Chemical injected DPC

Rising damp is caused by capillary action drawing moisture up through porous elements of a building’s fabric. This can result in:

• Condensation or damp patches (typically up to 1 m above the floor).
• Corrosion of metal elements such as beading.
• Damp odours.
• Timber decay, such as skirting boards.
• Damage to surface finishes.
• Tide marks and staining (typically up to 1 m above the floor).
• The presence of white salts.
• Health problems.

Modern buildings avoid rising damp by the inclusion of a damp-proof course (DPC), a barrier, usually formed by a membrane built into the walls. However, older buildings may not have a DPC. In this case, a chemical injected DPC can be inserted to create a continuous chemical barrier to rising damp.

A series of holes are drilled into the wall at low level, the number and pattern of which is determined by the construction of the wall and its thickness. High and low pressure injection can then used to introduce a water-repellent chemical fluid that penetrates across the wall and between the holes forming a continuous barrier.

Treatment generally also involves remedial work to any corroded or decayed elements of the building fabric, as well as hacking off and replacing existing plaster to a height of 1 m (sometimes replacing it with a waterproof plaster). However, this can be very disruptive as sockets have to be taken out, skirting boards removed, radiators removed and so on.

The technique is best suited to brick or block buildings, as they tend to be of a relatively uniform construction. However, it may not be effective if any gaps are left in the wall construction, or if gaps form over time with material deterioration. Equally, if the method is applied to walls that comprise materials of varying permeability levels, such as walls with rubble infill, it can be unreliable as the injected solution may not accumulate where it is required in the sufficient quantities. This can be due to the solution following the lines of least resistance in the wall material.

Damp in some older buildings may actually be caused by a leak or a defect in the wall construction, such as a cracking, rather than by rising damp, and this may not be rectified by the insertion of a damp-proof course. It is important therefore that any defects are identified and corrected first before accepting the cost and disruption of inserting a damp-proof course.

Other solutions might include the insertion of a DPC (rather than injection) or drainage solutions such as french drains.

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[edit] Related articles on Designing Buildings Wiki

• Breather membrane.
• Damp-proof course DPC.
• Damp proof membrane.
• Interstitial condensation.
• Rising damp.
• Rising damp in walls - diagnosis and treatment (DG 245).
• Vapour barrier.