How Much Support for Quartz Countertop

Installing a beautiful quartz countertop can greatly enhance the look and functionality of your kitchen or bathroom. However, proper support is crucial for ensuring your quartz countertop lasts for years to come without sagging, cracking or breaking. Here is a detailed overview of how much support quartz countertops require.

Choosing the Right Cabinetry

The cabinetry or base you install your quartz on top of plays a major role in providing adequate support.

  • Cabinetry should be sturdy and reinforced to bear the weight of the quartz without sagging over time. Opt for cabinetry made of robust wood like oak or maple. Avoid particle board or lower quality materials.
  • Cabinets should be securely fastened to wall studs and have additional corner bracing for maximum stability.
  • For peninsula or island installations, include extra structural supports like corbels or legs under the overhang.
  • Cabinet doors and drawers should open and close smoothly without rubbing against the countertop.

Proper Support Along the Perimeter

Installing perimeter support along the edges of your quartz countertop is crucial for preventing cracks and breakage over years of use.

  • A sturdy plywood subtop at least 3/4″ to 1″ thick should be screwed into the top of your cabinetry to support the perimeter. OSB and MDF are not recommended.
  • Support ledges around the edges should be 2-3″ wide for 1.2cm thick quartz. Go wider if you have thicker quartz.
  • Seams between cabinets should be completely flush and even. Any gaps or height differences could lead to cracks forming.

Adequate Support Throughout the Span

The right amount of supports distributed underneath the quartz surface ensures the weight is properly borne and prevents bending.

  • For standard 3cm thick countertops, supports are needed every 24″ along the underside. Go with 18-20″ spacing for thinner 2cm quartz.
  • For a peninsula or island, place an additional support beam down the center lengthwise.
  • Around cutouts for sinks and cooktops, use extra underlying support like wood blocks.
  • On overhangs longer than 10″, a metal bracket, corbel or other rigid support is recommended.

Proper Anchoring and Seaming

Adhering the quartz securely and seamlessly gives added structural reinforcement.

  • Use high quality flexible adhesive like silicone to anchor the quartz to the underlying supports.
  • Carefully join seams between slabs according to manufacturer specifications for smooth, gapless connections.
  • Allow adhesive and seams to fully cure before exposing quartz to any weight or use.


How much weight can quartz hold without support?

Quartz slabs 1.2cm thick can only hold around 10-15 lbs per square foot without support underneath. Anything more will risk cracks and breakage over time. Proper support is a must.

What thickness of plywood is best under quartz?

3/4″ to 1″ exterior grade plywood secured to your cabinets provides ideal support at the perimeter. Go with at least 5/8″ for standard counters up to 25″ depth. Deeper spans may require thicker plywood for stiffness.

Should I use a center support beam on a quartz island?

Absolutely. Islands and peninsulas should have a center support beam running their full length. This prevents the quartz from bowing or sagging in the middle over time under its own weight.

Can quartz overhang unsupported like granite?

No. Quartz lacks the stiffness of natural stone and requires brackets or corbels supporting any overhang longer than about 10″. The farther the overhang, the more support it needs underneath.

How far apart should quartz supports be?

Standard 3cm quartz needs supports spaced every 18-24″ across the underside. Thinner 2cm quartz requires tighter support spacing at 16-20″ intervals to prevent bending. Around cutouts may need added support.

What screws should I use to install quartz?

Choose high quality stainless steel or decking screws 1-1/4″ to 2″ long to firmly anchor quartz without risk of corrosion or cracking. Avoid drywall or wood screws which can work loose.


Installing adequate structural support ensures your beautiful quartz countertop retains its beauty and function for the long haul. Allowing proper perimeter, edge, and underside reinforcement prevents unsightly cracking, sagging, and damage over years of use. Paying attention to sturdy cabinetry, proper anchoring, and seamless installation gives your quartz the stability it needs to last a lifetime. With some planning and care taken during installation, you can enjoy durable, worry-free quartz countertops that stand the test of time.