Introduction
Installing new countertops can completely transform the look and feel of a kitchen or bathroom. Quartz countertops in particular have become incredibly popular in recent years due to their durability, stain resistance, and beautiful appearance. But what goes underneath those gorgeous quartz slabs? Many homeowners wonder whether they need to install plywood under quartz countertops for extra support. In this comprehensive guide, we’ll cover everything you need to know about installing plywood under quartz countertops.
Should You Install Plywood Under Quartz Countertops?
The short answer is yes – installing plywood under quartz countertops is highly recommended. Here’s why:
- Adds Support and Prevents Sagging: Quartz slabs are heavy and without proper support, they risk sagging, cracking, or pulling away from the base cabinets. Plywood adds critical structural support.
- Creates Smooth Surface: Plywood creates an even, smooth sub-surface for quartz installation. This prevents irregularities or imperfections from telegraphing through the quartz.
- Allows Adjustments: Plywood can be shimmed and sanded to make small adjustments and ensure a perfectly level installation surface.
- Reduces Noise: Plywood helps deaden noise from dishes, appliances, etc. This greatly improves the experience when working in the kitchen.
The small upfront cost of plywood is well worth it for the added structural integrity and performance it provides under quartz countertops. Most expert installers recommend 3/4″ thick, cabinet-grade plywood at a minimum.
Plywood Options for Under Quartz
Not all plywood is created equal when it comes to providing the right underlayment for quartz. Here are some things to look for:
Thickness
Opt for at least 3/4″ thick plywood for the best support. Thinner plywood around 1/2″ can work in some cases, but 3/4″ or thicker is better. Going up to 1″ thick plywood offers maximum sturdiness.
Exterior vs. Interior Grade
Exterior grade plywood contains weather-resistant glues and is designed to withstand moisture. This makes it a great choice for kitchens and bathrooms where spills and humidity are a concern. Interior grade plywood uses glues that break down more easily with prolonged moisture exposure.
Number of Plies
More plies (layers) make plywood stronger and more rigid. 5-ply or 7-ply plywood is ideal for quartz countertop underlayment. 3-ply plywood tends to not provide enough durability.
Wood Types
Baltic birch is the most popular choice as it offers strength, stability and a smooth surface. Oak or maple plywood can also work well. Avoid softwoods like pine that are prone to expanding and contracting.
Cabinet-Grade
Opt for cabinet-grade plywood with a nice, clean A-grade surface veneer for the best results under quartz. Lower grades of plywood may telegraph imperfections.
How to Install Plywood Under Quartz Countertops
Installing plywood under quartz countertops takes a bit of careful planning and preparation:
Step 1: Measure and Cut Plywood
Take detailed measurements of the cabinet bases and cut plywood pieces to size allowing for overhang. Be extremely precise for tight seams.
Step 2: Dry Fit Plywood
Test fit plywood pieces without glue to identify any gaps, high spots, or problem areas that need addressing. Mark problem areas.
Step 3: Shim and Sand
Use shims to fill any gaps between plywood and cabinet base. Sand down high spots. The plywood should sit completely flush.
Step 4: Glue and Fasten
Apply construction adhesive to cabinet bases, lay plywood pieces in place, fasten with screws. Wipe away any excess glue squeeze-out. Allow glue to dry fully.
Step 5: Seam Plywood
Fill plywood seams with wood filler, allow to dry, and sand seam areas smooth. The plywood should now look like one continuous surface.
Step 6: Final Preparation
Vacuum surface thoroughly. Address any remaining uneven spots. Clean surface for quartz installation.
Tips for Plywood Under Quartz
Here are some helpful tips to get the most out of plywood under quartz:
- Allow overhang for any areas where quartz will overhang the cabinets.
- Use moisture-resistant plywood for kitchens, bathrooms, and outdoor installations.
- Cut plywood pieces in order of installation to minimize errors. Label each piece.
- Pre-drill plywood when screwing into cabinet bases to prevent splitting.
- Opt for full plywood sheets to minimize seams which can telegraph through quartz.
- Use wood filler, not drywall compound, for smoothest seam filling results.
- Carefully select screw length to avoid penetrating through the plywood surface.
Conclusion
Installing high quality, cabinet-grade plywood beneath quartz countertops provides critical structural support and creates a smooth, seamless surface for quartz installation. While plywood does add some cost upfront, it pays dividends in added stability and quality. With careful planning, dry fitting, gluing, seam filling, and sanding, plywood underlayment helps ensure quartz counters turn out perfectly level and shockingly durable for years of beauty and performance. Consult a professional fabricator or installer if unsure about the plywood selection or installation process. But in most cases, plywood should always be used under quartz countertops.