Especially to Jeff Buck. I saw the picture you put up using Ditra. I’m in a bathroom now where I just laid plywood over joists on a second story. I was going to use CBU’s bedded in thinset, then thinset, then tile.
I’m trying to keep the finished level as low as possible, but want to add some more rigidity to the finished surface.
How is the Ditra applied, how thick is it, and if I’m trying to add some more rigidity to the finished surface, should I just go with CBU’s screwed into the ply?
What are benefits/negatives?
I’ll look through some old posts and see if I can see anything, but wanted to hear from you all as to your latest experiences.
Replies
Neither CBU nor Ditra is structural. Neither product will add any rigidity to the floor surface.
Ditra is fairly easy to install. Thinset is spread on the plywood and the Ditra is un-rolled and theoretically adheres to the thinset and plywood. I say in theory, because Ditra loves to curl up and ya'all may need some tile boxes bricks 2x4's etc to weight it down while it cures. I believe that Schulter specifies unmodified thinset below the Ditra and modified above it.
Check out the instructions: http://www.schluter.com/english/products/2002/sectionf/ditra/601-ditra.html#install
Then tile on top of the Ditra as you would any other surface. Ditra is very pricey, about a third higher than comparable membranes and double the price of CBU. It has its advantage that is is warranted to go over longer spans of thinner plywood than regular CBU, e.g., 5/8ths plywood. While it is only about an eight of an inch, quarter inch Hardibacker is half the price and one only gains an eigth of an inch. So I question its use if for only elevation reasons.
Again, its true advantage is the warranty over longer plywood spans. Whether or not it actually performs better, only time will tell, but apparently, Schulter is willing to warrant it. I think warranties are a waste of time and money, because you warrant to your customer the whole cost of the project; Schulter warrants only the cost of the Ditra. If it fails, you pick up the rest of the tab.
So I am not a super big fan of Ditra, and would rather engineer the substrate so it is solid rather than putting on Ditra and relying on the warranty. My two cents.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Thanks for your 2 cents. I appreciate it. I spent most of the day today cribbing and sistering to level a 4x5 bathroom floor. I've just put 3/4 CDX on it and screwed it down. I'm about a half inch from the finished height of the hall floor and am trying to keep the bathroom height to a minimum. If I use hardi do I use modified beneath and unmodified above? Opposite to the application of Ditra?
Unmodified below. The idea is that this stuff will not evaporate, e.g., lose moisture very much below the CBU so one runs a risk of it re-emulsifying (e.g., turning into mush) if exposed to water.
So unmodified below and modified above. But please please check the instructions for the particular CBU on their Web Page. Do not take my advice.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
what he said!
I got all my info from their website ....
first time around for me ...
only thing different than Boris ... even after being tightly rolled ... mine layed flat enough on it's own.
Jeff
Buck Construction Pittsburgh,PA
Artistry in Carpentry
Ok, not to beat a dead horse, but I just went to Ditra's website and they say "the mortar must bond to the substrate and mechanically anchor the fleece to the underside of the Ditra". They also say that the type depends on the type of substrate. To me, this means modified below, to adhere to the plywood, no?
Then it says "the tiles can be set using the thin-bed method". But they don't specify modified or unmodified.
So, am I looking in the wrong place for this information or am I just missing it?
Here's the newly published Ditra handbook:
http://www.schluter.com/english/products/2002/pdf/ditra_handbook.pdf
When installing Ditra, use modified below it and unmodified above it.
Billy
I used modified both top and bottom ...
I read the website ... just read the link to the handbook ... to say that the big concern was exterior or wet locations .... not letting the modified cure w/o taking on new moisture.
Just read the handbook .... looks like unmodified to be the safest way to go.
I'll be plenty good though .... as I'm not planning to grout for a coupla weeks anyway ... not till the last minute .... and also thinking about that whole moisture trap deal .. was planning on waiting because it's an epoxy grout ..... which I believe would "trap" moisture more than cement based grout.
Thinking I'm pretty safe ... especially as the setting bed grout was mixed real tight .... so the heavy tiles set without their weight settling them.
I used a half bag of rapid set in the closet .... didn't want to crack a whole bag for a small area ... that's probably the ideal thinset!
Luckily for me ... my dry.... air circulated ... cool ... basement is ideal for concrete curing .... but looks like next time I'll think about unmodified ....
Gonna be a hard habit to break .... gotta re-read that handbook again before I believe nonmodified can set porcelin tiles .....
JeffBuck Construction Pittsburgh,PA
Artistry in Carpentry
Lot of ignorance being bandied in this thread. Ditra is an uncoupling membrane, primarily. A waterproofing membrane secondarily. Its main purpose is to ISOLATE the tile from the substrate (subfloor).
It works well. In both cases.
The felt provides a porous medium for any water vapor to escape. In fact, it can be layed over "green" gypcrete on radiant heat floors. The felt also is the key to the "uncoupling" effect. Ditra does NOT bond the tile/membrane to the substrate. In fact, its purpose is just the OPPOSITE. Essentially the purpose of the thinset bed beneath the Ditra is to HOLD IT DOWN and to keep the membrane from shifting over the substrat while the tile is set. It is intended as a temporary and very WEAK bond-- somewhat like sticky tape. In fact, (perhaps ironically) tearing out a Ditra installation is EASY. The whole tile floor will peel up with a flat shovel with one man in an hour (generally speaking). Anyone who's ever torn out a tile installation can especially appreciate this aspect (The installation is permanent all right, but, hey, some folks just don't like tile).
The tile is then mortared to the top surface of the membrane via the dovetail indentations, which, when filled with thinset, lock the tile mechanically to the membrane. What results is technically a "floating" tile floor. While Ditra doesn't add any structural value to the substrate, it does, however, STIFFEN the floor considerably. The tile/thinset/membrane system becomes a 1/2" thick solid surface overlayed on a sufficient substrate. For this reason, it makes a 3/4" OSB subfloor on 16" o.c. joists a SUFFICIENT substrate for tile. The TCA handbook validates these claims and they endorse the product.
Also, it's NOT "twice as expensive" as CBUs. Here in Alaska, it's $1.25-1.45 /s.f. . CBUs run about $.90/s.f... BUT, the LABOR for installing Ditra more than washes out the increased material cost. Ditra is EASY and QUICK to install. (Here, tile setters add $2.00/s.f. for Ditra, installed--versus no underlayment at all). CBUs are generally twice the labor to install. And they are a substandard product, IMHO.
Finally, There is the waterproofing aspect of Ditra. If one uses the Kerdi tape on the seams (heck, even a bead of silicone would suffice), the membrane TOTALLY waterproofs the tile installation. No moisture can penetrate to the subfloor. Very important in a bathroom or entry installation. And no underlayment alone can accomplish this.
Ditra. Try it. You'll like it.
good info .. but lose the attitude.
thinking the ditra link isn't ignorance ...
all other info is direct use info ... real world counts for something.
Otherwise ... ya said the same thing the Ditra link said ...
feel better now?
BTW ... material cost ... $0.67 ... $10 for a 3x5 sheet of CBU ...
vs ... $ 1.71 for the Ditra I just picked up ....
installation time ... just about equal ... I know ... because I installed it myself.
OK ... add in the cost of a handfull of roofing nails if it was my typical CBU install ...
so what's that? .... 2.55 ..... something.
I coulda got it for $1.30 ft sq if I wanted 250 ft sq left over and sitting in my garage ...
Your mileage may differ.
Jeff
Buck Construction Pittsburgh,PA
Artistry in Carpentry
I found Ditra to be extremely expensive but absolutly loved using it.
I also think the price is a joke because I can't see why it costs so much in making the stuff.
I believe theyre charging us what they think they can get.
I doubt I'd use it again cept for what I have left over. Its way too expensive even with the ease of use.
Takes me all of about ten minutes more using Hardi back....
Its also hard to get around here without ordering more than I need.
I got my first roll from a HD on my way back from canada last winter.
Personally I like doing mud jobs so....
Be well
andyMy life is my practice!
http://CLIFFORDRENOVATIONS.COM
Of course, my mileage does differ.
In this region, CBU's run about $14/ea. That's nearly a dollar/s.f. Ditra sells to installers at the local tile supply for $1.35 or so. Any size piece.
Labor is indeed less with a Ditra install--especially with a cut up room. Cutting CBUs is a nasty and messy job.
But all that's secondary.
As I said, the real advantage of Ditra is the uncoupling and waterproofing. Gypcrete radiant floors are popular here. No underlayment/AFM I know of, other than Ditra, can be installed over gypcrete until it has cured 3 weeks. (And tile does NOT go over gypcrete directly). Same for green concrete slabs. Hence a construction delay.
Also, though it's not mentioned on the Ditra website, hauling 15 sheets of cement board up two flights of stairs for a large tile job sucks...The real world does count.
hauling 15 sheets of cement board up two flights of stairs for a large tile job sucks...The real world does count.
Totally agree....but in the real world theres also Hardiback which doesnt weigh a whole lot more than cardboard.
Around my parts Ditra is a whole lot more $$$$$ than by you....and far from readily available.....I still love it though.
Be floored
andyMy life is my practice!
http://CLIFFORDRENOVATIONS.COM