Can painted glass felt or glass fibre cloth be used as vapour barrier?

Amira El-Khattam, Mie Them Andersen, Kurt Kielsgaard Hansen, Eva B. Møller

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In most Nordic homes the interior surfaces of walls and ceilings have some kind of surface treatment for aesthetical reasons. The treatments can for example be glass felt or glass fibre cloth which are painted afterwards. To evaluate the hygrothermal performance of walls and ceilings it is essential to know how much influence a surface treatment has on the water vapour transport. Traditionally, there has been most focus on paints that affect the permeability as little as possible. However, sometimes water vapour resistance is desirable. Especially, this is relevant in existing buildings with a ventilated attic where the ceiling may be air tight but has no vapour barrier; post-insulation of the attic may cause the need for a vapour barrier. Placing a vapour barrier above the ceiling can be tiresome and it is difficult to ensure tightness. A simpler way is to paint a vapour barrier directly on the ceiling e.g. as an ordinary paint. This paper presents the results of an investigation of the water vapour resistance of surface treatments which are commonly used in-door. The water vapour resistance was measured by the cup method. Aerated concrete was investigated with and without various surface treatments. The surface treatments were glass felt or glass fibre cloth with different types of paints or just paint. The paint types were acrylic paint and silicate paint. The results show that the paint type has high influence on the water vapour resistance while the underlay i.e. glass felt or glass fibre cloth has very little impact. The measured water vapour resistance for specimens with acrylic paint was the highest, these were measured to be up to approximately 3·109 Pa·m 2 ·s/kg which is considerably less than 50·109 Pa·m2·s/kg as recommended for a vapour barrier. Therefore, two layers of ordinary acrylic paint on glass felt or glass fibre cloth cannot be used instead of a vapour barrier.
Original languageEnglish
Title of host publicationProceedings of the 10th Nordic Symposium on Building Physics: Nsb 2014
EditorsJesper Arfvidsson, Lars-Erik Harderup, Anders Kumlin, Bitte Rosencrantz
PublisherLund University
Publication date2014
Article number128
ISBN (Print)978-91-88722-51-5
Publication statusPublished - 2014
Event10th Nordic Symposium on Building Physics - Lund, Sweden
Duration: 15 Jun 201419 Jun 2014
Conference number: 10


Conference10th Nordic Symposium on Building Physics
Internet address


  • Acrylic paint
  • Silicate paint
  • Glass felt
  • Glass fibre cloth
  • Water vapour permeability
  • Water vapour resistance


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