Rising Damp explained
Brick and sandstone walls in contact with the ground absorb moisture from the ground because they are porous (like a sponge) this moisture will rise up the wall until it reaches the damp course if the damp course is in tact. If the damp course is broken or missing altogether then the moisture will continue to rise further up the wall.
If the wall is rendered or painted, the surface can become damaged due to the excessive moisture in the brick, causing the render or the paint to bubble or become pitted and fall off the wall.
Proper sub floor ventilation will help slow down the capillary action by having air flow passing along the wall and reducing the moisture by evaporation.
What is a Damp Course and what if I don’t have one?
The damp course in more recently constructed homes is a plastic membrane that runs horizontally in the brick wall. Moisture will rise to this level and stop as it cannot pass through the plastic.
In older homes a damp course can be made of slate of malthoid type material. Both of these become brittle with age and will crack if the house moves (as houses do) allowing moisture and termites to gain access through the cracks.
If a wall has no damp course, or the damp course has broken down, there are a few different options to install a damp course into existing homes, all of which are quite expensive and very messy.
The major options are
- Cut out mortar joint at damp course level and insert an envelope which pumps fluid into the joint and sets, this is done about 1 metre at a time around the entire house.
- Drill 2-3 holes per brick at damp course level and injecting a silicone product which absorbs into the brick and then sets. This silicone brick then becomes the damp course.
- Holes are drilled into the brick at damp course level and electrodes inserted. An electrical current is used to stop the moisture.
We recommend contacting a licenced and reputable builder for further information in installing a damp course and if you are looking to have a damp course installed, in most cases sub floor ventilation will still need to be improved.