Cracked Render and Failed Pointing: Damp Through Walls

A damp patch on an outside wall that gets worse after rain is a classic sign of water coming in through the wall itself. The culprit is often the wall's outer skin: render that has cracked or come away, or mortar joints that have crumbled. The patch indoors can look much bigger than the gap letting the water in, so look outside first.

Why render and pointing matter

GOV.UK guidance describes penetrating damp as water that gets into a building from outside through defects in the walls, roofs, windows or floors, and its external checks include cracks in render. The Property Care Association adds that poor pointing and deteriorated mortar joints are common causes, that weather wears down renders, paints, sealants, bricks and mortar over time, and that wind-driven rain or very heavy rainfall makes damp penetration more likely and more severe.

Rung 1: Look and map the problem (free)

Start outside, in daylight, ideally after rain. The Property Care Association advises an outside inspection of the roof and walls first, then checking inside for moisture. From the ground, look for:

• Cracks in the render, especially running from the corners of windows and doors.
• Patches that sound hollow when tapped gently, which can mean the render has come away from the wall.
• Mortar joints that are crumbling, recessed or missing, and bricks with flaking faces.
• Damp or stained reveals and sills around windows and doors.

Then go inside. Photograph the patch with the date, mark its edge in pencil, and check again after a dry spell and a wet one. If it grows in the wet and fades in the dry, water coming in is the likely cause. If it follows cold nights whatever the weather, read our guides to condensation and telling the types of damp apart.

Rung 2: Rule out the easy water sources (free to cheap)

Before blaming the wall finish, check the water is not being delivered to it. Blocked gutters, faulty downpipes and failing flashings are all listed by the Property Care Association as common causes, and they can soak the same stretch of wall again and again. Our guide to leaking gutters and downpipes covers that walk-round. Never overreach from a ladder.

Rung 3: Repair the way in (cheap to moderate)

The Property Care Association says to fix the entry point and stop further water getting in, then dry out the affected area. For render and pointing that usually means:

• Small, stable hairline cracks: have them sealed or filled with a suitable material and keep watching them.
• Hollow, loose or widely cracked render: cut back and renew the affected area rather than painting over it.
• Crumbling mortar: repoint the open joints, using a mortar mix that suits the wall, since an older solid-wall home does not always cope well with a very hard mix.
• Gaps around window frames and sills: reseal or repair so water is shed away from the reveal.

Painting over a damp patch only hides it, so repair first. Then let the wall dry before redecorating, which can take a good while on thick brick. If the source is not obvious, a competent specialist can trace the water's path.

Rung 4: When mechanical help makes sense (and when it does not)

A dehumidifier does nothing about rain entering through a cracked or open wall. If the render and pointing have not been repaired, the wall will keep getting wet and drying the indoor air will not change that.

Once the wall has been repaired and has dried, you may still have condensation on the colder walls, since the two often turn up together. In an owner-occupied home with a loft, a loft-mounted Dryzen unit can then help keep humidity near 50-55%, which helps stop the conditions mould and dust mites need. One unit covers up to 150 m2 and extracts up to 12 litres a day. It needs a loft to mount in and is not suitable for rented homes unless the landlord authorises the changes. It will not cure penetrating damp or rising damp, and mould already growing must be cleaned off.

Mistakes that let the damp come back

• Repainting or replastering inside before the outside defect is fixed.
• Patching with a filler or coating that does not suit the wall, so the crack reopens.
• Assuming the crack you can see is the only way in, when the wet patch can sit away from it.
• Buying a dehumidifier to deal with a wall that rain is soaking through.

In Chatham and the Medway Towns

Homes across Chatham and the Medway Towns range from older brick terraces to later estates, and in all of them the outer face of the wall is the first line of defence against the rain. Our area pages for Rochester and Gillingham have local help.

Questions we are asked

Related guides

• Leaking Gutters and Downpipes: Damp Walls Explained
• Rising, Penetrating or Condensation Damp? How to Tell
• Cold Spots and Cold Bridges: Why Damp Keeps Returning to the Same Place
• Why Victorian Terraces Get Damp Differently to New Builds

Local help

• Damp, mould and condensation help in Rochester
• Damp, mould and condensation help in Gillingham
• Damp, mould and condensation help in Upnor

Sources: GOV.UK: Understanding and addressing the health risks of damp and mould in the home; Property Care Association: Penetrating damp.