This, of course, largely depends on what environmental influences act on the concrete and also its condition. Let us take two examples :
1. Dry rooms, mild climate. Here we would advise, if the surfaces are smooth and no longer fresh, applying a base coat of a colourless of slightly pigmented copolymer paint or a synthetic resin based emulsion paint (acrylic, acrylate/styrene or vinylchloride/vinylacetate).
This is then followed be two or three coats of an alkyd paint which can be any colour. Such a system ensures excllent durability.
2. Exterior surfaces exposed to an industrial atmosphere, harsh climatic conditions, poor surface. This will require ceraful preparation : apply filler, allow to dry thoroughly, apply a thin coat of slightly pigmented paint, possibly two coats.
This paint can be based on a copolymer, chlorinated rubber, polyurethane or epoxy resin, one-pack. The top coat must be a very durable one, e.g. based on epoxy resin, polyurethane, silicone polyester or silicone alkyd resin.