Does Chemical Damp Proofing work?

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Chemical Damp Proofing with silicones


The technical review below summarises the problems of the last generation of liquid damp proofing systems. Our New Generation Creams are infinitely better for the following reasons:

  • no pressure used in placing the cream in the hole, so no losses down cracks and crevices
  • gradual spread of the cream giving even distribution, unlike liquid short term squirt and stop techniques
  • no solvents to evaporate, so no smell, no health hazards and nice slow spread
  • not caustic and non-staining, unlike the old water based DPC Fluids (Siliconates)
  • no solid stick to push into a ragged hole and a lot cheaper

For help with Silicone Creams call our experts on 01626 331351.


Unlike a physical damp-proof course these injected liquid damp-proof courses do not form a 'discrete impermeable plane', but more of a 'diffuse band'. When fluids are injected into a heterogeneous substrate such as brick/mortar they do not totally fill up the porous structures and neither do they completely push out the water in front of the advancing injection fluid as is so often claimed. Instead, the fluid tends to 'finger' within the substrate, a process known as 'viscous fingering'. The fingers of the injected material form when the fluid takes the lines of least resistance such as the larger pores and cracks. Unfortunately, such pathways are not the most important elements in the conductance of water up the wall. Furthermore, the damper the substrate the greater this fingering is likely to be, especially with solvent based systems since these are not miscible with the resident moisture. Fingering is also increased by injection at high pressure. Reduction of the phenomenon is obtained by low pressure injection or, better still, by gravity diffusion of the DPC fluid.

For help with pressure injected damp proof courses call our experts on 01626 331351.


The result of the damp-proofing fluids forming fingers give rise to non-impregnated 'pools' within the wall through which water can continue to rise. In the case of pressure injection damp-proof courses, this suggests that it is unlikely that the diffuse band of the damp-proofing agent will be totally complete. The resultant chemical damp-proof course may therefore not stop rising dampness by causing an immediate cutoff of rising water above the damp-proof course like that effected by a physical damp-proof course. Instead, a relatively rapid decline in the moisture gradient should occur above the inserted chemical damp-proof course due to the 'control' exerted. Thus, in practice, the rising ground water should be reduced to such a level that, in association with specialist replastering, it should no longer cause decorative spoiling or damage.

For help with pressure injected damp proof courses call our experts on 01626 331351.


The efficacy of the water repellent damp-proofing systems can be affected where there are detergents (surfactants) impregnated into the wall by, for example, past leakage from sink waste pipes. A similar problem may occur when walls are sterilised against dry rot infection by biocide formulations containing surfactants. The overall effectiveness of a remedial damp-proof course can be investigated by examining the relationship between the distribution of free moisture (water due to rising dampness or other source of active water ingress) and contaminant salts (chloride and nitrate). Where rising dampness is still active capillary moisture will be found to the full height of salts. The absence of capillary moisture in the presence of salts arising from rising dampness indicates that drying back has occurred and that the damp-proof course is effective. Intermediary stages are also found which demonstrate different degrees of control of the rising dampness. If chloride and nitrate are not detected in a sampled profile it is possible that the ingress of moisture is due to recently developed rising dampness or more likely through rainwater penetration, condensation, plumbing defect or other sources.

For help with pressure 'salts' analysis call our experts on 01626 331351.


When evaluating the efficacy of remedial damp-proof courses care must be taken not to misinterpret electrical moisture meter readings; high readings might not indicate that the damp-proof course itself has failed. They may reflect a number of possibilities including contaminated or inadequate plasterwork. Thus, an accurate assessment of the efficacy of a damp-proof course can only be undertaken by determining full moisture profiles linked with analysis for contaminant salts. It is also important to give consideration to the expected performance and limitations of the installed system as described above.

NOTE: It is identified in BS 6576:1985 that where timber suspended floors are encountered the damp-proof course must be injected, where possible, below joist level; this is to protect the embedded timbers from dampness and the risk of fungal decay. However, given the likely efficacy of injection systems the embedded joist ends could still remain in contact with damp masonry even if above the injected damp-proof course and may therefore remain at risk to fungal decay. It would be considered prudent that in all cases where a damp-proof course is installed in relation to a timber suspended floor, action is taken to protect any embedded timbers just above and certainly below the injected damp-proof course to prevent potential decay! Boron Gel, injected Boron Paste and the insertion of a plastic membrane can all be used to protect vulnerable joist ends and bearings. Do NOT bag joist ends in plastic - this can lead to serious decay, due to condensation and lack of breathing.

For help with testing a damp proof courses call our experts on 01626 331351.

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Site written by: David Moore

David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author


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