Damp below the level of the
damp proof course (DPC)
Property Repair Systems - 01626 331351 - where you can speak to real people
How to diagnose and repair dampness below DPC level
Question - is the damp natural or man-made? In other words, are we looking for a water leak?
Order and Free Technical Help - 01626 331351 - Kathy, David or Angela answers 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.
Damp below damp proof course level - ground floor, a quick summary checklist:
Tip 1 - if a concrete floor is damp all over it is hard to isolate the moisture source. As it dries out the damp retreats slowly back to the points of ingress, so if you are not able to see any isolated damp areas either ventilate and heat or shut all the doors and windows and use a dehumidifier.
Tip 2 - always check the relative level of your floor to the outside ground level and damp proof course. If the floor is below the damp proof course level according to the 6 inch (150mm) rule, you will need to 'tank' the overlap and seal the wall to floor joint, to prevent laterally penetrating dampness.
Symptom - isolated damp spots on a concrete floor, not touching the edges. This is probably due to small holes in the plastic membrane (Visqueen 1200 gauge is normally used) laid onto sharp hard core without a sufficient sand cover. A water leak will add to the problem, so always use our Leak Testing Check List (see Water Leak Testing Project).
Remedy - either dig up the floor and re-lay, or clean the surface and apply two coats of an our Epoxy Seal Coat membrane (see www.epoxy-info.co.uk) or fit our Slimline Floorseal Air Gap Membrane (see www.drywallandfloor.co.uk). Membrane of this type can be screeded (minimum 2 inches, 50mm) or carpet, timber flooring or a chipboard floor can be directly laid (a 'floating' floor, 18mm board).
Symptom - damp areas on a concrete floor, touching and emerging from the edges. This is probably due to a lack of joint material where the plastic membrane butts up to the wall edge. A water leak will add to the problem, so always use our Leak Testing Check List (see Water Leak Testing Project).
Remedy - clean out the floor to wall joint until you can find the plastic membrane all the way around the floor, chisel out a U shaped channel in the floor at least 25mm x 25mm (1 inch x 1 inch), vacuum and then fill with sand and cement (4:1 sand to cement) incorporating BondAcryl liquid, both in the sand and cement and applied as a liquid primer to all the faces of the prepared 'slot'. Or, you can use our Fillet Seal joint material, supplied as a powder.
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).
Remedy - 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,l right down to the skirting board - sometimes the skirting board will be rotten) that may come and go - you have 'hygroscopic' salts that are attracting moisture from the air.
Remedy - your damp proof course may be 'bridged' by high outside ground, plaster on the inside or debris in the cavity (cavity walls only). Clean out the floor to wall joint until you can find the plastic membrane all the way around the floor, chisel out a U shaped channel in the floor at least 25mm x 25mm (1 inch x 1 inch), vacuum out all debris and dust. Rectify any defects and 'tank' the wall area below the correct damp proof course level (6 inches or 150mm above outside ground level) into the floor to wall notch and then fill with sand and cement (4:1 sand to cement) incorporating BondAcryl liquid, both in the sand and cement and applied as a liquid primer to all the faces of the prepared 'slot'. Inject DPC 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 the base of 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.
Remedy - 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'.
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.
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').
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).
Installing a Quick Cream DPC - the modern Professional method used throughout the UK.
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
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 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
Typical 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
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
Property Repair Systems
Unit 3, Olympus Business Park, Kingsteignton Road Newton Abbot, Devon, TQ12 2SN
T: 01626 331351 F: 01626 331143
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