Quartz countertops are a popular choice for kitchen and bathroom remodels due to their durability, low maintenance, and stylish appearance. One consideration when installing quartz counters is understanding the psi (pounds per square inch) requirements to ensure proper support. Here is an in-depth look at psi recommendations for quartz countertops.
What is PSI for Countertops?
PSI stands for pounds per square inch and refers to the amount of weight or force applied over a square inch area. In countertop installation, psi indicates how much weight the base cabinets and supports can hold without sagging or structural damage.
Quartz is an engineered stone made from roughly 90% ground natural quartz blended with resins and pigments. It is harder and more durable than natural stone like granite or marble. However, it still requires adequate support to prevent cracking or weak spots over time.
Typical PSI Recommendations
Most quartz countertop manufacturers recommend supporting quartz with a substrate that can handle a minimum of 100 psi. However, standards can range from 100-150 psi depending on the brand.
Here are common psi recommendations:
- Caesarstone – 100 psi
- Cambria – 100 psi
- Silestone – 150 psi
- Viatera – 150 psi
- Zodiaq – 150 psi
These psi ratings assume proper installation on all required supports. The psi rating is not an indicator of the strength of the quartz material itself. Even quartz can crack under pressure if not fully supported.
Maximizing Support
There are a few ways to maximize support for your quartz countertops to meet psi recommendations:
Cabinets
Make sure cabinets are level and plumb with adequate bracing. Wall cabinets should have extra reinforcement to bear the weight.
Substrate
Choose a substrate material like 3/4” plywood with a 100 psi rating or higher. Particle board generally has insufficient psi strength.
Thicknesses
Go with the maximum thickness of 1-1/4” for more durability and strength. Thinner 3/4″ quartz is more prone to warping or cracks under pressure.
Installation
Proper installation is key. Slabs should be fully supported and anchored at seams. Following manufacturer instructions for overhang limits and reinforcement is crucial.
Span Lengths
Adhere to overhang guidelines based on quartz thickness and spacing between underlying supports. Reinforce overhangs as needed.
Do You Really Need 100+ PSI?
Aim for 100-150 psi support for quartz counters whenever possible. However, in some cases it may be impractical, such as limited space for extra reinforcement.
Many countertops are installed with less than 100 psi and perform fine. The key is proper installation and avoiding excessive pressure on vulnerable spots. Extra bracing can be added strategically to higher use areas.
Also consider quartz content. Formulas with more resin vs. natural stone typically have greater flexibility and impact resistance. Brands like Caesarstone with high quartz percentages may allow slightly lower psi.
Signs of Insufficient PSI
Watch for these red flags that your quartz lacks adequate underlying support:
- Visible sagging, bending, or cracking, especially on overhangs
- Popping or grinding noises when pressing down
- Gaps at seams widening over time
- Cracking around sinks or cooktops
- Radial cracks forming around impact points
If you notice any of these issues, reinforce problematic areas immediately before further damage occurs. Catching problems early makes corrections much simpler.
PSI Considerations by Quartz Thickness
3/4″ Quartz:
- Requires minimum 80 psi substrate
- Maximum overhang 6-8” without support
- Use sparingly for small spaces like backsplashes
1-1/4″ Quartz:
- Requires minimum 100 psi substrate
- Maximum overhang 10-12” without support
- Recommended for most applications
2″ Quartz:
- Requires minimum 120 psi substrate
- Maximum overhang 14-16” without support
- Best for heavy use areas
Achieving Proper Support
Installing quartz counters with adequate psi takes some planning:
- Verify cabinet bracing and levelness
- Select substrate material with 100+ psi strength
- Follow quartz manufacturer overhang guidelines
- Use maximum thickness quartz suitable for your budget
- Reinforce overhangs, seams, and high stress areas
- Ensure proper adhesion with anchors and seam support
- Avoid extreme point loading and overloading quartz
With proper underlying support, your beautiful quartz counters will last for decades and resist damage from typical household use. Adhering to psi recommendations will prevent undesirable sagging, cracks, and gaps.
Frequently Asked Questions
What is considered a heavyweight material in kitchen countertops?
Quartz, granite, marble, and solid surface materials like Corian are generally considered heavyweight. Tile, laminate, and butcher block are lightweight options.
What thickness of plywood should be used under quartz?
3/4” plywood is the minimum recommended thickness for quartz substrate. 5/8” plywood may flex too much unless reinforced. For heavy use areas, 1-1/4” plywood is best.
Can you use just concrete board under quartz?
Concrete board alone does not provide enough psi for quartz support. It should be layered over 3/4″ plywood to improve impact resistance.
What is the best way to reinforce quartz overhangs?
Adding wood corbels, metal brackets, or additional plywood support is best for longer overhangs. An overhang should not exceed 10-12” without reinforcement.
What causes cracks in quartz countertops?
Excessive impact force, inadequate underlying support, uneven cabinets, poor installation, and excessive overhangs without reinforcement can all lead to quartz cracks.
Conclusion
Supporting quartz counters with 100-150 psi gives them strength to withstand years of use. Careful attention to the substrate, overhangs, and installation practices prevents undesirable damage. When in doubt, add extra reinforcement to key areas. With proper psi support, quartz offers unbeatable durability, beauty, and value.