How do I use the chisel mode on an SDS drill?

The chisel setting is the capability that most separates an SDS from a combi drill, and it is the one most owners never use. It turns a drill into a small breaker: no rotation, just the piston firing the striker at the back of the chisel. Used properly it removes wall tiles, chases plaster, lifts render, breaks out a hearth and takes down blockwork.

Safety

What you'll need

• SDS drill with a hammer-only mode
• SDS point and flat chisels
• Goggles, FFP3 mask and ear defenders
• Cable and pipe detector
• Grease for the shanks (optional)
• Dust sheets and a vacuum (optional)

Step by step

1. Confirm the tool actually has the mode.Look for a symbol of a hammer alone, without a drill bit beside it, on the mode collar. Two-mode SDS drills — rotary and rotary hammer only — cannot chisel, and forcing the selector will not create the function.
2. Check the wall for services first.Use a detector across the whole area you intend to work, not just the start point, and treat the zones above and beside sockets and switches as live until proven otherwise. A chisel does not stop when it touches a cable.
3. Choose the chisel for the job.A pointed chisel concentrates all the energy at one spot and is for breaking into hard material and starting a hole. A flat or bolster chisel spreads the blow and is for lifting tile, render and plaster off a surface without digging in.
4. Grease the shank and fit it.A smear of grease on the SDS shank before it goes in. Pull back the holder collar, push the chisel in until it seats and clicks, then tug it to confirm it is locked and free to slide a few millimetres.
5. Set the chisel angle if the tool allows it.Most SDS drills have an intermediate collar position that lets the chisel rotate freely so you can set its edge horizontal or vertical, then a chisel position that locks it. Set the angle before you start, not while it is running.
6. Start at a free edge and work into the material.Attack an edge, a corner, or a hole you have already made. Starting in the middle of an intact surface just bounces, and bouncing is how you crack what you did not want to remove.
7. Work at a shallow angle for surfaces.Lifting tile or render, come in at 20 or 30 degrees so the chisel gets under the layer and pops it off. Going in at 90 degrees drives straight through the tile and into the substrate behind.
8. Let the weight of the tool do the work.Guide it, do not lean on it. Pushing harder does not increase blow energy — the piston delivers the same blow regardless — and it costs you control and your shoulders.
9. Stop and reposition when it stops progressing.A chisel that has stopped cutting is buried, and hammering a buried chisel achieves nothing but heat. Withdraw, move along 30 or 40mm, and work back towards the stuck point.

Tips

• Removing wall tiles with a flat chisel is one of the great uses of the tool, but it will take the plaster off with them. Expect to reboard or re-skim afterwards and plan for it.
• Take a break every ten or fifteen minutes. Hand-arm vibration damage is cumulative, permanent and much easier to acquire than people expect from a tool this size.
• Chiselling a chase for a cable is regulated work in terms of where cables may run and how deep the chase may be. Cut the chase, but understand the rules before you decide where it goes.

Common mistakes

• Using rotary hammer mode with a chisel fitted — The chisel spins, which is uncontrollable and dangerous, and it wrecks the chisel. Confirm the selector is on hammer-only before pulling the trigger.
• Chiselling into a wall without checking for cables — Cables are buried at plaster depth in exactly the places people chase. A chisel through a live cable at close range is a serious injury.
• Fitting a dry shank — The locking balls and holder wear rapidly without grease, and a worn holder is what makes chisels stick and eventually stops holding them at all.

Questions people ask