Do You Have to Use an Underlayment Under Quartz Countertops?

Quartz countertops are growing in popularity for kitchen and bathroom remodeling projects. With a mix of ground quartz and polymers, these engineered stone countertops are an attractive, durable, and low maintenance option. But do they require an underlayment layer like some other countertop materials? Let’s explore the factors to consider.

What is an Underlayment?

An underlayment is a layer of material installed under a finished countertop surface. It serves several purposes:

  • Levels out the substrate – Countertop underlayments help smooth over any imperfections or unevenness in the cabinet base or substrate underneath. This provides a perfectly flat surface for installing the countertop.
  • Prevents moisture damage – Underlayments create a moisture barrier between the solid surface countertop and the wood or composite substrate underneath. This prevents swelling, warping, and other moisture damage.
  • Adds support – The underlayment reinforces the countertop above, adding stability and preventing cracks or other damage.
  • Reduces noise – Applying an underlayment can help muffle sounds from dishes, appliances, etc. acting as a buffer between the countertop and cabinets.

Common underlayment materials include plywood, cement board, acrylic, cork, and foam.

Do You Need an Underlayment with Quartz Countertops?

The short answer is no, an underlayment is generally not required under quartz countertops. Here’s why:

Quartz is non-porous

Unlike natural stone, quartz countertops are non-porous, meaning liquids cannot penetrate into the material. This eliminates concerns about moisture penetration and damage. An underlayment to protect the substrate is unnecessary.

Highly durable surface

Quartz surfaces are incredibly hard and scratch resistant. Underlayments are often used to reinforce softer or more delicate surfaces prone to cracking. But quartz can withstand impacts and heavy use without an underlayment layer.

Already reinforced

The resin binders mixed into quartz make it strong and stable on its own. It does not depend on an underlayment for added support or structure.

Thickness provides structure

Quartz slabs are thicker than other countertops like laminate. Their 1.2 to 2-cm thickness means they don’t require underlayment support.

When to Use an Underlayment

While usually not necessary, there are some instances where an underlayment may be recommended under quartz countertops:

  • Uneven cabinet base – Adding a thin underlayment can help smooth over any significant unevenness or gaps between cabinets.
  • Lightweight substrate – For a substrate like drywall rather than plywood, a thin underlayment improves stability.
  • Acoustic isolation – Underlayments like cork can reduce noise transfer.
  • Moisture barrier – In areas with potential water exposure like behind a kitchen sink, an underlayment adds a layer of protection.
  • Old substrate – Applying new underlayment can strengthen damaged or unstable old substrate.

Consult the countertop installation experts if any of these situations apply to your project. They can determine if an underlayment should be added.

Best Practices for Underlayment Selection

If conditions indicate an underlayment for added moisture protection or stability, select the right product:

  • Cement board – The most common underlayment provides a ultra-smooth surface and blocks moisture. It resists damage if exposed to water.
  • Plywood – Structural-grade plywood at least 3/4-inches thick creates a sturdy base. The multiple layers stabilize the substrate.
  • Cork – Choose acoustic cork underlayment to reduce noise transfer and provide a bit of “give” underneath the rigid quartz.
  • Foam – Foam underlayments add cushion and support substantial countertop weight.

Always follow the quartz manufacturer’s recommendations to ensure proper installation and prevent invalidating the product warranty. An experienced countertop pro can also assess your unique situation and determine if underlayment is advised.

Installing Underlayment

If an underlayment is used, proper installation is crucial:

  • The underlayment must make full contact with the substrate below with no gaps, lifting edges, or bubbles.
  • Fasten underlayment securely to the cabinets/substrate below.
  • Thoroughly seal seams and edges with silicone caulk or adhesive.
  • Use materials designed for prolonged exposure to moisture.
  • Select a smooth, even underlayment – imperfections will mirror through the quartz.

Taking the time to correctly install underlayment protects your investment in beautiful quartz countertops.

The Bottom Line

Quartz countertops are an underlayment-friendly surface. Their durable non-porous material does not require reinforcement or moisture protection in most standard installations over stable wood or composite cabinetry. But for certain situations like an uneven substrate or added acoustic isolation, underlayments remain an option to improve the structure and function of your new quartz countertops. Consult a professional to determine if recommended for your specific kitchen or bath remodeling project. With or without an underlayment layer, quartz provides a gorgeous, hardy countertop surface.