How to cut roof slates

Durable, versatile, low maintenance, and attractive; slate roof tiles have it all. Best of all, with a little care and the right tools, anyone can learn how to cut slate roof tiles like a pro.

Getting Started

Sizing Your Tiles

Before you can start cutting roof slates, you need to know the correct size:

1. Measure the angle of your roof - Free smartphone apps are great for measuring roof pitch. We like Pitch Gauge or Roof Pitch Factor, but there are plenty of others out there.
2. Determine size.

Manufacturers typically provide instruction tables that list a range of appropriate sizes (height x width) for slates based on roof pitch. Now that you have the pitch angle, you can use the table to select the correct slate measurement.

Cutting Slate Roof Tiles

Always cut roof slates on the underside. This encourages spelching (splintering) on the visible surface to produce a natural, riven finish. It will also ensure any scratches or cutting guides don’t show on the finished roof.

To reduce the chances of your roof slates breaking, always cut them from the thickest part of the tile out towards the thinnest. Cutting with the grain of the slate will help to minimise damage to the tile.

Staying Safe

Slates can spall (chip and flake) when they’re being cut. Wearing glasses or protective goggles ensures small chips that fly off don’t damage your eyes. Cutting slate tiles by hand produces less dust than machine cutting, but it is never advisable to inhale any quantity of dust, so always wear a face mask.

Cutting Slates Tiles by Hand

Slate Cutter

For thin slates (under 28mm), the handheld Edma Slate Cutter is the best option, and will cut both natural and man-made slates.

To cut slate by hand:

1. Draw a cutting guide along the underside of the tile.
2. Place the thickest part of the slate between the blade and gently snip down the line. Take it easy, and clear the cutter of debris every few cuts to avoid jamming and breakages.
3. With a claw hammer, gently tap along the cut edge to remove any sharp splinters or loose flakes.

Makeshift Slater’s Axe

If you lack specialist tools, you can cut slates with a wall and a brick layer’s trowel.

1. Draw a cutting guide along the underside of the tile.
2. Place the tile on top of a wall or worktop. Line the cutting guide up with the edge, so the excess slate hangs over it.
3. Use the back of the trowel blade (nearest the handle) and carefully chip away at the overhanging slate.
4. Run a hammer along the cut edge to remove any sharp splinters or loose flakes.

Cutting Slates with an Angle Grinder

An angle grinder with a diamond blade can cut slates of all sizes. Opt for a 150mm angle grinder for tiles under one inch, and a 230mm cutter for those over one inch.

1. Score the underside of the tile to create a cutting guide.
2. Cut along the line with the angle grinder. Use light pressure and a sawing motion to clear the dust from the blade as you go.
3. Run a claw hammer along the cut edge to remove any sharp splinters.

Expert Hacks for Cutting Slate Roof Tiles

Claw Hammer

If you only have minor adjustments to make, you can cut your slate tiles with a claw hammer.

1. Draw a cutting line in chalk on the front of the slate (this is the only time you’ll hear us advising cutting the front face of the tile).
2. Starting at the outer edge, place the slate between the claws and apply gentle pressure. Remove small sections at a time to avoid breakages.
3. Finally, run the hammer along the cut edge to remove any sharp splinters or loose flakes.

Slate Cutter Drill Attachment from Armatool

Available in JJ Roofing Supplies Branches. Find your nearest branch here.

How to Cut Roof Slates: Top Tips from the Experts

• Cut slates from the thickest section to the thinnest.
• Work with the grain of the slate where possible.
• Clear the debris from your blade or cutter every few cuts to avoid jamming.
• After machine cutting roof slates, gently chip away at the top 2mm of the front face of the slate with a claw hammer to restore the riven finish.