Damp-proofing a Grade II listed building

Newton  Waterproofing staff have been approached with the following question: "I have a Grade II listed building that I intend to convert into habitable space. The age of the building means that the walls do not incorporate any form of damp-proof course. The walls are a combination of brick and stone construction and some are substantially thick – between 400 and 1200mm. Although none of the walls are overly wet, I suspect that there will be a level of residual and/or rising dampness; I can see visible salt deposits on the walls, especially in the low-level mortar joints. I recently had a survey done by a local damp-proofing company who have recommended injecting a chemical damp-proof course. In your experience, is this the right course of action?"

The reply from the Newton Waterproofing expert: "I would be very hesitant to recommend the insertion of a chemical damp-proof in the walls for the following reasons:

The whole process can largely be seen as hit and miss. You should only ever consider a chemical damp-proof course to be a prohibitive measure against rising damp and not a total cure.

It is quite an exact science in that you have to drill holes at the correct diameter to within 40mm of the opposite face of the wall being treated, and then gauge precisely the correct amount of fluid/cream to insert in order to achieve affective dissipation in to the substrate.

This is affected greatly by the type, porosity, condition and thickness of the wall. I have seen a lot of fluid pumped into walls that contain voids and fissures, where the fluid is simply running out of or filling the imperfections and voids. You are relying on a band of siliconate distributing itself evenly in to a substrate. The aforementioned process is hard enough to guarantee in walls of a standard thickness, let alone walls over 1m thick.

Companies that specify and install chemical DPCs will often do so in conjunction with a plaster incorporating a waterproof and salt-retardant additive, in the hope that the combination will deal with the effects of the rising dampness.

Also for walls where you suspect large fissures, cavities or areas of rubble, you should firstly inject a low-viscosity, cementitious-based grout in to the voids prior to applying the chemical damp-proof course. This will add further cost to a process that is usually very expensive in the first place. To add to the difficulty, you would also have to be able to access the walls from both sides.

With the above borne in mind you are right to be sceptical. There are companies who can install a chemical injection properly in walls of this thickness, but they would probably go down another avenue to be sure of success and indeed to be competitive on price.

Drying-out times for damp walls

In addition it is generally accepted that wet walls after treatment will have a level of retained dampness and that it takes in the region of 1 month per inch thickness of the walls to dry. That would mean that the walls in question here could take years to dry even after to insertion of an effective damp proof course and you know how likely I think that would be.

In my opinion a far more affective solution would be to apply a cavity drain damp proofing membrane such as our 803, or 803 Newtonite.

Newton 803 Newtonite is ideal for listed buildings as it is deemed 'reversible'

They are described as cavity membranes because the stud profile creates an air gap between the membrane and the wall to which it is applied. Once applied to the damp wall (usually up to at least 1m which is generally excepted as the extent to which dampness will rise), the membrane allows any moisture in the wall to evaporate into the air gap but because it is free to move unhindered it is not pushed to adjacent areas or higher up the wall and the membrane unlike any damp proof course will provide an impermeable separation barrier between the damp wall and the new wall finished which is permanently effective against damp, salts, staining etc. The membranes are attached using special sealed mushroom fixings and despite some concerns the membranes can be easily fixed through retrospectively if required. Plastered finish and dab fixed plasterboard , battens or dry lining framework and plasterboard provide the rooms usual aesthetic appearance with the peace of mind that the membrane will prolong their longevity. In my opinion this is a good and cost effective method of treatment which can be guaranteed by a Newton registered installer who for budgeting purposes will charge in the region of 25-30 per m2 supplied and fitted with an insured guarantee. Call us on 01732 360095 for a registered installer in your area.

Creating An Air Gap To Allow Ventilation

This form of damp proofing provides a physical separation barrier mechanically fixed internally to the affected areas and the air gap provided by the stud of the membrane allows the wall to “breathe” thus allowing dampness to move unhindered in all directions which does not change the status quo of the walls or push dampness to other areas and is not subject to guess work application like the alternative chemical injection processes.

Conforming to conservation authorities

Newton Waterproofing damp proof membranes almost always conform to the requirements of the conservation authorities for use on historic buildings and has been used on many grade I, II and II* listed buildings because they:

  • Allow the walls to ‘breathe’
  • Can be curtain-hung behind a framework
  • Are deemed reversible

In fact the Property Care Association (PCA) who are the UK’s damp proofing industry Trade Association say in their code of practice that for any wall in access of 400mm other forms of damp proofing other than a chemical damp proof course should be considered.