Exterior primer issue

[wwwebber]

Hi - we are in the process of re-painting the outside of our 1885 house. There are some areas that are quite powdery - especially the old lime mortar where the old paint has come away. We have bought the following product to resolve this prior to re-painting :-

http://www.dulux.co.uk/products/info/usage/weathershield_exterior_stabilising_primer.jsp

The instructions clearly say that new or sound surfaces must not be treated but it doesn't say why. Anyone here know why ?. As the surfaces we are working with are changeable we were intending on treating the entire surface - even the sound painted & bare areas as treating the trouble spots only would be almost impossible.

Some advice would be appreciated.

 

[TheDec]

A stabilising solution when applied to sound masonry will offer a finish of which becomes to smooth to accept the application of paint, in simple terms the paint will fail to bond, resulting in an early breakdown of the system. A pic or two would be handy here.

Dec