How to Remove a Boulder

Pro Tip: On a This Old House project in Brookline, contractor Charlie explained that choosing between an excavator with a hammer attachment versus drilling and blasting comes down to your neighbors: “We didn’t drill and blast for one main reason — we’d have to get all the houses within 250 feet, have a pre-blast survey done. And that entails a company coming in and documenting any crack on your foundation. You might have a crack on your plaster, something out of the door. A cabinet might be out of line. So they have to really record all of that, write a report with pictures.” That added step can significantly increase both cost and timeline.

On a This Old House project, landscape contractor John demonstrated that cost can escalate when smaller tools aren’t up to the task. After hand-held feathers and wedges only broke small pieces off a large rock, he had to bring in a diesel-powered air compressor connected to a rock hammer with carbide tips — a significant equipment upgrade that drives up rental costs. The lesson: always dig around the boulder first to gauge its full size before renting equipment, so you don’t end up paying for tools twice.

Steps:

1 Use a pointed shovel to dig around the rock to expose its size and shape.

2 Drill a series of ½-inch-diameter holes into the rock with an electric rotary hammer.

3 Blow dust from the holes with a bulb-type syringe.

4 Into each hole, drop two feathers and one wedge; be sure the wedges are inserted between the feathers, and that the feathers face out toward the edge of the rock.

5 Lightly tap each wedge with a hammer to tighten it into the hole.

6 Next, use a 3-pound sledgehammer to alternately pound the wedges into the holes; keep hitting the wedges a little at a time until the rock cracks.

7 Pry apart the split rock with a long-handled pry bar.

8 For very large boulders, rent a diesel-powered air compressor and rotary rock hammer.

9 Drill a series of large holes into the rock, then insert the extra-large feathers and wedges.

10 Tap the wedges with a hammer to set them into the holes.

11 Use the pneumatic jackhammer to drive in the wedges and split the rock.

12 Pry off the broken rock pieces with a pry bar.

13 Continue drilling holes and spitting off pieces until the rock is gone.

Pro Tip: As This Old House landscape contractor Roger Cook explains, the key to using feathers and wedges is patience and even pressure: “You’re trying to keep the same tension on every set so that the push is equal on all of them. And you can feel if one’s tighter than another and you can hear it too.” He also cautions against swinging too hard: “If you use too heavy of a hammer, you put so much pressure on an individual hole that it will actually blow the top surface of the hole right out and you lose your push.”

The spacing between drilled holes matters and should be adjusted based on the size of the boulder. As one This Old House stone expert notes, the size of the stone dictates the spacing: closer spacing for smaller stones, wider for larger ones. Keep the spacing fairly even so the force distributes uniformly, which helps produce a clean split along the intended line.