Slab radiant and handling pex depth

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Old 02-07-14, 06:51 PM
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Slab radiant and handling pex depth

So Im unsure how to suspend this stuff.
I will have a gravel base, 2" styrofoam and on that a metal grid and the PEX on it. BUT the metal will be setting on the styrofoam and my contractor wants concrete under it.

How do I suspend the grid and PEX up an inch up and the concrete people walk around on it and not smash it back down? we are already going to use a pump truck because they cant wheel it on all this stuff.
 
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Old 02-08-14, 09:46 AM
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Probably should also be a vapor barrier... unless there is NO chance of water wicking up into the concrete.

Contractor is not aware of the 'chairs' that are used to support rebar above the bottom?


image courtesy woodgears.ca
 
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Old 02-08-14, 11:47 AM
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I didnt really want rebar in it at all just more expense. Can the workers walk on that? Does not look like it.
 
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Old 02-08-14, 12:09 PM
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Can the workers walk on that?
No, not really, but they shouldn't have to. They should have tools (floats and such) with long handles that they can reach from the sides.

If your contractor is worth his salt, he should know this stuff.
 
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Old 02-08-14, 04:06 PM
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You DO want steel reinforcing bars or mesh to minimize cracking of the concrete. The reinforcing and the pex should be supported on "chairs" so that they are embedded at the proper height. Any good concrete contractor will know all about that.

I would insist that the concrete mix should be higher than 2000 psi, with fiber added. Best to have it 4" thick.

If the weather forecast is much below freezing, the slab should be covered with blankets to prevent frost damage to the concrete until it is cured.
 
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Old 02-08-14, 04:15 PM
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If the weather forecast is much below freezing, the slab should be covered with blankets to prevent frost damage to the concrete until it is cured.
To prevent a defect that you don't have to call a 'custom feature'... like my new sidewalk... I tell everyone that I paid extra for the 'fish scale' look.
 
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Old 02-09-14, 11:39 AM
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2" foam? Not too severe there for temperature in the winter?
 
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Old 02-09-14, 01:19 PM
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What are you saying Who? Skimp on the insulation? or add more?
 
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Old 02-09-14, 08:22 PM
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Just thought 4" was the norm... R5/Inch? Max 7...
 
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Old 02-10-14, 09:02 AM
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As I recall from a previous thread, this slab is basement, not a slab on grade as shown in the pic... that pic was for illustration purposes to show the 'chairs' that the rebar sets on.

Here's the original thread for reference:

http://www.doityourself.com/forum/bo...ones-each.html

Four inches might be advisable in a slab on grade application, but 6' down in the ground I should think that 2" is more than enough.
 
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Old 02-10-14, 06:42 PM
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2" should be enough. Im in southern Tennessee and it wont get bellow freezing around here but for a few days or a week at a time.

My contractor is wanting to poor 5 inches of concrete instead of 4". I dont want problems of cracking so its just maybe at the most another thousand in cost. What are yall's thoughts?
 
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Old 02-10-14, 06:52 PM
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I don't know that it's so much the thickness of the pour but the rebar that prevents the cracking.

Was that his reasoning? That a thicker slab will prevent cracking?
 
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Old 02-11-14, 06:34 PM
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no reasoning was (I think) to keep plenty of depth with the pex and still have plenty of concrete. I need him to get with his concrete guy and for me and him to stop guessing.. The radiant flooring isnt done much in the south so Im running into people who dont know left and right. If the concrete guy is unsure then Im up a creek!
 
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Old 02-11-14, 06:54 PM
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to keep plenty of depth with the pex
I don't think you want 'plenty of depth' with the PEX! My understanding is that you want the PEX within 2" of the surface. Someone will correct me if I'm wrong I hope.

My reasoning for this is that when the heat turns on, you don't want to have to heat the entire mass above the tubing before you start to get any heat out of it. Sure, with it closer to the surface you will still heat the mass of concrete eventually, but from the TOP DOWN, not from the BOTTOM UP, and heat will radiate into the space sooner... it will be more 'responsive'.

me and him to stop guessing
NOBODY should be GUESSING! As I've said before, you only have one chance with concrete to get it right the first time! BE SURE!
 
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Old 02-12-14, 06:21 AM
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I hope the pipe does not end up as close to the footing as depicted in the picture as there will be a lot of heat loss . It should be 18 inches from footing and if more pipe is needed put it in the center. Just the way I do it up here in Canada.
 
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Old 02-12-14, 07:54 AM
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It's not really possible to tell from that example picture whether or not there is perimeter insulation creating a 'thermal break' from the footing... there SHOULD be.

With a proper thermal break between the slab and the footing there is no issue with running the tubing next to the footing... in fact I would encourage CLOSER spacing between the tubing at the perimeter edges of the slab and not move the tubing away from the footing.

I don't understand why you would want the edge of the slab to remain cold...
 
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Old 02-12-14, 05:42 PM
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Without starting a new thread.. This 2" foam board under the slab, I notice there are different (or offered) compression ratings. where should I be?
example:
Rigid Foam
 
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