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Unread 12-14-2006, 11:25 AM   #1
jacobkoski
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Gypsum-Heat Mat-Ditra-Marble HOW?

I have read the various posts on these and related questions.
I have 260 sq ft the majority being on a gypsum subfloor and a small amount a plywood hallway at same level of gypsum.
Planning on using warmly yours Nuheat, and ditra, then marble-
Bigconcern is everything *flat* and not raising level of floor (no SLC or MUD)

Ideas then questions in somewhat pertinent order;

Over gypsum
1.Primer
2.Heating mat
3.Thinset, thickset
4.Second Layer of thinset leveled
5.Ditra
6.Unmodified thinset
7.Tile

1. What Primer options for gypsum (I know there are a lot)
2. I am assuming that heating mat is glued to gypsum- if so hot glue? Is 260 square feet over board for one thermostat?
3. Unmodified or modified thinset? Trowel size? Areas that do not contain mat just spread heavy? Allowed To cure?
4. Is this an unnecesary step? Should ditra be laid as first layer is spread? if not, modified? unmodified? Trowel size?
5. No questions!
6. Unmodified is mandatory correct?
7. We will be using a 4x11 liner size border tile on the perimeter from Zation is ditra going to make this really hard- it is on a mesh

Over Plywood
1.Heating mat stapled
2.Thinset, thickset
3.Second Layer of thinset leveled
4.Ditra
5.Unmodified thinset
6.Tile

1. correct me if I am wrong, also how many square feet can we get on one thermostat?
2. which? unmodified or not, trowel size?
3. unnecesary step, if not see questions for 2.
4. Just rollit!
5. I am assuming this is correct above the ditra
6. Same question as #7 above

I am sure this will Lead to more exciting questions thanks in advance

Jacob
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Last edited by jacobkoski; 12-14-2006 at 11:47 AM.
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Unread 12-14-2006, 11:31 AM   #2
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i think you got ask. is this a potential wet area. ie adjacent to a tub or shower? laudry room etc.
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Unread 12-14-2006, 11:42 AM   #3
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Good point,

No, it is an entry way with minimal wetness however we will be sealing with kerdiband just for the fun of it (also to protect gypsum)
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Unread 12-14-2006, 11:52 AM   #4
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ok let me see if this flys. redguard the gyp. priming with dilute (h2o) solution of red guard. two coats of red guard to the spec. thickness. set the heat mat with mod. thinset and set the tile on top of that with same. eliminate the ditra.
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Unread 12-14-2006, 11:58 AM   #5
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Warmly Yours will be here soon.

Have you checked the Deflecto yet? What is the substrate under the gyp?
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Unread 12-14-2006, 12:03 PM   #6
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gypcrete was poured over slab. plywood is half inch over 3" thick toung and groove boards (dont ask what they are or why they are) over slab- so I think we are pretty sturdy
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Unread 12-14-2006, 12:07 PM   #7
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higgins-

ditra will be applied, as on original slab beneath gyp there were two expansion joints and cracks. not to mention transfer from plywood to gypcrete (expansion joints will be relfected into tile layout as well) could you be more specific as to coverage of red guard and diluting proportions?

Also flatfloor- your signature doesnt take into account invitro fertilization
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Last edited by jacobkoski; 12-14-2006 at 12:19 PM.
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Unread 12-14-2006, 01:45 PM   #8
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We're here. Thanks Jim.

Jacob,

The methods you mentioned at the start are pretty good.
I would recommend Redguard underneath floor heating - the manufacturer (Custom) recommended it, so I have to agree with them. As for the application of the Redguard, others will be able to enlighten us more.

Attaching the heating mat to the primer can be done with hot glue. I have also seen liquid nails used in small amounts to hold the heating mat in place.

When using gypsum or wood as a substrate you will be fine with Ditra over the top of the heating mat. And as you correctly stated, modified thinset on top of the heating, beneath the ditra, then unmodified thinset on top of the ditra for the tile. This is Schluter's recommendation. You won't usually need two layers of thinset underneath the ditra. One layer can be used to cover the heating mat and be used for the ditra.

In areas where there is no heating mat, simply make up the slight height difference by spreading a slightly thicker layer of thinset before installing the ditra. 1/4" or 3/8" notch trowel will be fine over the heating mat.

You can safely install up to 240 sq ft of floor heating product on one thermostat, with a 240V electric line (This might be enough heating for a 300 sq ft room). For larger areas you can use one or more relay switches to allow for a lot more heating and still use just the one thermostat.
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Unread 12-14-2006, 02:05 PM   #9
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Exclamation

Thank you Guru

The owner may decide to warm only key areas- in that case how much square feet can a 120v thermostat handle? also I have used suntouch and found that the cords on th mats could at times be prohibitively short. And as this is quite a large room how are all the leads tied together in this situation? Assuming that the leads are not long enough to tie into one box on their own length? If the leads/cords were ran into the walls and then into plugboxes/junctionboxes and from there connected with romex or similar to the main theroswitch is the only way I can think of. Esp as there is nothing but slab below. Problem with this is GC is hoping to drywall before installing mat! then what? can the mats be ordered with esp long leads?

Jacob
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Unread 12-14-2006, 02:57 PM   #10
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Jacob,

A 120V thermostat can handle up to 120 sq ft of heating mats.

The leads on WarmlyYours mats are longer and thinner than some other systems. The leads on a WarmlyYours system can also be extended on site by the installers, and this junction or splice can be safely encased in the cement. WarmlyYours will calculate the required lead lengths and include them with the system.

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Unread 12-14-2006, 04:01 PM   #11
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Quote:
In areas where there is no heating mat, simply make up the slight height difference by spreading a slightly thicker layer of thinset before installing the ditra. 1/4" or 3/8" notch trowel will be fine over the heating mat.
You are correct about mod and un-mod thinset, but I believe Schluter does not reccomend installing Ditra with 1/4" or 3/8" notch trowel.
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Unread 12-14-2006, 09:30 PM   #12
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Question

what size is the appropriate size? and does the two layer technique of thinset seem more advantageous over the one for a flat ditra install?-

Matt- So the leads can be spliced in the floor?? what wire is used for the extra? Seams like junction = box in electrical world. And I was planning on installing the mats, so would it still flywith warranties and what not?
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Last edited by jacobkoski; 12-14-2006 at 09:36 PM.
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Unread 12-15-2006, 04:53 AM   #13
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Appropriate size trowell is 1/4" x 3/16" or 5/16" or 5/16" V notched trowel. Probably would be best to build up after the Ditra is installed or to skim coat that area of the floor (that is not getting heat mat) then Ditra.
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Unread 12-15-2006, 05:13 AM   #14
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Quote:
ok let me see if this flys. redguard the gyp. priming with dilute (h2o) solution of red guard. two coats of red guard to the spec. thickness.
I am going to STRONGLY Dosagree with Redgaurd as a GYP Primer.

Ive seen it fail in exactly this kind of application. I like the product, Just NOT here!!

Prime the Gypcrete with The Primer reccomended by the Gypcrete company.

Quote:
then unmodified thinset on top of the ditra for the tile. This is Schluter's recommendation.
I am going to reccomend Not using a Dryset here since this is marble and you will be far better off using a Medium Bed product when setting stone.
Schluter Also says you can use a Rapid Set type of Modified thinset on top of Ditra.
In this case Mapei Ultracontact RS will be Ideal having medium Bed characteristics along with Rapid setting features.

Kerabond /Keralastic Underneath the Ditra over Primed Gypcrete (using primer reccomended by gyp manufacturer has been very successful over the years.)

Personally, I'm not certain I would even take this job. I think it is a high liability job as spec'd. The Heat SHOULD have been installed in the gyp pour.

Marble is a very finicky animal ............I think I'd go on vacation and let my competition do this one unless I could Demo the Gyp, Insure a solid subfloor and Mud this Job!!.......When it comes to Marble I lean very HEAVILY to the cautious!!
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Unread 12-15-2006, 06:18 AM   #15
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Ultracontact is a contact mortar, not a medium bed. As long as the marble does not need a build-up over 3/8 a good unmodified would be fine, my 2 cents.
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