A common approach sold as a complete fix is a chemical damp-proof course injection followed by a waterproof render and new skirting, done without checking external ground levels or whether the cavity is actually clear. If the real cause is a patio built up over the years to sit above the original damp-proof course, the injection changes nothing, and the damp reappears above the new finish within a season or two.
A repair that actually lasts addresses the physical route the moisture is taking, in whatever form that turns out to be, before considering a damp-proof course measure at all.
The correct order of work
Ground level correction and cavity clearance come before any consideration of a new damp-proof measure, because in a large number of cases those two things are the actual cause, and a damp-proof course was never the problem to begin with. Injecting a new course into a wall that's still being bridged from outside doesn't stop the damp.
- Confirm the cause through proper survey — construction type, ground levels, cavity condition, and existing finishes
- Lower external ground levels where they've been built up above the damp-proof course, and form a proper margin or drainage channel
- Clear any debris or bridging material found in a cavity
- Reinstate an appropriate damp-proof measure for the specific construction, only where the original course has genuinely failed
- Strip affected internal finishes and replaster using a breathable system on solid walls
- Replace or repair any skirting and floor timber damaged by sustained moisture
Where a quick chemical injection falls short
A chemical injection targets one possible cause — a failed original damp-proof course — and does nothing for a bridged cavity or raised external ground level, which are at least as common in practice. Selling an injection without first ruling out those simpler, often cheaper-to-fix causes means paying for a treatment that may never have been the actual solution.
Similarly, a cement-based waterproof render applied over a solid wall that's still damp behind it traps moisture rather than resolving it, often pushing the damp to travel sideways or upward to a new location instead of disappearing.
Working with a damp specialist and other trades
Where the cause and appropriate remedial measure are genuinely uncertain, a specialist damp survey is worth commissioning before committing to plasterwork or a damp-proof measure. Ground level correction may need coordinating with landscaping or paving work outside, and any structural timber found to be affected, such as joist ends, should be assessed before it's simply boxed back in.
Confirming the repair has worked
After external ground levels are corrected and internal replastering has fully dried out — which with a breathable lime-based system can take a number of weeks depending on wall thickness — there should be no new staining reappearing at skirting height through at least one full winter. Persistent damp readings after that point mean the original diagnosis needs revisiting rather than simply repeating the same remedial measure.
Common questions
Do I always need a new damp-proof course injected?+
No — if the cause turns out to be raised external ground or a bridged cavity, correcting those may be all that's needed, with no injection required at all. It depends entirely on what the survey finds.
How long does replastering take to dry out properly?+
It depends on wall thickness and the plaster system used, but breathable lime-based systems on solid walls typically need a number of weeks to fully dry before final decoration, longer than a standard gypsum plaster would.
Can I lower the external ground level myself?+
It needs to be done carefully to maintain the correct margin below the damp-proof course and to manage drainage properly, so it's worth having done as part of a coordinated repair rather than as an isolated DIY job.
Get a written quote for a proper damp repair
We fix the actual moisture path — ground levels, cavities or finishes — before considering a damp-proof measure, and quote it all in writing.