opps said:
If DPCs don't do anything, why didn't the damp return?
The plaster they use stops any damp coming through
And what kind of plaster would that be? Please don't confuse plaster with waterproof render which is often used to make a building more flood-proof in the future (render dries out a lot faster than plaster after a flood)
A large percentage of the housing stock in my area is Victorian, stone or stone and brick built, so pyramid-form masonry foundations and no DPC. Some even older properties have rubble infill stone walls, again with no foundations, although the walls taper from the ground level upwards. The local stone is sandstone, both bedock and for building. Sandstone is most certainly not impervious to water.
I've lived in both types of houses - and they all seem to suffer from a form of "rising damp" in addition to condensation problems when you centrally heat them. At certain times of the year when rainfall is very high the water table gets very near to the ground surface level - near enough to soak into the brick or stone foundations. All the houses I've lived in have been on the valley sides - too great a risk of flooding in houses built on the flood plains in the valley bottoms for my liking - but one thing which is consistent is that damp measured in the masonry using a Tramex meter is always further up the walls on the uphill side than the downhill side in autumn and winter and the water seems to get drawn up into the sandstone masonry, although normally only a few feet above ground level. Put in an injection DPM and it stops a large percentage of that happening, but as said so many times in so many places, there is also a need to ventilate well, especially if you have double glazing and loft insulation
One of our houses was a stone-walled/rubble-infill house where damp inside the back (uphill) wall got to nearly 5ft above the floor level. This was not condensation. The "cure", used a lot locally, was to strip back the (lime) plaster to ceiling level and injection DPC the walls, which dried the wall out nicely. After 6 months I rendered the wall with a thin skim of waterproof rendering then I skim plastered over that. Before doing the DPC we'd endured two damp, miserable winters in this house (no CH downstairs, we had a wood burner in the living room, which itself requires a lot of air flow/ventilation, and a solid fuel Rayburn in the kitchen). The "non-essential" injection DPC cured the back wall's tendency to turn into a really cold, damp area in the winter.
I agree that firms selling injection DPC are often trying to sell a simple solution, but this type of product shouldn't just be written off. It has its' uses.
BTW, that comment about Dutch houses not having a DPM is a red herring (of een rode haring in Nederlands). The Dutch tend to build on a different foundation, which is several layers of different types of compacted gravel and sand which to the untutored eye looks like no foundations, but the masonry which goes on top in a modern building has to have a DPM. I built two houses for myself over there in the 1980s, a conventional timber frame and a SIPS panel respectively and both houses were built onto a concrete raft which had a conventional DPM