Is it really rising damp?

Rising Damp Perth arranges damp assessments across Perth metropolitan area.

What Perth inspectors actually find

Houspect, a building inspection firm working across WA, says it investigates water getting into walls almost every week, and that what it finds is predominantly lateral damp rather than rising damp. Lateral damp is water entering the wall from a point above the damp course, rather than climbing up from the ground below it.

Perth's soil is sand, and its houses are largely double brick. Water that reaches the outer leaf can be drawn straight through to the inner one, so a wet patch inside says nothing about where the water came from. It looks exactly like rising damp on the wall, and it is not.

The four things it usually turns out to be

In rough order of how often we see them in Perth:

1. Reticulation spraying the wall. A sprinkler that clips the brickwork twice a week on watering days will keep a wall permanently wet. This is the most common one, and it is free to fix.
2. Ground built up past the damp course. A garden bed, a slab, a new path or a raised lawn sitting above the damp course lets water step over the top of it. The damp course is still working. It is just no longer the highest thing.
3. Blocked weep holes. The gaps in the bottom course are drainage, not decoration. Rendered over, painted shut or buried under soil, the cavity holds water it was designed to let out.
4. An actual leak. A shower, a waste pipe, a downpipe discharging at the footing. A leak is wettest at its source and dries in every direction from there, which is the opposite of what rising damp does.

Why the moisture reading says wet either way

A surface moisture meter measures electrical conductivity. Salt left in a wall by years of evaporation conducts electricity and pulls moisture out of the air, so a salty wall reads wet even when it is dry. That is not a fault in the meter or the inspector. It is what the tool can honestly establish, and it is the reason a reading alone never settles the question.

Four checks you can do before you spend anything

• Watch where your sprinklers land. Run the retic and stand outside. If any spray reaches the wall, turn that head down and wait a month.
• Find the damp course. Look for a thin dark line in the mortar a few courses up from the ground outside. Now look at where the soil, paving or lawn sits. If the ground is higher than that line, you have found something.
• Check the weep holes. Bottom course, roughly every fourth brick. If you cannot see any, they are covered.
• Notice the timing. Rising damp is there all year. Damp that follows watering days, or heavy rain, or a long shower, is telling you where it comes from.

When it really is rising damp

It does happen here, and two Perth situations account for most of it.

Older limestone walls, particularly in Fremantle and the port suburbs, were often built with no damp course at all. Limestone is porous and takes up groundwater readily.

Pre-1980s double brick homes were built with bitumen or slate damp courses. Those materials work, but the ones still in service are now more than forty years old, and a damp course that has cracked, corroded or been bridged by later building work stops being a barrier.

Genuine rising damp leaves a level tide line at a consistent height, salt bloom below it, and perished mortar. It is present in summer as well as winter.

What being wrong actually costs

This is why the order matters. Using the Perth figures from our cost page:

• Turning a sprinkler head away from the wall — free.
• Cutting a garden bed back below the damp course — a few hundred dollars, often a weekend with a shovel.
• Clearing rendered-over weep holes — low hundreds.
• A chemical damp course — $180 to $340 per metre, before the replastering that has to follow it.

On a ten-metre wall that is the difference between nothing and several thousand dollars. It is worth an afternoon of checking.

What an injection does not do

Worth knowing even when rising damp is the right diagnosis. A chemical damp course stops water climbing. It does not remove the salt already in the wall, and salt is what blows the render and keeps paint from holding — which is why a proper specification deals with the render separately, and why that part is often the larger half of the bill.

It also does not dry the wall out on the day it goes in. A wall that has been wet for years holds a great deal of water, and it leaves slowly. Anyone promising you a dry wall next week is selling you something.

What we think, and it is an opinion

If somebody quotes you an injected damp course before they have looked at your reticulation, your ground levels and your weep holes, get a second opinion. An injection into a wall whose real problem is a garden bed will not fix the wall, and you will have paid for it.

We are a referral service, not the contractor, so this costs us nothing to say. It is also the reason the assessment comes before any quote here. An on-site assessment and written diagnosis is $450 plus GST, carried out by a damp specialist registered with the Building Services Board, and it is worth it precisely because four of the five answers are cheaper than the fifth.

Sources

• Houspect WA, on lateral damp being the predominant finding in Western Australian water-ingress investigations — houspect.com.au
• Building Services Board, WA building registration — commerce.wa.gov.au

Areas we cover

We arrange assessments across the Perth metropolitan area, including: