Quartz countertops are a popular choice for kitchen and bathroom renovations due to their durability, low maintenance, and stylish appearance. When installing quartz counters, a common question that arises is whether plywood is required underneath. Here is a detailed look at whether quartz countertops need plywood or not.
What is Quartz?
Quartz countertops, also known as engineered stone, are made from ground quartz crystals blended with polymer resins and pigments. The quartz content typically ranges from 90-94%. The resin binds the quartz particles together to create a hard, non-porous surface.
The main benefits of quartz counters are:
- Extremely durable – resistant to scratches, stains and heat
- Low maintenance – doesn’t require regular sealing
- Non-porous – does not harbor bacteria
- Available in a wide range of colors and patterns
- Does not need polishing or re-finishing
Do You Need Plywood Under Quartz?
Plywood is not an absolute requirement for quartz countertop installation. Quartz can be installed directly over solid surface countertops, existing tile, concrete, or well-built cabinetry.
However, plywood is highly recommended as an underlayment for the following reasons:
Provides a Smooth Base
Plywood creates an even, smooth surface for attaching the quartz. Minor imperfections in the underlayment can telegraph through quartz resulting in an uneven appearance. Plywood sanded to a smooth finish minimizes this issue.
Prevents Cracking & Warping
Quartz slabs are heavy, weighing approximately 15 lbs per square foot. The weight can cause unsupported quartz to bend or crack over time. Plywood strengthens the countertop and prevents bending, warping or cracking.
Allows Adjustment if Cabinets are Uneven
Plywood can be sanded down if the cabinet base is slightly uneven. This allows the quartz installer to create a perfectly level surface for seamless joint lines.
Helps Dampen Sound
Plywood provides a bit of a sound barrier between the solid quartz surface and the cabinetry. This can help minimize any noises from pots, plates or appliances placed on the countertop.
Gives Cabinets Added Support
The plywood provides extra structural support to the underlying cabinets and prevents them from shifting under the heavy weight of the quartz.
Easier for Do-It-Yourself Installs
Plywood gives DIYers an easier base surface to install quartz on versus directly on cabinets or an existing countertop substrate.
Plywood Thickness Recommendations
Most quartz fabricators recommend using 3/4″ thick plywood as the ideal underlayment. 5/8″ plywood is also acceptable, but provides slightly less strength. Anything thinner than 1/2″ is not recommended.
Waterproof plywood, such as marine grade, is best since occasional spills may occur before the quartz is installed. BC or AC grade plywood that is sanded smooth works as well.
Installation Over Different Base Materials
If you do not want to use plywood, here are some other options:
- Solid Surface Countertops: Quartz can be installed directly over existing solid surface (i.e. Corian) counters. The surfaces must be clean and free of waxes or polishes.
- Tile: Remove grout lines and make the surface smooth. May require a coat of thinset mortar first. Ensure the tile is well supported by the cabinetry.
- Concrete: Pour a thin layer of concrete over the surface to smooth it out. Allow to fully cure before installing quartz.
- Well-Built Cabinets: Can support quartz directly, but any gaps or unevenness will telegraph through the slabs. The cabinets must be level, plumb, and securely fastened.
Is Plywood Absolutely Necessary?
While plywood is not technically mandatory, it is highly advisable for the majority of quartz installations. The exceptions would be a concrete or solid surface substrate that has been confirmed to be perfectly smooth and structurally sound.
Plywood offers advantages in terms of smoothness, strength, and sound dampening that make it the preferred underlayment in most situations. Proper underlayment support helps ensure the quartz countertops remain beautiful and crack-free for decades. Consult with your quartz fabricator to see if they recommend a plywood substrate before proceeding with the installation.
FAQs About Plywood and Quartz Countertops
Does quartz need 3/4 or 5/8 plywood?
3/4” plywood is ideal, but 5/8” is often used with success too. Do not use anything thinner than 1/2″.
What thickness plywood is best for quartz?
3/4″ plywood is recommended. 5/8″ can work in some cases. Avoid plywood less than 1/2″ thick.
Can you put quartz straight on cabinets?
Quartz can be installed directly on cabinets but it is not ideal. Any unevenness in the cabinets will transfer through the quartz. Plywood helps create an even underlayment surface.
Is waterproof plywood necessary under quartz?
Waterproof plywood is the best choice, but regular BC or AC grade plywood also works well when properly sealed/finished.
Can quartz be installed over existing laminate countertops?
No, laminate countertops are not a suitable substrate for quartz installation. The laminate surface must be removed and replaced with plywood.
Does quartz need support like granite?
Yes, quartz requires a sturdy base just like natural stone counters. Plywood strengthens it and prevents bending or cracking.
Conclusion
Installing plywood before quartz countertops provides a smooth, strong foundation that prevents cracks and warping. While not always mandatory, plywood is highly recommended by most installers and manufacturers. For most homes, 3/4” plywood offers the ideal balance of rigidity and ease of installation under quartz surfaces. With proper underlayment support, quartz countertops will remain resilient and beautiful for many years.