John,

STOP! :eek: I believe you misunderstood what the Schluter rep meant. You MUST use modified thinset to install Ditra to plywood. Actually they always say,paraphrasing... " use a thinset appropriate for the subfloor type".

If you used unmod to set Ditra to plywood, you will not be a happy man the next day.

Use unmodified thinset to install your tiles to Ditra regardless if it's regular ceramic, soft bodied tiles or porcelain.

Schluter recommends a 3/16x1/4 V OR 5/16 V to install Ditra. That is a big leeway, and I never thought the smaller trowel left enough and so I cut bigger grooves in my trowel with the second installation I did many years ago. A few years ago they added the 5/16" recommendation.

Jaz

Thanks for clarifing that for me. Now looking through the Ditra manual I see that is says to use a latex Portland cement.

So I should go with the 5/16 V for applying the ditra?

When they say Fortified mortar, does that mean the same as modified?

Yes, use a 5/16" if you can find one. Otherwise cut deeper grooves in the smaller V. Some pros even use a very worn out 1/4x1/4 square. Try it on the first piece, spread, beat the Ditra into the thinset with a wood float, then lift the Ditra and check for thinset transfer. Modified, fortified, enhanced, enriched, etc. will meet or exceed A118.4 Unmodified will meet A118.1 It should say so on the bag. Do not buy the cheap unmod from the orange place even though it does meet minimum specs. We do not like to meet minimum requirements.

BTW, what brands of thinset are available where you are?

Jaz

Not sure of the brand names but the unmod I bought was $18 for 50 lbs and the modified is $31 for 50 lbs

I got the modified Mortar the name is Mapei KER 121 Proffessional grade polymer Modified Mortar.

Please let me know if that is the right stuff.

1. Another question I have is that I will be tiling my shower with 10 X 13 tiles. Can I use a regular unmodified thinset. They will be laid onto backer board.

2. I will also be laying tile half way up one of my walls. This will be applied on gyp. Does the gyp need to be primed or can I go right over it. Either way what thinset do I need to use there?

3. I will be doing a tile baseboard. Do I need to put an expansion joint between the floor and baseboard? Or can I just caulk the joint with silicone?

thanks

KER 121 is fine, yes it's modified and works well over most surfaces including plywood.

1. Although unmodified will work. All CBU manufacturers that I know of recommend modified.

2. When you say Gyp do you mean pure mud Gyp you apply and smooth out like plaster? Or do you mean wallboard?

3. The floor tile goes in first leaving a gap to the wall. The base sits on the floor tile, well leave a small gap and caulk that joint. I wouldn't use silicone, I recommend either a siliconized acrylic or acrylic caulk made by the grout maker which matches the grout.

Jaz

Quote:

---

Originally Posted by JazMan

2. When you say Gyp do you mean pure mud Gyp you apply and smooth out like plaster? Or do you mean wallboard?


Jaz

---

Wallboard

OK, wallboard, that is not gyp, the gypsum is under the paper. Either type of thinset will work, modified is better but?

This shower you're building, how is the base going to be built?

Jaz

Quote:

---

Originally Posted by JazMan

OK, wallboard, that is not gyp, the gypsum is under the paper. Either type of thinset will work, modified is better but?

This shower you're building, how is the base going to be built?

Jaz

---

The base is a premade bade by MaXX

Ok guys another question.

I was told in a previous post that I can go with an unmodified thinset when laying tile over wall board. But I want a proper intsall, in this case should I go with Modified or will the unmodified work just as well?

In the shower I am using Fibrerock Aqua tough tile backerboard. In their literature it only states the following "Type I organic adhesive or latex fortified mortar" I am assuming this means that if I go with a thinset that it has to be modified?

Thanks for the help

For your shower walls, use only modifed thinset. Organic adhesives are fine in non wet areas, but not with the tile size you've selected. Seeing as how you have Mapei products available to you, while any mapei modifed thisnet will do, Ultralight is a nonsag thinset and they are great for working vertical surfaces as they have the grip and gravity resistant properties that make mastics popular with hack installers. Otherwise, just find the low point of the room, measure up the size of the tile, 1/8" for caulk at the bottom, and the size of a grout joint and then mark a level line around the room. Tack a ledger board to the line and use that to support your tile as you work up and once that sets up, remove the board and cut in your bottom row of tile around the room and the shower.

I don't know if this was touched on because I did not read through the entire post, but you do want a moisture barrier of 15 lb roofing felt or 4 mil poly sheeting behid your shower walls. If you missed that step, you can go back over your walls with any liquid waterproofing membrane, or since schluter products are available to you, you could Kerdi the walls and use unmodifed within the shower and modified around the rest.

I am using fibrerock aquatough backerboard which I was told acts as a vapor barrier. Please let me know if this is wrong

Fiberock is neither a vapor barrier nor a moisture barrier.

Quote:

---

Originally Posted by Bljack

Fiberock is neither a vapor barrier nor a moisture barrier.

---

Well they definitely claim it as a moisture barrier that is why it is called aqua tough and is suggested for use within showers with no water resistant membrane.

Look here

Quote:

---

FIBEROCK® Aqua-Tough™ tile backerboard is a unique, fiber-reinforced gypsum product that represents a new era in substrate performance for wet or dry areas, as recognized within the TCNA Handbook and International Residential Code. This durable panel offers superior performance and tile bond in addition to an integral water-resistant core.

Unlike traditional water-resistant gypsum board, FIBEROCK Aqua-Tough tile backerboard derives both strength and water-resistance from its uniform composition. Made of a uniquely engineered gypsum/cellulose-fiber combination, it is strong, water resistant, and mold resistant, scoring a 10, the highest possible rating on ASTM D 3273. With no paper face to delaminate, tear, or scratch, it maintains its integrity, even when wet.

The backerboard can be finished with ceramic tile or painted, and has a 20 year limited warranty. It is environmentally friendly, made from 95-percent recycled materials, earning it Green Cross Certification from Scientific Certification Systems.

---

I say give it a shot, you are going to do it anyway no matter what people have told you. You can always take it back down.

Quote:

---

Fiberock is neither a vapor barrier nor a moisture barrier.

---

I really should have expanded that answer. For not doing so, I apologize. Yes, it is true that in fact, you are not required to use a moisture barrier behind the board, but when you go deep into the details, you start to notice what does or does not have an Achilles heal and in a shower, the bottom two feet of backer, the taped and thinsetted joints are not waterproofed. Furthermore, the accepted method (W247 Fiber-reinforced water resistant gypsum backer board) also requries the furring of the walls to allow the Fiberock to ride over the flange of the shower pan or tub and stop just above the deck where it will get caulked to provide a waterproof seal. Real life installations (and unless you notched your studs or furred out all the walls adjoining the fiberock walls), the board is stopped 1/8" above the flange with the moisture barrier overlapping the flange. When there is only one version of a product on the market, if it gets accepted and approved by whichever voting committee accepts it's inclusion in the handbook, then it's pretty much manufacuterer specifications and until an equal competitor comes out, they can sneak in whatever marketing they want into the method.

That's why I wondered about the moisture barrier. 15 lb roofing felt or 4 mil plastic sheeting would be a moisture barrier, not to be confused with or concerned with creating a moisture sandwich because they are not vapor barriers. Kind of wondering about the whole entire install. Understand where my concerns come from?

Half my life in the trade and I see a lot of marketing vs reality. Heck, mastics still say outstanding for tub and shower installations. Now, though, you've got me wondering. I'm going to see if I got any Fiberock scrap in the garage. If so, I'll silicone a piece of pvc to it, let it set up over the next 2 days and then fill it with water and see if anything goes through.

Is there really that much water that gets absorbed by the tile where it would penetrate into the backerboard? I mean in a shower the contact of the water on the tile is minimal as it is not submersed fully underwater. I was under the assumption that it is only the grout that can let water penetrate and that is why you need to seal the grout.

Sealing grout is an optional step for maintenance only, not for waterproofing. Shower and tub surrounds need to be able to fully contain all water before any tile even goes on the wall. I will never equate water resistant and waterproof. Tile backers for wet areas need to be impervious to the effects of water, but certainly does not mean they will be "water proof" or "water proofers". I'm not so sure how familiar you are with your southern neighbors, but here in New Jersey, profiling still abounds. People in NJ can generally be profiled into 2 categories... lawyers and plaintiffs. :eek: Tends to make one working under those conditions a bit more conservative.

But to answer my question... Does tile absorb water?

Yes. Some bisques soak up water like a sponge. Is there a code on your box?
"W.A. #-#%" ?