I've Applied Your Paint, But Am Seeing Blistering On The Surface

Blistering is quite common and can be caused by a number of factors:

- The high temperature of the substrate, air or painting in direct sunlight
- The reaction between the substrate and new paint film (cissing)
- Loss of adhesion between coats
- Excessive moisture content in the substrate
- Resin or Resin gasses
- Direct moisture ingress from an architectural defect

The most common three causes are covered in more detail below:

Blistering during high temperatures

This normally happens when using WB materials internally on walls or WB materials externally on doors and substrates with larger surface areas. The cause is the rapid drying of the first few microns of the surface paint film due to the temperature. This drying forms a solid paint film at the surface which prevents the moisture vapour evaporating from the wet product below escaping. The trapped water vapour causes a blister to form. This process can happen internally (walls/ woodwork) or externally, cladding, weatherboard, doors soffit facia.

Prevention is the best cure, if the substrate or atmosphere surrounding the surface to be painted is too hot then reduce the temperature of it (don’t paint in direct sunlight) wait for the shade etc. or if internal rooms are very warm open windows, insert a fan and ensure good movement of air. Slowing the drying process is the solution.

Cissing/ Reaction between the substrate and new film

Reactions happen, the best way to avoid any possible reaction is to ensure all surfaces are thoroughly clean and stable. If chemical contamination is left on surfaces there is a probability that localised cissing will occur, an example would be localised cissing blistering on a kitchen in an area where oil or contamination was left.

Another cause of blistering due to chemical reaction is when Latex-based products (not just Tikkurila) are applied over emulsion surfaces with very high vinyl contents. This is common when applying emulsions over “mist coated” surfaces where vinyl-based products have been used as the high dilution rate effectively leaves a very concentrated level of vinyl on the surface which can react with the latex-based finishing coats.

In order to prevent cissing or blistering, it is essential all surfaces to be painted are cleaned with appropriate cleaning agents that are suitable for the surface and its potential contamination. In order to avoid any potential vinyl reaction if it is possible that the scenario above has occurred use the appropriate primer (Optiva Primer as the first coat)

Adhesion loss between coats

Generally caused by lack or wrong primer and or insufficient preparation. Blisters can occur during the curing process as the newly applied film tightens and is not able to bond correctly to the existing surface whether that is painted or unpainted. During the curing process, it is also possible to have blisters form even when the new paint film adheres to the existing if the bond between the old film and the surface underneath is poor.

In order to avoid blistering due to inter-coat adhesion, failure preparation is critical. Ensure all surfaces are washed and free from contamination, remove unstable paint with sandpaper and use appropriate primers. It needs to be stated that if the existing paint film looks stable and well adhered but a blister forms after application of the new coating and that blister is back to bare timber or the coating before the existing it is the case that the previous coatings do not adhere and the application of a new paint film with its film tension has caused the blister.

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