Primer G 786

All surfaces to be primed must be dry, clean and completely free of dust, dirt, rust, oil, ect. Porous substrates should be cleaned by brushing, sanding or sandblasting. Substrates containing bitumen or tar do not usually bond satisfactorily to ELASTOSIL^® RTV1 silicone rubber, even if carefully primed. This is because this substances affect the adhesion of the primer to the substrate and also penetrate the primer film and act as release agents. It should also be mentioned that such substances may cause discoloration of the silicone rubber. The drying time given apply at room temperature and should be strictly observed since it decisively influences the adhesion of ELASTOSIL^® RTV1 silicone rubbers. The drying time is increasing at ambient temperatures and decreasing at high ones. Contamination of the primed substrate surfaces will reduce the adhesion of silicone sealants. Ensure, therefore, that the substrate surface is protected after the primer has been applied and that the silicone sealant is applied as soon as possible after the primer coat has dried.


Primer G 786 is used wherever strongly alkaline surfaces are involved, eg. in the jointing of fresh concrete. Two coats of primer should be applied to highly absorbent surfaces such as aerated concrete. If the surface is only moderately absorbent, on the other hand, it is advisable to dilute the primer with a solvent such as xylene or methyl ethyl ketone. Exposed surfaces which have been contaminated with Primer G 786 may discolor slightly after a while, whitout losing their effectiveness. The edges of the joint should be covered with masking tape to form a neat clean joint. Consumption of Primer G 786 is 100 - 300 g/m², depending on the absorbency of the substrate.