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MA General Contractor: Concrete and Masonry Construction

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Concrete and Masonry Construction

Concrete is specified by strength, not appearance. Typical residential foundation concrete is 2,500–3,000 psi at 28 days; exterior flatwork should be air-entrained at roughly 5–7 percent to survive Massachusetts freeze-thaw, with a water-cement ratio near 0.45–0.50 and a slump in the 4–5 in range. Adding water on site to ease placement is the classic strength killer. Test cylinders are taken at ACI frequency and broken at 28 days.

Details that get tested: minimum cover over reinforcement (about 3 in cast against earth, 2 in exposed to weather); lap splices; dowels into footings and walls; anchor-bolt embedment of 7 in for sill plates; hold-downs set per plan; and a 6-mil vapor retarder plus capillary break under slab-on-grade. Cure slabs about 7 days. Control joints are cut to about one-quarter of slab depth at spacing of roughly 2 to 3 times the slab thickness in feet - a 4 in slab gets joints about 8–12 ft apart.

Masonry: 8x8x16 CMU with mortar per specification (Type S below grade, Type N above is a common pairing); concave tooled joints; flashing and weep holes at the base of veneer and above openings; corrosion-resistant ties at 16 in by 24 in; and a 1 in air space behind brick veneer. Chimneys must satisfy the 2-ft-in-10-ft rule, be lined, and be reinforced where required.

Trap: confusing dampproofing with waterproofing. Habitable below-grade space needs waterproofing plus drainage, not a damp coat.