You got to love what some people do. Was doing a shower change over yesterday & noticed a lot of movement in the floor & a cracked tile. Customer asked if I could replace the cracked tile so lifted it to find it was tiled onto an unsecured MDF substrate. Removing the tile was moving the whole floor. No idea what the fitter used as an adhesive & more so, what he used to apply it. Looks like it was applied with a jagged Evo stick impact adhesive spreader. Grout was also the adhesive which is the only thing holding the floor in place.
Ah, the good old DIY'er will keep us in business for many years to come!