Do You Put Plywood Under Outdoor Kitchen Quartz Countertops?

Installing quartz countertops in your outdoor kitchen can provide an elegant and durable surface, but proper installation is key. Here is a detailed guide on whether you need to put plywood under quartz for an outdoor kitchen installation.


Quartz countertops are a popular choice for outdoor kitchens because of their strength, durability, and aesthetic appeal. Made from crushed quartz blended with resins and pigments, quartz counters are non-porous, stain-resistant, and heat-tolerant – perfect for withstanding the elements.

However, quartz is also very heavy, weighing upwards of 15 pounds per square foot. Proper support and installation are critical to prevent cracking or damage over time. This leads to the key question: should you put plywood under quartz countertops in an outdoor kitchen?

The Importance of Plywood Support

In short – yes, installing plywood under quartz countertops is highly recommended for outdoor kitchens. Here’s why:

  • Weight distribution: The plywood helps distribute the weight of the dense quartz slabs. Without support, the solid surface could crack under its own mass.
  • Moisture protection: Plywood creates a moisture barrier between the countertop and cabinetry. This prevents warping or water damage.
  • Level surface: Any imperfections or unevenness in the cabinetry can be smoothed out with a plywood sub-surface. This provides a flat base for quartz installation.
  • Thermal insulation: Plywood offers some thermal insulation, helping protect against temperature fluctuations that could potentially crack quartz.
  • Easy installation: Plywood gives you a clean, smooth surface for attaching quartz securely.

Best Practices for Installation

When installing quartz over plywood, follow these best practices:

  • Use high-quality, moisture-resistant exterior grade plywood in thickness of 3/4″ or 1″.
  • Verify plywood sheets are flat – sand down any bumps or uneven spots.
  • Allow 1/8″ gap between plywood sheets to account for expansion. Seal seams with silicone caulk.
  • Pre-drill holes 2” from the edge every 8” to 10” around the perimeter and every 12” across the plywood. This prevents cracking.
  • Attach plywood securely to cabinets with screws into studs if possible.
  • Follow manufacturer instructions for quartz adhesive, ensuring proper cured time.
  • Use additional support braces under overhangs longer than 12”.

Alternative Options to Plywood

While plywood is preferred, here are some other options:

  • MDF boards: moisture-resistant medium density fiberboard provides rigidity. Must be sealed properly.
  • Aluminum honeycomb panels: very lightweight but adds strength. More expensive.
  • Reinforced concrete: pours a thin, reinforced concrete layer for sturdiness.
  • Additional corbels or support frames: increases support for overhangs.

However, properly installed plywood is generally the easiest, most affordable and effective method for securing quartz countertops in outdoor kitchens.

FAQs About Using Plywood Under Quartz

Should I use pressure-treated plywood outside?

Pressure-treated lumber contains chemicals that could potentially leach through quartz. Use exterior grade, non-treated plywood.

What thickness of plywood should be used?

3/4” and 1” are standard. Thicker plywood provides more support. Long spans may require 1 1/4” thickness.

Can I use OSB instead of plywood?

Oriented strand board (OSB) swells and deteriorates faster than plywood. Plywood is more water-resistant for long-term durability.

How much overhang support is needed?

Don’t exceed 12” unsupported overhangs. Use an additional support ledge or corbels beyond 12”.

Should I seal or finish the plywood?

Yes, seal the edges and surfaces of the plywood with silicone caulk to prevent moisture damage. Do not apply varnish or paint.


Installing plywood underneath provides essential support and stability for quartz countertops in outdoor kitchens. Be sure to use exterior grade, pre-drill holes, and follow all manufacturer specifications for attaching quartz securely over the plywood sub-surface. With proper installation, you can enjoy beautiful and durable quartz countertops outside that will last for many years.