Can Concrete Slabs Be Laid on Sand?

When planning a patio, walkway, or even a small outdoor space, homeowners often ask: Can concrete slabs be laid on sand? The short answer is yes, but only in the right context. Let’s break down when it works—and when it doesn’t.

When It’s OK to Lay Slabs on Sand

Concrete slabs or pavers can be laid on sand when they’re being used for non-structural purposes like:

• Backyard patios
• Garden walkways
• Outdoor seating areas
• Decorative hardscapes

In these cases, a properly compacted gravel base is usually laid first, followed by a 1–2 inch layer of sharp sand. The slabs are then leveled and placed on top. The sand allows for flexibility, leveling, and drainage, which helps keep the slabs in place over time.

Best Practice: Layered Installation

A typical base installation for laying concrete pavers or slabs looks like this:

1. Excavate the area to remove loose soil.
2. Lay 4–6 inches of crushed gravel and compact it firmly.
3. Add a 1–2 inch layer of sand, screeded for evenness.
4. Place your slabs or pavers on top of the sand.
5. Sweep sand into the joints for added stability.

This method ensures your outdoor surface stays level, drains properly, and avoids shifting over time.

When Sand Is NOT Enough

If you're working on a structural slab—like the foundation of a home, a garage floor, or a detached unit (DADU)—sand alone is not a sufficient base.

Structural concrete slabs require:

• A compacted gravel or crushed stone base
• A moisture barrier (polyethylene sheet)
• Reinforcement like rebar or mesh
• Concrete poured to meet local building codes

Using sand as the only base for these types of slabs can lead to cracking, settling, or water issues.

Final Takeaway

If you’re installing pavers or decorative slabs for landscaping, laying them on a sand base over gravel is a tried-and-true method. But for anything structural, always go with a professionally engineered base to ensure long-term stability and safety.

Need help with your patio or foundation project in the Seattle area?
At F&M Construction and Remodeling, we help homeowners design and build projects that last—whether it’s a custom patio or a new DADU. Contact us for a quote or consultation.