Can IKOpro Synthaprufe Original be brushed on to quarry tiles in a dinning room then self leveler be applied after? No. The application of IKOpro Synthaprufe Original should be followed by a min 50mm sand/ cement screed as per the published product datasheet. If I put decking on top of your felt covering (on a flat roof) will that void your manufacturers warranty? I would like to know if the 2 insulation layers may have a structural function and be sufficient to support the tiles, or if battens and counter battens are needed anyway?