The following excerts are taken from the book "Understanding Dampness" written by Peter Trotman, Chris Sanders and Harry Harrison of the Building Research Establishment (BRE) in England

Installing a new DPC

The methods for installing a new DPC are described generally as 'traditional' (the insertion of a physical DPC) or 'non traditional'.  We strongly recommend that you consider only those that have been awarded an Agrement or other third party certificate. Chemical injection is the only method that satisfies this requirement and is the only method which BRE considers suitable where it is not suitable to insert a physical DPC. Physical DPCs can only be placed in brickwork or coursed stonework, random stone walls or rubble infilled walls are not suitable. Unusually thick walls can rarely be treated and it can be dangerous to attempt installations of this type for structural reasons. Chemical injections systems can be used in most types of structure.

Chemical injection systems

The success of chemical injection systems depends on the efficiency of the fluid penetration of the damp structure. The repellents are injected or transfused into closely spaced holes in brick or mortar courses along the DPC line. Treatment must be carried out at different depths to ensure penetration through the entire thickness of the structure. The transfusion methods, carried out at low pressures with aqueous repellents should, in principle penetrate more effectively than high pressure systems since they depend entirely on diffusion processes which are the only processes that can eventually give complete penetration.

Recent new products such as Dryzone are known generically as creams or gels. The cream is a concentrated viscous silane/siloxane emulsion, inserted by a low pressure gun through 12mm diameter holes drilled at the base of the wall at intervals of up to 120mm. No carrier fluid is used so the curing process is more rapid. British Board of Agrements (BBA) Certificates are available for some products.

DRYZONE