Building up of layers: the meaning of the primer for floor coatings

How important is the primer?

Subsurfaces with mineral foundations (cement screed, calcium sulphate floor fill, magnesia flooring) but also other subsurfaces such as mastic asphalt, wood, dry screed etc. have to be prepared with a floor surface and flooring layering primer (pre-coat).

A primer is the base layer for all coating systems and is the adhesive bond between the existing subsurface and the subsequent floor coating. A primer is absolutely necessary in the majority of cases.

Preparation of the subsurface is necessary before applying a primer and this normally involves a mechanical process such as shot blasting or grinding and then sweeping and vacuuming. The subsurface has to meet standards, meaning it must be stable and clean and meet requirements for strength and residual moisture. When all conditions have been met the primer bonds perfectly with the subsurface.

The primer resin is chosen depending on the type, characteristic and position of the subsurface. Due to environmental and technical considerations, the resin consists mainly of solvent-free or water-based epoxy resins as these are very resistant to alkaline subsurfaces such as cementitious screeds and concrete.

With floor coatings, the filled primer also serves as a pore filler for the subsurface. A primer which fills pores and forms a film prevents the formation of bubbles in the coating.

Primers are normally applied with a rubber slider or a spatula and are subsequently evened out with a roller. Whether primer is applied in one or two layers depends on the type of subsurface (concrete, cement screed or other) and its condition (e.g. porous, damp or close to soil).

For example if the subsurface is in contact with soil a moisture vapour permeable primer can be applied, which can be treated with a diffusible coating. With reverse moisture penetration normally a moisture blocking primer with moisture tolerant resin is used, which is applied twice. In this case the first primer layer should not be sanded, in order to ensure a top surface which is pore-tight. This pore seal is necessary to stop bubbles forming through the process of osmosis.


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