Hi all, have a 40m2 uncalibrated slate job coming up soon, in one of the rooms, half is a concrete floor and half is 22mm ply, butted up against the concrete,. If i use ditra will this be safe to bridge the join?

just one other thing what do you guys find is the best cleaner and sealer for slate?

If there's no deflection on the wooden floor then you could use ditra for any lateral movement, if the ply is hard butted against the concrete I would be tempted to run a circular saw or jigsaw down the joint so as to leave 1 - 2mm for expansion. You could really do with using an expansion joint above where the 2 surfaces meet though, to be right. Lithofin do a great range of cleaners and sealers.

I'd be wanting a 2mm gap between the ply and concrete, as long as there is no deflection on the substrates I'd use durabase ci uncoupling membrane over the full area. Best sealers and cleaners are LTP products imo

The ply is yet to be put down, ive already stressed that there must be no deflection and the floor must be absolutly solid, i'll also tell them to leave a 2mm gap,
thanks fellas

kev

If the ply isn't yet laid get them to prime the underside and the edges with a sbr primer

remember to grade your slate into thicknesses kev, uncallibrated can be a pain! I'd start with the thick ones first and build up addy thickness for the thinner ones

hi kev

it is definately not advisable to bridge the gap where the 2 seperate substrates meet unfortunately mate...

there should be an expansion joint according to british standards. your ditra should stop at the point of the expansion joint and then continue on the other side (definately not bridge.. expansion has a much greater force of uncomprimised energy at the point of movement then deflection.

2mm is not enough of a gap between the concrete and the 22mm ply imo because most expansion gaps rely on 6-11mm of rubber and a couple of mil of trim either side. when you fit any timber flooring, the perimeter gap should be 10mm ie where it meets walls or in this case the concrete floor. 2mm is fine between boards when laying because the 2mm gaps accumulate to a larger amount over distance to allow for deflection..

hope this makes a bit of sense kev, recap dont bridge the gap with ditra and increase the join between the 2 substrates to accomodate an expansion joints,,

regards
Ed

Originally Posted by AstonTiling

hi kev

it is definately not advisable to bridge the gap where the 2 seperate substrates meet unfortunately mate...

there should be an expansion joint according to british standards. your ditra should stop at the point of the expansion joint and then continue on the other side (definately not bridge.. expansion has a much greater force of uncomprimised energy at the point of movement then deflection.

2mm is not enough of a gap between the concrete and the 22mm ply imo because most expansion gaps rely on 6-11mm of rubber and a couple of mil of trim either side. when you fit any timber flooring, the perimeter gap should be 10mm ie where it meets walls or in this case the concrete floor. 2mm is fine between boards when laying because the 2mm gaps accumulate to a larger amount over distance to allow for deflection..

hope this makes a bit of sense kev, recap dont bridge the gap with ditra and increase the join between the 2 substrates to accomodate an expansion joints,,

regards
Ed

my mistake, yep as aston says, taken my eye off the ball today

If the joint is a nice straight one then Yes!! deffo use an expansion joint..but if the break in substrates is staggered/uneven in line.. then the option to make sure deflection is zero and uncouple is there...It will work..but needs to be fully secure deflection wise...

Ok thanks chaps, would you still need to use the ditramat or just an expansion joint?

Where is the best place to get a joint?

cheers

kev

Originally Posted by kev

Ok thanks chaps, would you still need to use the ditramat or just an expansion joint?

Where is the best place to get a joint?

cheers

kev

Amsterdam?

You can fill a joint gap with silicone to make your own expansion joint.

Personally with slate, i wouldn't bother with the ditra as slate is quite tough stuff. Just make sure you have the correct expansion gap.

so would i use normal grey silicone about the same width as my grout lines?

Originally Posted by kev

so would i use normal grey silicone about the same width as my grout lines?

If you can get silicone to match your grout, even better (mapei!) Alternatively you can you a proprietory expansion joint from the likes of Genesis or Schluter.

ok, just to update, i contacted schluter and explained what i wanted to do, they say i could use the mat but they would not give a garantee the tiles wouldnt crack in time over the join..... will only garantee an expansion joint,(and they have 2 different shades of grey to match the grout) so an expansion joint is the way to go.
thanks chaps

kev