Wall and foundation care means keeping water out of the wall and away from its base: keep the ground falling at least 2% away from every building, keep drains flowing, repair plaster cracks wider than 3 mm, probe straw bale and earth walls at the base for damp, and keep wood from touching the ground. Water is the cause of nearly every wall and foundation failure, so the job is mostly drainage and plaster.
Part of Building Maintenance Schedules
Wall and foundation care is the upkeep of a building’s plaster, base and surrounding ground so that rain, groundwater and pests cannot weaken it.
A Wall Fails From The Base And The Skin First
The maintenance guide lists what water does to a building: it rots wood, dissolves earth plaster, erodes foundations, cracks stone and masonry when it freezes, and invites mould and insects. For walls it asks for a perimeter walk looking for cracks, flaking plaster, erosion at the base and rodent holes; repair of any crack wider than 3 mm or running vertically; probing of straw bale walls at the base; and ground that falls away from the building at 2% or more. For foundations it asks for French drains that flow, a stem wall free of cracks and settlement, and no standing water nearby.
Three articles carry the detail: Plaster Crack Repair, Foundation Drainage Checks and Pest Inspection.
Worked Example: Reading A Crack
A crack tells you its cause by its width, its direction and whether it is moving. The maintenance guide’s threshold is 3 mm or vertical.
- Hairline cracks in earth plaster are normal and are filled with a thin slip coat.
- A crack wider than 3 mm needs repair. For a 3 m crack, 3 mm wide, in a 15 mm coat the gap holds 3,000 × 3 × 15 = 135,000 mm³, 0.135 L, so it needs a small, deliberate fill and not a smear.
- A crack that was marked at both ends in spring and has grown past the marks by autumn is moving; filling it is wasted until the cause is found, which is usually settlement or water at the foot of the wall.
What You Need
- A pencil or chalk and a tape to mark the ends of cracks and date them
- A long probe or screwdriver for the wall base
- A string and level for the ground fall
- Plaster, slip, gravel and tools for repairs
- The log
Method: Walk The Perimeter
Step 1: Walk round the building looking at the lowest 1 m of the wall for damp, flaking and holes, and at the plaster for cracks.
Step 2: Mark and date each crack.
Step 3: Probe the base where straw bale, earth or wood meets the ground.
Step 4: Check the ground fall and where the roof water goes.
Step 5: Check drains and outlets and clear them.
Step 6: Check that no wood touches the ground: the shelter guide says to raise wood 15 cm or more above ground on stone, because rot and termites destroy it within 2-5 years.
Common Mistakes
- Plastering over damp. The wall rots behind the plaster.
- Piling soil or firewood against the wall. It holds water against the base.
- Filling a moving crack. It reopens.
- Ignoring rodent holes. They let in water and animals.
Safety
Lime burns, and walls can fall
Wet lime plaster burns skin and eyes, so wear gloves and eye protection when mixing and applying it (Lime Plaster, Exterior). A wall that is leaning or cracking further is unstable: stay out of its fall zone, which reaches as far as the wall is high, and brace it from outside with timber shores. Work from a footed ladder or low scaffold, not a pile of boxes.
What’s Next
- Learn next: Plaster Crack Repair — the commonest job
- Combine with: Foundation Drainage Checks — keeping water from the base