tile and radiant floor heat [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-17-2001, 05:00 PM
I'm planning new construction (2000 sq ft) and want to do about 900 sq ft in tile (2 baths, kit, dining, family rm, laundry rm and covered porch). I'd like electric radiant floor heat under the tiles. This will be for floor warming only, as we will also have a heat pump.

From what I've researched, they would lay the electric cables on the subfloor and then pour a self leveling compound (such as gypcrete) over. Then lay the tiles right on the gypcrete.

My builder has not done this before. The tile guy has done this for a small bath only, but not in this large an area. I can't find anyone locally who has done the gypcrete pour. My heart is set on having the radiant under the tile, but my husband does not want to pay a fortune to get it done, and we don't want to have a big mess on our hands.

Has anyone here done tiles in this manner? Let me know what you think.

BTW, I'm so glad I found this forum. You guys are great. Can you tell I love tile! I've done a countertop and backsplash for my son and will be doing a bath for my other son soon. So I'll have lots of questions in the future also!


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Bud Cline
08-17-2001, 05:42 PM
You came to the right place, we all love tile, and return with your questions whenever the urge strikes.

But first, you must go wash your mouth out with soap for even mentioning Gypcrete. Gypcrete is not compatible with many/any floor covering products/procedures and most especially tile.

There are two/three ways you can do this. One would be to cover your heating elements with "self leveling cement" (SLC), in fact we have an SLC Manufacturer/Expert right here. Will the real "flatfloor please step forward"?

The next choice that is coming on strong is a product called DITRA, and we can get into that.

The third choice would be just plain ole thinset, this method is not compatible with all floor heating products however.

OK guys, your turn, but just remember John and I saw'em first.

08-17-2001, 05:59 PM
Hi CB,
A heated floor is definitely a luxury(read:expensive)so you want it to last.As far as I know I would not use anything gypsum based under tile mortars.There are companies that will pump a self levelling compound in but this is very expensive.Also make sure that your subfloor and joists are adequate and secured to handle the weight and prevent movement.
Personally I would lay the heating wires and spacers in a reinforced old fashioned mud bed,but conditions aren't always ideal for a full mud bed.
I've installed many "NU-HEAT" systems which is a thin membrane that's fairly easy to install and I know that they stand behind their products.With Nu-Heat you install the membrane(many sizes available)in a thin-set mortar and install the tile right on top.Nu-heat is more expensive than the custom wired systems but the prep work is less expensive.They have a web-site I'm sure.Their base is in Vancouver.

Derek & Jacqui
08-17-2001, 06:57 PM
We have installed radiant heating in bathrooms. The system we used was D.K. Heating Systems out of Illinois. You give them a drawing of your project and they will send you a measured plan of where the system should be installed and installation advice.
Call them: 1 800 959 9276
Fax them: 630 787 0573
We have had no problems with this system.
They do insist that a qualified electrician does the hookup work.
Hope this helps you out.

John Bridge
08-17-2001, 07:30 PM
Hey CB, Glad you found us.

Having spent my entire tiling career in the Sun Belt, I've never encountered anyone who felt a need for in-floor heating. I do, however, have an idea or two.

I worry about expansion and contraction, and I know that people have had problems (with gypcrete systems and others) when expansion/movement joints haven't been provided. It seems bathrooms aren't much of a problem, but larger expanses certainly could be. If I were ever to try it, it would be over a conventional mortar bed (an inch and a half or so of mud, reinforced with some sort of metallic mesh).

You haven't mentioned what part of the world you are in.

Bud Cline
08-17-2001, 07:58 PM
I think flatfloor is real familiar with Gypcrete and the penalties of its use.

08-17-2001, 08:13 PM
Bud - Thanks for setting me straight on the gypcrete. I guess I read that somewhere, but now I know better!

Ron - I've read about NuHeat, but thought the mats wouldn't work in so large an area. I'm hoping to use this though in my son's bath remodel.

D & J - Thanks; I'll check out DK Heating.

John - The electric cables say you need a minimum of 1/2 inch self leveling compound. Are you saying you think that wouldn't be enough. I'm from Pennsylvania.

Rob Z
08-17-2001, 10:04 PM

I see you already got the scoop about gypcrete.

The Nuheat product that Ron mentioned is a good one. They will make the mats for as big as an are that you need, so size shouldn't be an issue. The mats get a bit pricey, though.

I will ask Jim to stop by and fill you in on SLC's.


We LOVE people to come to this forum that LOVE tile! Come back and see us again.

08-18-2001, 01:57 AM
You may also want to consider using cement backer board as the underlayment and then apply the "heating system".

What part of Pa. are you from? We have a fella, JC, who is from the Pittsbugh area who pops in once in awhile. I used to call on Distributors in Pa. and may be able to recomend some to you for some of your choices.

Stop back and let us know how things are going, you are in good hands with our installation specialists. We salesman just hang around to keep them on their toes.

Art Phenis

08-18-2001, 01:07 PM
forget gypcrete...just go with a mortar bed.

08-18-2001, 05:49 PM
Hi CB, Glad the others clued you in on gypcrete.

The procedure for a self leveling PORTLAND cement is the same as gypcrete with the exception that we require the installation of 2.5 Diamond lath wire mesh on top of a wood subfloor and then the cable. The addition of the mesh will raise the floor height 1/4". If the area you are on is concrete, skip the mesh.

The question you have to ask is; Mortar v SLC, is it within your budget?

Figure 50 bags of material TO COVER MESH ONLY, depending on thickness of your cables you will require additional material, which will cost between $25 & $32 per bag depending on mfg. and where in Pa you are.. Plus 2 gals. Of primer about $30 per gal. Oops, almost forgot the mesh, not sure what that cost is check with your local masonry supply yard.

Labor should run about 32 man hours max. This does NOT include the electric cable installation.

Big advantage to an slc is it's done in one day and it's a beautifully smooth flat floor, plus I suspect your heat supplier wants a 1/2" of gypcrete on top because it is not as "strong" as amortar or slc.

If your in the Pittsburgh or Philly area we have installers.

BTW, the reason you can't find a gypcrete installer is they are franchised and your job is very small, they usually only do large commercial projects. If they agreed to do it the surcharge would bring it up to the cost of a Portland slc.

[Edited by flatfloor on 08-18-2001 at 09:55 PM]

Rob Z
08-18-2001, 08:29 PM

thanks for the info.


08-18-2001, 10:19 PM
What is the coverage per bag at 1/4" thick for SLC?

John Bridge
08-19-2001, 07:34 AM
2.5 metal lath (diamond mesh) about .20 per sq. ft.

08-19-2001, 09:28 AM
Schluter products such as "Ditra" although costly are able to go over gypcrete if other options are limited.


08-19-2001, 10:58 AM
Keith, at 1/4" 30 SF.

John has been kind enough to make my signature a hot link to our site. We have complete specs, MSDS and installation tips there.

08-19-2001, 03:32 PM
Thank you so much for the info, Jim and everyone. Based on what you said, I've calculated $180 for the metal lath, and $1500 to $1920 for the SLC (1/2 inch thick pour which is the minimum for the cables) and then about 32 man hours of labor (which I have no idea how to price).

I am located right in the center of the state - State College, PA - mid way between Philly and Pittsburgh.

Do you know anyone in that area that does the SLC? Or what type of contractor should I be calling to inquire?

I still need to get my prices for the electric cables and installation on that. If we can't afford to have all the areas done that I want, I'll have to rethink this and maybe only put the radiant in certain rooms and do less tile.

08-19-2001, 05:45 PM
Jim -You said "The question you have to ask is; Mortar v SLC, is it within your budget?"

I know this is a naive question, but what is the difference between mortar and SLC.

08-19-2001, 06:56 PM
You have 2 excellent floor covering distributors who service State College.

One is Sorce Inc. based in Clarion, Pa. and the other is Connestoga Tile, in Harrisburg, Pa. Both of these distributors service retailers in your area. They can help you with the decisions you need to make.

Give cement backer board serious consideration, the matt can be applied over the top of it, and under the tile and thin set.

For #'s of either of the above, call 800-738-1621 and ask for customer service. They will be more than happy to help.

Good luck,


Rob Z
08-19-2001, 08:41 PM

Conestoga Tile is the distributor I use here in NO VA. They are a top notch outfit, and carry good products. My store manager used to work up at the Harrisburg store, and may be able to recommend good installers. How far is harrisburg from you? Email me if you'd like to talk to Brian. I'll make sure that you get in touch with him.

The difference between mortar and SLC is quite profound. Mortar (aka "mud" or "drypack") is composed of sand and portland cement, in a ratio of about 4 to 1, and is mixed with very little water and pushed, packed, screeded, and troweled into its final shape. It is very strong and very labor intensive. It is a method that has been around for 1000's of years-at least since the Romans.

Self leveling compounds are made of fine sand and portland cement, as well as a lot of other stuff (Jim would have to explain that), and is mixed so that it is very, very wet-it looks like soup it is so runny. It is dumped, poured or pumped into location, with minimal troweling and pushing to get it into place. The fluid nature of SLC enables it to seek its own level, or nearly so. SLC is fairly quick and easy to install, but the material is very expensive in comparison to mortar.

Both mortar and SLC are reinforced with lath over wood subfloors.

John Bridge
08-20-2001, 06:29 AM
1. The mortar (mud) method requires the services of a mud man, maybe two, and their helpers. Mud men are becoming extinct, thus hard to come by.

2. You still haven't contended with the expansion joint issue, which will be paramount in an installation as large as yours.

08-20-2001, 08:12 AM
John, Please explain the "expansion joint issue" to me. I'm not sure what this is and what I should be concerned about in my large installation.

08-20-2001, 09:53 AM
John, I just reread your previous post and think I now understand that you need to provide for expansion/contraction. Guess my question now is:
How is this provided for when using a SLC? Jim, can you shed some light on that?

08-20-2001, 12:47 PM
Rob, thanks for saving me the typing, excellent definitions. As far as "the other stuff" it's Pixie Dust. Seriously there are polymers involved and every mfr. has a proprietary formula.

CB, I'm going to sort of evade your question in that it has never been an issue we have had to deal with. Not to say John's concerns are not valid. We usually do large areas some of which involve ceramic or quarry tiles (caps?)I.E. Country club and school locker rooms, commercial kitchens, etc. I have never encountered a problem in this area. I ASSUME this question is addressed by the tile contractor as he installs tile on top of my product. Usually we are gone from the site when the TC starts.

Dave Gobis, one of the reigning tile gurus in the US, and I once had a very brief, exploratory, Email exchange on this subject without any conclusion. I did suggest that if it were a real concern, closed cell Backer Rod might be used as an expansion joint where deemed necessary.

Backer Rod is a flexible plastic solid tubing that comes in rolls of various lengths and thicknesses. Having said this,
I think we are going to get a request to move this part of the procedures to another forum. We will be back.

On another note the Pitts. installer begged off, busy and too far to travel. I'm going to contact someone in Lancaster County.

08-20-2001, 01:42 PM
CB, who's heating system are you planning to use?

You have gotten me re-started on research I had started but it fell by the wayside when I received no response from electric heat mfrs.

Today I received an Email from NuHeat and I followed up with a phone call.

I spoke with one of their Tech reps., Jonathan, who had no objection to the method I propose. However, I have a concern, picture this- their system is a big electric blanket that you roll out on top of a mud bed and then cover with your thinset (1/4" is all that is required)- now, as Rob mentioned slc is very soupy, I believe the blanket will float to the top, the tech rep said no, I say yes, then he admitted he had never sen an slc in action, now we have a maybe. I asked if I could staple the blanket to the floor? Nope! you'll void the warranty.

So, I think your back to mud and rethink your elevations depending on the mfr. NuHeat's 'blanket is only about 1/8" thick and requires 1/4" topping.

See what you started!:)

Bud Cline
08-20-2001, 02:44 PM
Funny you should mention floor heating manufacturers not getting back to you. Last winter I thought I wanted to align myself with a couple of those guys to have a credible link for customers/visitors to my website.

I searched and searched and contacted every manufacturer I could find including those that have display ads in trade magazines. I know I must have contacted a minimum of six of these guys, I think it was more. Only one responded to me and he had a policy that he would only sell to installers that had attended his company schooling. That's probably a good idea. Trouble was not only did I have my transportation, lodging and meals to pay for for three to five days at his location, he also had a tuition charge for me to learn to install HIS product.


08-20-2001, 03:26 PM
I wouldn't rule out the Nuheat product.Actually a 1/4" trowel is used to install the mat onto the thinset.I always trowel another coat of thinset over the mat(s) and start tiling the next day.If your floor is flat enough for tile you do not need to pour slc over the mats(which has been done with success)

John Bridge
08-20-2001, 03:42 PM
I know I said expansion, but I think I should have said "movement," and in the tile installation, not necessarily in the substrate.

I think the current recommendation is every 30 feet maximum for an interior installation, but that is not considering the heating and cooling that will occur in this situation.

Anyway, CB (is it Claire?), I'm not the best qualified guy in this case, because I have never installed tile over a heated floor. I would think, though, that doubling the standard recommendation for movement joints in the tiled surface would be prudent.

I also must iterate that a heated floor of the size you propose is very uncommon, so there won't be a lot of expertise anywhere. See what you've started? :)

And yes, I think we should move this to the Hangout. Let's give everyone a chance to read this, though. Then we'll move it.

08-20-2001, 04:15 PM
Ron, I wasn't ruling out NuHeat, I was ruling out using it with a SLC. Your comment about using it with the mat very interesting, no floatation problem?

BTW, interesting note, according to NuHeat this is not an acceptable product in a commercial venue, not sure what constitutes a commercial usage.

[Edited by flatfloor on 08-20-2001 at 06:21 PM]

08-20-2001, 04:49 PM
If you've ever read their warranty requirements,limitations and such,they really make sure that they are covered.I wouldn't hesitate to use it in a commercial application.My father and brother have been selling and promoting Nuheat since the late 80's(they are importers and retailers of tile)in Toronto and have had nothing but success with this product.Personally I like the idea of the separate wire systems since it is less expensive,more versatile and I actually enjoy the challenge and the pride that is involved in installing full mud beds reinforced with 2x2 mesh.
But Nuheat is the only heating system I install since my brother's store sells only their product.
I think maybe the reason they don't encourage the use of their product in commercial applications is the cleaning factor.Offices and such usually have janitors that saturate the floors with dirty water and various chemicals which may attack the integrity of the wires.

John Bridge
08-20-2001, 04:58 PM

Sounds like you know more about this than a lot of us. Will you please address the expansion and contraction aspects of a floor 400 sq. ft. in area? Don't know the actual dimensions. And is a floor this size common?

08-20-2001, 05:36 PM
Don't know the width and length of each room but I would assume that the kitchen,living and dining room are together.I don't particularly like the look of expansion joints in the middle of a room but I know that 10 years later they will be worth the extra effort,and you'll appreciate them more.If they are done with some planning and with the right products,they really don't stand out too much.
I try to keep them in doorways if possible.If the room is longer than 20 feet then,yes,it is necessary to incorporate a joint somewhere.I use the ones from Schluter that are installed with the tile.If she is having a floor pumped in or a mud bed done,definitely a perimeter expansion joint should be installed first.These could be a foam type or the really nice ones from Schluter.If the use of expansion joints is necessary in the middle of the rooms then these must be incorporated in the mud bed,slc and also the tile.It would get pretty technical then but if done properly you'd have a heated(or not) floor that will last indefinitely.

CB I don't think you would need to heat the entire floor though.I think you should choose areas where you want the heat.This way,especially using the connecting Nuheat mats,it would be cheaper to buy and to run.
Did a 100 s.f. bathroom with it,the electrician there said it would cost about the same as running 2 60 watt bulbs all day.

08-20-2001, 05:50 PM
24' to 36' interior.

08-20-2001, 09:03 PM
Wow, what a great thread. Thanks to all for the input. I met with my builder tonight and finally have a set of plans. I'm thinking that I have the following options:

(1) No one in this area does mud (too bad, huh). The electrician will do the electric cables and the tile guy said he can do the SLC. He mixes it in a bucket. I thought we would need a truck to mix and pump it in because of the large area. He said no, he's done areas this large before, and it's not a problem. I will get a quote from them for this.
(2) I'm going to send the plans to NuHeat and see what the mats would cost.
(3) If the first two options are cost prohibitive to us, I'm thinking of only doing the radiant in the baths, covered porch, and kitchen. I would then do wood in the dining and family room.

08-21-2001, 05:03 PM
CB, your tile contractor is correct, on a project of your size it is normally mixed in a barrel about the size of a 30 gal. garbage pail and mixed with a drill, usually two bags at a time. The material starts to harden in about 15-20 minutes and 2 hours later you can walk on it. Just make sure it's a Portland based material. Good Luck!

08-23-2001, 08:52 AM
John Bridge saw my post (follows) on DoItYourself.com and notified me of this discussion thread.

For the benefit of CB, I can say that I am very happy with the tech support I have received from WarmlyYours (the manufacturer of the floor heater I am installing). I bugged them three or four times before even making the purchase and once or twice afterwards. I found the price to be reasonable for the grid system. Of course, I only bought a small roll - roughly 12 sq. ft. of coverage (it's a 1.5' roll, 8' long, w/4' run , one twist of the roll ). I had the electrician run the new 15 amp circuit, but I actually wired up the thermostat myself and did the advised circuit testing with the multi-tester. It wasn't that hard.

My concern is that if I go with more thinset to fill the areas left undone before even starting laying tile, I am going to have a hard time getting a decent level surface -- I mean, I can't really lay my level down into the thinset to get a reading -- I suppose I could tape it to the top of a scree. But this seems dicey to me. If I go with SLC, how much working time would I have to set the tiles directly into the SLC? Or should I use mortar to set the tiles? (All discussed below). Can I even have different layers in the same floor? Will the added heat cause different expansion rates (enough to matter)?

I don't want to move away from CB's concerns -- it's her post. Though I do think she may be interested in the answers. I do know that with 900 sq ft, you are talking about several "zones" and many separate circuits. You might consider just heating traffic areas and leaving "cold spots" under the dining room table, sideboards, etc. to save money on the grid elements where they wouldn't be noticed anyway. The temperature differential should not be that great. According to WarmlyYours, the heat doesn't travel very far and it is not rapid heating we are talking about - the tile and bed should be able to handle the drop off in temperature. (Again, that is my guess as a basic consumer who has done some research.)

My thread is at:

Original Post:
I am in the middle of a bathroom remodel where a contractor is doing most of the work. I am doing all of the finish work -- paint, light fixtures, etc. -- as well as installing a new tile floor and the vanity/top/faucet combo. The contractor is almost done, so this past Saturday I started laying the floor.

The existing floor was concrete slab/old layer of tile/newer layer of tile. Prior to the contractor starting, I had torn up the top layer of tiles using a floor buddy -- a nice shovel-like tool that really gets under the tiles. Most of it came up quick, revealing the old god-awful 1950s era yellow tile. The floor buddy couldn't make a dent in that layer, however. It must be set directly in concrete. (It was on the walls, too -- but all of the tile on the walls is gone and going to stay gone.)

Having to leave the tile in place, I am left with an uneven surface and was considering using self-leveling cement, but the package said "not for use in wet areas".

Oh, and did I mention that I am putting in an electric radiant heating grid (Warmly Yours) which is 1/8" thick and supposed to be covered by another 1/4" of mortar (so 3/8" layer total). But the grid only covers half of the floor (the toilet and vanity sit on the other half).

Mainly because of the warning on the self-leveling cement and partly because I liked the idea of doing a little bit at a time so I can work up the expertise, I went with a standard thinset/acrylic admix mixture. I scuffed up (wire wheel drill bit and palm sander) the yellow tile, layed out the heating grid and started working the thinset over the grid. Because the wires of the grid were an 1/8" thick, I had a ready-made guide for the thickness I wanted. It troweled out pretty well and I did a fair job of smoothing it. There are a few small ridge lines, but nothing terrible. The tops of the wires are just barely visible and the edge where it meets the rest of the yellow tile is feathered nicely.

My main question is what to do about the remaining 2' swath of yellow tile (3' wide of heating grid + 2 ' = 5' width (4' length from door to start of tub) of my tiny bathroom). I want a level floor when the tile goes on. Do I mix another box of mortar and use it to fill the remaining half of the floor (and the voids along the wall)? (Call this Option 1.)

Or is there a self leveling mix I can use in a bathroom that I can do the entire 20 sq. ft. area with at once, bringing the surface up to the 1/4" over the grid I need and set the tiles directly into that? (Call this Option 2.)

It seemed to me from reading the bag of self-leveling mix that I would have lots of time to work with the surface once it started to set up. Can I get all the tiles set in time? I'd have to start at the doorway and work out -- meaning I'd be putting my weight onto freshly set tiles (but I could kneel on a shelf board or something to distribute it). Do you butter tiles with self-leveling mix? Or just give them a good twist?

My concern with thinset is that I won't be able to level the floor properly if I have to work in small sections.

I am considering using a thin layer of self leveling over the current grid and mortar (another 1/8") and thicker in the other parts of the floor, letting that cure, then going back with a skim coat of thinset, buttering each tile as I go. (Call this Option 3.) But the resulting Oreo cookie layering has me concerned.

Which approach can you recommend? Any hints for what I should see along the way? (Especially if I go all self-leveling -- what consistency/tackiness should I be at when setting tile?)

Many thanks for the assistance.

08-23-2001, 10:41 AM
Sorry, slc cannot be used as a setting bed. The material will start to harden within 15 minutes. Not only that it is the consistency of, say a pancake batter, and as you put tile into it the tile weight will displace the slc. What you could do is use the slc for it's intended purpose, leveling the floor, using enough material to cover the wires. After 24 hours use thinset to set the tile.

As far as not using an slc in wet areas, it should not present a problem if it is a Portland cement based product. I suspect that the one you are looking at is gypsum based and that is a whole other can of worms.

08-23-2001, 02:00 PM
OK. Good to know. Any foreseable problems in using SLC to surround the existing mortar/heater "island" and bring the whole floor up to consistent height? If there is a thin layer over the heating elements, will it expand at a significantly different rate than the thinset that would be above and below it?

08-23-2001, 02:15 PM
No & no to be very plain and simple. Good Luck!

John Bridge
08-23-2001, 03:28 PM
Jim, modest and shy as he is, didn't tell you he is actually a SLC manufacturer. Even though I'm not experienced in radiant heat, I know that SLC is the way to go in a small area.

Bud Cline
08-23-2001, 04:32 PM

I'm just curious.....

What's the variance between the top of your heating improvement and your existing subfloor? Did I miss this information somewhere?

Dave Gobis
08-23-2001, 04:50 PM
Jim, I really would like to save myself from typing a response to the perimeter issue but would be glad to discuss it. I am at 864-222-2131. As for expansion joint recommendations let's see if this works......
EXPANSION JOINTS ( Movement accommodation joints )

Vertical & Horizontal
Joint Design Essentials EJ171

Use these details for Control, Contraction, and Isolation joints.

Design: Expansion joints are essential for the success of most tile installations. Various methods require proper design and location of expansion joints as shown in Method EJ171 below.
Because of the limitless conditions and structural systems on which tile can be installed, the Architect, or Designer, shall show locations and details of expansion joints on project drawings.

It is not the intent of this guide to make expansion joint recommendations for specific projects. Architects must specify expansion joints and show location and details on the drawings.

Materials: Expansion joint sealants include silicone, urethane and polysulfide. Generally, urethane sealants are recommended for expansion joints on exterior vertical surfaces and for expansion joints on both exterior and interior horizontal tile surfaces. Because of their abrasion and penetration resistance, urethane sealants are recommended for expansion joints in tiled traffic areas.
Silicone sealants may be used in expansion joints on both exterior and interior vertical tile surfaces. One-part mildew-resistant silicone sealants are formulated with fungicide for sealing interior joints in ceramic tile showers, around tubs, sinks and plumbing fixtures.
Sealants are available in both single and multi-component formulations. Either formulation is generally suitable for expansion joints in tilework. Single-component sealants are furnished in
pre-packed cartridges, or other forms requiring no job-site mixing. Multi-component sealants require job-site rnixing, but cure faster than single-component counterparts, making them advantageous for traffic areas.
Sealants should comply with ASTM C920 as described below in Method EJ171, Materials.

NOTE: Preparation of openings left by the tile contractor and installation of back-up strip and sealant should be specified in the Caulking and Sealant section of the job specification.

(insert drawings)

· interior — 24' to 36' in each direction.
· exterior — 12' to 16' in each direction.
· interior tilework exposed to direct sunlight or moisture — 8' to 12' in each direction.
· where tilework abuts restraining surfaces such as perimeter walls, dissimilar floors, curbs, columns, pipes, ceilings, and where changes occur in backing materials.
· all expansion, control, construction, cold and seismic joints in the structure should continue through the tilework including such joints at vertical surfaces.
· joints through tilework directly over structural joints must never be narrower than the structural joint.
Expansion Joint Width (Vertical & Horizontal):
· exterior (all tile) — minimum 3/8" for joints 12' on center, minimum 1/2" for joints 16' on center. Minimum widths must be increased 1/16" for each 15Ί F tile surface temperature change greater than 100Ί F between summer high and winter low. (Decks exposed to the sky in northern U.S.A. usually require 3/4" wide joints on 12' centers.)
· interior for quarry tile and paver tile — same as grout joint, but not less than 1/4".

· interior for ceramic mosaic tile and glazed wall tile — preferred not less than 1/4", but never less than 1/8".
· tile edges to which the sealant will bond must be clean and dry. Sanding or grinding of these edges is recommended to obtain optimum sealant bond.
· primer on these tile edges is mandatory when recommended by the sealant manufacturer. Care must be taken to keep primer off tile faces.
· back-up strip shall be a flexible and compressible type of closed-cell foam polyethylene, butyl rubber, or open cell and closed cell polyurethane, rounded at surface to contact sealant, as shown in details above, and as recommended by sealant manufacturers. It must fit neatly into the joint without compacting and to such a height to allow a sealant depth of 1/2 the width of the joint. Sealant must not bond to the back-up material.
· suitable sealants include silicone, urethane, and polysulfide. Generally, urethane sealants are recommended for exterior vertical tile surfaces and both exterior and interior horizontal tile surfaces, including tiled traffic areas. Sealants in traffic areas require a Shore A hardness of 35 or greater.
· silicone sealants may be used on both exterior and interior vertical tile surfaces. Single component mildew-resistant silicone sealants are formulated with fungicide for sealing interior joints in ceramic tile showers, and around tubs, sinks and plumbing fixtures.
· use sealants complying with ASTM C920, which designates sealants according to Type, Grade, Class and Uses. The following are suitable for use in tile work.
· Type S — single-component sealant.
· Type M — multi-component sealant.
· Grade P — sealants for joints on horizontal surfaces.
· Grade NS — non-sagging sealants for joints in vertical surfaces.
· Class 25 and 12½ — identifies sealants which can withstand an increase and decrease of +/-25% or +/-12½% of joint width.
· Use T — use in joints subjected to pedestrian and vehicle traffic.
· Use NT — sealants for nontraffic exposures.
· Uses M and G — sealants that will remain adhered to mortar (M) and glass (G) are suitable for use with tilework.
· some sealants require edge priming. Consult manufacturer' s specifications.
· manufactured/pre-formed joint profiles are available. Consult manufacturer.

Cold Joints

(insert drawing)
Cold Joints:
· cold joints are formed primarily between slab pours where the size of a concrete slab may be too large to be poured at one time. The remainder of the slab would be poured at a later time forming a cold joint between the two sections. Such joints should be shown on architectural drawings.
· a cold joint becomes a weakened joint that upon movement will crack, permitting leakage or buckling and cracking of a tile floor set over the slab.
· some large slabs on grade are poured monolithically, then later saw cut at intervals providing control joints to allow for cracking at these weakened points.
· expansion joints in tile should be located over all cold joints and saw-cut control joints.
· joints in tile and setting materials shall never be less than the width of the saw-cut control width. Preparation and installation shall be as required for expansion joints.
· to insure that location of joints in tile work align with existing joints in substrate, joints in tile work should be constructed during installation of mortar beds and/or tile, rather than saw-cutting joints after installation.
· keep expansion joint cavities open and free of dirt, debris, grout, mortar and setting materials.
· set compressible back-up strip when mortar is placed or utilize removable wood strip to provide space for back-up after mortar has cured.
· install sealant after tile work and grout is dry. Follow sealant manufacturer’s recommendations.
· refer to sealant section in ANSI tile installation specification.

NOTES: In very small rooms (less than 12’ wide) and also along the sides of narrow corridors (less than 12’) expansion joints may not be needed.

The performance requirements of certain special locations, such as exterior swimming pools, dairies, food plants, etc., may exceed the minimum requirements of the sealant specifications given above. Therefore, follow recommendations of experienced manufacturers as to specific sealants suitable in the job environment. In some severe environments a program for regular maintenance of sealant in joints may be required.

Architect must specify expansion joints and show location and details on drawings.

All specifications for ceramic tile installations must conform to local building codes, ordinances, trade practices and climatic conditions.

Copyright 2001 Tile Council of America, Inc.

Rob Z
08-23-2001, 07:34 PM
Now THAT'S a post!

Bud Cline
08-23-2001, 07:42 PM
Yeh but what do you mean Dave?

Dave Gobis
08-24-2001, 04:37 AM
I cheated, cut and paste.

Thats why I know I will always have a job, Hear that a lot.

08-24-2001, 08:37 AM
OK... now that the experts have weighed in (for which I am grateful)... I'm going to pour just enough SLC to cover the remaining old tile bed, and to just cover the mortar/heating elelment layer I've already layed down. That will be on Saturday. Then I'm going to go see a movie while it sets. On Sunday, I should be able to start laying tile on my now perfectly level floor, using a skim coat and buttering technique.

Now if I read the expansion joint manifesto correctly, I should not have to worry about my small installation (20 sq ft), but I should put a silicone sealant bead at the edges where it meets the wall (and tub along one side).

LAST QUESTION: Do I put this sealant at the edges of the tile alone, or do I need to shim out a 1/8" perimeter before pouring the SLC and caulk that gap too? (I was sort of thinking of shimming out from the tub, anyway.) If so, what's the best material to use to shim out with so I can easily pull it out once the SLC has set?

Thanks again.

John Bridge
08-24-2001, 02:36 PM
Well, you know, it wouldn't hurt to tack corregated cardboard around the edges before you pour. It'll keep the stuff from getting on your walls/baseboards. Then when the stuff has set (after the movie), you could trim the cardboard down to the level of the slc with a razor knife/utility knife. Why not, eh?

Bud Cline
08-24-2001, 03:36 PM
I've done that John and it works really good. Cardboard (corrugated) can also be glued to the tub. A little water later dripped along the top of the cardboard after trimming it flush with floors surface will allow you to remove (dig out) the cardboard so that a more permanent and waterproof caulk or silicone can be installed.

Dave Gobis
08-25-2001, 10:21 AM
Sill seal is my favorite.

John Bridge
08-25-2001, 12:41 PM
You gonna tell me what sill seal is, or are you gonna make me show my ignorance by having to ask? C'mon, Dave. I've got a lot of people convinced I know everything. ;)

Dave Gobis
08-25-2001, 01:13 PM
Thats why your the meister and we are but your serfs. Sill seal is the 3/16 or 1/4"x 8",10",or 12" foam band they normally lay on block before installing the sill plate which would be the bottom plate of the floor sytstem around the house. Comes in varying widths. I usually tack it on the wall when I mud and cut it off when I finish. Keeps you from hitting the wall with the trowel and provides a movement joint for the opposing stresses of the floor and wall. Works especially well when the wall plate ends up off the joist. The mud doesn't get hooked up in the bottom at the edge of the drywall and stud and will let the wall go if it wants to. Are you telling me this is strictly Yankee construction? They have us bolt our houses down to the foundations in many areas. Depends on local code.

John Bridge
08-25-2001, 02:03 PM
Well, I haven't worked on a new house in so many years I can't remember, except for the couple of "castles" we work on each year exclusively for one builder. By the time I arrive on the scene all that has been handled. The only thing I recall seeing is the yellow foam all over the place, peeking out from under the drywall sometimes.

Way back when I was building houses, we'd bolt down treated bottom plates over a bead of construction adhesive (the black stuff).

Anyway, sounds like a winner.

08-25-2001, 05:28 PM
Dave, do you remember you had mentioned Sill Seal to me? I went crazy looking for a Mfr. named sill. Thanks John, now I feel better.

Dave Gobis
08-25-2001, 08:46 PM
Give me a call and we can talk about it. I am actually going to approach this subject in conjunction with some other SCL's at technical committee meeting Sept. 18 in Nashville. Headed to WI tomorrow. 262-752-0223 till Thursday PM. Then I am on vacation for a week.

10-05-2003, 11:34 PM
Hello Flatfloor
I am doing a similar project, however am using tubing from my boiler in the floor. I have a concrete slab for a foundation /floor, and have allowed 2 inches for the pour with the tubing in it.
Like CB I was told to use gypcrete but have found no one in the Rochester NY area who does it. Could you tell me the mix for the SCL, and how one goes about having it poured (does it come in a cement truch and out of the chute like regular concrete?)
thanks for your help in advance

10-06-2003, 05:48 AM
Welcome to the forum, Batffp14! Got a real first name?

I don't think anyone here will like tileing over gypcrete, and SLC is very expensive, so you probably ought to be thinking concrete or deck mud for your fill. Your local concrete company should be able to help you with a good mix for your application. The Mudmen here will help you if you decide to mix and place the mud yourself.

Give us a few more particulars about your project, and the pros will jump in with some more comments.


10-06-2003, 05:53 AM
Call Maxxon corp at 800-969-5977. They are the maker of the
Therma-Floor gypsum underlayment I am having installed thoughout our house except for under the shower and tub.

www.maxxon.com (http://www.maxxon.com)

-Peter D

10-06-2003, 06:59 AM
Thanks Bob
I'm Darrin
Well as I said it is a concrete base in a 13' x 16" room which will be a masterbath and master closet. I will tile the floor, and carpet only in the closet area. The rest of my home has radiant floor head. It must have been done with copper since the house was built in 1951, and I'm fairly certain it wasn't an add on later. I love this heat, and with the concrete slab to radiate the heat out slowly , my boiler runs very little. I want to continue this in the new additon I mentioned, and the add it to 2 rooms which were definately additons since they are on a different heating system. the floors in those rooms are concrete as well.
I like the slurry/self leveling propertiesso that I have a nice level base for the finished flooring, and was just wondering if I had an idea of the mix I could discuss it with one of my local concrete distributors.

10-06-2003, 07:00 AM
Thanks Bob
I'm Darrin
Well as I said it is a concrete base in a 13' x 16" room which will be a masterbath and master closet. I will tile the floor, and carpet only in the closet area. The rest of my home has radiant floor head. It must have been done with copper since the house was built in 1951, and I'm fairly certain it wasn't an add on later. I love this heat, and with the concrete slab to radiate the heat out slowly , my boiler runs very little. I want to continue this in the new additon I mentioned, and the add it to 2 rooms which were definately additons since they are on a different heating system. the floors in those rooms are concrete as well.
I like the slurry/self leveling properties so that I have a nice level base for the finished flooring, and was just wondering if I had an idea of the mix I could discuss it with one of my local concrete distributors.

10-06-2003, 05:15 PM
Hi Darrin, SLCs cannot be mixed onsite. They require chemicals which are not available to redi-mix companies and have to be mixed in a controlled environment.

Bob is right, for a 2" deep pour they would be cost prohibitive for the average DIYer.

We came up with a mix for one of our moderators who was doing an entire house in radiant. I'll see if I can find it.

Whatever you do stay away from gypsum products.

10-06-2003, 08:26 PM
Thank you Flatfloor
I'll look forward to the mix you have when you can find it.
And don't worry after reading this forum , gypcrete is off my list.
thanks again
hope to hear from you soon

John Bridge
10-07-2003, 05:38 PM
Hi Darren,

Jim's still licking his wounds over the NFL on Sunday. May take him a while. Shoot him an email if he doesn't show up promptly. :D

10-07-2003, 05:49 PM
John, while you're busy verbally (or is that scripturally) abusing me I have been feverishly searching for Cami's thread where we came up with a formula for her house. Any idea where it might be?

10-08-2003, 06:30 PM
Darren, I searched .....a lot, couldn't find the specific thread. :(

Get a 3,000 PSI mix with 3/8" pea gravel and fibre reinforcement that will do it.

10-10-2003, 01:13 PM
Ok so all the experts state do not use gypcrete under tile. But no one explained why it isn't suitable. So why not??

10-10-2003, 01:56 PM
there can be a chemical reaction between the Gypsum and the thin set causing the tile to uncouple or disbond.That is why most reccomend a membrane be used.

10-10-2003, 03:16 PM
If I where to seal the gypcrete with what ever the gypcrete manufacturer recommends and then use Ditra, will this be OK?

10-10-2003, 03:41 PM
Go straight to the source, Westie. :)

Schluter will tell you everything you need to know about Ditra.

Eric (e3) can tell you everything you need to know about the Noble membranes.

10-10-2003, 05:25 PM
If you happen to have Hacker Industies based gypsum, NobleSeal is reccommended, and you can bond the sheet with NobleBond 21 adhesive.Either way the Gypsum should be sealed,but you can keep the bond to a single source.Maxxon the other major mfg. of Gypsum pours will also allow Nobleseal and others.

10-10-2003, 05:53 PM
Allow? :shades:

Eric, not knocking you or Noble or anybody else but it gives them a great place to shift blame.

10-13-2003, 05:11 AM
My HVAC contractor gave me a recipe for a 1 cubic yard of 3000 psi @ 28 day concrete topping from the Radiant Panel Association

Type 1 Portland cement: 517 lbs
Concrete sand: 1639 lbs
#1A (1/4" maximum) peastone:Air entrainment agent:1485 lbs
Hycol (water reducing agent): 4.14 oz
Fiber mesh: 1.5lbs
Superplasticizer (WRDA-19): 51.7 oz
Water: about 20 gallons

Coverage is about 200 sq ft of floor per cubic yard at 1.5" slab thickness.

This mix add about 18 lbs per sq ft to the "dead loading" of the floor it is installed on

I can fax a copy of the page my HVAC contractor gave me and it might be worth adding to the library.

-Peter D

10-13-2003, 06:10 AM
For those following this thread
From Floor Covering Installer's Joe Grady Tech Expert in the october issue
Gypcrete and ceramic tile
"The use of an isolation membrane or a special flexible bonding agent is reccomended.A variety of products are approved by membrane manufacturers two examples of which are Noble companys sheet membrane(he doesnt state which one) and Bosticks liquid urethane bonding adhesive.
Another important point worth noting is that when using portland cement thinset morters a chemical reaction known as ettringite may occur.The reaction can take place rather quickly or develop years later Ettrengite has an expansive effect which causes disbonding.As a safety measure before you proceed with the installation,you can apply an acrylic skim coating followed by a skim coating of portland cement morter.The alternative would be to use the membranes and bonding agents mentioned above.Before you use any product,make sure the manufacturer's approval is forthcoming."

John Bridge
10-13-2003, 05:28 PM
I do not like GypCrete or other lightweight concretes (sic). However, Schluter does write a spec for Ditra over the stuff.


This is one case where it seems a membrane applied with something other than thin set might be in order. Here's your lead-in, Eric. You'll never get a better shot. :D

12-30-2003, 11:11 AM
I welcome input and feedback on this... We have been installing tile over Gypecrete directly on Townhouse projects for years. If the area is less than 20 sf (small enties or baths) we have had good results. This is not recommended however and when we get into larger areas, (the few we have done under pressure to save money by the builder), and have not used an anti fracture membrane have had mixed results... no huge failures but some fractures have caused tiles to crack in isolated areas.

For custom homes with in floor heat the best solution we have found to date is a membrane called Toray Prolayment CS. It does have a small R factor which is not ideal for in floor heating but the benefit of no failures far out weigh that. It also has good IIC and STC sound deadening qualities. It costs .25 - .50 per sf (depends how much you buy) and is a fast install. Comes is rolls 4' wide and is 1/32" thick. I won't do large areas without it anymore. This costs much less than Ditra which is overkill unless you are doing a a commercial project with large loads or car dealership and they plan on driving on the tile!

John Bridge
12-30-2003, 04:22 PM
Hi David, Glad to have you aboard. :)

Looks like good stuff, but I don't see where they intend it for ceramic tile installations. Pulled this off the web site. http://www.torayfoam.com/prolaymentSB.html?PHPSESSID=3d489b82cf4363f12fc0e8b29f8a77de

"ProLayment ™ SB is part of Toray Industries new revolutionary line of underlayment foam for the floor covering industry. This cross-linked polyolefin underlayment is the ideal material of choice for sound control & moisture barrier protection under hardwood, laminates, and resilient flooring."

How long has it been around?

12-30-2003, 05:22 PM
Hi David & John.

I am sorry the Toray web site is not updated to include ProLayment CS, which is designed for tile. The SB product is for laminates and hardwoods. There is more information at my site; advancedtile.com I have been working with this manufacturer for many years to develop this.

This product has been in place for over three years now as I was the first to use it for this purpose. I have installed over 100,000 square feet of this stuff and it works like a champ. We gained a heavy rating on the "Robinson" test and a 54 IIC over concrete.

I would be happy to provide more information on this product.

Kurt Todd
Advanced Floor Systems, Inc.

12-30-2003, 05:28 PM
Hi John,

The link for the ProLayment CS is at the bottom of the page you linked. Here it is though.


John Bridge
12-30-2003, 05:32 PM
Hi Kurt,

Fire away. :D We're happy to hear about new things. Some of the old farts around here get a little rusty. :D

Please start a thread in our Pro Hangout, though. You'll get more of the full-time tile and stone people there. Newbies are welcome too, though. ;)


01-13-2004, 11:34 AM
mudmeister, been out of town so late reply. Prolayment CS is the product not SB which is for wood floor or laminate floor sound mitigation. Go to the Austrailian web site to get info, the american site does not have it!

01-13-2004, 11:37 AM
oops, should have read all the postings since last on.... started quite the discussion I see.