Master Painters Australia
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Master Painters Australia |
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FOR IMMEDIATE RELEASE
BLISTERING OF NEW PAINT OVER PREVIOUSLY PAINTED SURFACESWhy it happens and how contract documentation should cover the riskToday's Date -- 19 June 2003 Blistering of new paint films applied over multiple layers of old paint films is not caused by the new film itself, but is generally attributable to an increase in pressure behind the new coating caused by expansion of liquid, gas, efflorescence (salts) or the like contained in, under or between the previous coatings or in the substrate beneath those coatings. Although the new paint film may adhere well to the layer immediately beneath it, blistering can commence at lower levels where the adhesion between any two previous layers is weakest (sometimes where there is a layer of an “inferior” material) causing delamination at that level and causing all the layers above to lift and blister together.
To assess the probability of such blistering occurring, the existing surface can be tested for moisture, salt content and strength of adhesion.
Because all three classes of tests are “destructive”, it is impractical to perform multiple tests across the full extent of a surface to ensure that adhesion levels, moisture content and inter-layer contaminant levels are consistent across the full surface to be painted. Moisture levels and strength of adhesion may vary from place to place over a painted surface, and it is therefore not possible to predict with certainty whether a “positive/strong” adhesion test result or “low/dry” moisture test result obtained from sampling at one point indicates that the level of adhesion and probability of blistering will be consistent across the entire surface.
Unless it is possible, practicable and permitted by the building owner to use destructive methods to conduct adhesion tests and moisture/contaminant tests over a truly representative range and number of locations on a surface, it is not possible for a painting contractor to predict with certainty whether blistering or delamination will or will not occur when a new paint film is applied over a previously painted surface.
The Association therefore recommends that the contract and specification should state, and make clear to the client, that the contractor assumes that the surface to be painted, whether tested as above or not, is sound and fit to be painted. In the event that blistering or delamination should occur during the application of the new paint or in a period soon afterwards, remedial action to completely strip all layers of the previously painted surface and apply a new paint film should be regarded as a variation to the originally specified scope of works. Addition costs and time to complete works according to that variation should be allowed. However, unless the contract and specification has made it clear that a claim will be made for such a variation, the contractor may be denied the right to claim for the additional cost incurred.
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