How do I fix into a concrete ceiling or soffit?

Overhead fixings are the one place in domestic DIY where a failure lands on a person. The technique differs from a wall in three ways: dust behaves differently, resin runs out, and reinforcement is close to the surface.

Safety

What you'll need

• SDS drill with dust extraction
• hole brush and blow pump
• overhead-rated anchors or thixotropic resin
• eye protection
• dust mask

Step by step

1. Find out what the slab is.A cast in-situ slab, a beam-and-block floor and a prestressed hollow-core plank all behave differently. In a flat or a converted building, hollow-core planks are common and their tendons must never be drilled.
2. Establish the load and be honest about it.A pendant light is trivial. A hoist, a punch bag, a heavy track or a bike lift is not, and those need a specified anchor, not a guess.
3. Scan for services and reinforcement.Ceiling voids carry cables constantly. A rebar detector or a good multi-detector will also show reinforcement so you can drill between bars.
4. Keep the hole shallow.Reinforcement in a slab commonly sits within the top and bottom 25 to 40mm. Use the shortest embedment the fixing allows and stop at that depth.
5. Use dust extraction.Overhead drilling drops all the dust straight down. A drill-mounted extraction shroud, or a helper with a vacuum nozzle, transforms both the mess and the health risk.
6. Clean the hole thoroughly.Overhead holes hold dust that gravity will not remove. Brush and blow repeatedly, and expect it to take longer than a wall.
7. Choose the fixing family.Concrete screws for light and medium loads and easy removal; throughbolts in sound concrete for medium loads; overhead-rated resin for heavy or safety-critical work.
8. Use a thixotropic resin overhead.Ordinary resin runs out of an upward hole. Products rated for overhead use are formulated not to, and their approval covers this orientation specifically.
9. Support the anchor while it cures.A wedge or a prop keeps the stud in place and undisturbed. Any movement during cure destroys the bond.
10. Wait the full cure and then test.Double the stated time in cold conditions. Load progressively rather than all at once, and never hang from it to test it.
11. Get advice for anything substantial.Ceiling hoists, gym equipment and structural connections are not DIY specification decisions. A structural engineer's note is cheap relative to the consequence.

Tips

• Safety glasses are not optional overhead. Debris falls into your eyes by default rather than by accident.
• Hollow-core prestressed planks are common in flats and their tendons must never be drilled — if the ceiling sounds hollow in a regular pattern, stop and check.
• A drill with a dust extraction attachment costs little to hire and makes overhead work far less unpleasant.

Common mistakes

• Using an ordinary resin overhead — It runs back out of the hole under gravity before it gels, leaving a partly filled anchor with a fraction of its strength and no visible sign of the problem.
• Drilling deep to be safe — Depth is what brings you into contact with reinforcement or, in hollow-core planks, into the void or the tendons. Correct embedment, no more.

If it doesn't work

Questions people ask