Longer than most people expect. Once the source is fixed, a thick solid wall can take many months to dry out fully, depending on its thickness, materials, how wet it was and the conditions. A commonly quoted rule of thumb is around 25mm of wall thickness per month in good drying conditions.
After any damp repair, whether it’s a fixed gutter, a new DPC, a repaired leak or a lowered patio, people want to know when the wall will be dry. The honest answer is: slowly.
Why it takes so long
Masonry can hold a lot of water, and it can only lose it from its surfaces, mostly by evaporation. Water deep in the middle of a thick wall has a long way to travel. A commonly used rule of thumb is that walls dry at roughly 25mm of thickness per month in reasonable conditions. That means a solid nine-inch brick wall, or a thick stone wall, can take many months, and the worst-affected areas longest of all. Treat it as a guide, not a promise.
What affects drying
- Wall thickness and material. Thick solid walls and dense stone take longer.
- How wet it was, and for how long. A wall that’s been soaked for years holds more water.
- Weather and season. Walls dry better in warm, breezy, dry weather than in a cold, damp winter.
- Finishes. Non-breathable paint, vinyl wallpaper, cement render and impermeable coatings slow drying a lot.
- Salts. Hygroscopic salts keep pulling moisture from the air, so salty plaster may never dry properly until it’s replaced.
- Ventilation and heating inside.
Helping it dry
- Make sure the cause really has been fixed.
- Remove finishes that trap moisture, where practical.
- Keep the room ventilated and gently heated. A dehumidifier with the door shut can help.
- Don’t use very high heat to force it. Rapid drying can crack plaster and pull salts to the surface.
- Use breathable finishes when you redecorate. Follow your contractor’s advice on timescales for paint and wallpaper.
Don’t panic too early
Damp meter readings and dark patches can persist for a while after the cause has been fixed. That doesn’t necessarily mean the repair has failed. What you want to see is a steady improvement over time. If the readings or patches aren’t improving, or get worse after rain, have it re-checked.
Be patient. A wall that’s been wet for years won’t dry in a fortnight.
When to call a specialist
If a wall isn't drying out after the damp source has been fixed, get it re-inspected to check for salts, a missed moisture source or a finish trapping moisture. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Frequently asked questions
How long does a wall take to dry after damp proofing?
Often several months for solid walls; a common rule of thumb is about 25mm of thickness per month.
Can I speed up drying a damp wall?
Gentle heat, ventilation and a dehumidifier help, but avoid very high heat.
Why is my wall still damp months after repair?
It may still be drying, or salts or a missed moisture source may be keeping it damp.