Module 3 Hmk Quiz Q6

[Ben Gorman]

Here is Question 6, along with my thoughts about how to answer it. I don’t know whether or not I have the correct answer. I would be really interested in your comments.

Be aware that the online quiz tends to change the order of the answer options.

**** BACKGROUND TO QUIZ QUESTION ****

Walls
The bricks used have some imperfections – a result of variation in quality of the local clay used and an inconsistent firing process – and so are relatively rough and fissured in texture. However they appear have stood up to the exposed weather conditions reasonably well. Nonetheless there are areas of the brickwork surface that have spalled (area f).

**** QUIZ QUESTION ****

Quiz question 6
The old plaster just above the junction between the 1m high damp proofing interior render has lost its adhesion to the brickwork behind and ‘blown’ (area m). Why might this be?
1. The chemical composition of the plaster and wallpaper glue has caused a reaction and expanded the plaster at the junction, leading to salt solutions damaging the plaster.
2. The paint and wallpaper used has not been of a correct specification to cope with the two types of plaster, breathable paint would have avoided this problem.
3. The injected damp proof course is ineffective, and rain is penetrating through the brickwork and at this junction strong evaporation leads to salts crystallising behind the old plaster.

**** MY THOUGHTS ****

I chose 3 here because I know DPC can often be ineffective and I know evaporation can cause salts to crystallise.

[Tim Gilbert]

Hi Ben,

There are two conflicting points.

A failed DPC and impermeable layer would drive damp higher but the DPC does not need to have failed if driving rain is soaking through the wall, particularly if there were salts left in the wall from before the new DPC was installed.

Tim

[Author]

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