Crack in cement slab

Typical slab crack running under contiguous tiles. 

To protect the house from dust we installed a plastic tent enclosure to the ceiling.

We use a 2-part system (powder and liquid) especially made for movement by Sienna, EP200.  This is an expensive product but worth the price.  Over the years I have successfully spanned large slab cracks with this product and the tiles set with it do not re-crack.