Why would you want expansion joints if the 100sqm is divided by 4 seperate areas? an expansion joint is only needed on a 9 linear metre run...
Nobody does 3mm anymore, old school.
Hi,
I'd go for the decoupling matting all the time, natural stone or porcelains, most tilers use flexible adhesive these days anyway but that wont help for movement transmission from your screed plus most tilers will guarantee their work then. £1940 for materials and labour to lay the matting...