Old Canaan Building Materials

Mortared cobblestone and Belgian block paving fails at the mortar joint. The stones themselves are essentially indestructible. The mortar between them is not. In a New England freeze-thaw environment, water in a mortar joint freezes and expands and eventually pops the mortar out. Correctly specified mortar, with the right flexibility and the right drainage, stays in place. Incorrectly specified mortar — too hard, too inflexible, or over a base that doesn't drain — fails in the first hard winter.

The joint in a mortared cobblestone or Belgian block installation is narrow — 3/8" to 1/2" — and flush or slightly below the top of the stone. It does not dominate the surface. The stone reads as the surface; the joint reads as the line between stones. A joint that is cracked or missing reads as a maintenance failure, not as the character of the material.

Mortar for cobblestone and Belgian block in a New England climate should be a Type S polymer-modified mortar — strong enough to resist traffic loads, flexible enough to accommodate slight seasonal movement, and set over a base that drains freely. The base is the critical element: 6 inches of compacted crushed stone, well-graded and free-draining, prevents water accumulation under the paving that would freeze and heave the stones.

Polymer-modified Type S mortar in a cobblestone or Belgian block application with a well-drained base performs well in New England conditions. The polymer additive provides enough flexibility to survive freeze-thaw movement without cracking. Without drainage, no mortar specification will survive. The water has to go somewhere.

The alternative to mortared joints — sand or stone dust joints — is correct for some applications but migrates with traffic over time. Mortared joints are the appropriate specification for driveway courts, entry aprons, and any installation where stability and appearance must be maintained over decades without periodic resetting.

Polymer-modified Type S mortar is available from masonry suppliers. Specify the polymer additive explicitly — standard Type S without polymer modification is too brittle for paving joint applications in a freeze-thaw climate. The base specification — 6 inches compacted crushed stone — is non-negotiable.