Damp walls are cold walls. Moisture passing through a wall carries dissolved ‘salts’. When salt reaches the surface of plaster or paint it spoils the decorations and eventually ‘blows’ the plaster. Such walls are also very prone to Condensation and hence Black Spot Mould. (Click here for Mould Help).
If the walls are below the damp proof course, partially below ground, or ‘earth retaining’, they will always be damp. Traditionally the way around this problem was to cover up the damp with wooden paneling, but this tends to rot. So, ‘tanking’ was invented – in its original form a waterproof, liquid coating that bonds to damp masonry.
If you need any help with damp walls or ‘tanking’ products, Property Repair Systems staff will be pleased to give you completely free, no obligation advice on 01626 336180. The information you need may be in the project below. If not, call them.
Tanking Walls – choice of methodsThe three main methods are;
- Liquid bitumen coating – painted onto the cleaned brickwork, stone, block or render – difficult to apply to old, damp salty masonry, prone to separation from the wall and render coats due to incomplete curing. Best for non-critical small jobs, or external coating below the damp proof course.
- Cement based slurry – applied by soft brush onto damped, cleaned brickwork, stone, block or render – easier to apply because the cement base wants to amalgamate with the masonry and mortar. Not a true vapour barrier, so needs to be finished with ‘breathing’ materials. Ideal for partial below ground situations or exterior coating on foundation walls.
- Air gap membranes – not strictly ‘tanking’ in the same way as liquids – it is a dimpled plastic sheet fixed onto brick, stone, block or render with plastic plugs to form an air gap cavity. These Membranes can have a plain surface, for battening or a Mesh surface for direct plastering or plaster boarding. Ideal for cold, single leaf walls and for lining rooms with cold solid 9 inch walls.
Cementitious Slurry – how to apply
- Hack off all old plaster, render, paint and loose masonry. Remove all wooden plugs and bonding timbers. Wash with fresh water and then apply salt neutraliser.
- Ensure that you have no ‘active’ water weeping from the wall – if there is any activity you will need to install relief holes and a temporary drainage method (Ring for help on 01626 336180).
- Whilst damp make good all holes and joints with mortar, sand (washed) and cement, 4:1 mix ratio, plus Renderproof.
- Re-damp the wall and apply a coat of Slurry – this is a powder mixed with water to a thick, smooth soup-like consistency – use of soft paste brush and brush gently to finish in horizontal strokes
- As soon as the surface is tack-free apply a second coat, brushing to finish in vertical strokes (this hopefully covers any pinholes that you missed with the first coat.
- The finished surface can be plastered with a Renovating Plaster, painted with Microporous Replastering Paint or rendered with sand and cement.
Air Gap Membranes – how to install
- Remove all gypsum plaster (solid sand and cement render can stay), wooden plugs and bonding timbers.
- Check whether you have any ‘active’ water weeping from the wall, or if the area has ever suffered from flooding. If there has been any activity you will need to install a drainage method – either a traditional drain or a sump and pump. (Ring for help on 01626 336180).
- Choose your wall finishing method – battens and nailed plaster board (with or without insulation between the battens) or direct plastering with Bonding Plaster, or Plaster Board on adhesive ‘dabs’.
- Battens and nailed plaster board – use Kontract Membrane – the plug heads have pre-formed holes ready for No.12 self tapping screws, to fix the battens.
- Plastering or Plaster Board dab fixed – Mesh Membrane – the welded-on mesh supports the plaster or the adhesive.
- The floor may also need to be covered with Kontract Membrane – a ‘floating’ tongued and grooved chipboard or concrete screeded floor can then be laid. Where liquid water is involved this floor Membrane has to be joined to the wall Membrane – this is called the ‘sealed system’ and must incorporate a drain or a sump and pump.
Salt Neutraliser - a clear liquid used to neutralise 'salts' in render, plaster or masonry, either in an 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').
Quick 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.
If you need any help with damp walls or ‘tanking’ products, Property Repair Systems staff will be pleased to give you completely free, no obligation advice on 01626 336180.