Big Basement Challenge - Ceramic Tile Advice Forums

FredF · 08-30-2007, 09:46 PM

All,
I'm currently refinishing my basement and am planning to lay ceramic. I'm an avid DIYer but even this project seems daunting to me.

The basement is 42' by 26'. There is a concrete slab floor that is nearly completely uniformly level (1/32 valleys here and there). The foundation has several cracks that I have monitored for some time and are not expanding (The house is 25 years old-i think major foundation movements are unlikely.

I am planning on installing 18x18 ceramic tiles; but have not picked them out. I am also planning on installing thermosoft's (TS) thermotile heating element throughout the entire basement. According to TS, this will require 4 heating zones.

The slab has no expansion joints, and I've repaired the cracks that were present. I know that I will need to put expansion joints in the tile field b/c the field is so large. Recommendations on how many expansion joints are required are welcome.

My research has told me that my best bet is to hot glue the TT mats to the slab, fill 1/4" with self-leveling mortar, and then install the tile on top of the SLM. On another thread, there is a discussion of using a ditra product to de-couple the tile from the underlying slab (i assume because the expansion coefficient of the slab and walls is different and could cause cracking.

my room is essentially a rectangle with a 6x6 utility closet in the middle of the room. Can someone help with what layers/materials I should use to get the best installation possible?

I was thinking (from top to bottom):

Ceramic
thin-set mortar
self-leveing mortar
TT product
slab

Now I think I may need to add in a "de-coupling" and "moisture barrier" layer for this to be successful.

Also, since the tile field will require expansion joint(s), at what "layer" do I need to worry about these joints? (I know that at least the ceramic and top level of thin-set will need to have the fields compleletly isolated... what about the TT product?

Thanks!

T_Hulse · 08-30-2007, 10:33 PM

Hi Fred,
I also use the Ditra underlayment in a situation like this, especially when there are slab cracks. It goes right under the tile. Expansion joints go in the grout joint in place of the grout.

FredF · 08-31-2007, 07:45 AM

So, is this a complete strategy:

(From bottom up)

Slab
ThermoTile heating element (mats hot glued to floor)
Self-leveling mortar
Unmodified thin-set
Ditra product
----
Unmodified thin-set
Tile and Grout

** Items listed below the "---" must be separated with appropriate expansion joints because my tile area is 39x25. (Is this correct? Or, does the expansion joint need to go all the way through the ditra product and/or the heating element?

cx · 08-31-2007, 08:57 AM

Welcome, Fred.

I don't know how your heating system manufacturer wants you to deal with movement accommodation (expansion joinst, etc) for their products, and I think you should discuss it with them for a room that size.

Since you report no expansion joints in your slab, I presume that means no "control" joints, either?

You should review Schluter's requirements for "movement joints" in their literature. They are pretty specific on how they want each type treated, including dimentional guidelines for installations over heated floors.

If you are not honoring any expansion joints in the substrate, you'll generally not need to break the Ditra surface, but you can. Schluter has a product for treating such joints if you intend to waterproof the Ditra surface.

My opinon; worth price charged.

FredF · 09-03-2007, 06:53 PM

I'm planning to install radiant flooring under a large field of tile in a basement (900 sq. ft.) The vendor of the radiant floor is thermotile, and they recommend (require) installation under a floor with an r-value no higher than 1.0. I plan to install ceramic (r-value est: .15), and would like to put large area rugs on the floor. Has anyone installed an electric radiant heat product and put area rugs on top of it? Are there ways to determine the R-value of a rug? I'll take any advice on the subject.

(Yes, I've already e-mailed thermotile and am awaiting a response).

e3 · 09-03-2007, 07:02 PM

never heard of thermo tile....but i would think a rug would be higher then 1.

flatfloor · 09-03-2007, 07:17 PM

I tend to agree with Eric. The material the rug is made of will tell you more than anything.

dnlblank2 · 09-03-2007, 07:25 PM

It depends so much on the rug.

John Siegenthaler lists the following in the Appendix to Modern Hydronic Heating.

1/4 inch nylon level loop R=1.36
1/2 inch polyester plush R=1.92
Foam padding 8 lb. density R=4.4 per inch

The padding really gets you on the R value.

If you don't have Siegenthaler's book you might want to give it a read. You might find it at the library of a trade or technical school.

David

cx · 09-03-2007, 07:30 PM

I dunno, I've heard of carpet with R values as high as 2. Without the pad.

Could be rugs that high, too, I would guess.

You trying to heat the room with this radiant floor, Fred, or just warm your tootsies? Seems like if it's just to keep from walking on cold tile, you could save a lot of dinero by eliminating the heating system and using the rugs, eh?

My opinion; worth price charged.

Young David's quick, eh?

FredF · 09-05-2007, 10:51 AM

I'm posting this just in case someone is later reading this thread after searching for radiant flooring, area rugs, r-value, thermotile, warmlyyours, etc.

The sales folks at ThermoTile wrote me back about the area rug issue. While the installation demands flooring with an r-value of 1.0 or less, the thermotile product passed UL testing with an r-value of 11. The manufacturer recommends not approaching this limit with anything sitting on the floor; but taking a margin of safety of 50%, that would give you r 5.5. I've found some indexes of common r-values. Looks like absent other information, wood has an r-value of 1 for every inch of thickness. Carpets are generally rated by multiplying 2.6 times the thickness of the carpet.

---
CX, I am using the radiant heat as the secondary source for heating in this space; but have experienced tile in a basement in a baltimore winter-even with a decent amount of forced air circulating in the room. My experience is that the tile is frigid...

FredF · 09-05-2007, 10:52 AM

David,
Thanks for the info on the book; I'm going to check it out online. If you're interested, my previous follow-up post had some information.

FredF · 09-05-2007, 10:57 AM

CX,
Thanks for the info. Schluter recommends expansion joints every 12' to 16' in all directions on top of Ditra. ThermoTile suggests using a latex-modified grout for the entire application; haven't verified this with Schluter yet, but I plan to discuss with them.

JTG · 09-05-2007, 01:01 PM

Fred.
If you use the Ditra try and get Ditra Set mortar. When you use tile that are that large with Ditra you will want to use this mortar or a non latex modified mortar or it will take forever for the mortar to dry.
Remember that 18x18 tile are not easy to set if the substrate has ANY bumps, waves etc. so you want FLAT
For getting self leveler on the area as large as you have I would look to have a company that does this type of thing come in and do the pour or you are going to be fighting a mix and pour battle that if you start to fall behind is going to lead to an uneaven floor. You will need lots of help to keep everything moving from start to finish.
Compare the cost of doing the self level with using a mat heating system such as Nuheat. A system that you wouldn't need to pour a self levelor over.
Good Luck
JTG

FredF · 09-05-2007, 01:16 PM

Jerry,
Thanks much for the advice. We have been considering the challenges of pouring that much SLC. I'll take a look at getting a contractor as another option.

FredF · 09-07-2007, 09:11 AM

All,

I'm going to be pouring SLC over an electric radiant flooring installation. I'm a DIYer - this will be my first attempt at radiant flooriing, and my first experience with SLC - needless to say, I'm a bit nervous.

The Home Depot by my house carries a product called LevelQuik for about $29.00/50lb. bag. I'm doing a large area, and will need to buy many bags, so price/unit is a concern.

What's the best brand of SLC for price/quality? Any better places to shop other than HD to get the stuff? I also have a Lowes/84 lumber nearby and haven't checked either yet; but suspected it would be close to Depot's price.

Why is SLC so expensive?

Fred