Who this guide is for
- Owners preparing to dryline or panel an existing room
- Anyone considering internal insulation on an external wall
- People who have seen staining, salts or mould on a wall they intend to cover
- Readers who want a record of a building before it becomes invisible
- Anyone briefing a surveyor before fit-out work begins
What the wall is, before what the lining will be
Whether a wall is solid or of cavity construction, and what has previously been applied to it, are the first facts any retrofit assessment establishes. A solid wall manages water by wetting and drying; a cavity wall breaks the path with a void. The same repair does not transfer between them.
Older walls are commonly found carrying later coatings, linings and repairs that were never considered together, and their present behaviour is the sum of all of them rather than of the original construction.
Moisture condition, and why it decides the method
The base wall's moisture behaviour is the single fact that most often changes which support method is chosen. A lining changes the temperature and vapour conditions of the wall it covers whether or not insulation is added, so the assessment has to happen before the specification rather than after it.
Covering a damp wall changes where the moisture goes rather than whether it is there. Signs of damp are investigated and resolved by a qualified professional before any lining is fixed, and a covering applied over an uninvestigated problem simply hides it from view.
What has to be corrected first
Rainwater defects, ground levels and gutter faults are better corrected before a wall is lined, because afterwards they act on a wall that can no longer dry inward. Raised external ground, blocked drainage or a bridged cavity are more often the route than the wall itself.
Salts left in masonry by earlier damp continue to attract moisture after the original cause is fixed, which can make a successful repair look like a failure. Knowing they are there before the wall disappears is what allows that to be interpreted later.
The line at the base of the wall
Where the wall carries a damp-resisting course near floor level, the lining and its support cross that line. Whether the support bridges it, stops short of it or is separated from it is a detailing decision for a qualified professional rather than a site improvisation.
The same reasoning applies to the corner where a floor barrier and a wall course meet, which is the clearest case of two complete components producing an incomplete assembly. Both perform across their own area while a continuous path runs between them.
What the background will hold
What can actually be fixed to an old wall is often discovered rather than specified, because the background is uneven, dusty and of unknown composition. That uncertainty is why opening up and trial areas are worth more here than on new construction.
Adhesion for a bonded lining depends entirely on the state of the masonry face, and battening does not improve a background that will not hold a fixing. Neither question can be answered from a drawing.
What is already in the wall
Timber members built into a wall sit behind the new lining in conditions different from those they have been in, and assessing what that change means for them precedes the work rather than following it.
Existing services in or on the wall may need moving before any lining goes up, and services chased into the wall behind a control layer undo the purpose of building the lining at all.
The baseline record
Establishing a baseline record of the wall's condition before it is covered is what makes later diagnosis possible. Photographs of each elevation, notes of staining, salts, previous repairs and coatings, and the position of anything built into the wall cost an hour and are irreplaceable afterwards.
A finished lining is indistinguishable from an ordinary wall, so the record is also what tells a later occupant that fixing into it is not a neutral act.
Before-covering checklist
- 1Establish whether the wall is solid or of cavity construction
- 2Record what has previously been applied to each face
- 3Have the moisture condition assessed by someone qualified to assess it
- 4Investigate any staining, salts or mould before specifying anything
- 5Check external ground levels, gutters and rainwater goods first
- 6Ask whether any correction should happen before the wall is covered
- 7Establish where any damp-resisting course sits relative to the lining
- 8Ask how the support crosses that line
- 9Open up a trial area to find out what the background will hold
- 10Identify any timber members built into the wall
- 11Decide whether existing services move before the lining goes up
- 12Photograph every elevation before anything is fixed to it
- 13Record salts, repairs and coatings in that baseline
- 14Keep the baseline where a future diagnosis will find it
Common mistakes to avoid
- Covering a wall to deal with damp rather than diagnosing the damp first
- Specifying the lining before the wall has been assessed
- Leaving a rainwater or ground-level defect to be dealt with later
- Assuming a trial area is unnecessary because the wall looks sound
- Treating the base of the wall as an ordinary junction
- Losing the chance to photograph a wall that is about to vanish
- Reading damp appearing after the work as proof the lining failed
When to involve a professional
- Whether a wall is damp, and why, is a diagnosis for a qualified professional before any covering is considered
- Insulating or treating a solid wall changes its moisture behaviour and requires assessment by someone qualified in that field
- How a lining and its support cross a damp-resisting line is a detailing decision for a qualified professional
- Whether interstitial condensation is a risk depends on the whole build-up, the internal conditions and the climate
- What an existing background will hold is established by opening up rather than assumed from its appearance
Frequently asked questions
Questions readers ask about this topic
Will lining a damp wall solve the damp?
It changes where the moisture goes rather than whether it is there. Damp has causes that require diagnosis by a qualified professional, and covering a wall over an uninvestigated problem removes the evidence while leaving the cause in place.
Why does the wall's construction change the lining choice?
Because a solid wall handles water by absorbing and releasing it, while a cavity wall breaks the path with a void. Anything applied to a solid wall's face changes a drying direction, so the same lining means different things on the two constructions.
What should a baseline record contain?
Photographs of each elevation before work, notes of staining, salts, previous repairs and coatings, the position of anything built into the wall, and what the trial opening revealed. It costs about an hour and cannot be reconstructed afterwards.
Should gutters and ground levels be dealt with first?
Correcting them beforehand is generally preferred, because afterwards they act on a wall that can no longer dry inward. Raised external ground and blocked drainage are common routes for moisture that is later attributed to the wall itself.
Does damp appearing afterwards mean the lining failed?
Not necessarily. It may equally reveal a rainwater or ground moisture problem that the wall previously masked by drying inward. Interpreting it depends on knowing what the wall was doing before it was covered, which is what the baseline record provides.
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