Flotex will take a lot of agitation and the stiffest black brushes are a massive step up from white on the Envirodri machines. Select chemistry as appropriate to the fibre, dye and soiling and use plenty, but not too much that it runs underneath the kitchen units.
I will vac, dry brush with my Envirodri, vac again. Repeat if necessary. Be warned, this can be a VERY dusty process.
Prespray, agitate, rinse. Repeat if necessary. If using high pH, neutralise.
A rotary can be a lethal weapon on Flotex, so be warned

Be wary of some rust removers (Hydroflouric Acid) They have the potential to damage the fibreglass backing strands.
Safe and happy cleaning

Ken