Quartz countertops are an increasingly popular choice for kitchen and bathroom remodeling projects. Made from ground quartz aggregate held together with resin, these engineered stone slabs are praised for their durability, low maintenance, and customizability. When installing quartz countertops, a common question that arises is whether or not underlayment is needed underneath the slab. Here is a detailed look at the factors to consider when deciding if underlayment is necessary for quartz countertops.
What is Underlayment?
Underlayment refers to a material installed underneath flooring or countertops to provide a smooth, uniform surface. For countertops, common underlayment options include:
- Plywood – Budget-friendly panels made from thin sheets of wood veneer glued together. Provides a stable surface.
- MDF – Medium density fiberboard offers a smooth, consistent subsurface. MDF underlayment is dense and resists warping.
- Adhesive underlayment – Liquid or trowel-applied compounds that dry to a seamless underlayment layer. Often used for waterproofing.
- Cork – Provides a cushioned subsurface that absorbs impact. Effective at reducing condensation underneath countertops.
- Foam – Foam underlays add resilience underneath countertops. Helpful for noise reduction.
Do You Need Underlayment for Quartz Countertops?
For quartz countertops, underlayment is usually not required as long as the base cabinets provide a flat, smooth surface:
- Quartz slabs are engineered to be highly durable and resist cracking or warping. Underlayment is often not needed for structural support.
- The resin binder makes quartz countertops rigid enough that they do not require underlayment for smoothing or filling gaps.
- Quartz has water-resistance built in due to its non-porous nature. Additional underlayment for waterproofing is generally not necessary.
However, under certain circumstances underlayment can be beneficial:
- If the substrate is uneven or damaged, underlayment can create a flat surface for quartz installation.
- In kitchen island or peninsula installs, underlayment adds stability where base cabinet support is lacking.
- Cork or foam underlays provide sound-dampening and heat insulation.
- Underlayment can protect quartz from moisture exposure during accidents or spills.
Best Practices for Underlayment Selection
When underlayment is called for, follow these best practices:
- Assess the substrate – Underlayment needs are determined by the substrate material (plywood, OSB, concrete, etc.) and its condition. Fix any uneven spots prior to underlayment.
- Choose a stable, smooth product – Look for underlayments like birch plywood or MDF that resist swelling and settling over time.
- Follow manufacturer instructions – Consult quartz manufacturer guidelines for any required or recommended underlayments.
- Meet structural needs – Use thicker, more rigid underlayment on open spans like islands that lack cabinet support.
- Consider foam or cork for resilience – In high-impact kitchens, these add a cushioned layer to prevent cracking.
- Use moisture-resistant products – Underlayment can safeguard against spills and accidents penetrating the quartz.
When installing underlayment for quartz:
- Remove old countertop and inspect substrate for levelness. Grind down high spots.
- Check underlayment panels for flatness before installing. Shim any gaps or bowed areas.
- Cut underlayment pieces to size leaving small gaps for expansion. Stagger seams like flooring.
- Fasten underlayment with screws into the cabinet frame or substrate. Avoid nailing.
- Fill seams with adhesive rather than gaps that can telegraph through quartz.
- Apply adhesives uniformly following manufacturer directions. Use a 1/4” notch trowel usually.
- Ensure underlayment is clean and dry before applying quartz.
The Bottom Line
Quartz countertops are durable enough for direct installation on cabinetry in most cases. But underlayment can be used strategically when the substrate is problematic, or when extra moisture protection, soundproofing, or heat insulation is desired. By selecting the right underlayment for your specific needs, you can enhance the performance and lifespan of your beautiful new quartz countertops.
Frequently Asked Questions
What thickness of underlayment should be used under quartz?
For most countertop applications, 3/4″ thick underlayment panels are recommended. Go up to 1″ thickness for spans over 24″ where more rigidity is needed.
Can you use particle board as underlayment for quartz?
Particle board is prone to expansion and moisture damage over time. Plywood, MDF or moisture-resistant boards are better options for durable underlayment.
Should you use underlayment with quartz on concrete?
Concrete can be uneven and needs a smooth subsurface. Self-leveling underlayments help create a flat, consistent layer to install quartz on concrete.
Is cork a good underlayment for quartz in kitchens?
Cork underlayment provides a cushioned, resilient layer that dampens noises from dishes and appliances in kitchen quartz countertops.
Can you install quartz directly on drywall?
Drywall alone does not provide enough support for quartz slabs. It should be reinforced with 3/4″ plywood underlayment before installing quartz.
Underlayment for quartz countertops is not universally required but can be beneficial in many situations. Assessing the substrate condition, structural needs, moisture concerns, and desired functionality will determine if underlayment should be used. With proper selection and installation of underlay materials, they can enhance the beauty and longevity of quartz countertops in kitchens, baths, and other environments. Carefully weigh the costs and benefits when deciding on underlayment for quartz counters.