long as you don't sawcut too deep, I don't think it matters.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[atrizzy]

Won't the reduced slab thickness at the tube locations promote cracking? Like an internal crack control joint?

 

[Enable]

I've only seen it exclusively on top. That said, my experience is limited to heated ramp toppings for underground parking garages so it may be different in other circumstances. But putting it on the bottom seems pretty bold for the following:

A) it is a crazy amount more labour for installing cable loops (how are they going to keep them together until mesh is installed)
B) we now have to chair between loops, which basically means using individual chairs to the mesh as opposed to ladder chairs and being done with it
C) likely the mesh will fall to the bottom off the shitty chairing mentioned in B and you will have your tubes in the dirt

Do it on top and if you have the contractor do a proper 7-day wet cure w/soft-cuts, it'll turn out just fine.

CWB (W47.1) Div 1 Fabricator
Temporary Works Design

https://www.enable-inc.com/

 

[atrizzy]

OK so I'm convinced that this is typically done and without issues (providing appropriate cover, etc.

But there's something I'm missing. Can somebody please explain to me why a 1" deep sawcut every 12' o.c. will direct cracks to it while a 1" dia tube embedded in the slab every 6" o.c. will not?

 

[MotorCity]

Technically speaking, I agree it should go below the WWM. When a crack forms in the top of the slab, it will propagate through the slab and will have to bypass the tubing before being arrested by the WWM. You'd want the crack to encounter the WWM first.

Practically speaking, it would be very difficult to place the tubing below the WWM from a constructability perspective.

 

[dik]

It has to be sawcut at the right time... and haven't you heard of polypropylene reinforcing fibres... think of the tubing as a big fibre...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Canuck65]

As others have pointed out, I have in the past seen the tubing installed ontop of the WWM. In this case there should be enough concrete cover over the tubing so that cracks don't develop at the tube locations. At least an 1-1/4" minimum in my opinion. However, I would never specify control joints be sawcut into the slab as typically there is a floor finish (carpet, laminate, etc...) put over top and no one will ever see the shrinkage cracks. Too risky to cut the tubing. If they want a polished concrete floor, then there is a different approach.

Nowadays what I see is that there is a layer of insulation laid on the subgrade. The insulation panels are specially made so that the plastic tubing snaps in tightly to channels within the top layer of the insulation, seems quite a good system. Therefore, the tubing tends to be closer to the bottom of the slab and as such it will use somewhat more energy and the thermal lag will be longer, however, the base insulation helps the overall performance quite a lot. This gives the opportunity to then place (with chairs) WWM above the tubing. If you want an exposed floor and shrinkage cracking must be controlled, this gives you the flexibility to A) put mesh or rebar in near the top surface and B) sawcut the slab with low risk of cutting the tubes.

 

[Brad805]

Here is a product for below slab:

https://nudura.com/products/integrated-series/hydrofoam/

 

[SwinnyGG]

But there's something I'm missing. Can somebody please explain to me why a 1" deep sawcut every 12' o.c. will direct cracks to it while a 1" dia tube embedded in the slab every 6" o.c. will not?

The tubing doesn't bisect the area of the placed concrete which is undergoing the most shrinkage during curing - the surface- while the sawcut does.

I've done this a lot, 95% of which has been parking garages and flatwork near entrances to buildings. Tubing is always on top of reinforcement, usually with 2" or so of cover. Laying out tubes such that they do not cross your sawcut layout is not difficult. I've never had a tube get get cut; you know where the sawcuts are going to be before the concrete is placed.

 

[dik]

This arrived this AM...

https://cdn.annexbusinessmedia.com/...um=email&utm_campaign=&*URLENCODE({{*JobID}})

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik