What is Wall Sawing?

Wall sawing, also called track sawing, is a diamond blade running on a rail bolted to the surface being cut. The track holds the line. The blade is driven hydraulically or electrically. The result is a straight cut to a set depth, in a plane a floor saw cannot work in. Vertical, horizontal and overhead are all normal. Most wall sawing is not really cutting at all. It is forming openings.

At Shepherd and Sons we cut and drill on live sites across the South East. From working with clients inside occupied buildings, we've found the sawing is rarely the hard part. Two other things are. What happens at the corners, and what happens to the panel when the last cut completes.

Door and window openings in solid or reinforced walls. Lift shafts and riser shafts. Stair openings through slabs. Plant openings in decks, and access holes through basement retaining walls.

It is also the method for taking a section out of a structure that has to keep standing. That is a different problem from demolition, and it is where most of the planning goes.

The finished opening is square and cut to line. It needs no making good. That is the entire reason for choosing it over breaking out. On a structural alteration inside a finished building it is usually the only acceptable method.

Depth is set by blade diameter, and a wall saw cuts a little under half of it. Across a current manufacturer range the ratio sits at roughly 44 to 46 per cent. The shortfall is taken up by the blade guard and the arbor.

In practical numbers, the largest wall saws in common use take a 1,600mm blade. That cuts to about 730mm from one face. It is the deepest cut in the range, not a starting point.

Cutting from both faces doubles the depth achievable. On that same machine it takes you to roughly 1,460mm. It is worth being precise, because the obvious phrasing is wrong. Two faces gives twice the single-face depth, not the blade's diameter.

Both faces also have to be accessible, and the two cuts have to line up. That is a setting-out problem rather than a sawing one. Past that point the job stops being wall sawing altogether, and a section thicker than a blade can reach from both sides is wire sawing work.

A deep cut is not made in one go. The operator starts with a smaller blade and works upwards through sizes, cutting progressively deeper on the same line.

That is why a wall sawing quote lists several blades rather than one. It also explains why depth costs more than length. Each increase in blade size is another pass along the whole run.

The blade must sit at ninety degrees to the surface throughout. The track is levelled to achieve that, and a blade running out of square is a safety problem rather than a quality one.

A circular blade cannot cut a square internal corner. The blade is round. As it reaches full depth at the end of a cut, it has only reached full depth at one point, and the face behind is under-cut.

There are three honest ways to deal with it. Over-run the cut on the hidden face, where an over-cut does no harm. Finish the corner by core drilling. Or use a hydraulic chainsaw, which cuts a genuine right-angled corner.

In our experience, agreeing the corner treatment before mobilising works better than deciding it on site. The answer changes what plant comes on the lorry. A method statement that does not say which of the three is happening has not been thought through.

The moment the final cut completes, the piece is free. A wall panel or slab section is heavy, unbalanced, and in exactly the wrong place.

The sawing guidance deals with this by restraint. Steel wedges and supports. Cross bars or anchors. Mounting the saw onto the surrounding structure rather than the panel when the last cut is made.

Structural stability is a separate discipline again. Where removing a section affects how the building stands up, temporary support has to be designed and installed properly. Regulation 19 of CDM 2015 puts that duty in law, and HSE guidance on structural stability is the readable version.

The lift itself sits under LOLER. None of that is sawing expertise, which is rather the point. On an occupied building the temporary works and the lift are most of the risk assessment. The cut is a line on a drawing.

Wall sawing is a wet process. Water cools the blade and flushes the kerf, and it suppresses the respirable crystalline silica that dry cutting throws off.

That last point is the health one. HSE treats water suppression as a primary control for silica on this kind of work, and it is not something to trade away for convenience.

Inside a building the slurry becomes the problem instead. It runs downhill, it stains, and it finds lift pits and service risers. Containment and collection are planned with the same care as the cut, because a slurry escape into a finished floor below costs more than the opening did.

A great deal of wall sawing is not done at floor level. Openings in upper storeys, soffit cuts and high-level penetrations are all worked from access equipment.

That changes the job in three ways. The saw and the track have to be set up and levelled from a platform. The lines have to be routed so nobody trips on them. And the panel, when it comes free, comes free above people.

Sequencing therefore matters more than usual. The rule is simple: nothing is cut until the means of restraining and lowering the piece is already in place.

Overhead cutting also inverts the water problem. Slurry runs back down the blade, along the track, and onto whoever is operating it. Full waterproofs and face protection are normal rather than cautious. Collection has to be arranged below the cut rather than beside it.

None of that is exotic. It is simply why an overhead opening takes longer than the same opening at floor level. A quote that prices the two the same has not been to site.

• Floor sawing for horizontal surfaces: roads, slabs, decks and aprons.
• Wall sawing for vertical, overhead and angled planes, and for forming openings to line.
• Diamond drilling for holes, penetrations and finishing corners.
• Wire sawing where the section is beyond a blade from both faces, or where vibration rules a disc out.

Most real jobs use two or three of those together. That is why it is worth appointing one contractor who runs all of them, rather than co-ordinating specialists across a single opening.

A single opening in a basement wall can easily use three. Core drilling for the corners, wall sawing for the four sides, and diamond drilling again for the fixings that follow. Splitting that across two firms adds interfaces without adding capability.

For wall and track sawing on structural alterations across Kent, London and the South East, get in touch with our team.