Dryzone Damp-proofing Cream

Rising damp occurs mostly in older buildings (100 years or more) where there is no DPC (damp proof course). It will usually climb to a maximum height of one metre in a wall before it runs out of energy and climbs no more. If you have a physical DPC, even an old one, it is fairly unlikely that it has failed. Damp proof courses don’t wear out. Even an old slate damp proof course, which may have cracked in a few places with building settlement, is unlikely to let significant damp past.

If you have a DPC, you should be able to see a continuous line of black bitumen, plastic or slate around the brickwork just above ground level. Buildings used to be built with locally sourced materials. So in some areas they used to use two course of hard engineering bricks (which are waterproof) with water proof mortar, to form two damp proof courses. In stone buildings with no regular horizontal course there is unlikely to be a damp proof course.

How To Tell If Your Damp Is Rising

If you have damp on the inside walls at low level, don’t immediately assume that you have rising damp. If you call in a surveyor from a damp proof specialist company they are likely to find rising damp with their little meter. This is because they are salesmen not surveyors, many have families to feed and they have no real interest in looking for other causes for the damp. It is therefore up to you or an independent surveyor to look for other causes.

These could be:

• Ground levels built up over the DPC which causes bridging from below the DPC to above it. Ideally the ground should be at least 150mm below the DPC to prevent bridging or splashing.
• Sand and cement render that has been applied over the DPC. This also causes bridging and needs to be hacked off.
• Leaking gutters. Also check downpipes to see if they are leaking around the back and causing water to pour down the walls. Ensure that excessive amounts of water isn’t falling on the ground from leaking or blocked gutters. The best way to do this is to go out in the rain and take a walk around your property. Don’t worry if your neighbours think you are mad, they probably do anyway.
• Condensation. Another very common cause of damp is condensation. Fortunes have been spent and lifetimes wasted trying to waterproof walls from the outside or even from the inside with water proof paint only to find that the real cause of the damp is condensation. (Check out our podcast on condensation and ways to deal with it). To find out if you have condensation tape some cooking foil patches on the wall and see how quickly they mist up. If it has a film of damp on it in the morning then condensation is a possible cause of the damp.
• Internal Bridging is a cause that is often overlooked. If you have eliminated all the above then it is possible that mortar or debris has filled the cavity and bridged it which allows water to pass from the outer to the inner skin. The only way to find out is to take a brick out where the damp is and have a look. A mirror and a torch will be useful for looking along the cavity. Alternatively put a small point and shot camera in the hole and take some pictures. The cavity should be clear.

If you decide that you have got a problem with rising damp then chemical injection is the cheapest way to cure it. It isn’t 100% guaranteed but it can be fairly effective in reducing damp to a negligible level. If you need a certificate for a mortgage company then you will have to have it done professionally just to buy the piece of paper but if you just want to cure the damp then DIY damp proofing is a real option which you can do for a fraction of the cost of a professional firm.

What To Use

Products such as silicone sprays and damp proof paint should be avoided unless you have a clear idea of what you are trying to do. Many just track moisture in or seal it in. Injecting chemicals is much more effective and easier than it sounds, but it won’t work in basements. If you inject a DPC you can buy the same products as professionals use, and they are often cheaper than DIY products. Professionals will not usually guarantee their injection jobs unless they are able to hack off the internal plaster and render the wall with waterproofed sand and cement. This is because hydroscopic salts may have migrated into the plaster and these attract moisture from the air. This may or may not be the case depending on the ground and brick work and if you don’t see the white salt on the surface it is unlikely to be there.

How To Do Your Own Damp Proof Injection

If you decide that rising damp is the problem then it is fairly easy to inject chemicals. In the past the silicone fluid used to be pumped in under high pressure, but the modern alternative is a cream which you pump in by hand.

We used Dryzone cream from Safeguard Chemicals to put a damp proof course in an old cottage. Dryzone cream is injected into walls but rather than forcing its way through the capillary tracts in the bricks, it diffuses along the mortar drawn by the moisture.

This means that you are treating the mortar course rather than the bricks, which in most cases should be a more realistic proposition. The makers claim that the treatment is more effective than silicone fluid injection and Dryzone has been given a BBA certificate. The lack of pressure means that there is no chance of the chemical flooding into the cavity or neighbouring properties. You don’t need to hire equipment or even have electricity if you have a battery drill. The absence of solvents means that there aren’t any smells associated with the product.

It is possible to drill through both skins of a cavity from one side. You need to regulate the depth of the holes with a depth stop so the back hole is 10mm short of the full depth of the brick. Complete the filling of the back hole first then do the front one gently squeezing the trigger whilst pulling out the nozzle. It is (almost) better than sex.

Injection can also be used in stone buildings in the mortar joints. You have to think about how the damp will track through the courses and just stop it finding a route. There is no risk of applying too much so just pump it in where you can.

When the injection has been completed give it a few weeks and check the internal plaster for hydroscopic salts. The usual practice is to hack off plaster up to one metre and render with an additive. Such as Sika One or Safeguard chemicals Renderguard Gold. Care needs to be taken to use washed sand for the rendering.

In truth the water-proofer in the render is belt and braces because it does as much as the chemical injection to hold back the damp. The drawback is that render is a hard cold waterproof surface which is more likely to attract condensation so even after the rendering and re-plastering work the walls might still appear damp to the touch. A better bet is a specialist lime based plaster such as Izonal that is specifically formulated for damp proofing.