Following on from my last blog, regarding damp in a three month old extension, I recently encountered a similar issue, whereby a newly constructed extension, was again affected by damp and decorative spoiling within a few months of the extension being completed. The affected wall, would have once formed the rear wall of this building, before the recent addition of a new rear kitchen extension.
New or Pre-Existing Damp?
The homeowner saw the obvious coincidence, that the dampness must be related to the new construction works, whereas the constructor, thought this was a pre-existing problem with damp, and nothing to do with the new extension.
We did see obvious decorative spoiling to the wall, with the emulsion paint, blistering and flaking from the plasterwork, and further recorded high relative surface readings using the Protimeter MMS2 in pin mode.
To establish, whether this was new or pre-existing damp, we then carried out testing for moisture at depth, both at wall base, and to other areas which seemed worse affected by decorative spoiling. The highest reading obtained was 1.5% total moisture content. This is a fairly insignificant level of moisture, and certainly not high enough to cause decorative spoiling.
Often, new plaster has been applied without an air gap, at the wall base, so it is in direct contact with the solid floor slab. Since plaster is significantly more permeable than the underlying masonry, then it can wick up moisture, and cause spoiling of the plasterwork. To rule out this potential issue, we removed a small section of skirting board at wall base. As can be seen, this was not the issue.
The Problem with Newly Plastered Walls
Since there is no significant problem with moisture at depth, and the plaster has been applied correctly, then what can we conclude?
Hard plastered walls generally take circa 6 months to dry out, and the general rule of thumb, is that you should only apply a single mist coat of emulsion, until the plaster has dried out, after which, the walls can be fully decorated. After speaking to both the contractor, and the homeowner, it was clear that the walls were fully decorated within a week or two of the plaster being applied. It was therefore my opinion that construction moisture had caused the decorative spoiling.
Is it the Contractors fault?
Not necessarily, and in fact the homeowner was clear, that she wasn’t prepared to wait 6 months for the walls the dry, and accepted, the inherent risk, in rushing to apply decorative finishes to walls that had just been plastered. The one piece of advice I’d give to any contractor, is that you should insert a caveat into your contractural arrangements, to state that newly plastered walls should be given 6 months drying time, prior to being fully decorated. In this case the contractor did not do that, or warn the client of this inherent risk. In this case, both the contractor, and the homeowner, were both reasonable people, and this wasn’t the cause of any major dispute, but it’s easy to see how it could be.
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