First ditra project [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-12-2011, 07:36 PM
Does deflectolator take into account other factors that may affect floor loading? I am redoing my kitchen with tile as the floor finish. I am sistering every joist to get the proper deflecto rating, but I am concerned about appliances, high end cabinets, and granite counters. I am thinking that I should triple the joists at the refrigerator and under the cabinets of a peninsula that extends 6 ft from the outside wall and is parrallel to the joists. I am planning to use Ditra and a floor warming system. Any input from the pros will be greatly appreciated. Thank you in advance.

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07-12-2011, 07:45 PM
Welcome back, jpyle. Please put a first name in a permanent signature line for us to use. :)

The Deflect calculates deflection based upon customary residential code requirements of ten pounds per square foot dead load and forty pounds live load. But it is very conservative in that it uses the combination of the loads rather than only the live load.

Nothing you mentioned would be likely to exceed those loads, but we'd need to know more specifics if you think you have an uncommon situation. With the information at hand, I can't tell if you need to sister your joists to achieve the required L/360 or not.

The subflooring is generally more of a problem than the joist structure, but again, without more information we can't determine where you stand on that, either.

My opinion; worth price charged.

07-12-2011, 08:30 PM
What CX said.

What is the joist size, spacing and maximum unsupported span? What material is above the joists, what grade & how thick? How is it installed?

How big & heavy is the refer? and the range? Are they both next to walls? What type of counter top material? What c.t. material on the peninsula? :)

07-14-2011, 06:31 AM
My name is Jerry. House was built around 1960. 2x8 joists on 16" centers. Only marking on old joists that I can make out is "CONST". New sistered joists are 2x8 from HD #2 DF. Sistered joists are bolted and glued with PL Premium. Maximum unsupported span is 11'5'.Subfloor is to be new 3/4 T&G plywood. Range weighs 155#. Refrigerator weighs 300#. Back of refrigerator is against the wall that is directly over the center girder of the house. Granite is about 19#/sqft. Tile to be 12x12 approx. 3/8 thick. Let me know if I forgot anything.

07-14-2011, 06:48 AM
Your joists would be good for a deflection rating of at least L/500, so you should be fine for ceramic tile.

Refrigerator: 300 pounds over a foot print of about 5 square feet is about 60 psf. It will be a problem when moving it back into the space, but after that, it really becomes dead load. This is the one object we usually worry about when telling folks when it is safe to walk over new tile or grout. As far as the subfloor is concerned, 3/4" plywood would be fine with a 300 lb point load.

Stove: No problem

Granite: No problem

07-14-2011, 08:16 AM
We'll often put plywood down over the tile before sliding the fridge around, so you're spreading out the loads over a number of tiles. Still need to wait until the mortar cures properly according to the manufacturers installation instructions, that can be found on their website or on the bag. :)

You can also use an air-sled type appliance mover, which rides on a cushion of air. The fridge never touches the floor til you get it in place. Might find one at a local rental yard. :tup1:

08-01-2011, 05:39 PM
Finished the floor reframing this weekend and got the subfloor in. Did sister in an extra joist at the four joists that are under the peninsula and fridge. Didn't want to worry about it. Now I am trying to find a thread on how the temp sensor in a floorwarming system gets installed in a ditra installation. Thanks for the input.

08-02-2011, 08:37 AM
Install the heat mat and sensor as if you were not installing Ditra. Two separate installations, follow each manufacturer's instructions without regard to the other one

09-12-2011, 06:17 PM
Am moving slower than expected(imagine that) and am just getting to the install of the floor warming system. I went with Flextherm's green wire. For ease of installation I am considering the install of the heat wire before the cabinet installation. My concerns are with the durability of thinset vs.SLC, and with getting the unheated areas(fridge,dishwasher,range) even with the wired area. The Flextherm gauges are 3/16 high. I am planning to dam up the areas under the cabinets with 1/4 inch material. Can I use this method to screed thinset mortar or is SLC a better option? Does the SLC need to be thicker than 1/16 above the gauges? Is thinset durable enough to work on to install the cabinets? Could I install the Ditra befor the cabinet install also? My floor is flat but is 5/16 out of level over 16 1/2 feet(done to minimize room transition). Is SLC accurate enough that I would lose the 5/16 difference(Iwould prefer not to)? I know I asked a lot of questions. Input on any of them will be appreciated. Thanks.

09-12-2011, 08:38 PM
After hours of searching over many days, finally found a couple of threads saying 1/2" min and lath for SLC. Too much buildup for me if this is correct. Thinset as per Schluter-Ditra D-RE-10 installation handbook looks to be the way to go.

09-13-2011, 04:24 AM
Jerry, to be sure, read the data sheet for the SLC you propose to use. They all have different minimum and maximum thickness requirements. That may not help, though, as lath will require at least 1/4 to 3/8" of SLC to cover.

09-13-2011, 06:47 PM
Watched the Flextherm installation video. Plywood, heat wires, primer, SLC, thinset,tile. Read the installation book. They defer to the manufacturers' instructions for other products used while installing Flextherm products.

09-13-2011, 07:21 PM
Was just reading through Andy's bathroom project#2. Is it acceptabe to use 1/4 inch hardie backer in the areas that do not get heated? Or should the product under the ditra be the same throughout? I also read some conflicting thoughts about working over a Ditra install before tiling. Does it make a difference if you prefill/skim the top of the Ditra after installing it?

09-14-2011, 04:17 AM
The use of backerboard in non-heated areas is to reduce the amount of SLC or thinset needed. Both have to be installed correctly. Once done (and done correctly), Ditra won't care which it is installed over.

Schluter doesn't mind if you pre-fill the waffles. The advantage is that you can more easily mark and see your layouts. The disadvantage is that some thinset remains on top of the waffles, and that flakes off easily when you spread you setting mortar.

10-17-2011, 09:06 PM
Does a Ditra installation give the tile a "hollow" sound? Ran intto a "tile guy" who told me that is what I could expect. Also, picked up the Ditra for my project and was suprised at the construction. The fleece to plastic connection seems like the weakest link in the installation. With all the discussion about bonding to the substrate and making sure the thinset is adhering to the tile, the ease at which thefleece can be pulled from the plastic waffles doesn't seem to jive. Anyone care to explain? Thanks.

10-17-2011, 09:15 PM
No hollow sound for me its not like a super dense sound like setting on concrete, but it works good i use it frequently no issues for me.

10-17-2011, 09:36 PM
Jerry, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered.

If you've installed the Ditra correctly, your hollow sound would likely be from another cause.

As for pulling off the fleece, install a test patch of Ditra as you intend to do on your floor and wait seven days. Then try pulling it off the floor. Think you'll find you meet with considerable resistance. Not to mention that your tiles will seldom try to pull themselves vertically off the floor, eh? :)

My opinion; worth price charged.

11-08-2011, 07:46 PM
Just to update my progress. Did floor warming system install 3 weekends ago. Finished wire install late Saturday night. Covered with thinset on Sunday. The screeding didn't go like I thought. I would describe it as to much drag by the aluminum straightedge. Did get everything covered with no real noticable high or low spots. The next day It seemed like the thinset had shrunk. There were depressions in the spaces between the wires. Decided to go over the floor with another application of thinset using a large trowel with firm pressure riding on the high spots(the lines formed by the wires). seemed to do the trick. Looked better. When dry I covered the floor with luan ply. Proceeeded to do cabinet install the following weekend. Finally got tile ordered and am ready to proceed with ditra install. Uncovered the floor again and it seems like shrinkage has left the areas between my screed surfaces slightly lower( 1/16-3/32 ). Do I need to refill these areas with another application of thinset? What is the flatness tolerance for a surface that is to receive an application of Ditra? Will the Ditra installation do anything to fill he low spots somewhat? What is the flatness tolerance for a Ditra surface that is to receive porcelain tile( 12x12, 12x6, 6x6 random pattern)? As a side note , it took 6 trips to tile stores for my wife and I to come to an agreement on the tile selection. It was so difficult I stopped looking at price and concentrated on selection. Got sticker shock when I placed the order. 175 feet ordered at $1400!

11-08-2011, 08:20 PM
Forgot to mention that I used Mapei Ultra Flex 2 thinset.

Houston Remodeler
11-08-2011, 09:15 PM
remember those low spots when you are installing your ditra and drag the trowel over those spots to bridge then so they get filled in when troweling. Install the ditra as usual.

Those large tiles will recieve the benefit of yet another troweling with an even larger notched trowel to ride those little dips just easily.

Separating your questions from the main body of your post and numbering them helps those of us with bad eyesight and short attention spans. Just sayin... :gerg: