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Old 05-10-2018, 01:00 PM   #1
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Slab thickness and pex question


I’m in the process of getting my foundation ready to pour a basement slab. I was going to put 2” xps with a vapor barrier under the whole thing. My issue is my mason goofed and made my door buck up 4” from the top of the footing. My thought is place my 2” xps so it’s level with the top of the footing. On top of the footings use 1” xps. When the floor is poured I will have 4” of concrete throughout most of it. Along the edges over the footings will only have 3”. Do you think this is acceptable?

Also I have a question regarding radiant heat. I have been under the impression you want the wire mesh with the pex roughly in the middle of the slab. Everyone I’ve talked to around town says the guys doing the floor will just leave the wire mesh and rebar at the bottom of the slab which leaves about 4” concrete over it. Will this be a huge issue? A few home owners I’ve talked to say that’s how theirs were done and don’t have any issues.
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Old 05-10-2018, 05:33 PM   #2
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Re: Slab thickness and pex question


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Also I have a question regarding radiant heat.
Ayuh,..... Just My thoughts, 'n the way I've done, 'n am 'bout to do again,.....

Ya, do the 1" foam over the footer, 'n up the sides, with the top of the edge foam cut at 45*, whether 1", or 2",.....

I lay the poly, then the foam, then the pex, with the steel over it to keep it sunk in the wet concrete,.....

Ideally, I roll out ole chainlink fence, tie the pex in-place on it, 'n cover that with mesh mats,....
I stumbled into some 3" foam for my next pour, 'n don't have alotta space for concrete, the ole fencin', or top mats may not fit in,...
had planned on 2" foam,.... just a walkin' floor, so it'll be ok, anyways,....
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Old 05-10-2018, 05:45 PM   #3
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Re: Slab thickness and pex question


You worry about having steel with in 2 inches of the surface of concrete because of rust, So use galvanized mesh and it can stay at the bottom of the slab.
Usually the foam goes level with the footing and the concrete goes over that.
If you have room for the door to move up you could just put a board on the outside of the door way for a form and pour the concrete to your required height.
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Old 05-13-2018, 02:15 AM   #4
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Re: Slab thickness and pex question


I don't think you want the metal in the middle of the slab, as that would be in the neutral plane. Bottom, I believe, is better, but the concrete guys/gals will probably lift it a tad to ensure that it is covered, so it ends up "somewhere". I've always seen the pex stapled to the foam, metal above it, which is how we did our two pours. The location of the pex affects reaction time; lower means slower to heat. With radiant, I see no reason to fiddle with the thermostat anyway, as your slab (if real well insulated, and it should be) will be very slow to change temp anyway. Set the thermo and forget it. Also, if your house is super insulated, you will not have warm floors all the time. Doing so would cook you out. But, you will not have cold floors, either. Enjoy the place.
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Old 05-13-2018, 02:19 AM   #5
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Re: Slab thickness and pex question


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Originally Posted by Nealtw View Post
You worry about having steel with in 2 inches of the surface of concrete because of rust....
I thought that applied only to the edges of the slab, if subject to water, like in a garage. Not 100% sure, but if rust were an issue all over the slab, then every home w/ rebar or regular wire would be in stink, it seems to me. Cheers. j
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Old 05-13-2018, 10:50 PM   #6
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Re: Slab thickness and pex question


Mesh or rebar needs to be at least 2" from either side of the slab to work effectively. Putting it on the bottom does absolutely no good. Another option you might want to consider is putting fiber in the concrete for the slab. It's mixed throughout the concrete and you don't have to worry about its placement.

Many people experience in concrete don't really believe that mesh or even rebar does much good in the slab like this. They feel the only thing it does is hold the pieces together after it cracks and they just end up making it harder to demo and disposes of the slab in the long run.
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Old 05-13-2018, 11:13 PM   #7
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Re: Slab thickness and pex question


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Originally Posted by jklingel View Post
I thought that applied only to the edges of the slab, if subject to water, like in a garage. Not 100% sure, but if rust were an issue all over the slab, then every home w/ rebar or regular wire would be in stink, it seems to me. Cheers. j
Many of our builders put rebar in driveways to no bad effect but if air and water get to it. it can be a problem. Wire mesh can not be set on chairs like rebar and you rely on the concrete placer to lift it up in the concrete, even if he does that how hard is it to get it to the middle of the concrete and still have the pipe deep enough. I think you should consider it an anchor for the pipe and leave it below and protect it from rust by buying galvanized..
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Old 05-13-2018, 11:15 PM   #8
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Re: Slab thickness and pex question


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Originally Posted by jklingel View Post
I thought that applied only to the edges of the slab, if subject to water, like in a garage. Not 100% sure, but if rust were an issue all over the slab, then every home w/ rebar or regular wire would be in stink, it seems to me. Cheers. j
https://www.google.ca/search?q=rebar...9QEIOjAC#imgrc=_
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Old 05-14-2018, 12:09 AM   #9
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Re: Slab thickness and pex question


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Originally Posted by Msradell View Post
Mesh or rebar needs to be at least 2" from either side of the slab to work effectively. Putting it on the bottom does absolutely no good. Another option you might want to consider is putting fiber in the concrete for the slab. It's mixed throughout the concrete and you don't have to worry about its placement.

Many people experience in concrete don't really believe that mesh or even rebar does much good in the slab like this. They feel the only thing it does is hold the pieces together after it cracks and they just end up making it harder to demo and disposes of the slab in the long run.
I've never heard steel doing anything but being of great assistance.
http://www.concreteconstruction.net/...einforcement_o

http://www.concreteconstruction.net/...uch-stronger_c

yes, you are right. place in upper half, apparently. cheers. j

http://www.cement.org/cement-concret...lab-on-ground-
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Old 05-17-2018, 06:47 PM   #10
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I have one more question. How level does the dirt need to be under the rigid insulation. I thought a did a pretty good job and put down a few pieces but on certain ones if you step on them the opposite side comes up an inch. So obviously I didn’t do as good of a job as leveling as I thought.

Does the dirt need to be completely level so when I walk on the insulation they are completely solid and don’t move at all?
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Old 05-17-2018, 06:53 PM   #11
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Re: Slab thickness and pex question


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Originally Posted by Cjohnsen View Post
I have one more question. How level does the dirt need to be under the rigid insulation. I thought a did a pretty good job and put down a few pieces but on certain ones if you step on them the opposite side comes up an inch. So obviously I didnít do as good of a job as leveling as I thought.

Does the dirt need to be completely level so when I walk on the insulation they are completely solid and donít move at all?
Will the foam break under the weight of the concrete, maybe.
There is a trick to leveling dirt. Figure the distance you need from the dirt to the floor joist and cut a 2x4 that long and add a cross tee 2x4 to both ends hold one end to the joists and swing the other end. that will tell you when high or low.
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Old 05-18-2018, 05:28 PM   #12
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Thanks for the tip to help leveling.

But still do it need it 100% flat or will the concrete flatten listless inconsistencies with the foam not laying completely flat?
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