Hi, can I please ask for some advice. I am laying 70m2 of porcelain tiles in 4 size opus pattern.

The floor is one half new extension (floor levelled about 2 months ago), the other old concrete.

I am laying electric underfloor heating.

I have patched the old floor to make it as even as possible, then I am priming the floor and laying 10mm insulation boards on flexible adhesive, then four electric UFH mats linked to 2 thermostats and then SLC.

My question is how and where do I put an expansion joint in an opus pattern. Could I use a silicone sealant in the same colour as the grout and apply to the top edge of tiles from right to left, or do I have to end all the tiles in one place and put a straight joint accross (if this makes sense).

Any tips on how to keep on the opus design on track over such a huge area. I usually use the 30,40, 50 method, but am a bit nervous at the huge area I need to cover.

Any words of wisdom would be gratefully received.

Many thanks

Steve

Best way is to use a silicone colour matched to the grout (mapei). Also consider a de-coupling membrane for such a large area, porcelain should be fine without, just something to consider.

If you do any controlled joints they should be straight, cracks don't follow joints on opus patterns

Sorry, what is a controlled joint?

Same thing, an expansion joint is sometimes called a control joint as in it controlls the movement

Thanks for that - are you saying that I won't need one? If so, what will give if there is any movement? Could I put a controlled joint around the edges or do I need a horizontal straight joint?