Monday, March 10, 2014

Underlayment For Porcelain Tiles

I am installing porcelain tiles in my bathroom. I have a question about appropriate underlayment for this. It is a main floor bathroom with a basement underneath. The subfloor is plywood and now is covered with levelquick compound for leveling. it is quite level now. My question is can I lay the tiles directly on the levelquick (which I beleive is some kind of cement) or do I need to put some backerboard? The levelquick has been on for a couple of weeks and is starting to show some hairline cracks running through.

I'll assume you used the primer and the lathe over the plywood before you poured the levelquik. If the pour is 1/2 or more in the thinist part of the pour, you can install the tile over the levelquik. Dont put cement board over the levelquik. If you were going to use cement board, the levelquik would go on top of the cement board. It would be a good idea to install an isolation membrane like ditra over the levelquik. You can check out ditra at

Thanks for the reply and advice, heresjohnny. Actually, I did use a primer over the plywood but not a lathe. I was not advised by the HD people and i don't even know what it is. Do I now have a fatal flaw? Also, the level quick is probably around 1/4 to 1/2 at the very thickest. Do I need to add more and thicken this up or can I proceed with the tiling? Also, I don't know what ditra is nor where it goes; between the plywood and levelquick or between the levelquick and the tiles? I appreciate your advice. thanks.

Lath is required over all plywood installations. Its in levelquik's installation instructions. Cut and past this link into your browser and read about installations over plywood.
The lath helps to make the thin pour more solid over the plywood floor. Without it youll likely experience some cracking. My opinion is your taking a chance by not fixing it now, but thats your call. Ditra is an isloation membrane. It goes over the levelquik, and helps to isolate any movement in the floor below the membrane from the tile installation above. There are other isolation membranes besides ditra that you can use. Unfortunately, HD people are not a good source for information as they are often ill informed about whats required.

Thanks aggain, HeresJohnny. It sounds like I have a potential problem. You suggest fixing it now. I tend to agree, but how? I will have to remove the levelquick, right? How do I do that?

OK, I learned all about uncoupling underlayment. sounds like a good idea and I will take your advice and put it on the levelquick. However, I ran into an issue that seems bothersome to me and I hope that you (or anyone else) can inform me (the HD guy could not help in this respect). I picked up the Ditra membrane at HD and I picked up a bag of FlexBond thin set. Then I read on the Ditra package instructions that only UNMODIFIED thin set is to be used. HD has 3 kinds of thin set---the FlexBond which is polymer modified, the VersaBond which is also modified and the Custom Blend which is unmodified. They range in price from about $30, $15 and $5, respectively. Should I really use the unmodified (re: unfortified and cheaper (i.e., you get what you pay for)) thin set for this? The Ditra instructions are quite clear and they state it twice; Use unmodified thin set.... I don't want to make a big mistake here. From what I can gather the polymer modified thin set is recommended for difficult-to-adhere to surfaces like plywood (not me, I am laying the Ditra on levelquick and the tiles on Ditra) and for porcelain tiles. I am using porcelain tiles. Does anyone have some advice or assurances? Should I really use the unmodified thin set or should I go with one of the others that I mentioned? Thanks.

Follow the instructions. Ditra is an uncoupling membrane. There are two schools of thought with tile adhesion. One, which is the one I adhere to, is the uncoupling school. Although I have personally never used this membrane, the theory is that, over time, the bond between the membrane and the surface it's on will break and they will uncouple. Modified thinset will hamper this process. There are others on this site with lots of actual experience with this product and can give you much more detailed why information and, hopefully, they'll weigh in soon.

Yes, you need to use an umodified thinset under the ditra if you are going over concrete. If you are going over plywood, then you need to use a modified thinset between the ditra and the plywood. you need to use unmodified to set the tile over ditra. I dont do much with the Custom Building Products thinsets, but I wouldnt use the customblend. Its real low end stuff so I hear. Custom Building Products makes a better unmodified. I think its call Masterblend but dont quote me. If you have a good tile store in the neighborhood, a good unmodified that I use with ditra is Tec Full Set.
Some tips with the ditra. Thinset comes in grey and white. Use the grey under the ditra. When you embed the ditra into the thinset you will be able to see the grey thinset through the ditra. You'll be able to see if the ditra is making full contact and is embedded fully in the thinset. The little squares in the ditra are actually dovetailed, and the thinset actually gets locked into the dovetail squares as it sets up. Thats what holds the tile to the ditra. Ditra is also a waterproofing membrane. Modified thinsets wont cure fast enough because they need air to set up, whereas unmodifieds do not. This is why you must use the unmodified over the ditra. Modified thinsets used with ditra can take a long time to cure and may void your warranty on the product.

thanks for the information, guys. Actually, I took some time out earlier and found the Ditra guide on the Schluter website. Their info matches nicely what you say and it provides data to support their recommendation for unmodified thin set. I am learning a lot... I've cut all the Ditra pieces to fit the room but I haven't set them yet. I'll do that tomorrow, after I return the CustomBlend thin set and try to locate the one you suggested (or at least one that doesn't say economy grade on the package like the custom blend does). And thanks for the installation tips. Here is a question. Am I supposed to push on the Ditra so that the thin set goes through the white mesh and fills the crevices of the underside of the orange part of the membrane or is it just supposed to go through the white mesh only?
P.S. Just want to mention that I emailed Schluter today to ask them this question and two of their representatives replied within hours. Nice customer service...

Glad you went to the schluter website and did your homework. Thats more than half the battle and too may people dont bother to do it until after they have a problem. You need to make sure that the fabric on the bottom makes 100% contact with the thinset. You can pull up a section of a piece to make sure. Yes they are a great company with very good support people.

I am looking for a good quality non-modified thin set to use with the Ditra membrane but I am having some trouble finding some locally. None of the tile stores around my place sell any. The nearest Lowe's has laticrete 273 and 317. Does anyone know if either of these are any good for laying Ditra to levelquick and porcelain tiles to Ditra? The packages for these products say nothing about them meeting A118.1 standard which is what Schluter recommends. I've got the Ditra ready to go but nothing to stick it with!

In addition to the laticrete 273 and 317 there is one outlet close by that sells Durabond Premium D5 thin set mortar. It doesn't specifiy that it is modified so I assume it isn't. Can you tell me if this is a good quality mortar to use to lay tiles on the Ditra membrane? Thanks.

If you found a supply house that sells Durabond, they make a product called Durabond D-25 Ditraset. Its exactly what you need. Im not that familiar with the laticrete products. I looked at the info online on the laticrete website. The 317 looks like it would be fine also.

Yes. In my attempts to learn more about Durabond premium D-5 I also discovered teh D-25 DitraSet. I'm going over to the place that sells the Durabond in he hopes that they have the Ditraset. If not then I guess I will go with the Durabond premium D-5 or the Laticrete 317. Thanks for your help.

Tags: underlayment, porcelain, tiles, over plywood, over levelquik, cement board, Ditra membrane, going over, sells Durabond, that sells, that sells Durabond, tiles Ditra