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Unread 07-29-2010, 04:53 PM   #1
alacrity
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Need some advice on a job

I'm working on an estimate for a GC that involves a floor with radiant heat. Typically I install an electric heat mat, but he wants to use the hydronic PEX system, so another contractor will be installing that. The radiant heat guy said he plans on putting down a barrier like Tyvek and then attaching the PEX tubing directly on top of that. (I'm not sure why he wants to put down the Tyvek underneath the tubing?) The addition is approximately 23'x19', which will be attached to the dining room and kitchen that also gets tiled, so they all have to be in the same plane. Since part of this is new construction, the framing height can be adjusted accordingly.

This leaves me with a couple options.


1.) Pour SLC over the whole floor, 1/2" above tubing, then cover with Ditra. Obviously the Tyvek couldn't be under the tubing with this one, so it would be: 3/4" ply>primer>PEX>primer>SLC>Ditra>tile.

2.) Do a wet-bed 3/4" above tubing, which would give me the 1 ¼" minimum, then cover with Ditra. So it would be: 3/4" ply>cleavage membrane>metal lath>PEX>1¼"wet-bed>Ditra>tile.

3.) Install 5/8" ply in between the tubes, leaving ¼" for expansion and then fill all voids with speed-set and cover everything with Ditra. I don't wanna go inventing any new methods, so I'm not sure about this one.

So what does everyone think? Thanks in advance
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Unread 07-29-2010, 05:49 PM   #2
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I like no 2. It gives you the flexibility to meet with the existing floor. the cost of portland and sand is low, but more labor intensive. Best finish, IMO, too.
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Unread 07-29-2010, 06:13 PM   #3
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He is using the tyvek as he is anticipating light weight concrete or gypcrete. I am in the nexy month getting ready for the radiant in my house and having a company call Elastizell come out and pour a light weight concrete an 1-1/2 thick. They are sending me a building paper to put down under the tubing and then pouring the light weight product is their proprietary system. I do know it has fiber in the mix. I am not a fan of gypcrete.
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Unread 07-29-2010, 06:36 PM   #4
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hey monty I'll take door number 2

given the choice . . . 2 is good if you are a solid mud guy

as for 1, I don't like slc over ply even with primer -- the only brands that I know
of that spec that are mapei plano 1 and ardex liquid backerboard.
makes me nervous . . .

If you did go the slc route I'd go plywood/1/4 wonderboard/primer/pex/reprime/ level lite/ditra/ tile

Bag #3 altogether . . . way to many movement issues . . .


which ever you do don't forget perimeter expansion

good luck
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Unread 07-29-2010, 07:38 PM   #5
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I'm leaning towards doing the mud at this point, SLC makes me nervous even in small rooms, and sand+portland is way cheaper. The only problem with that is I'm a mud novice and usually only do shower pans and small rooms. If I go with mud the Tyvek will still go down because of the heat being an issue with tar paper.
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Unread 07-29-2010, 07:39 PM   #6
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#2 also
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Unread 07-29-2010, 08:13 PM   #7
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#2 also, We usually would have a vapor barrier down already, either 4 mil poly or tyveck, we would put down wire, heating contractor puts the PEX down, then we come back and gauge the mud. Oh yea, get Rick to come and gauge it for you. Pay him the big bucks and he'll make quick work of it.
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Unread 07-29-2010, 08:24 PM   #8
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Quote:
Originally Posted by Chuck
Oh yea, get Rick to come and gauge it for you. Pay him the big bucks and he'll make quick work of it.
I already had those wheels turning in my head, it's probably a 45 min drive for him, I'll shoot him a PM eventually. If he's not able to help I have some other people in mind.
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Unread 07-29-2010, 08:46 PM   #9
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Eric, if you're trying to meet some industry standard or use a published method with what you proposed with your number 2, you're not reading anything with which I'm familiar.

If, on the other hand, you're just fixin' to do something on your own that you figger will work, that's a different discussion.

The 1 1/4" mud bed method I believe you're thinking of requires the minimum 1 1/4" of mud with reinforcing wire mesh in the center of it on top of a cleavage membrane over the mud-filled hydronic tubing area. Look for F141 in your Handbook.

My opinion; worth price charged.
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Unread 07-29-2010, 09:21 PM   #10
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Eric,


give me a call I am free if you need a days work from me.
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Unread 07-29-2010, 09:57 PM   #11
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FWIW - Tyvek isnt a vapor barrier. As designed - it is a breathable wrap, to stop air draft infiltration and BULK water from reaching the sheathing - but allows vapor to penetrate and more importantly to escape. If it is just being used as a curing membrane for a mud bed it will probably suffice at stopping the ply from wicking moisture and weakening the cure - but why use expensive tyvek when poly is cheaper and is certain to act as a good curing membrane?

As far as using it under gypcrete - I'm no expert but it seems like an even worse idea. Gypcrete has a ton of water in it initially and all of that water has to go somewhere since it is an evaporative product unlike portland based products. Since it is not a vapor barrier it is possible and likely that some of that water will go through the tyvek and into the ply or osb as vapor. That is a good recipe for hidden mold that you will never see growing. I can't think of any reason why this would be a good thing - except maybe to allow future life-cycle moisture to escape as fast as possible since we all know that gypcrap turns into a pumpkin when wet...Anyone know if this is the case or did some confused builder/ gypcrap contractor just start a bad trend?
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Unread 07-30-2010, 03:54 PM   #12
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Rick, I'll be giving you a call soon

Quote:
Originally Posted by cx
Eric, if you're trying to meet some industry standard or use a published method with what you proposed with your number 2, you're not reading anything with which I'm familiar.
Yes, I am trying to meet industry standards, and with my choices it looks like #1 is the only one approved (RH123)

Quote:
The 1 1/4" mud bed method I believe you're thinking of requires the minimum 1 1/4" of mud with reinforcing wire mesh in the center of it on top of a cleavage membrane over the mud-filled hydronic tubing area. Look for F141 in your Handbook.
So with this method, it would be poly>lath?>½"PEX/mud>poly>1¼" mud with reinforcing>Ditra>tile. Does there need to be lath under the PEX? It's not listed in the handbook. It's my understanding that any mud that thin requires lath.

Quote:
Originally Posted by Kyle
FWIW - Tyvek isnt a vapor barrier. As designed - it is a breathable wrap, to stop air draft infiltration and BULK water from reaching the sheathing - but allows vapor to penetrate and more importantly to escape.
I think the GC is using the term Tyvek and thinking it's synonymous with poly. I'm willing to bet that's it.
Quote:
I can't think of any reason why this would be a good thing - except maybe to allow future life-cycle moisture to escape as fast as possible since we all know that gypcrap turns into a pumpkin when wet...Anyone know if this is the case or did some confused builder/ gypcrap contractor just start a bad trend?
That's the reason I asked about Tyvek specifically, I'm not sure if he knows something I don't, or if it's just a case of miswording.




Should I consider telling the GC to have a gypcrete contractor come in and pour minimum of ¾" over tubing? (RH122 in the handbook)
I've never dealt with gypcrete and have only heard bad things about it, everyone I talked to about it hated it and referred to it as gypcrap. How much does it cost compared to SLC?
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Unread 07-30-2010, 11:42 PM   #13
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Yes. Then lay your ditra.
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Unread 07-31-2010, 07:37 AM   #14
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The gypcrete is gonna cost you a substantial drying time and will save only a half-inch vertical over the F-141 method. And it would be at least a quarter of an inch thicker than the SLC method you mentioned.

If the GC is paying for all this, why not let him decide all that and just contract for the tile installation? He may have a buddy in the gypcrete bidness or maybe get a really good deal on SLC, or whatever, eh? Then if it's not done correctly, you can just tell him you ain't fixin' to tile over that.

Doing the mud yourself gives you a good bit more control over the installation and would make me feel a lot better about the whole thing, but it does cost you some vertical height.

And for F-141 I don't believe there is any need for lath under the hydronics. The mud to the top of the tubes is just a filler over which you'll install your cleavage membrane and reinforced mud bed. Nice and flat.

My opinion; worth price charged.
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Unread 08-02-2010, 05:35 PM   #15
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I have always done these with lath under the heat, we don't use 15lb tar paper though because the heat will make it smell.
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