Damp patches and spots on walls

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How to diagnose and repair damp patches on walls

The most important question - is the damp natural or man-made? In other words, are we looking for a water leak? Bear in mind that Damp Proof Courses do not generally fail. Most damp is caused by poor building practice or lack of maintenance.

Order and Free Technical Help - 01626 336180 - our Experts answer your call - discuss your building problem with a Qualified Dampness Expert (C.R.D.S.)

A 'damp meter' and surface thermometer (see www.dampness-info.co.uk/meters.htm)are useful tools for this diagnosis - if not available use the back of your hand to assess the relative dampness of one affected area to another unaffected area.

What causes Damp Patches and Spots on Indoor Walls

A quick summary checklist: a 'damp meter' and surface thermometer (see www.dampness-info.co.uk/meters.htm)are useful tools for this diagnosis - if not available use the back of your hand to assess the relative dampness of one affected area to another unaffected area.

Symptom - white, fluffy salts, plaster possibly 'blowing' off the wall - 'efflorescence' - you have a water source which needs to be found and eliminated. Use our Water Leak Checklist (click here).

Answer - Salt Neutraliser might work if you can find and stop the leak, or the plaster may be too damaged and need replacement to our Specification.

Symptom - damp patches (at low level, right down to the skirting board) that come and go - you have 'hygroscopic' salts that are attracting moisture from the air.

Answer - you may have Rising Dampness, or your damp proof course may be 'bridged' by high outside ground, plaster on the inside or debris in the cavity (cavity walls only). Rectify any defects and if necessary inject Quick Cream at the correct level to form a new Damp Proof Course. The plaster will need replacement to our Specification.

Symptom - damp patches on or around chimney breasts - sometimes showing yellow or brown stains in wallpaper or paint - you have 'hygroscopic' chimney salts that are attracting moisture from the air, which may include tars and other chemicals from burning wood or coal.

Answer - these 'salts' are very difficult to hold back in the wall, even with the replastering to our Specification carried out to perfection. We recommend using Mesh Membrane - a type of dry lining - to allow you to replaster using normal, lightweight plaster, with no risk of further 'salting'.

Damp treatment products mentioned above

Salt Neutraliser - a clear liquid used to neutralise 'salts' in render, plaster or masonry, either to attempt to save otherwise sound plaster or as a preparation prior to re-plastering to our Specification. Apply two coats, wetting in between with fresh water.

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Mesh Membrane - easy to install dimpled plastic 'air gap' dry lining membrane, supplied in rolls like wallpaper. Designed to cover damp or salty walls and provide a fresh surface for replastering with a modern lightweight plaster (usually 'bonding').

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DPC Cream - new, easy to install, cream damp proofing product - no pump required, no mess, no smell - includes injection nozzle extension. Designed to gently diffuse into the wall to form a water repellent layer - a 'damp proof course' (DPC). It is approved by the British Board of Agrèment - BBA Test Certificate No: 02/3961 - as used by the professionals. The BBA is a Government Approved organisation which has been testing building materials for over 30 years. Note - not all damp proofing materials have passed these tests - beware of cheap imitations).

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Want more advice or assurance about dampness treatments?

click here for a check list if you want to diagnose your damp

click here if you would like to read a genuine testimonial

Installing a Quick Cream DPC - the modern Professional method used throughout the UK.

Injecting a wall using damp proofing cream

As used by the Trade - Quick Cream is inserted into 12mm holes (380cc mastic tube type illustrated - uses standard skeleton gun)

Now available - Measured Dose Calibrated Skeleton Gun - ensures that you waste no DPC Cream

1. Free injection nozzle extension with every Order

(charged as additional cost from other suppliers)

2. Comes in a standard 'mastic' tube, ready to use

(no need to transfer the cream to a pump)

3. No special tools required

(special pumps needed with other makes)

4. Quick to install - just drill & gently inject

(no pressure required)

5. No electric pumps to hire or messy, smelly fluids to spill

(does not flow, or spread, or smell)

6. Effective - fully BBA tested and approved

(your guarantee of a quality product)

How to install a damp proof course

First, check for high ground levels, leaking gutters and downpipes, water leaks. A Damp Proof Course must be at least 6 inches (150mm) above abutting ground level (whether internal or external), to avoid splash up or 'bridging'.

How Rising Dampness is Blocked

Damp rising by capillary action - no damp proof courseBefore Treatment

After Treatment Damp replelled by a damp proof course

Method of installing a Cream Damp Proof Course

1. Drill 12mm diameter holes at 120mm intervals in the mortar course (or via the brickwork, angled down to meet the mortar course) selected to be at least 150mm above outside or abutting ground level

2. Fit the extension nozzle to the cartridge tube and load into the skeleton gun

3. Inject cream from the bottom of the hole outwards until the hole is full.

4. Replaster to our specification.

5. Treat any skirting boards or joinery with Boron Ultra Gel.

6. Holes can be capped with mortar or fitted with a plastic plug

Replastering to a minimum of 1.2 metres internally, to our specification, using sand and cement and Renderproof integral waterproofer, is required to finish the job and to prevent 'salts' damage to plaster finishes and decorations.

Our Dampness Treatment Products required:

Quick Cream DPC, Skeleton Gun - either a 380cc or professional 1000cc, Option - Calibrated Dose Gun.

Optional Products: Renderproof Replastering Additive (5 litre), Wall Plugs, Boron Ultra Gel (2.5 litre), UltraProof exterior wall treatment (5 litre or 25 litre), Anti-Mould Paint (2.5 litre), Professional Skeleton Guns (380cc or 1000cc), Professional Extension Nozzle (for repeated use with 1000cc cartridges)

Tools Required: 12mm masonry bit, electric hammer drill, eye protection

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Typical damp proofing cream usage rates:

4.5 inch thick (115mm) single leaf wall - 1000cc (1 litre) per 9 metres, inject from either side

9 inch thick wall (230mm) double leaf solid or cavity - 1000cc(1 litre) per 4.5 metres, inject from one side or from both sides.

18 inch thick wall (460mm) solid or random fill - 1000cc (1 litre) per 2 metres, inject from both sides

Replastering Notes

Don't forget that replastering is essential if dampness has affected your plaster because of the 'salts' that come with the water: you have two options - either replaster to our specification using sand and cement, with Renderpruf salt inhibitor/waterproofer in the water or look at the Wall Membrane option. Wall Membranes offer a considerable improvement over sand and cement - they produce a warmer surface, can be insulated easily and can be directly plastered with lightweight, modern plasters, like Carlite Bonding.

For easy fix Membrane information go to: www.drywallandfloor.co.uk

Hammering a plastic plaster plug through Mesh MembraneRolling Kontract Membrane onto a floor - no fixings required.

Mesh Membrane being fixed to the wall. Kontract Membrane being rolled onto a floor.

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Property Repair Systems

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Site written by: David Moore

David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author


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