I like to punch the tiles with my fist, hit them with the palm of my hand or use the rubber mallet what ever beats them into the mortar mix and yields me solid coverage.
Originally Posted by chefwong
I have not seen the Mapelath go in at the same time as the self levelling stage before. Whose idea was this? Did Mapei recommend it? Is the Mapeilath installed the right way up?
Originally Posted by jch
If your self lever has been installed for a few days and sounds "solid" when tapped you should be OK. Perhaps call Mapei - one of their new reps lives in Victoria and was a setter for years, I'm blanking on his name.
Some times when you get cracks like this it is a sign of over watering the self leveller.
You might wait another four days and try one of my rules for tiling. "Never tile anything you can't hit with a hammer". If you give a few well placed blows to the floor (in between heating wires) and you don't blow away your prep or your prep work doesn't crumble it should be OK.
I tried to follow the TCNA 2011 Handbook and Mapei's Technical Data Sheet as closely as possible.
Originally Posted by johnfrwhipple
TCNA specifies the following when installing Interior Floors with Radiant Heat over Wood (RH140-11, p. 103):
Mapei's Technical Data Sheets also recommend installing Mapelath before pouring Novoplan Easy:
"When applying MAPEI underlayments to plywood flooring, mechanically fasten MapelathTM or diamond mesh on top of the primed surface (meeting the requirements of ASTM C847) before application of Novoplan Easy. Refer to the current Mapelath TDS for installation instructions."
The Mapelath TDS says:
"1. Install Mapelath over the primed plywood or OSB. The lath should have a 2" (5 cm) overlap at all seams, stapled flat and uniformly.
2. Apply a MAPEI self-leveling underlayment at a minimum thickness of 3/8" (10 mm), completely encapsulating the Mapelath. Reference the TDS for the leveler to be used and for in-depth application instructions."
and "Lay out Mapelath over the substrate ridge-side down. Cut to fit." which is what I did.
Novoplan Easy's TDS says:
Originally Posted by johnfrwhipple
"Into a clean mixing container, pour the required amount of cool, clean potable water. If available water is not cool, chill water to 70°F (21°C). Add Novoplan Easy powder while slowly stirring. Mix water and Novoplan Easy powder to a mixing ratio of 5 to 5.28 U.S. qts. (4,73 to 5,0 L) water per 50-lb. (22,7-kg) bag of Novoplan Easy. The mixing ratio must remain consistent. Do not overwater material."
I measured 5L of cool water into each bucket (with a measuring cup!) and used a timer to make sure I didn't mix it beyond 2 minutes so should be in the right range. It was a cool rainy day though (about 60% humidity) so that may have been enough to push the water content over the edge.
I called Mapei again and they said it should be pretty much done shrinking by now (4 days) and that the cracks (too small to fit a piece of paper into) should be fine if the floor feels solid (which it does), but I should put an anti-fracture membrane down (as you folks have recommended).
It's just a matter now of choosing which one.
The lath is there to strengthen the slc...so, it must get installed before pouring. WIth a 'normal' concrete slab, you want your reinforcement in the middle, but that isn't what's called for with slc where it should end up with intimate contact because of the viscosity of the material, fully encasing it.
Well this is a good thread.
If you have the lath installed and it's solid you would think that it is going to add a ton of strength to this subfloor. But the fact we have hairline cracks is cause for perhaps another step.
I'm thinking you should just go with the Ditra or wait for my next Noble order to arrive. I'm ordering another roll of Noble Seal TS and a part roll of Noble Seal SIS for a sound proofing job I'm working on.
If you want a part roll of the Mapei Sound and Crack I'm sure my friend Kip can sell you some - he uses it all the time.
I have to say John you are doing a great job of showing up most pros with your attention to detail - nice work. Thanks for sharing!
Mapei said that the hairline cracks are probably not all the way through the pour--just on the surface. There is definitely no visible change in crack width when I bounce my full body weight near them. My guess is that the hairline cracks are from having slightly too much water in the mix--I used the upper end of the prescribed range but it was a super humid day. The cracks didn't appear until day 3--long after most pros would've started tiling.
That said, I agree that a crack-isolation layer would be wise. Ditra is available locally by the foot so I think I'll go with that.
Question: Which specific thinset should I use to attach the Ditra to the SLC? Over wood I know I would use a modified thinset, but over SLC I'm not so sure. Locally I can get Mapei and Ardex products. Just not sure which specific version is appropriate.
Thanks again for your help.
If you don't have it, download the Ditra handbook from the www.schluter.com website. It gives you all you need to know about installing it over all acceptable substrates. It's a good reference to have.
From page 9:
Setting and Grouting Materials
Unmodified thin-set mortar – ANSI A118.1
You want a premium quality dryset mortar, not the ecomony price leader in the line.
You have gone this far with the Mapei line of materials. Why not use their Kerabond setting material. If you buy some Keralastic you can mix up some modified thin set for your tile install over the Aqua Defence.
Using a plain non-modifed thin-set it is important to note that they take a longer time to get a good bite. Do not set the Ditra and then tile the same day. Any checking of coverage will cause a suction effect on the Ditra and could cause a bond failure as the Ditra is pulled off the self leveller.
Better be safe and set the Ditra and then let it cure out a good couple days. I've layed a lot of Ditra with modified setting material and do so at my own risk, knowing that Schluter does not allow or warranty this work without written permission from head office. If your in a hurry and I don't think you are then finsih the floor with Ardex setting materials from setting the tile to grouting - this will allow you to use premium modifed thin sets and even double your warranty if you use the right products.
Kerabond is a great non-modifed thinset. I spoke with a top tech at Schluter some time back and he suggested using 'White' non-modifed thinset. I can not remember the entire conversation but I believe that white thinset is a better quality than grey when comparing apples to apples. I have followed this advice and when working with non-modifed thinsets prefer the white for my bonding applications.
Kerabond is sold in white and gray. Next time I see my rep I'll ask him if he knows if one is stronger or better than the other.
In a class I went to, they said that the reason white thinset was more expensive (often a buck or two a bag) is that to get it white, they have to use cleaner, higher quality sand and components. Now, I don't know if it is actually stronger (never compared the tech data sheets, and don't know if they even are different), but by using cleaner, better sorted materials, it likely is. Unless you are planning something like black grout, white thinset tends to work quite well for most anything.
Jim I also think it has something to do with "Fly Ash".
It appears that the cement industry is using more and more of this and it's hard to know what the Portland ratio is in relation to "Fly Ash" ratio. I have heard in my Mapei training classes that this is generating huge problems on commercial projects and Mapei has recommended to me that I inquire on the cement type and mix ratio for any commercial project.
I'm not sure if companies like Laticrete, Custom, Mapei or the like use any "Fly Ash" in their production or if they even know it's included perhaps with a portland cement order.
Thanks. Turns out the data sheet I need is the one that doesn't use Keralastic as an additive, just Kerabond plus water:
Based on what you've both said, I'll get some Ditra and a bag of Kerabond White (for both over and underneath the Ditra).
- How does 1/4"x1/4" square trowel sound for using to bond the Ditra to the SLC with Kerabond?
- What size trowel do I use on top of the Ditra when installing my 12" x 24" porcelain tiles? 1/2" U-notch?
How do I know if I'm using the right sized trowel? i.e. how do I know when I've got the wrong size during the job?? (V, square, U-notch)?
Water with Kerabond keeps it unmod.
Keralastic with Kerabond makes it mod.
1/4 x 3/16 V notch for Ditra
Try to use a medium set thinset.
I like a 1/4 x 1/2 for that sized tile - U notch
Like setting anything you need to ensure you have proper coverage under the Ditra. I find that the V Knotch trowels don't cut it with a Ditra install myself.
Originally Posted by chefwong
Personally I like to use a 1/4" x 1/4" trowel for the first pass. This leaves a good amount of thin-set (too much) but allows the Ditra to get well coated. We have a Ditra Trowel and after we pull up our Ditra we comb it with the proper trowel. This two step approach gets full coverage under are Ditra every time.
After all that work you do not want to have only 60% coverage under your Ditra. I also don't like over watering my setting material and find it is too hard to get proper coverage onto Ditra if you mix your thin-sets as per the manufacture's instructions.
On Occassion when it's hot we will even back butter our Ditra and lay it over trowel lines.
It's easy to tell if you have proper coverage. Just lift it up and look.
Using something to weigh the corners down is a good idea to keep the corners from curling up.
FWIW, the texture and consistency of any thinset will vary a HUGE amount depending on how it is mixed. A decent paddle, proper RPM, and duration is critical. Most people mix until it looks good, but that may not be right. Sometimes, the use of a timer, and rechecking the RPM available can make a big difference. The shape of the paddle can make a big difference, too. Some end up putting too much air in the mix, which affects it.
I think those small cracks are plastic shrinkage cracks and you could find similar cracks on almost every single monolithic slc pour if you got out a magnifying glass, no?