Do You Need to Put Plywood Under Quartz Countertops?

Installing new countertops can significantly upgrade the look and feel of your kitchen. Quartz countertops in particular have become a popular choice due to their durability, low maintenance, and stylish appearance. However, proper installation is key to ensuring your new quartz countertops last for years to come. One common question that arises is whether you need to put plywood under quartz countertops during installation.

What is Quartz?

Quartz countertops, sometimes referred to as engineered stone, are made from ground quartz crystals combined with resin and pigments. The result is a non-porous, highly durable material that resists scratches, stains, and heat.

Compared to natural stone like granite, quartz requires very little maintenance. It does not need to be regularly sealed and is not as prone to etching from acidic foods. The man-made manufacturing process also allows quartz to come in a wide array of consistent colors and patterns.

Do You Need Plywood Underneath Quartz?

Installing plywood under quartz countertops is recommended in most situations. Here’s why:

Provides a Stable Base

Plywood helps create a stable, sturdy base for quartz countertops to adhere to. The solid plywood prevents the countertop from sagging or cracking over time. This is especially important for larger expanses like kitchen islands.

Smooths Out Minor Imperfections

The underlying cabinet base may have small gaps, uneven surfaces, or protruding fasteners. A plywood sub-base helps bridge these imperfections to provide a flat, even surface for quartz installation.

Gives Added Support

Quartz is very dense and heavier than natural stone. The added layer of plywood helps bear some of this weight and reduce strain on the underlying cabinets.

Allows Flexibility for Undermount Sinks

Plywood offers a solid surface to cut out and install an undermount sink within the quartz countertop. Without plywood, undermount sinks may not be properly supported.

Prevents Moisture Damage

Plywood forms a protective barrier between the quartz and underlying cabinetry. This prevents any moisture from leaking through and warping or rotting the cabinets.

When Can You Skip the Plywood?

In some circumstances, plywood may not be necessary under quartz:

  • If the existing countertop substrate is already completely flat and seamless.
  • For sections adhered directly to stone or masonry.
  • For lightweight accent pieces or islands with added structural support.

However, most installers still recommend using plywood whenever possible for strength and stability. Many quartz manufacturers’ warranties may also require a plywood substrate.

Choosing the Right Plywood

Not all plywood is suited for undermounting quartz. Here are some tips for choosing appropriate plywood:

  • Use plywood at least 3/4-inch thick for adequate support. 5/8-inch can also work for smaller countertops.
  • Look for void-free plywood without knots or gaps.
  • Avoid softwood plywoods like pine which may dent. Opt for hardwood birch or oak.
  • Ensure the plywood has an A-grade sanded surface on both sides for a perfectly smooth finish.
  • The plywood should be exterior grade to deal with potential moisture issues.
  • High-quality Baltic birch is an excellent choice that meets all requirements.

Proper installation of the plywood according to the manufacturer’s guidelines is also crucial. The sub-base must be totally secure without flex or movement before installing the quartz.

The Bottom Line

Installing high-quality plywood beneath your quartz countertops provides extra strength, durability, and long-term performance. The minimal cost is well worth it for the added peace of mind. With proper plywood support, you can enjoy flawless, rock-solid quartz countertops that will last for many years in your home.

Frequently Asked Questions

Is plywood 100% necessary under quartz?

It’s not an absolute requirement, but plywood is highly recommended in most cases. It provides extra support and helps avoid future problems. Many manufacturers warranties stipulate a plywood substrate.

What thickness of plywood should be used?

3/4-inch is ideal for most standard countertops. 5/8-inch can work for shorter spans. Go thicker for larger surfaces like kitchen islands that require additional support.

Can I use particle board instead of plywood?

Particle board is prone to swelling and deterioration from moisture over time. Plywood is more durable and better suited for the demands of undermounting quartz countertops.

What’s the best way to attach the plywood?

Screws spaced 4 to 6 inches apart around the perimeter and every 8 to 10 inches in the field provide solid attachment. Construction adhesive between the cabinets and plywood adds stability.

Can I install my kitchen island quartz directly on top of the wood base?

It’s best to still install plywood atop the island framing for maximum support and to smooth out any imperfections in the wood surface.

Should I put adhesive between the plywood and quartz?

The quartz installer will use adhesive and seam tape specifically formulated for quartz. Extra adhesive between the plywood and quartz is usually not required.