How to Cut Quartz Countertops Already Installed

Quartz countertops are a popular choice for many homeowners due to their durability, aesthetics, and ease of maintenance. However, sometimes you may need to cut or alter quartz countertops that are already installed. Here is a detailed guide on how to cut quartz countertops that are already in place.


Cutting already-installed quartz countertops is possible but requires precision and care. Quartz is an engineered stone made from natural quartz crystals blended with resins and pigments, making it very hard and dense. This hardness makes quartz more difficult to cut than natural stone. With the right tools and techniques, you can achieve clean cuts without damaging the surrounding countertop.

Before You Begin Cutting

Before cutting, gather all the necessary supplies:

  • Diamond-bladed angle grinder – Select a 4-inch or 4 1/2-inch grinder with a diamond blade designed for cutting stone. The diamond blades last longer than abrasive blades when cutting quartz.
  • Safety gear – Wear safety glasses to protect your eyes from debris. Use an N95 dust mask and ear protection as cutting will produce dust.
  • Clamps – Use C-clamps to secure a straightedge cutting guide to the countertop.
  • Vacuum – Have a vacuum ready to control dust.
  • Silicone sealant – After cutting, use clear silicone to seal the new edge.
  • Marking tools – Use a carpenter’s pencil or narrow masking tape to mark the cut line.
  • Straightedge – A straight 2×4 board can serve as an edge guide for your grinder.
  • Spray bottle – Have a spray bottle filled with water to keep the blade wet while cutting.

How to Cut Already-Installed Quartz Countertops

Follow these steps for smooth cuts:

1. Mark the Cut Line

  • Measure and mark your cut line using a carpenter’s pencil and straightedge. marks must be made on the backside of the quartz.
  • For curved cuts, trace the curve on the backside using narrow masking tape.
  • Check that your marks are accurate by comparing to your desired cut shape.

2. Set Up a Cutting Guide

  • Clamp a straight 2×4 board to the countertop edge to serve as a cutting guide.
  • Position it parallel to the cut mark to ensure the angle grinder moves steadily along the line.
  • For curved cuts, use a curved template as your guide.

3. Cut the Quartz

  • Fit the angle grinder with a diamond blade made for cutting stone.
  • Start the grinder and allow it to reach full speed before touching the stone.
  • Keeping the grinder flush against the guide, slowly cut along the marked line. Allow the blade to do the work.
  • Periodically spray the blade with water to keep it cool.
  • Make several shallow passes until cutting through the full thickness of the quartz.

4. Finish and Smooth the Cut Edge

  • Examine the cut edge for any rough spots and use the grinder to smooth them out.
  • Carefully round over and polish the edges and corners. Be careful not to chip the edges.
  • Wipe away all dust and vacuum up debris thoroughly.

5. Seal the Cut Edge

  • Clean and dry the cut edge thoroughly before applying silicone.
  • Use a clear silicone sealant formulated for stone to seal the fresh edge.
  • Apply silicone and tool it into a smooth, consistent bead. Remove any excess.
  • Allow the silicone to fully cure for 24-48 hours before use.

Tips for Clean Cuts

Follow these tips to get perfect cuts when working with installed quartz countertops:

  • Take it slow – Don’t rush the cutting process. Go at a steady, controlled pace.
  • Keep the grinding disc flush with the guide – This prevents blade wandering and jagged cuts.
  • Use light pressure – Let the diamond blade do the work. Too much pressure causes chipping.
  • Keep the blade wet – The water prevents overheating and extends the blade’s life.
  • Check blade condition – Replace worn blades for best results. Sharper blades make smoother cuts.
  • Support overhangs – For cuts near a counter edge, support the overhanging portion to prevent cracks.
  • Clean as you work – Frequently wipe away cutting dust to maintain visibility.
  • Polish edges smooth – Careful edge polishing removes minor imperfections left by the blade.

Common Cutting Issues

Here are some common problems and how to avoid them:

Uneven Cuts – The grinder shifted or tilted while cutting. Use clamps to secure a sturdy guide.

Chipping – Too much downward pressure was applied. Ease up on pressure and use a sharper blade.

Burn Marks – The blade overheated. Keep it wet and take slower passes.

Cracked Surface – The quartz wasn’t properly supported near the cut. Add supports.

Dull Finish – The blade was worn or the wrong type. Use a new diamond blade.

When to Call a Professional

For complicated cuts like cutouts for sinks and cooktops, it’s best to have a professional fabricator handle the job to get perfect results. Professionals have specialized tools and expertise.

Only attempt simple straight cuts on your quartz countertops. Seek help for any cutouts, intricate shapes, or disconnections needed.


Cutting quartz countertops already installed in your home is possible with some patience and the right approach. Always use sharp diamond-cutting blades and proper safety gear. Mark cut lines precisely and set up a secure cutting guide. Make multiple light passes while keeping the blade wet. Finally, polish the cut edge and seal it to create a long-lasting finish. Seek help for complex custom cuts to avoid damage. With care and caution, you can cut your quartz countertops to the perfect size and shape.

Frequently Asked Questions

Q: Can I cut already-installed quartz countertops with a circular saw?

A: It is not recommended. A handheld circular saw is challenging to keep steady and flush against a guide. Angle grinders allow better control and smoother cuts.

Q: How deep of a cut can I make in my quartz?

A: Quartz should be cut to no more than 1/3 of its total thickness in a single pass. Make multiple passes to cut through the full thickness. Removing more than 1/3 increases the risk of cracking.

Q: What RPM diamond blade should be used on quartz?

A: Use a diamond blade designed for cutting stone that spins between 8,500 – 10,000 RPM for the best cutting action on quartz. Lower RPMs can burn or bind.

Q: Is it safe for a DIYer to cut their own quartz?

A: Minor straight cuts can be DIYed if you use the right blade and techniques. But extensive cutouts and disconnections are best left to the professionals. Know your limits.

Q: Does the type of quartz make a difference when cutting?

A: The specific quartz formulation can vary the hardness slightly. But in general, all quartz requires diamond-blades and careful handling when cutting to avoid chipping.