Tiling across floor slab expansion

[Monkey Wrench]

I laid around 70sqm of 20mm limestone tiles (500mm x 600-1000mm) over Christmas in the downstairs of our home through a number of rooms. The substrate was a new sand and cement screeded floor containing wet underfloor heating which was laid in September. It has all gone to plan with the exception of an area which I suspected might cause a problem...

Between an open plan kitchen and living area, there is a transition from stone tile to engineered wood. However, the exact line where the tiles meet the wood is approximately 250mm over the expansion joint between the floor slabs. I had hoped the flexibility in the adhesive and grout would have accommodated any movement but sadly no. I noticed a crack pretty much following the expansion gap below across the 3m transition. The crack is pretty small but nevertheless there and this is the time to try to put it right before I lay the wooden flooring.

kitchen floor crack.jpg (371.35 KiB) Viewed 2016 times

What are my options?
1) Cut the broken tiles out and fix new ones that have had their length reduced so that the tile does not straddle the expansion joint below. This is not ideal as the tiles will look like shorter cuts - generally I've avoided laying small sections of tiles and the threshold is better suited to the original position.
2) Can I use a decoupling membrane such as Schluter Ditra to span the gap? then tile over? From looking into this, it would suggest this product is more suited to floor slabs that are likely to crack rather than for stabilising the area either side of an expansion gap. I should point out that I caulked the expansion gap before tiling. The floor slab in the kitchen is approx 4mx5m and the living area is 10mx4.5m.

Thanks in advance for any good ideas!

Matt

[wes56]

Essentially, the wood and the tile should have met over the crack ie. the junction of the two slabs.

1. The tiles appear to be going over and beyond the line where the two slabs meet?
2. Is the transition line where the old dividing wall between kitchen & dining room was knocked through?
3. The "crack" between the two slabs should have been cut out, sealed.
4. A movement joint should have been installed - you could have used a transition piece, attached on the wood side, to cover the joint.
5. I presume the UFH is only under the tile?

[Wayne_Norcros]

In addition to the good information you have received on the above post. Other factors that could contribute to cracks appearing are:

1. The screed should have been left for 21 days after installation and then a full commission that basically means bringing the heating up to a temperature over several days and then down again in order to expose weak spots in the screed

2. Once tiling was completed, it should be left for 1 week and then bought up to operating temperature at 5 degrees C per day up to operating temperature, This allows any movement to occur in the buildup at the same rate.

Whilst adhesives and grouts being flexible can allow for small amounts of thermal expansion and contraction, the flexibility is more of an aid in adhesion. A tile being a rigid finish will always crack if there is any movement within the substrate.

Ditra matting and other anti fracture membranes allow for expansion and contraction over the whole floor surface and can bridge a potential crack of 3mm or under, your description is accurate in that it is for potential cracks not for existing.

You will need to identify the issue which would appear to be a lack of a movement joint and then this should be installed as per the above post prior to replacing the tiles.

Good Luck