Why Prime?
Primers fulfill several important functions: they bind loose dust and particles on the surface, regulate substrate absorbency (so paint or adhesive is absorbed evenly), improve adhesion of the subsequent material, and can block discolorations.
Without primer, paint may dry unevenly, plaster may detach, tile adhesive may not bond properly and wallpaper may peel off. Priming is therefore not an optional step but an investment in the durability of the entire surface treatment.
Deep Primer: The All-Rounder
Deep primer (also called penetrating primer) is a water-based acrylate dispersion. It penetrates deep into the substrate, strengthens it and regulates absorbency. It is the standard primer for mineral substrates.
Application areas: Plaster (lime, gypsum, cement), concrete, aerated concrete, drywall, masonry. Not suitable for: metal, wood, plastic, already painted surfaces with intact coating.
Coverage: 100-250 ml/sqm depending on absorbency. Normally absorbent surfaces: approx. 150 ml/sqm. Highly absorbent surfaces: 200-300 ml/sqm. On highly absorbent substrates, work in two passes: first pass diluted 1:1 with water, second pass undiluted.
Drying time: 2-4 hours at 20 degrees Celsius and normal humidity. In cool or humid conditions, up to 12 hours. The primer must be completely dry before overpainting or plastering.
Bonding Primer: For Smooth Surfaces
Bonding primer (also quartz primer or adhesion promoter) contains fine quartz sand that creates a rough surface. This gives subsequent plaster mechanical grip on smooth surfaces where it would otherwise not adhere.
Application areas: Smooth concrete (fair-faced concrete, concrete ceilings), precast concrete elements, old tiles before over-plastering, calcium silicate masonry, natural stone. Applied undiluted with roller or brush.
Coverage: 200-300 ml/sqm. Application must be opaque to create a uniformly rough surface. Do not apply too thickly, as the quartz grains will float in the dispersion and provide no grip.
Drying time: 12-24 hours. Bonding primer needs longer than deep primer due to the thicker layer and quartz grains.
Concrete Contact: The Premium Solution
Concrete contact is the strongest form of bonding primer. It contains coarser quartz sand and a more concentrated dispersion. The result is an extremely grippy surface that reliably adheres even to mirror-smooth concrete.
Application areas: Concrete ceilings before plastering, old tiles as substrate for new plaster, extremely smooth concrete surfaces. More expensive than bonding primer but offers the best adhesion.
Coverage: 250-350 ml/sqm. Drying time: 4-6 hours. Important: Concrete contact must not be overpainted -- it is only intended as a plaster base.
Barrier Primer: Against Discolorations
Barrier primer (also sealing primer or nicotine blocker) seals the substrate and prevents discolorations from bleeding through the new paint. Typical problem areas: nicotine deposits, water stains, soot stains, wood tannins.
Barrier primers are solvent-based or shellac-based and form an impermeable barrier layer. Applied undiluted, often in two coats. Coverage: approx. 100-150 ml/sqm per coat.
Drying time: 1-4 hours depending on product. Solvent-based barriers dry faster but smell stronger. Water-based barriers are less odorous but take longer to dry and are less effective against heavy staining.
Wood Primer: The Special Case
Wood requires a special primer because it has different properties than mineral substrates: it is absorbent (differently in longitudinal and transverse directions), contains substances (resins, tannins) that can bleed through, and moves (swells and shrinks) with air humidity.
Wood primers are usually alkyd or acrylate-based and contain biocides against mold and blue stain. They regulate absorbency, isolate wood substances and provide a good base for the topcoat.
Coverage: approx. 100-150 ml/sqm. For resin-rich woods (pine, larch), a pre-coat with shellac may be required to block resin spots.