Hi, Im sure this has been answered before but the best thing I’ve found for holding back REALLY dry substrate is Thistle GYPRIME, but at over £100 for 10l was wondering if anyone knows If/effectiveness of adding SBR to diluted PVA or Neat Bostik Green grit at holding back porous backgrounds. If so how much are you adding? Was thinking about keeping a 5l in van for those occasions…… Many thanks