How to Build a Base for a Quartz Countertop


Installing a quartz countertop can greatly enhance the look and functionality of your kitchen. Quartz is an engineered stone that is very strong, non-porous, and low maintenance compared to other countertop materials like granite or marble. When installing a quartz countertop, it is critical to build a proper base that will provide long-lasting support. Here is a step-by-step guide on how to build a base for a quartz countertop.

Check the Existing Cabinetry

The first step is to examine the existing cabinetry and ensure it is in good condition to support the weight of the quartz. Quartz is a heavy material, around 15 lbs per square foot on average. The cabinets must be level, plumb, and securely fastened to provide a stable foundation. If the current cabinetry is damaged, improperly installed, or unstable, it will need repairing or replacing before installing the quartz.

Choose the Base Material

The base material provides the support layer between the cabinetry and quartz slab. Good options include:

  • Plywood – At least 3/4″ thick exterior grade. Avoid voids and knots.
  • Reinforcement boards – Specialty boards like Hardibacker cement board add extra strength.
  • Quartz underlayment – Some manufacturers make underlayments designed for quartz installation.

Plywood is the most common choice as it is affordable and provides a smooth surface. Select a thickness that matches the cabinetry height to make a flush surface.

Check for Level

Using a long level or straightedge, check that the cabinet tops are level front to back and side to side. Any uneven spots greater than 1/8″ across 4 feet will need to be remedied by:

  • Sanding down high spots
  • Shimming up low spots
  • Adjusting cabinetry

Ensuring a flat and level surface prevents cracking or chipping of the quartz once installed.

Cut the Base Pieces

Measure the cabinetry dimensions and cut the base material to size using a circular saw. Having multiple smaller pieces is better than one large piece for seamless support. Be sure to make cuts straight and smooth.

Leave a 1/8″ gap between the base pieces and walls for expansion. Secure pieces with fasteners every 6 inches. Glue or construction adhesive can also be applied between pieces for increased stability.

Secure the Base

Screw the base pieces to the cabinetry using screws long enough to penetrate at least 1″ into cabinet framing. Aim for a screw every 12 inches around the perimeter and interior. Predrill holes to prevent splitting the wood.

For added strength, also adhere base pieces using a thin layer of high-quality silicone. Avoid adhesives like liquid nails that take longer to cure.

Check for Smoothness

Once the base pieces are fully secured, check for any unevenness. Sand down any bumps and fill any gaps with a sanded filler compound. The goal is a completely smooth and seamless surface.

Apply Moisture Barrier

Tape plastic sheeting or a liquid membrane onto the base surface to prevent moisture damage. Seal all seams and edges thoroughly. This protects the cabinetry from spills and moisture exposure once the quartz is installed.

You Are Ready for Quartz Installation!

With a sturdy, flat, and seamless base established, you are now ready for the quartz fabrication company to come in and complete the countertop installation. They will fully adhere the slabs to the base you have created.

Be sure the base remains clean and dry before installation day. A proper base is crucial to preventing cracks, misalignment, and other issues with the finished quartz countertop. Investing the time into following these steps will ensure your new quartz countertop lasts for many years!

Frequently Asked Questions

How thick should the plywood base be for a quartz countertop?

3/4″ exterior grade plywood is recommended. Go with 1″ thick for longer spans or additional durability.

What can I use instead of plywood?

Other options include MDF boards, cement boards, quartz underlayment boards, or high-quality OSB boards. Plywood tends to be the most common choice.

Should I glue down the plywood base?

Yes, using silicone or construction adhesive between the boards and cabinetry adds more stability and prevention of movement or separation.

How perfectly level does the base need to be?

Aim to get the surface level within 1/8″ over 4 feet. High and low spots exceeding this can lead to cracking.

How far should the base overlap the cabinetry?

There should be a 1/8″ overhang over the cabinet face frames. This helps support the edges of the quartz.

Can I use shims to level out the existing cabinetry?

Yes, shims are a good solution for leveling minor high and low spots. Make sure they are securely fastened.

What fasteners should I use to secure the plywood?

Deck screws or drywall screws work well. Use at least 2″ length screws and predrill holes to prevent splitting the ply.

How much overhang should there be for a breakfast bar?

For an unsupported breakfast bar, the overhang should be limited to no more than 6 inches without additional support.

What if my cabinets have an uneven finish under them?

Use filler compound or millwork to create an even surface. The base must fully support the quartz, not just the cabinet edges.


Installing a proper base is one of the most vital steps in the quartz countertop process. Taking the time to ensure the base is sturdy, flat, and seamless will help prevent cracks, chips, misalignment, and other issues from occurring down the road. Be sure to properly check the cabinets, choose suitable base material, level everything appropriately, and fully secure the base. With the right prep work completed ahead of time, you can feel confident your beautiful new quartz countertop will last for many years of heavy use. Reach out to fabrication specialists if you need assistance determining the best base building method for your specific kitchen layout and cabinetry.