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Priming for skim coats

Find out why primers are crucial before skim coat application.

Crucial to know

skim coat application 2 hours after priming

room temperature 5 to 25oC

Tools needed

a brush

a roller

a bucket for mixing

electric grinding tools

Step 1

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Why priming before skim coats

Reasons for priming before skim coats

When substrate was checked and accepted, all cracks and holes are filled inn, surface is clean and vacuumed it is time for priming with suitable product. Why priming is needed?

  • To reduce water absorption of the substrate. 
  • To increase strength of the substrate.
  • To increase the adhesion to the substrate.
  • To protect substrate against moisture.

The Ceresit primers recommended for skim coat application are: Ceresit IN 10 and Ceresit CT 17 Profi.

Step 2

The substrates

Substrates for skim coats

All kinds of skim coats can be applied on load-bearing substrates that are dry and free from grease, bitumen, dust, loose plaster grains and other substances decreasing adhesion:

  • cement and cement-lime plasters (age above 28 days, moisture ≤ 4%), concrete (age above 3 months, moisture ≤ 4%) – primed with Ceresit IN 10 primer or Ceresit CT 17 diluted with water 1:1,
  • gypsum substrates with moisture content below 1% – primed with Ceresit IN 10 primer or Ceresit CT 17 diluted with water 1:1,
  • gypsum-fibre boards and plaster boards, fixed according to the recommendations of board manufacturers – primed with Ceresit IN 10 primer or Ceresit CT 17 diluted with water 1:1,
  • paint coats – strong, highly adhesive.

Tips & Tricks

For professionals

How to tackle uneven substrate?

If substrate is uneven at first glance, apply a regular plaster or fix a gypsum board on the substrate before skim coat application. 

In case of peeling paint or shiny oil base paint, fix a gypsum board or frame construction with a gypsum board.

products used

  • ${/content/heliux/adhesive/ceresit/com/en/products/interoir-finishing/product#/ceresit-ct-17/SAP_0201JAC014F1/searchResult.productFields.MainImageAltText}
    CERESIT CT 17
    Primer for surface strengthening of all absorbent substrates for indoor and outdoor application, prior to fixing ceramic tiles, pouring floors or fixing thermal insulation boards. 
  • ${/content/heliux/adhesive/ceresit/com/en/products/interoir-finishing/product#/ceresit-in-10/SAP_0201JAC014Z9/searchResult.productFields.MainImageAltText}
    CERESIT IN 10
    Penetrating primer for use on absorbent substrates, suitable for finishing skim coats, paint coats and decorative coatings. 

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