Installing a quartz countertop can greatly upgrade the look and functionality of your kitchen. Quartz is an engineered stone that is popular for countertops due to its durability, aesthetics, and ease of maintenance. When installing a quartz countertop, proper support and preparation of the underlayer is crucial for a long-lasting result. So an important question that arises is: does plywood go under quartz countertop?
What is Quartz Countertop?
Quartz countertop, also known as engineered stone, is made from ground natural quartz crystals combined with resin and pigments. The quartz makes up over 90% of the material while the resin binds it together and allows coloring.
Some key features of quartz countertops:
- Extremely durable and scratch resistant surface.
- Available in a wide range of colors and patterns that mimic natural stone.
- Non-porous so does not need sealing.
- Resistant to stains, etching and heat.
- Easy to clean and maintain.
- Seamless appearance as slabs are manufactured.
Brands like Silestone, Caesarstone and Cambria are popular quartz countertop manufacturers. The material costs anywhere from $50 to $100 per square foot installed.
Does Plywood Go Under Quartz Countertop?
Yes, plywood is a suitable underlayer for installing quartz countertops. High quality plywood provides a stable, secure base that supports the weight of the countertop.
Plywood is commonly used instead of materials like particle board because it is stronger and less prone to sagging or warping from moisture over time. The layered construction of cross-grained wood veneers makes plywood a solid, rigid substrate.
When selecting plywood, opt for good quality ply with at least 7 plys. The more plys, the less likely the plywood will bend or flex under the weight of the quartz. Many countertop installers recommend using 3/4” thick plywood as the ideal thickness for strength and stability.
Benefits of Using Plywood Under Quartz
There are several benefits to using plywood under quartz countertops:
- Strong and stable: The sturdy layered construction prevents sagging or cracking over time. This provides long-term durability and support.
- Smooth surface: The smooth sanded face creates an even substrate for installing the quartz slabs. This prevents telegraphing any imperfections through the surface.
- Affordable: Good quality plywood costs less than materials like granite or concrete backerboard.
- Easy to work with: Plywood can be cut and installed using basic carpentry tools. Seams and edges are simple to fill and smooth.
- Adds thickness: The 3/4” thickness builds up the countertop assembly which imparts strength. This allows securely anchoring the top and handles natural use over time.
- Moisture resistant: The layers of resin in plywood make it resistant to moisture and humidity changes. This prevents warping or de-lamination under quartz slabs.
Preparing & Installing the Plywood
Proper preparation and installation of the plywood is key to creating a stable underlayer:
- Use moisture resistant or exterior grade plywood to prevent swelling from water damage.
- Cut sheets to lay flat across the cabinet frames without seams on top of cabinet joints.
- Allow 1/8” gap between sheets and next to walls. This allows expansion and prevents buckling.
- Stagger the plywood seams so they do not align with the quartz seams.
- Secure plywood to cabinets using screws into studs every 6 inches around the perimeter and every 12 inches in the field.
- Fill seams with silicone caulk and smooth edges with sandpaper for flat surface.
- Pre-drill holes 2” from all edges for anchoring the quartz above.
Following these best practices ensures the plywood provides an ideal substrate for the quartz installation.
Other Underlayment Options Besides Plywood
While plywood is the most common underlayment for quartz countertops, there are several other options:
MDF (Medium Density Fiberboard)
- Made from wood fibers pressed with adhesives into sheets.
- Smooth, uniform surface good for flat quartz installation.
- Prone to swelling and sagging if exposed to moisture. Must be well sealed.
- Only use for indoor applications.
Particle Board
- Made from wood particles pressed into sheets.
- Prone to damage from moisture and impact. Requires additional support.
- Not recommended for heavy use countertops due to tendency to sag.
Cement Backerboard
- Cement or fiber cement panel reinforced with fiberglass mesh.
- Provides extremely rigid surface for natural stone or quartz slabs.
- More difficult to cut and install compared to plywood.
OSB (Oriented Strand Board)
- Made from wood chips compressed with adhesives.
- Cheaper alternative to plywood but not as smooth or stable.
- Requires sealing edges to prevent moisture damage.
Laminates
- Plywood with plastic laminate sheets bonded to the surface.
- Provides built-in waterproof, protective top layer.
- Seams between sheets are more visible underneath quartz.
In summary, plywood remains the first choice for most quartz countertop installers because of its strength, moisture resistance, ease of installation, and smooth surface. Cement backerboard would be the next best option for a ultra-rigid underlayer.
Installing Quartz Countertops Over Plywood
Once you have prepared and installed the plywood substrate, you are ready to complete the quartz countertop installation:
- Inspect slabs – Ensure quartz slabs are in good condition and match dye lots if using multiple pieces.
- Make template – Place slabs on plywood and make cardboard template of the layout and seams.
- Cut slabs – Use a diamond bladed wet saw to cut quartz pieces according to template.
- Apply adhesive – Spread thinset adhesive evenly across plywood using recommended notch trowel.
- Set slabs – Carefully lower cut quartz pieces into place and press firmly into adhesive.
- Fill seams – Use matching colored caulk between slabs and smooth with putty knife for invisible seams.
- Anchor top – Screw through quartz edges into plywood backing every 8-12 inches around perimeter.
- Seal surface – Apply sealant to all quartz edges and around sinks/faucets.
- Clean up – Remove all excess caulk, adhesive, dust to complete the installation.
Following manufacturer instructions for approved adhesives, proper seam placement, and anchoring will result in a secure, lasting quartz installation.
FAQs About Plywood Under Quartz
Does quartz need plywood underneath?
Quartz does not necessarily require plywood underneath but it is highly recommended as the optimal substrate. Plywood provides a strong, stable base to support the weight of the quartz without sagging or damage.
What thickness of plywood is best under quartz?
3/4” thick plywood is the ideal thickness for undermounting quartz countertops. This provides sufficient strength and rigidity. 5/8” and 1/2” plywood may also be used but may not be as sturdy over time.
How is plywood attached under quartz countertop?
Plywood under quartz should be securely fastened to the cabinet boxes using screws into the wall studs. Around the perimeter fasten every 6 inches and every 12 inches through the field of the plywood. This prevents any movement or separation.
Should you seal plywood before installing quartz?
It is not mandatory but recommended to seal plywood prior to quartz installation to prevent moisture absorption. An oil-based primer or dedicated wood sealant will protect edges and surfaces from minor water exposure during installation.
Can you put quartz over existing laminate countertop?
In most cases it is not advisable to install quartz directly over old laminate countertops. The seams and unevenness of the laminate are likely to telegraph through the rigid quartz material. It is better to remove old laminate and start fresh with new plywood substrate.
Is 3/4 plywood strong enough for quartz?
Yes, 3/4” thick plywood is sufficiently strong to support quartz countertops without sagging or warping over time. As long as good quality, multi-ply plywood is installed correctly on rigid cabinets it will maintain the durability and performance of the quartz surface.
Conclusion
In conclusion, good quality plywood makes an excellent underlayment for quartz countertops. Plywood’s strength, moisture resistance, smooth finish and easy installation provide ideal support for long-lasting quartz countertops. Following best practices for installing and anchoring the plywood ensures the countertop assembly remains flat and secure for the lifetime of the kitchen. With proper preparation, you can install beautiful, durable quartz over plywood substrates.