How to Install Plywood for Quartz Countertops

Installing plywood as a substrate for quartz countertops is an important step that ensures durability and stability. With the right techniques and materials, you can create a smooth, level surface ready for quartz installation. Here is a detailed guide on how to properly install plywood for quartz countertops.

Choosing the Right Plywood

Using high-quality plywood is key for a long-lasting quartz countertop installation. Here are some tips on selecting the best plywood:

  • Opt for plywood with at least 7 plies. This prevents warping better than plywood with fewer plies.
  • Go for AA grade plywood with a sanded surface. This results in a smooth finish under the quartz.
  • Use plywood with a thickness of 3/4 inches for sturdiness and stability.
  • Choose plywood panels large enough to minimize seams under the quartz.
  • Select plywood rated for use as a countertop substrate, such as underlayment grade.
  • Avoid plywood with knots, cracks, or defects which can telegraph through the quartz.

Preparing the Cabinets

Proper preparation of the cabinet boxes is crucial before installing the plywood:

  • Ensure the cabinets are level, with no high or low spots. Shim as needed to level.
  • Confirm the cabinets are securely fastened to each other and the wall.
  • Remove any protruding nails, screws or staples.
  • Fill any gaps between cabinets with wood filler for a flush surface.
  • Sand any rough areas on the cabinet face frames.

Cutting the Plywood

Measure the cabinet run length and depth carefully to cut the plywood panels to size:

  • Use a circular saw with a sharp blade to cut the plywood. Make cuts slow and steady.
  • Cut panels 1/4 inches smaller than the cabinet opening on all sides. This allows for expansion.
  • Make neat, straight cuts. Irregular edges can complicate installation.
  • Use a jigsaw to cut out notches if needed to fit around pipes or outlets.

Securing the Plywood

Attaching the plywood securely is vital to prevent movement or separation under the quartz:

  • Apply a bead of construction adhesive on the cabinet tops before placing the plywood.
  • Use screws designed for fastening plywood every 4-6 inches along the cabinet frames.
  • Drill pilot holes to prevent the plywood from splitting when driving screws.
  • Make sure the plywood panels are fully supported and not overhanging.
  • Use C-clamps to hold panels tightly together at seams while fastening.

Smoothing Seams and Gaps

Careful finishing ensures smooth seams between plywood panels:

  • Use seam tape or veneer tape to cover any cracks or gaps between panels.
  • Apply wood filler thinly over the taped seams to even the surface.
  • Once dry, sand the seams smooth and flat with 120-150 grit sandpaper.
  • Avoid over-sanding, which can create uneven spots or depressions.
  • Make sure seams are flush for an even subsurface under the quartz.

Prepping for Quartz Installation

The plywood needs proper cleaning and prep before installing the quartz:

  • Vacuum and wipe down the plywood with a damp cloth to remove dust.
  • Fill any imperfections in the plywood with bondo or resin filler. Allow to fully cure.
  • Lightly sand again with 180-220 grit sandpaper for a very smooth finish.
  • Apply primer to seal and prepare the porous plywood surface.
  • Ensure the plywood is perfectly clean and dry before quartz fabrication.

With high-quality plywood installed securely and seams smoothed properly, you can have peace of mind that your quartz countertop will last for many years. Let the plywood cure fully before quartz fabrication for best results.

Frequently Asked Questions

What screw type should I use to secure the plywood?

Use coarse thread wood screws that are 1 1/4 to 1 1/2 inches long. Screws designed for subflooring or decking work well. Make sure they are rated for fastening plywood.

Can I use MDF instead of plywood?

Plywood is preferable as it resists warping better. MDF can swell and deform from moisture exposure. Go with exterior grade plywood for highest durability.

Should I use construction adhesive and screws?

Yes, it is best to use both adhesives and mechanical fasteners. Adhesive creates a moisture barrier and bonds panels, while screws provide added clamping strength and reinforcement.

How do I get a seamless look between plywood panels?

Use seam tape and wood filler to create flush seams, then sand thoroughly. Stagger the plywood panels like bricks for fewer seams in the main counterspace.

What should I do if my cabinets are uneven?

Use shims secured with construction adhesive to level any high or low spots. The plywood must fasten to a flat, even cabinet surface.


Installing high-quality plywood properly is one of the most vital steps for a successful quartz countertop installation. Taking the time to prepare cabinets, cut precise panels, securely fasten, and smooth seams will provide a perfectly flat underlayer for long-lasting quartz counters. With attention to detail and robust construction, your new quartz countertops will last for many years of beauty and performance.