Damp Proofing and Tanking: The Complete Guide for South African Properties

Damp is one of the most misunderstood problems in South African homes and buildings. A tide mark on a wall, bubbling plaster, a musty smell in a basement or water seeping through a retaining wall can each have several possible causes, and each cause has a different fix. Spend money on the wrong treatment and the damp comes straight back.

This guide explains the different kinds of damp, how to tell them apart, the treatments that actually work, how below-ground structures are waterproofed by tanking, and how to keep damp from returning. It is written from EcoProof Africa’s experience surveying and treating damp across Gauteng and the East Rand.

In this guide

1. Waterproofing, damp proofing and tanking: the difference
2. The five types of damp
3. How to diagnose damp
4. Rising damp: causes and treatments
5. Penetrating damp: causes and treatments
6. Below-ground waterproofing and tanking
7. The damp survey and treatment process, step by step
8. Preventing damp
9. What affects the cost
10. Damp in specific parts of a property
11. Damp, mould and your home
12. Common damp treatment mistakes
13. Damp when buying or selling property
14. Tanking specific structures
15. Questions to ask a damp specialist
16. All damp and tanking guides
17. Frequently asked questions

Waterproofing, Damp Proofing and Tanking: The Difference

These three terms are often used interchangeably, but they describe different jobs:

• Waterproofing stops liquid water from getting through a surface that is exposed to rain, such as a roof, gutter, balcony or slab. See our roof waterproofing guide.
• Damp proofing stops moisture moving up or through walls, most commonly rising damp from the ground. It works at a lower level of water exposure than waterproofing.
• Tanking is waterproofing for structures that are below ground or hold water, such as basements, cellars, lift pits, retaining walls, planters and ponds. It has to resist water pushing against the structure, sometimes constantly.

Getting the term right matters, because a roof does not need damp proofing and a basement does not need the same system as a flat roof. For definitions of these and other terms, see the waterproofing glossary.

The Five Types of Damp

Rising damp

Ground moisture is drawn up through the pores of brick and mortar because the damp proof course (DPC), a horizontal barrier built into the wall just above ground level, has failed, was never installed or has been bridged. It shows at the bottom of walls, typically up to about a metre, often with a horizontal tide mark and white salt deposits.

Penetrating damp

Water travels sideways through external walls, through cracked plaster, porous brickwork, failed pointing, poorly sealed window frames or blocked weep holes. It appears on the inside of outside walls at any height, and gets worse during and after rain.

Water from above

Leaking roofs, box gutters, parapets, balconies and flat slabs let water run down inside walls before it appears lower down. This is often mistaken for penetrating or even rising damp. If the damp follows the rain and starts high on the wall, look up first.

Plumbing leaks

A leaking pipe, shower waste or geyser overflow keeps a wall wet whatever the weather, usually spreading from one point near a bathroom, kitchen or geyser.

Condensation

Moist indoor air from cooking, showering and drying laundry condenses on cold surfaces, causing black mould in corners, behind cupboards and around windows, mostly in winter. It is a ventilation issue, not a building defect.

For a side-by-side comparison of these causes, read damp walls: rising damp, penetrating damp or a roof leak?

How to Diagnose Damp

Before any treatment, work out where the water is coming from. These clues help:

Clue	Points towards
Band of damp along the bottom of walls, present all year	Rising damp
Horizontal tide mark with white, powdery salts	Rising damp
Damp patches on outside walls that grow after rain	Penetrating damp
Damp starting near the ceiling or cornice after storms	Roof, gutter or parapet leak
Patch spreading from one spot regardless of weather	Plumbing leak
Black mould in corners and around windows in winter	Condensation
Water seeping through a basement or retaining wall	Ground water and hydrostatic pressure; tanking needed

More than one cause can be present at once, and moisture meters alone can give misleading readings on salty plaster. That is why a proper survey looks at the whole building, inside and out. See what to expect from a damp survey.

Rising Damp: Causes and Treatments

Why the damp proof course fails

• Bridging: soil, paving, flower beds or a raised driveway built up above the DPC let moisture bypass it. This is very common and the cheapest to fix.
• External plaster or render carried down past the DPC to the ground acts as a wick.
• Damaged or missing DPC in older buildings, or one that has deteriorated with age.

Treatments

• Remove the bridge: lower ground levels or paving so the DPC is exposed again, and cut back plaster that runs below it.
• Chemical damp proof course: a damp proofing cream or fluid is injected into a line of holes drilled into the mortar course, forming a new water-repellent barrier.
• Electro-osmotic systems: an alternative method used on some walls.
• Replastering: salt-contaminated plaster keeps drawing moisture from the air even after the DPC is fixed, so affected plaster is usually removed and replaced with a salt-resistant plaster once the wall has had time to dry.

Painting over rising damp with damp-resistant paint only traps it; the water then finds its way out higher up the wall. See damp proofing in Boksburg and the East Rand.

Penetrating Damp: Causes and Treatments

• Repair cracks in external plaster and repoint failed mortar joints
• Seal around window and door frames and check that sills shed water away from the wall
• Clear blocked weep holes and fix leaking gutters and downpipes that soak the wall
• Apply a breathable, water-repellent or elastomeric coating to exposed walls where needed
• Check parapets and copings, which let water into the top of the wall

Fix the water source first, let the wall dry, then repair internal finishes. Repainting inside before the wall dries simply causes the paint to blister again.

Below-Ground Waterproofing and Tanking

Below-ground structures face a harder job than roofs. Soil holds water against the wall, and when the water table or surface water rises, it pushes on the structure with hydrostatic pressure. Construction joints, where the floor meets the wall or one concrete pour meets another, and pipe penetrations are the usual weak points.

Positive side and negative side

Tanking applied on the side where the water is (the outside face of a basement wall or the soil side of a retaining wall) is called positive side waterproofing. It keeps water out of the wall altogether and is the preferred option when building or when the outside can be excavated. Where the outside cannot be reached, tanking is applied on the inside, the negative side, and must be bonded well enough to resist water pushing from behind.

Systems used

• Liquid-applied membranes: seamless and fully bonded, ideal for complicated shapes, planters, ponds and positive side applications. EcoProof needs no flames or solvents, which matters in confined spaces.
• Cementitious systems: rigid, chemically bonded coatings well suited to below-ground concrete that sees little temperature movement.
• Cavity drain membranes: studded membranes that let water drain behind them to a sump rather than holding it back, used in some basement conversions.
• Resin injection: used to seal active cracks and leaking joints.

Retaining walls

A retaining wall needs both waterproofing and drainage. Without weep holes, a drainage layer and a subsoil drain at the base, water builds up behind the wall, increasing pressure and pushing damp through. See our tanking page for the applications we cover.

The Damp Survey and Treatment Process, Step by Step

1. Survey the property. Inspect affected walls inside and out, the ground levels, the damp proof course, gutters, roof and plumbing, and record where and when the damp appears.
2. Identify the cause. Determine whether the moisture is rising, penetrating, coming from above, from plumbing or from condensation, as more than one cause can be present.
3. Write up the findings. Provide a written report setting out the cause, the treatment needed and the cost, and flag anything outside the damp specialist’s scope, such as plumbing.
4. Deal with the water source. Remove bridging, repair gutters or roofs, seal external walls or fix the plumbing before treating the symptoms.
5. Install the treatment. Inject a new damp proof course, apply tanking to below-ground structures, or repair and coat external walls as specified.
6. Let the structure dry. Allow walls time to dry out; masonry dries slowly, and rushing this step causes new finishes to fail.
7. Restore the finishes. Remove salt-contaminated plaster, replaster with a suitable plaster and repaint once the wall is dry.

Preventing Damp

• Keep soil, paving and flower beds well below the damp proof course, ideally at least 150 mm (about two brick courses)
• Clean gutters and downpipes so they do not overflow down walls
• Make sure ground slopes away from the building and stormwater drains are clear
• Keep weep holes in walls and retaining walls open
• Repair cracks in external plaster promptly
• Ventilate bathrooms and kitchens and open windows to reduce condensation
• Have the roof checked, because many damp problems start there

What Affects the Cost

• The cause and how many causes are present
• The length of wall to be treated and its thickness
• How much plaster must be removed and replaced
• For tanking, whether the positive side can be reached or work must be done from inside
• Access, excavation and drainage work for basements and retaining walls

The most expensive damp treatment is the one that targets the wrong cause. A survey first is the cheapest route to a lasting fix.

Damp in Specific Parts of a Property

Bathrooms and showers

Damp around a shower or bath is usually a failed seal, cracked grout, a leaking waste or a missing waterproofing layer under the tiles, rather than rising damp. Look for damp on the other side of the shower wall or in the ceiling below an upstairs bathroom. Condensation from showers without an extractor fan is another common cause of mould in bathrooms.

Kitchens and laundries

Damp behind kitchen units often comes from a leaking pipe, dishwasher or washing machine connection. Because cupboards hide the wall, it can go unnoticed until skirting boards swell or a musty smell appears.

Garages and outbuildings

Garages are often built with lower floor levels and less attention to the damp proof course, and driveways frequently slope towards them. Rising damp and stormwater entering under the door are both common.

Boundary and garden walls

Freestanding walls get wet from both sides and from the top. Failed copings, cracked plaster and soil built up against one side lead to flaking paint and salt staining. A sealed coping and a breathable protective coating usually help; a porous surface can be bound first with EcoFuse.

Floors and slabs

Damp coming up through a ground floor slab points to a missing or damaged damp proof membrane under the slab. Floor coverings that trap moisture, such as vinyl or laminate, show it first by lifting or smelling musty.

New buildings and extensions

New plaster, screeds and concrete hold a lot of water and can take months to dry fully. Damp patches in a new building are not always a defect, but they should dry out steadily over the first season. Damp that persists or grows after that needs investigating.

Damp, Mould and Your Home

Persistent damp encourages mould growth, which damages finishes, furniture and stored items, and can aggravate allergies and breathing problems for some people. It also attracts insects and can lead to wood rot in skirting boards, door frames and roof timbers. Dealing with damp promptly protects both the building and the people in it. If anyone in the household has health concerns linked to mould, speak to a medical professional.

Common Damp Treatment Mistakes

• Painting over the problem. Damp-resistant paint hides symptoms but traps moisture, which comes out elsewhere.
• Treating rising damp that is not rising damp. Injecting a new damp proof course will not stop a gutter leak running down a wall or condensation in a bathroom.
• Replastering too soon. New plaster on a wet, salty wall will blister and stain again.
• Using cement-heavy, non-breathable materials. Sealing a wall that needs to dry can push moisture further up or into adjoining rooms.
• Ignoring drainage outside. Paving that slopes towards the house, blocked gutters and missing weep holes keep feeding water into walls.

Damp When Buying or Selling Property

Fresh paint low down on walls, new skirting boards in an otherwise older house, a strong smell of air freshener or furniture pushed tight against walls can all be signs that damp has been covered up. If you are buying, look closely at walls, ceilings and cupboards, ask about previous damp treatment and any guarantee, and consider a damp survey before you commit. If you are selling, dealing with damp properly and keeping the paperwork helps avoid disputes later. Defects that the seller knows about should be disclosed to the buyer; if you are unsure of your obligations, ask your conveyancer or estate agent.

Tanking Specific Structures

Ponds and water features

Ponds hold water permanently, so any crack or joint in the lining leaks continuously. The pond is drained, cleaned and allowed to dry, cracks are repaired, and a seamless liquid membrane is applied over the whole shell and up past the water line. Because the membrane bonds to the shape of the structure, it handles curves, steps and inlets that are hard to line with sheets.

Planters and roof gardens

Planter boxes built against walls or on top of slabs hold wet soil against the structure all year. Without tanking, they are a classic cause of damp in the wall behind or the ceiling below. The inside of the planter is tanked, a drainage layer and outlet are added so water does not sit at the bottom, and the membrane is protected from roots and digging tools.

Lift pits and service trenches

These sit at the lowest point of a building and often below the water table. They need a fully bonded system that resists water pressure, with careful sealing around the floor-wall junction and any pipe or cable entries.

Dams and reservoirs

Farm dams, reservoirs and water tanks built from concrete or masonry can be lined with a seamless membrane to stop seepage, provided the structure itself is sound.

Questions to Ask a Damp Specialist

• What do you think is causing the damp, and how did you reach that conclusion?
• Could there be more than one cause, such as a gutter leak as well as rising damp?
• What exactly will the treatment involve, and what will happen to the plaster?
• How long should the wall be left to dry before replastering and painting?
• What guarantee do you give, and what would void it?
• Is anything you found outside your scope, such as plumbing or structural issues?

A specialist who recommends a treatment without explaining the cause, or who offers the same fix for every damp wall, is worth a second opinion.

All Damp and Tanking Guides

Every article in our damp and tanking series, including new guides as they are published:

• What Are the Categories of Waterproofing?
• Damp Walls: Rising Damp, Penetrating Damp or a Roof Leak?

Service pages: damp surveys, damp proofing in Boksburg and the East Rand and tanking. Related guides: roof waterproofing and commercial and industrial roofs.

Frequently Asked Questions

What is the difference between damp proofing and waterproofing?

Waterproofing stops liquid water getting through surfaces exposed to rain, such as roofs and gutters. Damp proofing stops moisture moving up or through walls, such as rising damp. Tanking is waterproofing for below-ground structures.

How do I know if I have rising damp?

Look for a horizontal tide mark up to about a metre high on interior walls, white salt deposits, bubbling or crumbling plaster and damp skirting boards. Rising damp is usually present all year rather than only after rain.

Can rising damp be fixed permanently?

Yes, when the cause is dealt with. That may mean removing whatever is bridging the damp proof course, injecting a new chemical damp proof course, and replacing salt-contaminated plaster once the wall has dried.

Does damp-proof paint stop rising damp?

No. It may hide the symptoms for a while, but it traps moisture in the wall, which then appears higher up or behind the paint.

What is tanking?

Tanking is a continuous waterproof barrier applied to structures that are below ground or hold water, such as basements, retaining walls, planters and ponds, so that water cannot pass through them.

Can a basement be waterproofed from the inside?

Often, yes, when the outside cannot be reached. Inside, or negative side, tanking must be well bonded to resist water pushing from behind, and the right system depends on the water pressure and the condition of the walls.

Why is my retaining wall damp?

Usually because water is building up behind it. Retaining walls need waterproofing on the soil side plus drainage, such as weep holes and a subsoil drain, to relieve the water pressure.

How long does a wall take to dry after damp treatment?

It depends on the wall thickness, the materials and the weather, but masonry dries slowly, often over several months. Replastering and repainting too soon is a common reason finishes fail again.

Not sure what is causing your damp? Contact EcoProof Africa or call 011 894 3535 to book a damp survey.