Rising Damp
I am often asked the following questions:
How do you cure damp? How do you cure rising damp? What is rising damp?
The surveyor's survey says the house needs a chemical dpc. What does that mean?
The cure to damp in walls is in some ways easy but the diagnosis often is not so straight forward but there are things you can do and look out for before you call a surveyor. The first interesting thing to note is that in all the years I have been surveying I have never come across a real case of true rising damp. It is rarer than you think. It is not uncommon however to find walls injected with a chemical DPC that didn't need it.
What is a DPC? What is Rising Damp? What is a chemical DPC?
DPC stands for Damp proof course. A brick will absorb water and pass it on to the other bricks around it. This way water can appear to "rise" up a wall. When water rises up from the ground through bricks we call it "rising damp". By placing a waterproof layer (DPC) at the bottom of the wall the theory goes that water cannot rise up. If the wall has no DPC it is possible to inject a chemical to make the bricks water resistant and this is called a chemical DPC. You actually need quite a high water table to create rising damp to levels occupants complain about.
What Causes walls to get wet?
Bricks can get wet in a number of ways, the most obvious is when it rains and conversely they dry out when it's warm. Basically every time it rains walls get wet and when it is sunny walls dry out. If the wall is made of solid brick then as long as the wall dries out before the water reaches the inside no one need worry. To stop water getting to the inside modern walls are in fact two walls separated by a gap (cavity). The outside wall can get as wet as it likes because the inside one will stay dry. These walls are connected together by ties and sometimes these connecting ties carry the water over to the dry wall. This is not rising damp. The next biggest cause of water getting into the walls is found in human breath and hot water in the house (baths, sinks and tumble dryers). You cannot see this water but if it touches a cold enough wall it will soak in and the wall appears wet. This is not rising damp.
If solid walls get wet because of moisture coming from inside and cannot dry out because there is a water proof surface on the front (eg cement render or a water sealant) then the wall "fills up" and can appear damp all over. This is not rising damp.
In the damp / drying cycle if there is more damp time than drying time then the wall may not cope. Walls soaked by leaking gutters, copings, parapets or rainwater pipes or are in the shade will not cope as well and can stay damp. This is not rising damp.
As there is more than one way to get a wall damp it follows that the wall could be damp because all of the causes are present. Removing one cause may not be enough. You need to be methodical.
Cure for damp?
Here are some top tips for keeping your walls dry before you start looking for cures. If symptoms persist then call a chartered surveyor.
- Have patience with walls because they do not dry out quickly. Allow 1 month per 25mm of thickness. If you make adjustments wait to see what happens.
- Keep your house well ventilated. You only need to open a window for a few seconds to reduce the moisture in the room.
- Keep bathroom and kitchen doors closed when cooking or bathing and vent those rooms well.
- Keep gutters and rainwater pipes leak free.
- Remove heavy plants from walls ie Ivy
- Look for a Damp Proof Course. It must be 150 mm above the ground. If it is not or it is covered over because the wall is rendered or the ground has been raised then this should be remedied.
- Check underground waste pipes near the wall are not cracked.
- Check if there are any water pipes in the wall and check they are not leaking.
- If you have a solid wall don't paint on water seal before you know what the consequences could be.
- Walls in basements don't get rising damp. Its more complicated than that so it would be best to call us if you need advise on basement walls.