My silicate paint has not bonded to the wall. What are the causes?

My silicate paint does not appear to have bonded to the wall. What are the possible causes?

The pure silicate paint works by forming a silification bond with the background i.e. a physical bond with the silica sand in the stone/mortar/render. If for any reason this silification bond is prevented the paint will just sit on the surface and will be more vulnerable to degradation.

Reasons for the failure of bond include:
• The paint being affected by frost before it has cured
• Non-permeable, non-absorbent backgrounds which do not allow the water glass solution to penetrate (this can happen on random rubblestone walls where some stones are geologically different and on renders with a closed surface).
• Rapid drying due to winds/direct sunlight
• Waterproofing agents on surfaces
• Pollution and green growth on surfaces
• Paint applied too thickly without correct thinning and/or without leaving at least 12 hours between coats.

If the paint does not form this bond and sits on the surface because it does not have an acrylic binder to ‘stick’ the paint onto the substrate (not having acrylic is a good thing for vapour permeability and building health) then areas can flake fairly rapidly unlike a modern acrylic which will ‘hold on’ until moisture builds up and it fails wholesale.

The best thing to check is absorbency on these areas - a quick mist with water will show you. Make sure all pollution and green growth is removed and re-apply fixative and the correctly diluted paint – With strong colours touching up can often show so keep this to a minimum and just touch up around the areas of bare wall – if you simply paint a square over the bare wall this will show up.

Onto surfaces which lack a key and are not ‘open’ for the silicate bond quartz filler can be used after applying the fixative and before applying the paint.