Marianne - Pattern Staining

I wonder if you can help?

After lining the living room walls, my husband then painted them a pale yellow colour.  The result was brilliant, but now, some years later, there are dark lines showing through in a pattern which resembles the edges of the breeze blocks underneath the plaster.  Is this a common problem?  What should we do to prevent it happening again now we want to re-decorate?

Marianne 

Marianne

 

You almost had the reason for this problem when you mentioned the word pattern.

It is in fact known as 'pattern staining' and occurs because there is a difference of temperature between the breeze block and the mortar joints.

 

The blocks contain many air holes and are warmer than the more dense cement joints.

Warm air in your room, which carries fine particles of dust, is attracted to the colder parts of the wall, in this case the mortar, and over a period of time a pattern of the joints will appear.

 

The solution. The first and most expensive is to inject the cavity with insulation, this work must be carried out by a qualified installer. Or you could line the wall with expanded polystyrene before normal decoration, but do not forget, expanded polystyrene is highly flammable. Decorating the problem area more often may be your solution, or using a different colour.

 

Hope this goes some way to solving your problem.

 

Fred Biddulph