Damp proofing rods: how they work.

Damp proofing rods are a simple and inexpensive way of doing a damp proof course (DPC). And, in a nutshell, that's why we prefer them to other damp proofing methods such as chemical injection.

In the video below, John explains how damp rods (sometimes called damp sticks) work, and why they are so effective at stopping rising damp. He also shows where you need to install them for them to properly take effect.

Other brands are available, but at HYPE Building, we use Dryrod damp proofing rods.

Firstly, because they are easy to install. Secondly, because they deliver exactly the right amount of water repellent material, known as silane concentrate. Hence, there's no waste, like you can sometimes get with the injection cream.

Each rod is a fibre stick carrying a fixed dose of silane concentrate. Once it is sitting in a drilled hole in the mortar bed, that silane migrates out into the surrounding mortar and reacts with it, forming a water repellent barrier the full thickness of the wall.

The barrier is horizontal and continuous. Water rising up through the masonry by capillary action reaches it and can go no further, so the wall above it starts to dry out and stays dry.

The useful part is that you can see it happening. Each rod pushes a dark halo of silane out into the brickwork around it. Once the halo from one perpend has spread far enough to meet the one next to it, the barrier is continuous and the job has worked.

Plaster is removed from the bottom of the walls up to a height of 1.5m. This is because rising damp can reach a height of up to approximately 1.2m. Rising damp not only brings moisture, it also brings hygroscopic salts, nitrates and chlorides. By removing 1.5m of plaster, you are effectively eliminating any contaminated plaster.

This matters more than people expect. Salt-contaminated plaster pulls moisture out of the air on its own, so a wall can read as damp long after the damp course has done its job, purely because the old plaster is still on it. Leave it up and you will be arguing about whether the treatment worked.

Holes are drilled into the mortar, usually the first layer of mortar after the first row of bricks from the floor, at the perpend junctions. So approximately every half-brick, which Safeguard specify as 120mm intervals. The depth of the hole depends on the depth of damp proofing rod you require. We use Dryrods, which come in lengths of 180mm that can be cut to size. For walls thicker than 9 inches, multiple rods can be combined.

The damp proofing rods are then inserted into the pre-drilled holes and left to cure. Each rod contains exactly the right amount of water repellent material, so there is no measuring and no guesswork about dosage.

Once cured, the silane concentrate seeps into the wall to form an extremely effective damp barrier. It will dry out the damp wall and stop rising damp from setting back in.

0:09 · The plaster is removed from the bottom of the walls up to a height of 1.5m. Thus, eliminating any contaminated plaster.

0:52 · Holes are drilled at the perpend junctions. Usually at the layer of mortar after the first row of bricks from the floor.

1:09 · The damp proofing rods are inserted into the pre-drilled holes. Each rod contains exactly the right amount of chemicals.

1:36 · Once cured, the chemical water repellent (silane concentrate) seeps into the wall to form an extremely effective damp barrier.

There is no single honest number here, and anyone who gives you one is guessing at the part that varies.

Two different things are happening and they run on different clocks. The barrier itself forms quickly: the silane starts moving as soon as the rods are in, and on the job in the video you can already see the haloes spreading and meeting. The wall then losing the moisture it has been holding, sometimes for years, is the slow part, and it depends on how thick the wall is, how saturated it got, and how well the room is ventilated.

BS 6576, the code of practice for diagnosing rising damp and installing chemical damp proof courses, deals with this by saying treated walls should be left as long as possible after treatment so the wall dries out as much as it can before replastering.

Safeguard put a figure on the replastering step specifically: wait four to six weeks before applying their plaster-based systems, so the active fully disperses and does not stain the new plaster.

So the practical answer is that the rods are done in an afternoon, and the programme after them is built around letting the wall dry rather than rushing to skim it.

Dryrod holds a BBA certificate, and the British Board of Agrement has certified it as effective against rising damp for up to 20 years after installation. The German WTA has approved it as well.

Read that as a certification period rather than an expiry date. It is the length of time the testing supports, not the point at which the chemistry is known to stop.

Worth keeping in proportion: on the sort of Victorian and Edwardian stock we work on in Stoke-on-Trent, the reason a new damp course is needed at all is usually that the original one has been bridged by a raised path or a render coat, rather than that it simply wore out.

A question we are commonly asked is whether to use damp proof rods or cream to do a damp course.

The honest answer is that both methods can work extremely well, and a lot of it is down to preference. We prefer the rods for three reasons.

Once the holes are drilled to the right depth, inserting the rods is quick, and there is no guesswork about how much product goes in each hole.

With cream, there is potential for waste if you drill too far through the mortar. A hole that is too big can let cream seep out the other side. The rods fit snugly into the pre-drilled hole and can be cut to size.

On performance, Safeguard publish that Dryrod outperforms creams, gels and liquids, and that it has been proven on walls up to 95% saturation. That is the manufacturer's own claim rather than an independent comparison, and we quote it as such. What we can say from our own jobs is that we have not had to go back to one.

At HYPE Building we deal with damp in one form or another on most refurbishments. Two ways it usually reaches us.

For property investors and landlords: a new damp proof course is normally part of a wider refurbishment. Going back to brick is what lets us be sure any existing damp problem is dealt with rather than covered up, and that a new one is unlikely.

For homeowners across the Potteries: we have diagnosed and advised on a lot of damp, including plenty of cases that turned out not to be rising damp at all.

Here is feedback from a homeowner we recently helped:

You can watch the entire Damp Causes and Fixes playlist on our YouTube channel, HYPE TV. Two of the most watched in the series: