What is a scrape coat?
A scrape coat (Dutch: schraaplaag or schraplaag) is a thin, resin-bound intermediate layer for levelling and sealing substrates such as sand-cement screeds and concrete. The layer is applied after the primer and before the actual epoxy or polyurethane (PU) seamless floor.
The name comes from the method: the layer is applied with a flat trowel in a “scraping” action, so that the open pores and small irregularities of the substrate are filled. A scrape coat usually consists of two components (resin and hardener), often supplemented with fine quartz sand, and should be solvent-free. The layer makes the substrate liquid-tight and provides a closed, flat base.
Application
A scrape coat is used only on (virtually) horizontal surfaces, as part of a seamless floor system:
- Prepare the substrate: grind or shot-blast, remove laitance and loose material, vacuum until dust-free.
- Apply primer to saturate the substrate and provide adhesion.
- Apply the scrape coat with a flat trowel in a scraping action, so that pores and shrinkage cracks are closed.
- Apply the seamless floor in the layer thickness specified by the manufacturer.
- Optionally a topcoat or sealer for extra wear resistance or a matt finish.
Common mistakes:
- Substrate too damp: measure the residual moisture before starting; too much moisture in the screed causes blistering or delamination.
- Skipping the primer: without primer the substrate soaks up resin and air bubbles (pinholes) form in the following layers.
- Wrong temperature: work within the temperature and humidity limits in the technical data sheet; too cold results in poor curing.
- Ignoring the overcoating time: apply the next layer within the specified time, otherwise it must first be sanded for adhesion.
- Mixing systems: use primer, scrape coat and seamless floor from one system by the same supplier.
Related Terms
- Seamless floor
- Primer
- Screed
- Epoxy adhesive
- Primer standing time
- Screed curling
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