Hi, I'm doing a house renovation and I've got a 4" concrete subfloor with 2" sand/cement screed. I'm going to be laying 12.5/20mm Marmox board with Mapei KeraQuick direct to the screed. In some rooms, there's a residual layer of some rubbery adhesive that was used to bond vinyl and wood tiles down. It seems stable (I can't touch it scraping with a spade) and is a couple of mm thick. Is it really necessary to remove it before gluing the Marmox down? If so, what machine would you recommend I hire for max speed/minimum effort? I wonder if the potential damage to the subfloor is worth the effort of taking some sort of scarifying machine to it... Ta in advance, Tim  Depending on finish, some areas tiled, some areas engineered wood.  Subfloor has no DPM and no insulation (1950's house). Athough I can't lose too much headroom (or I'll bang me head on the door frames), 20mm thermal insulation under the tiles will help matters no end, and Marmox technical told me that Marmox will act as a DPM is I tape the joints. 2 birds one stone.  Mapei recommended this - although they couldn't guarantee it would survive any hydrostatic pressure forever, they said it had the best chance of all their products. Given Marmox boards are 1.2x0.6m, I think the risk of localised bond failure isn't too much of an issue, especially as the weight of the floor will tend to hold it down.