Selecting the right plywood substrate is a crucial step when installing a quartz countertop. The plywood provides the structural support and stability for the countertop, so using the proper thickness and quality is imperative. In this comprehensive guide, we will discuss the key factors in choosing plywood for quartz countertops.
Overview of Quartz Countertops
Before diving into plywood selection, let’s briefly overview quartz countertops. Quartz countertops, sometimes referred to as engineered stone, are composed of ground natural quartz crystals combined with resin and pigments. The result is a highly durable, non-porous surface resistant to scratches, stains, and heat.
Quartz offers distinct advantages over natural stone like granite. Since it is engineered, the color and pattern consistency is superior to natural materials. The resin binders also make quartz more flexible for fabrication and installation. For these reasons, quartz has surged in popularity in recent years as a premium countertop choice.
Why Plywood is Used Under Quartz
Quartz countertop slabs are typically 3/4″ thick. These slabs are adhered over a substrate to build up the countertop thickness and provide structural reinforcement.
Plywood is the most common substrate used under quartz for several reasons:
- Stability – The layered construction of plywood resists expansion and contraction better than solid wood. This is essential for long-term durability of the countertop.
- Smoothness – Good quality plywood has a smooth, even surface that allows for proper adhesion of the quartz.
- Strength – Plywood is stronger and stiffer than natural wood. This prevents bending or flexing under the heavy weight of a quartz slab.
- Affordability – Plywood is an affordable and readily available substrate option.
What Thickness of Plywood is Required?
For a standard 1.25″ thick quartz countertop, 3/4″ plywood is most often used. This builds up the overall thickness to the desired 1.25″ depth. Most quartz fabricators recommend a minimum 3/4″ plywood substrate.
However, some opt for a 1″ or 1 1/4″ plywood for a thicker, more rigid underlayer. This is especially prudent for longer spans or overhangs that require added support. The extra thickness may also allow sanding or refinishing if the countertop ever needs to be replaced.
Ultimately, 3/4″ plywood is sufficient for most residential kitchen quartz installations. Commercial projects may warrant thicker plywood for maximum durability under heavy usage.
What Grade of Plywood is Best?
Plywood comes in different grades, with each denoting the quality of the wood veneers used. For quartz countertops, a Grade A-A or A-C exterior grade plywood is ideal.
- A-A Grade – Highest quality with no repairs on the face or back veneers. Provides the smoothest surface for installing quartz.
- A-C Grade – Allows minor repairs only on the back side veneer. Very durable and affordable option.
Other key characteristics to look for include:
- 5 or 7 ply construction
- Moisture resistant adhesive
- Formaldehyde-free
- No voids or knots on surface
Going with the highest grade plywood within your budget will provide the best underlayer for long-lasting quartz countertops.
plywood grain direction
The strength and stability of plywood is largely derived from alternating the grain direction with each layered veneer. However, for a quartz substrate, it is best to use plywood with the grain running parallel to the countertop length.
This prevents cross-grain expansion and contraction which could otherwise cause small cracks in the quartz above. The top veneer grain should always run parallel to the finished quartz slab.
Can Other Substrates Be Used?
While plywood is most common, other substrates can support quartz slabs:
- MDF – Dense, smooth fiber board. Prone to expansion from moisture.
- Particle Board – Not recommended. Lacks strength and rigidity.
- Recycled Composite – Made from recycled wood/plastics. Eco-friendly but expensive.
- Metal – Aluminum, galvanized steel. For very high use/abuse applications.
Plywood remains the substrate of choice for DIY and professional installers alike. It hits the sweet spot between performance, ease of use, and affordability.
FAQ
Here are answers to some frequently asked questions about plywood under quartz:
Should I use pre-made or raw plywood?
Pre-fabricated plywood panels designed for countertops can be easier to install. But raw plywood allows you to cut everything to exact size. Both will work.
What edge treatment should the plywood have?
A clean, square factory edge is preferred. Avoid plywood with veneer overhangs or rough edges.
Can I use fire-rated plywood?
Yes, fire-rated plywood meeting A-C grade requirements can be used. Ensure the resin does not inhibit adhesion.
How is the plywood secured to cabinets?
Plywood is screwed into the cabinet using wood screws every 6 inches along the front and back. No fasteners should go through the surface.
Does plywood need to be sealed before installing quartz?
Sealing plywood is often recommended for water resistance. Consult your fabricator, as some adhesives bond better to raw plywood.
Conclusion
Choosing the proper plywood substrate provides the foundation for a beautiful, durable quartz countertop installation. A 3/4″ thick A-grade plywood with smooth face veneers running parallel to the length offers an ideal balance of strength, stability, and cost-effectiveness. With high quality plywood properly fastened underneath, you can enjoy strong, stunning quartz countertops for years to come.