Select an appropriate mortar type (M, S, N, O, K) for a masonry project without purchasing the full ASTM C270 standard

Steps

1. Recognize ASTM C270 (Standard Specification for Mortar for Unit Masonry) itself is paywalled (store.astm.org) — don't attempt to quote its proportion/property tables verbatim from secondary sources.
2. Use BIA's free Technical Note 8B ('Mortars for Brickwork – Selection and Quality Assurance,' gobrick.com) for freely citable, practically-oriented guidance on choosing among the five ASTM-defined mortar types.
3. Cross-check against publicly available masonry-association PDFs excerpting PCA 'Masonry Mortars' guidance for load-bearing vs. non-load-bearing and above/below-grade selection logic.
4. For final compliance, confirm the project specification cites the correct ASTM C270 edition/mix method (proportion vs. property specification) — that determination should come from the actual standard or the engineer of record, not a secondary summary alone.
5. Document mortar-type selection rationale (exposure, loading, grade condition) referencing the free secondary sources used, while flagging that final proportions must trace back to the licensed ASTM C270 text.