How do I fix something into a stone wall?

A stone wall is not one substrate. It can be granite that eats masonry bits, soft sandstone or limestone that drills like chalk, or a rubble wall whose two faces are held together by mortar and gravity. All three are common in the UK, they need different techniques, and the only way to know which you have is to drill an exploratory hole and look at the dust.

Safety

What you'll need

• Good quality masonry bits, or SDS bits in a rotary hammer
• Chemical anchor resin and studbar
• Perforated resin sleeves, for rubble or voided walls (optional)
• A vacuum and a blow pump
• A cable and pipe detector
• Dust mask and eye protection

Step by step

1. Work out what the wall is before you commit to a position.Drill a small exploratory hole somewhere it will not show. Very hard going with grey or sparkling dust means granite or a hard igneous stone. Easy going with pale powdery dust means limestone or a soft sandstone. A bit that suddenly drops through means you have found the rubble core.
2. Decide whether to fix into stone or into the joint.In a wall of large sound stones, always fix into the stone. In a rubble wall of small stones with wide joints, a deep resin anchor bridging both may be all that is available — but never fix into soft lime pointing alone.
3. Drill without hammer action in soft stone.Hammer action shatters soft limestone and sandstone into a crater. Use rotary only, a sharp bit, and let it cut. In hard stone you will need hammer or SDS, but keep the pressure steady rather than heavy.
4. Use resin as the default anchor.Chemical anchor resin exerts no outward pressure, so it does not split soft stone or lever a face off, and it fills whatever irregular shape the hole has ended up as. In stone, this is the fixing that works when nothing else does.
5. Use a perforated sleeve where the hole breaks into a void.A mesh sleeve pushed into the hole contains the resin so it forms a plug rather than disappearing into the rubble core. Without one, you will empty a cartridge into the wall and get nothing.
6. Clean the hole thoroughly and more than once.Blow, brush, blow again. Resin bonds to the hole wall and stone dust prevents that bond completely. This is the step that decides whether the fixing works.
7. Let it cure fully before loading.Cure times lengthen considerably in cold weather, and a stone wall in winter is cold. Read the chart on the cartridge for the temperature you are actually working in, and then leave it longer.
8. Spread the load over more fixings than you think you need.Stone walls are variable. Four modest fixings spread across the wall are far more reliable than two large ones, because you are averaging out the variability rather than betting on it.
9. Abandon a bad hole rather than persevering.If a hole is loose, crumbling or breaks into a void and you cannot sleeve it, move. A hole that has already failed will not improve.

Tips

• Old stone buildings usually have lime mortar, which is deliberately weaker than the stone so that movement and moisture go through the joints. Do not treat it as if it were cement.
• Flint and cobble walls are effectively unfixable in the face — the stones are round, hard and held by mortar alone. Fix into a substantial quoin or into a timber plate spanning several stones.
• Where the item allows, a timber batten resin-anchored into the wall at several points, with the item then screwed to the batten, converts an unpredictable wall into a predictable timber fixing.

Common mistakes

• Using an expansion plug or a sleeve anchor in soft stone — Outward pressure splits soft stone and pops a lens off the face, often taking a piece of the building with it. Use resin, which applies no pressure.
• Drilling on hammer through a soft stone face — You get a large crater rather than a hole, the fixing has nothing round to sit in, and the visible damage is permanent.

If it doesn't work