CSLB C-27 Landscaping ContractorHardscape and FeaturesMedium
A landscape contractor is planning to install a flagstone patio over an existing compacted gravel base. The client wants a stable, level surface that allows for some permeability. Which bedding material is most appropriate for setting the flagstones?
- AFine-grained sand (e.g., masonry sand)
- BCoarse-grained sand (e.g., concrete sand)
- CDry-mixed concrete (sand and cement)
- DDecomposed granite (DG)
Show answer & explanationAnswer & explanation
Correct answer: B. Coarse-grained sand (e.g., concrete sand)
Coarse-grained sand (concrete sand) provides excellent drainage and interlocking properties, allowing it to compact well and create a stable, permeable bedding layer for flagstones. Fine-grained sand can retain too much moisture and become unstable, while dry concrete can lead to cracking, and decomposed granite might not provide a consistent, level bed for irregularly shaped flagstones.
Why the other options are wrong
- A. Fine-grained sand can become overly saturated, leading to instability and 'pumping' of fines, and has poor drainage.
- C. Dry-mixed concrete is typically used for a rigid base, not a permeable, flexible bedding layer, and can lead to cracking under flagstones.
- D. Decomposed granite can be used as a base, but as a bedding layer for flagstones, it may not offer the same consistent, stable, and permeable bed as coarse sand.
Flagstone Bedding Material
The layer of material directly beneath flagstones, providing a stable, level, and often permeable surface for their installation.
- Must allow for drainage.
- Needs to be compactable for stability.
- Should accommodate irregular stone shapes.
Memory trick: Flagstones need a GRITTY, DRAINABLE bed to stay put, like a sandy beach.