Thinking of painting the outside of your home? Chartered Surveyor Stephen Cornish PhD MA BSc FRICS FFPWS explains the importance of allowing your home to breathe!
Since the 1970s the painting of external walls to houses has often been considered an opportunity to improve weather proofing in addition to decoration. However, there is extensive evidence that the use of some modern paints applied to some external walls of houses has increased dampness and frost damage.
Our forebears in the construction industry never considered that decorations to walls, whether it was applied to brick or render, should be relied upon to prevent damp penetration. Instead, reliance was placed upon clay bricks, lime-based mortar and render absorbing rainwater before the structure dried-out naturally through the effects of the sun and wind.
The use of the wrong type of paint and/or poor-quality preparation of the painted surfaces can lead to splits developing in the paint film allowing rainwater to find its way in and saturate the wall.
The remaining “impervious” paint then acts as a cloak to entrapped moisture, preventing it from freely evaporating into the atmosphere. During the freezing winter months, the moisture within the wall will expand and can cause the surfaces of bricks to soften, flake and crumble.
Moisture also moves from the interior to the exterior by heat transference or filtration without causing significant problems to walls; in other words, the buildings ‘breathe.’ An impervious paint film prevents this natural ‘breathing’ process which can promote major condensation problems; if it combines with the effects of entrapped moisture the damage to the walls could prove costly.
Woodward Chartered Surveyors will look for the defects of non-breathable paints when undertaking a Building Survey or report for a home buyer (see Choosing the right survey).