BRE Digest 245 states that a physical damp-proof course is the only fully reliable and permanent method of retro-fitting a d.p.c. but it is a time consuming and labour intensive process and consequently very expensive compared to other forms of damp-proofing.
An early method of physical damp-proofing was simply the replacement of bricks with Class B engineering bricks at the appropriate height, typically 150mm above ground level, but this method is only suitable for short runs and if longer sections of wall are need then diamond tipped chainsaws are used to cut a section through the full thickness of the wall, including the internal and external finishes, to from a gap in the brickwork wide enough to allow the insertion on the damp-proof course which is then sandwiched in a dense mortar above and below it. The damp-proof membrane is overlapped with the neighbouring section of DPC membrane to ensure a watertight finish. Slate wedges are placed approximately 100mm -125mm centres, from both sides of the wall, and staggered. These are driven home in order to compress the mortar as well as providing adequate structural support for the wall. The slate wedges are then trimmed and made flush with the external brickwork and internal walls. The mortar joint can then be re-pointed in the normal way and the internal surface should be made good and skirting boards etc replaced.
To prevent any structural instability the cutting can only be done in short lengths, usually around one metre and alternated in a similar way to carrying out underpinning. The damp-proof membrane is usually copper or bitumous felt and both of these are sufficient to prevent rising dampness from the ground. There is also a system of forcing ribbed stainless steel sheets into the groove using a pneumatic hammer to push the steel through the full thickness of the wall.
The lifespan of a physical damp course is far longer than any form of chemical damp-proofing, electro-osmotic damp-proofing or evaporative siphon damp control systems and it creates a total barrier against rising damp with firms who fit physical damp-proof courses offering 50 year guarantees against the recurrence of rising dampness from the ground.
If you need any more information about the installation of physical damp-course then please call us on 020 8226 3101 or e-mail