What is the best way to chalk lines on Ditra?? I find when I use regular chalk it just rubs off. Any suggestions?

I usually go over any chalk lines with a sharpie and a straight edge but recently read that a little hairspray over the line seals it enough to keep it there and won't interfere with the bonding--haven't tried it so don't really know how well it works.

I've read about the hairspray trick as well. Since thinset doesn't really bond chemically to Ditra, the hairspray isn't a problem.

Many times I fill all the cavities with thinset the day before I set the tile. A chalk line is easily visible over that. The only downside is that walking on it generates a little dust which has to be swept up.

I have tried filling the pockets up in the past, it works ok but because the mortar does not adhere to the ditra when you walk on it the next day the mortar pops out of the pockets leaving these little balls of mortar. It can be a bit annoying when setting. There has to be some miracle chalking contraption!

MK,

If thin set pops out of the Ditra squares I would say you're not filling them completely. The sides of the depressions are back-angleled so the mortar can not come out if completely filled.

Personally I don't recommend or see the value of filling and then setting the next day. All that would do is create a place where a bond failure can happen. I might consider it if I had to install small mosaics over it though, since the smallest recommended size is 2x2".

I know the hair spray works but have no plans of doing it. I snap a line, then get the permanent marker to work.

Jaz

I would have to agree with Jaz. The weakest link on a prefilled grid is the small footprint over the squares for the setting layer of thinset to bond to.

I personally think its a bad idea.

Get a straight edge out and use a Sharpie marker.

If the proper amount of thinset is used and 80-100% coverage is achieved, there is no difference except that there is one more link in the chain in this method. Instead of a simple mechanical bond, there is now a chemical bond as well. However, I've done it both ways with success.

For what it's worth, Schluter stops short of telling installer not to do it that way.

The 3 companies ive worked for in tile over the last 6 years, have all used clear coat primer over cement, plywood or cement board without any problems. I always use it to seal my lines. In large areas, I seal the ends of all the lines so that they can be re-snapped if necessary. I can't see a problem with using it over ditra but because my experience has been mostly in commercial work, I have not had much experience with using it.

The secret to pre-filling the pockets in Ditra is to use a grout float to fill them. The float fills the pockets to the top, and leaves the grid on top clean. The next day there isn't any flaking off the grid.

We use a lazer and then sharpie all layout lines, no hairspary or equal, just to be sure, also there is an ink chaulk line that can be used, a little messy.