Installing new quartz countertops can transform the look and feel of your kitchen. With their sleek, modern aesthetic and extreme durability, quartz countertops are a popular choice for homeowners looking to upgrade. But before installing new quartz countertops, an important question arises – do you need to put plywood under quartz countertops? Here is a detailed look at whether plywood is recommended under quartz, the pros and cons, and best practices for installation.
What is Quartz?
Before diving into whether plywood is recommended under quartz countertops, let’s first take a quick look at what quartz countertops are made of.
Quartz countertops are engineered stone slabs created from quartz particles combined with resins and pigments. The quartz provides strength and hardness, while the resins bind the material together. Quartz slabs are non-porous, making them stain and scratch-resistant.
Unlike natural stone countertops which are mined from quarries, quartz slabs are manufactured. This allows much more control and consistency in the finished product. The manufacturing process also allows quartz to come in a wide variety of colors and patterns not found in natural stone.
Should You Put Plywood Under Quartz?
Now onto the main question – is plywood recommended under quartz countertops? The short answer is no, plywood is generally not required as a substrate under quartz.
Quartz slabs are engineered to be extremely strong and rigid. At 2 cm thick, a quartz slab can easily span gaps and imperfections below it without sagging. Provided the base cabinets are level and stable, quartz can be installed directly over them.
However, that doesn’t mean using plywood under quartz is never recommended. Here are some instances where plywood may be advised:
- Poor cabinet condition – If cabinets are not level or are unstable, a plywood underlayment can provide extra support for the quartz. This includes older cabinets that may sag over time.
- Large overhangs – Quartz slabs should not overhang open air more than 8-10″. Overhangs larger than that may require plywood support underneath.
- Tile or laminate countertops – Directly installing quartz over old tile or laminate provides an unstable base. Plywood helps smooth out the surface.
- Cutouts and seams – Plywood helps strengthen seams between multiple slabs and provides backing support around sink cutouts.
So in summary, plywood is generally not required under quartz counters except in specific circumstances where extra support is needed. Many quartz installations are done successfully without any plywood underlayment.
Pros of Using Plywood Under Quartz
While not always necessary, there are some advantages to using plywood under quartz countertops:
- Provides extra support – As mentioned already, plywood creates a strong, stable surface that prevents any flexing or movement in the quartz. This can be useful for less-than-perfect cabinetry.
- Smooths uneven surfaces – Plywood can compensate for uneven cabinet tops and create a flat surface for installing the quartz slabs.
- Hides imperfections – Minor dents, stains or damage to the cabinet base can be concealed by a plywood substrate.
- Backing for cutouts – Any cutouts for sinks and cooktops will have the plywood behind them for added durability.
- Ease of installation – Plywood offers a consistent surface, making it faster and simpler to install the quartz. Shims may be needed on uneven cabinets without plywood.
Cons of Using Plywood Under Quartz
There are also a few potential downsides to keep in mind when using plywood under quartz:
- Added cost – Good quality plywood or MDF substrate will add to the overall project expense.
- Extra labor – Preparing and installing the plywood correctly takes time and work.
- Height – The plywood may raise the countertop height slightly if the cabinets are shallow.
- Moisture risk – Any water leaks could damage plywood faster than other materials. Proper sealing is essential.
- May still require shims – Depending on the evenness of the plywood, shims might still be needed during quartz installation.
Best Practices for Plywood Installation
If you do opt to use plywood substrate for your quartz countertops, here are some best practices to follow:
- Use high quality, void-free plywood at least 3/4″ thick. Moisture-resistant products like CDX are ideal.
- Cut pieces to fully support all seams and overhangs. Use several narrow pieces rather than one wide sheet if needed.
- Secure plywood tightly to cabinets with construction adhesive and screws. Shim any gaps or low spots.
- Make sure top surface is flat. Sand down high spots. Fill low areas with thinset mortar.
- Prime and paint both sides and edges of plywood for moisture protection.
- Leave 1/8″ gap between plywood sheets and next to walls for expansion.
- Follow manufacturer instructions for attaching quartz to plywood using adhesive and screws.
Properly installing a plywood substrate takes precision, but can provide a stable base for flawless quartz countertops. Consult with your installation pro to see if plywood makes sense for your specific project.
FAQ About Plywood Under Quartz
Many homeowners have additional questions about using plywood under quartz countertops. Here are answers to some of the most frequently asked questions.
Should I use plywood or MDF?
Either plywood or MDF can work as a substrate for quartz. Plywood is stronger and more resistant to moisture. MDF is more affordable and offers an extremely smooth surface. Consult your fabricator for the best option.
What thickness of plywood should be used?
A minimum of 3/4″ thick plywood is recommended. This provides ample strength and stability. 5/8″ plywood can also be used in some cases.
How is the plywood secured to the cabinets?
Plywood should be screwed into the cabinet bases every 6-8 inches around the perimeter and every 12 inches in the field. Construction adhesive between the plywood and cabinets also helps strengthen the bond.
Should there be a gap between plywood sheets?
Yes, leave a 1/8″ gap between plywood sheets and next to walls. This allows space for expansion and prevents buckling. Do not butt sheets tightly together.
Can I install quartz directly over plywood?
In most cases, yes. Quartz adhesive and screws can be applied directly to properly prepared plywood. Consult your fabricator to ensure the plywood surface has been properly primed and secured.
Should I use anything over the plywood before installing quartz?
Some extra moisture protection between the plywood and quartz is a good idea. Materials like RedGard waterproof membrane or vinyl can be applied over the plywood prior to quartz installation.
Conclusion
Although plywood is not always required under new quartz countertops, it can provide added support and stability in many situations. Be sure to consult with quartz fabrication specialists to determine if plywood makes sense for your specific kitchen layout and cabinetry. With some careful planning and proper installation, plywood and quartz can team up to deliver perfectly flawless countertops for years to come.