Property Repair Systems

Garages - Damp Walls

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Summary: Garage wall preparation, covering and plastering

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Damp Walls in Garages

If you need any help with garage floors or walls, including dampness problems Property Repair Systems staff will give you completely free, no obligation advice on 01626 336180. The information you need may be in the project below. If not, call them.

Property Repair Systems offers you information regarding all types of garage floor and wall repair and coating. This includes a helpline manned by experts. Click on the logo above to find out more.

Garage Basics

Garage floors were NOT laid by the Builder of your property to be used indoors, as part of your inhabited area. Similarly, the walls were not usually constructed with conversion in mind. These two facts mean that you have to deal with three problems if you want to use your garage as a living or truly dry storage area;

  1. The concrete floor will be damp – it probably does not have a ‘membrane’ (a sheet of plastic laid under the concrete when indoor floors are constructed). This may not be a problem with newer homes, but you need to test the floor to be sure. You could buy a Damp Test Meter to help you in assessing the walls and floors.
  2. The damp proof course (DPC) may not be at the correct level – in garages it is usually above floor level – look for a black line in the mortar joints. This means that the exposed part of the wall below the DPC will always be damp. You may need to inject a Silicone Injection Cream DPC product, like UltraCure and ‘tank’ any parts of the wall that are underground (earth retaining) with something such as Aquastop Tanking slurry.
  3. The main house wall, against which the garage may be built, may not have any cavity trays or weeps above the line of the garage roof. This means that the ‘party’ wall with the garage will always be slightly damp. This can be best dealt with by fitting an Air Gap Membrane, which allows the wall to breathe, but into which you can plaster or plasterboard without fear of damp spoiling your decorations.

So, to be able to cover the floor with any type of flooring you need to:

  • check the DPC level – find the black line and measure its height above the floor (inside) and the ground (outside).
  • check for damp – use our simple test below

To check for damp:

You could buy a Damp Test Meter, or carry out a more basic test as follows;

- brush a small area free of all loose material and stick a square of clear plastic (say about 100mm x 100mm) to the concrete with plastic tape. Leave overnight. If there is any moisture under the plastic in the morning you have some damp in the concrete.

When you are ready to proceed with these checks call Property Repair Systems on 01626 336180 for detailed advice – your particular garage construction needs to be discussed, so that your new floor is laid correctly.

Salt Neutraliser

Mesh Membranes - install as a barrier, then plaster directly or plasterboard

Air Gap Membrane

Click to buy Kontract Membrane – install as a barrier, then batten and plasterboard

Wall Coverings

The main problems are;

  • cold outer walls, usually single leaf block or brick, which is prone to condensation and penetrating damp
  • cold ‘party’ wall with the main house. This wall is partially outdoors, probably has no cavity trays or weeps, so is likely to be cold and damp.
  • The damp proof course level. The DPC will probably be above the level of the concrete floor.

The best way around these problems is to use the Air Gap Membrane system and fit insulation and plasterboard. This gives you a guaranteed vapour barrier, a warm wall and a brand new plastered surface, with no future risks of damp or ‘salts’ penetrating your lovely decorations.


Warning – do not apply modern gypsum plasters to garage walls unless they are bone dry and ‘salt’ free. If you use these plasters your decorations may be ruined by damp patches.

There are three methods in common use;

  • Air Gap Membranes – these dimpled plastic sheets are fixed to the walls with special sealed plastic plugs. You can then either plaster direct, plasterboard on ‘dabs’ of adhesive, or batten and line with plasterboard. The last type also allows you to fit insulation in between the battens, for improved thermal efficiency.
  • Sand and cement plastering – this ‘render’ acts as a semi-waterproof backing coat, to hold back damp and salt. It is finished with a ‘skim’ of Multi-Finish plaster. It has the virtue of being a cheap material, but to be successful it must be applied exactly as specified, complete with a special Admixture, Renderproof, and it is still a cold and condensation prone surface.
  • Stud Partitioning – this is best used in conjunction with an Air Gap Membrane, but is an ideal solution if you have old, irregular stone walls or loose, difficult to fix to walls. The partition is built as a timber frame which sits on the Membrane, on the floor and is fastened through the Membrane to the ceiling, floor and walls. Insulation can be built-in and this method avoids having to drill lots of holes in the wall.

If you need help with Garage Floors or Walls, or coating products Property Repair Systems staff will be pleased to give you completely free, no obligation advice on 01626 336180.

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