How Does an Injected Damp Proof Course Work?
In the majority of cases, an injected DPC will involve drilling the mortar beds in a wall, and inserting a cream, which carries materials which are considered to be a PORE LINER.
These pore lining materials are typically silane/siloxane, derived from silicone.
How do they work? If you read my previous post (link) concerning capillary action, this discussed the mechanism behind the surface tension of water, and the way in which this, and the bond between water and the sides of a container (pores/capillaries in this case), causes water to curve upwards - this being observable with water placed in a clear glass - with that upwards curve.
This upwards curve is called the meniscus curve, AND WHERE WATER CAN BOND TO A MATERIAL, that curve will be CONCAVE.
It is this combination of surface tension and bond, resulting in an upwards (concave meniscus) curve which allows moisture to rise through pores and capillaries.
So what do pore liners achieve? They are water repellents (hydrophobic) and defeat the bond between water and the pores/capillaries.
The effect of this is that the meniscus curve is not concave / curving upwards, it is convex and curving downwards, and so the surface tension cannot pull moisture upwards, hence they prevent rise of moisture via capillary action.
NB #1: Not all injected DPC's are pore liners.
NB #2: The fact that pores are not blocked maintains vapour permeability, although it may be reduced.
NB #3: Injected DPC's are not the ubiquitous solution for all damp issues and understanding of issue and structure must drive specification - my point in writing these is to provide understanding (always a good thing) and hopefully better decisions can then be made.
NB #4: A 'DPC' is typically a 'system' comprising an injected material and an associated replastering specification - the above simply covers the injection component intended to defeat capillary action.
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