Can I use cinder blocks for a foundation?

Only if they meet ASTM C90 and local code allows it. Most builders use standard-weight CMU for foundations.

Are they safe for raised garden beds?

Yes. Modern cinder blocks do not leach harmful chemicals at levels affecting plants or food safety.

For structural walls yes, use Type S mortar. For simple garden projects under 3 feet, dry-stacking is acceptable.

Concrete & Masonry

Blocks

$1.25-$2.50 per block

Cinder Blocks: Lightweight Masonry Building Units (2026)

Prepared by Lumberama's Building Materials Team

|Last updated June 12, 2026|Sources & methodology

Cinder blocks are lightweight concrete masonry units originally made with coal cinder aggregate. Modern versions use lightweight expanded shale or clay to reduce weight while maintaining adequate strength for non-structural applications. They are popular for garden walls, raised beds, and utility projects.

Key Features

Lightweight design; Standard 8x8x16 inch size; Easy to cut and modify; Affordable building material; Stackable without mortar for some uses

Specifications

Size: 8x8x16 in nominal. Weight: 22-28 lbs. Compressive strength: 1000-1900 PSI. Hollow core design.

Applications

Garden walls; Raised bed planters; Utility shelving; Non-structural partitions; Temporary barriers

Installation Overview

For mortared walls, follow standard CMU installation on a concrete footing. For dry-stack garden projects, level the first course on compacted gravel, stack with staggered joints. Fill cores with soil or gravel for stability.

Pros & Cons

Pros

✓ Lighter than standard CMU; Very affordable; Versatile for DIY; Easy to stack; Widely available

Cons

✗ Lower strength than standard CMU; Not rated structurally in many codes; Absorbs more water; Can crumble at edges; Limited aesthetics

Top Brands

Oldcastle

Pavestone

Code Requirements

Lightweight CMU must meet ASTM C90 if used structurally. Many codes restrict lightweight blocks to non-load-bearing applications.

Buying Tips

Inspect for cracks before buying - lightweight blocks chip easily. Hollow cores make excellent planters when filled with soil. Buy locally to avoid shipping costs.