Damp Proof Coursing (DPC) is such an important aspect of bricklaying and it is something that is so overlooked, given it has the potential to create many ongoing and costly problems.
As practicing Bricklayers and contractors, we have been handed down so much more responsibility and extra work (unpaid also) in installing DPC. It has to be constructed in a way as to not only stop water penetrating into dwellings, but also to prevent rising damp. The issue of rising damp is often overlooked and creates huge dramas if not addressed correctly in construction.
It is a known fact that rising damp may penetrate through a concrete slab. The general thinking is that the concreter would have placed plastic under the slab. However, if there is a footing under the slab there will not be any plastic.
Now to the corners
Many carpenters have little idea of cutting in corners which leaves gaping holes requiring another piece of dampcourse cut to patch the hole later on. I am vigilant about this. Corners, no matter how much we try, have more mortar dropping from them, than on the average straight wall because the bricks are laid from both directions.
This results in significantly more mortar collecting in the cavity at the corners. As Bricklayers we have to be on the lookout, especially when the DPC has not been fitted correctly.
Some builders place the DPC on brick veneers under the wall frame to combat rising damp. This is not good as the DPC only has a potential of about 30mm under the plate. Any droppings in the cavity over this will allow water to penetrate under the bottom plate.
It is really important that the DPC has plenty of height. Rain, pushed by driving wind, can force the water into the cavity through the weep holes, resulting in the water backing up. If the DPC is not high enough to penetrate under the bottom plate, carpets and such like, as well as rotting skirting and timber work can result.
Keeping the cavity and the weep holes clean is always good policy.
I still believe in putting on a row of ties on top of the first course of bricks laid directly on the DPC. The ties which can be bent into the holes of the brick are attached to the wall frame, unlike the method in the AS3700 where the DPC is to be sandwiched in mortar. This never looks tidy as the flashing ends up wavy.
This is also my rule for cavity brickwork. The damp-proof coursing usually sits up one course higher on the inside skin, so put the wire cavity ties on top of this course (embedding them into the mortar), this gives a much stronger result.
I am writing this as a Bricklayer who has had to deal with problems in these areas. Believe you me that it is so much easier to spend a little time with DPC.
Author: Bricklaying – The Art
For further information on DPC refer to Bricklaying – The Art by Peter Cartwright – The Ultimate Guide to Bricklaying for the Beginner through to the Professional