Rising Damp: Why It Keeps Coming Back

Rising damp keeps coming back because most of what gets done about it treats the wall rather than the path the water is using. Seal the surface and the moisture simply goes further up and further in.

Rising Damp: Why It Keeps Coming Back — practical guidance from the team running damp proofing on the Garden Route. Below is how to recognise rising damp against the two things it is most often confused with, why coatings make it worse, and the fixes that actually work.

What it actually is

Rising damp is groundwater drawn upward through masonry by capillary action — the same effect that pulls water up a paper towel. Brick, mortar and plaster are full of fine pores, and water climbs them.

It stops where evaporation from the wall face balances the rate at which water is being drawn up, which is why the classic tide mark sits at a fairly consistent height, typically somewhere around a metre.

The water is not clean. It carries dissolved salts out of the ground and the masonry, and as it evaporates at the surface those salts are left behind. That is why rising damp produces the characteristic white efflorescence and why the plaster blows — the salt crystals expand and push the plaster off the wall from behind.

The salts also stay after the water is gone. They are hygroscopic; they attract moisture from the air. A wall that has had rising damp for years will look damp in humid weather even after the source is fixed, until the contaminated plaster is removed. That is why so many “failed” damp treatments were actually successful treatments followed by nobody replastering.

Where a chemical damp-proof course is genuinely the right answer, it is a specified injection system — silane or siloxane cream or fluid injected at set centres into a drilled course — and Sika, a.b.e. and the specialist damp houses supply them. What it is not is a coating. Painting a wall with a waterproofing product from a merchant shelf, whatever the brand, traps moisture in the masonry and pushes the damp line higher, which is precisely why the problem appears to return worse each time. The diagnosis has to come before any product decision.

Telling it apart from the other two

Three problems present as damp on a wall and they have entirely different fixes. Getting this wrong is the single most expensive mistake in damp work.

Rising damp: a broadly horizontal tide mark up to roughly a metre from floor level, worse in winter, salt deposits on the surface, plaster blowing at the base, and it affects ground-floor walls only.

Penetrating damp: follows the weather rather than the floor line. Appears after driving rain, concentrates on the exposed elevation, and the damp patch is often at height rather than at the base. Tracks cracks, failed pointing, a defective sill, or a parapet above.

Condensation: shows on cold surfaces and in corners, in rooms with poor ventilation, typically with black mould rather than white salting. Worse in winter and worse in rooms where moisture is generated. No amount of external waterproofing touches it.

And a fourth to rule out: a leaking pipe. Persistent localised damp with no seasonal pattern, in a wall carrying plumbing, is worth investigating before anybody applies a treatment.

	Rising damp	Penetrating damp	Condensation
Pattern	Horizontal tide mark, low	Follows the exposed elevation	Cold surfaces, corners
Height	Up to about a metre	Often at height	Anywhere, often high corners
Timing	Worse in winter, constant	After driving rain	Cold weather, poor ventilation
Signature	White salting, blown plaster	Staining, tracking a defect	Black mould
Fix	DPC and external levels	Repair the defect; coat if appropriate	Ventilation and heating

Why coating the wall makes it worse

This is the part worth being blunt about, because it is done constantly.

A wall with rising damp is in equilibrium: water enters at the base, travels up, and evaporates from the face. Seal the face with an impermeable coating and you have not stopped the water entering. You have only stopped it leaving.

So the water goes further. It rises higher up the wall looking for a surface it can evaporate from, and it moves inward, appearing on the internal face of a wall that was previously only damp outside. The tide mark moves up and the problem gets bigger.

The coating itself then fails, because salts crystallising behind it push it off. Now the wall needs the coating removed before anything else can be done, and you have paid twice.

The same logic applies to cement-rich renders and non-breathable paints. Anything that reduces the wall’s ability to dry outward makes rising damp worse, not better.

What actually fixes it

Start with the external levels, because this is free and it is frequently the whole problem. A damp-proof course only works if nothing bridges it. Paving, a flower bed, a path, built-up soil or plaster carried down across the DPC all give water a route around it. Lowering the external level below the DPC, or forming a drained gap against the wall, fixes a surprising proportion of rising damp cases without any treatment at all.

Then check whether there is a DPC to bridge. Older Garden Route houses may never have had one.

Install a damp-proof course where there is none or where the original has failed. The common methods are chemical injection — a water-repellent fluid injected into a line of holes drilled in the mortar course, which then cures to form a barrier — or physical insertion, cutting the mortar bed in sections and inserting a membrane. Injection is far less disruptive and is the usual choice; physical insertion is more certain and much more invasive.

Then replaster. This is the step most often skipped and the reason treatments appear to fail. The existing plaster is contaminated with hygroscopic salts and will keep looking damp forever. Hack off to a height above the tide mark, allow the wall to dry, and replaster with a salt-retardant render system.

And be patient. A wall that has been wet for years holds a great deal of water. Drying happens over months, not weeks, and redecorating too early traps it.

What to expect from a proper diagnosis

Anyone quoting a rising damp treatment before diagnosing is guessing with your money.

A proper assessment looks at the pattern and height of the damp, the external ground and paving levels relative to the DPC, whether a DPC exists and where, the condition of gutters and downpipes discharging near the wall, evidence of salting, and moisture readings taken at several heights and both faces.

It should also actively rule out the alternatives: a leaking pipe, a failed gutter or downpipe soaking one area of wall, a bridged cavity, penetrating damp on an exposed elevation, and condensation.

Beware the free survey. The damp-proofing industry has a long history of free inspections that discover rising damp in buildings that do not have it, because the inspection is paid for by the treatment. A paid diagnosis from someone who is not selling the injection is a good investment.

And beware the guarantee. A twenty-year guarantee on a chemical DPC is only worth the company standing behind it, and it usually excludes exactly the things most likely to happen — bridged levels, replastering not done, and salt contamination. Read what it excludes rather than the number of years.

Frequently asked questions

How do I know if it is rising damp?

Look for a broadly horizontal tide mark up to roughly a metre from floor level, worse in winter, with white salt deposits on the surface and plaster blowing or crumbling at the base — and only on ground-floor walls. If the damp follows driving rain and appears on one exposed elevation, often at height, that is penetrating damp. If it shows on cold surfaces and in corners with black mould rather than salting, that is condensation. The three have entirely different fixes.

Why does rising damp keep coming back after treatment?

Usually one of three reasons. The external ground or paving level is bridging the damp-proof course, so water simply goes around it. Or the contaminated plaster was never removed — the salts left behind by years of evaporation are hygroscopic, so the wall keeps looking damp in humid weather even after the source is fixed. Or the wall was redecorated before it had finished drying, which takes months rather than weeks.

Can I just paint over rising damp?

No, and it actively makes things worse. A wall with rising damp is in balance: water enters at the base and evaporates from the face. Sealing the face does not stop the water entering, only leaving — so it rises higher and moves inward, appearing on internal faces that were previously dry. The coating then fails as salts crystallise behind it, and now it has to be removed before anything can be done properly.

What is a chemical DPC and does it work?

A water-repellent fluid injected into a line of holes drilled along a mortar course, which cures to form a barrier against capillary rise. It works when it is installed correctly in a suitable wall, at the right height, in a continuous line, and — critically — when it is followed by removing the salt-contaminated plaster and replastering with a salt-retardant system. It fails when any of those steps is skipped, and most apparent failures are actually one of those omissions.

Does rising damp affect upstairs walls?

No. Rising damp is groundwater drawn up by capillary action, and it stops where evaporation balances the rise — typically around a metre from floor level on a ground-floor wall. Damp on an upper floor is penetrating damp, condensation, or a leak. If somebody diagnoses rising damp on a first-floor wall, get a second opinion.

How long does a wall take to dry after treatment?

Months rather than weeks, and longer for a thick wall that has been wet for years. Masonry holds a great deal of water and it leaves slowly. Redecorating too early traps it and the finish fails, which then gets blamed on the treatment. The honest sequence is: fix the source, remove the contaminated plaster, let it dry, replaster with a salt-retardant system, and only then decorate.

Damp wall you have already had treated once?

We diagnose before we quote, and we will tell you if the answer is dropping your paving level rather than injecting your wall. That conversation costs you nothing and it saves some people the whole job.

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