Building Stone Mortar

SPEC MIX® Building Stone Mortars are especially designed for masons building masonry walls with full depth stone units. Whether the specification calls for soft or hard stone, SPEC MIX stone mortar mixes are engineered to match the specific properties of each stone to increase the mortar-to-stone bond strength while allowing the mason to lay more stone every day. Meets ASTM C270, ASTM C 1714 and CSA A179 requirements.

SPEC MIX Building Stone Mortar is produced under strict manufacturing standards supported by complete quality control measures. A digital printout displaying the proper proportions per batch may be kept as a permanent record. Each SPEC MIX manufacturer certifies that SPEC MIX masonry products are designed to meet applicable ASTM, TMS, and CSA standards.

Each product is 100% dry, preblended in 80 lb. or 3,000 bags, eliminating the need to measure and add liquid admixtures on site which in turn ensures quality control while increasing jobsite productivity—EVERY JOB!


  • Total quality control with every bag
  • ASTM C 270 laboratory tested mix designs
  • Preblended with sand to minimize labor cost
  • Consistency from batch to batch, everyday
  • Great workability and board life
  • No sand piles or wasted materials left on site

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Application / Stone Type Compressive strength at 28 days, minimum, psi Water retention minimum %
Hard Stone 1800 75
Soft Stone 750 75
Product Application / Stone Type Minimum compressive strength, MPa Water Retention, Minimum %
Building Stone Mortar Hard Stone 12.5 70
Building Stone Mortar Soft Stone 5 70

Building Stone Mortar Installation/Application

Mortar type should correlate with the particular masonry unit to be used. SPEC MIX Building Stone Mortar is available in formulations for hard stones such as granite and soft stone such as limestone. The specifier should evaluate the density of the stone masonry unit specified to ensure that the appropriate mortar is selected to match to the hardness of the stone masonry units for the project. For stone installation procedures, please refer to the Building Stone Institutes Guide “BSI Recommended Practices for the use of Natural Stone in Construction 3rd Edition”, The Indiana Limestone Handbook 22nd Edition or TMS 402/602 Specification for Masonry Structures. For thin veneer applications, use SPEC MIX Adhered Veneer Mortar or SPEC MIX Polymer Modified Adhered Veneer Mortar.

Colored Building Stone Mortars are easily achieved through the SPEC MIX preblended approach perfected for over 20 years. SPEC MIX colored Building Stone Mortar uniformity starts with sourcing high quality, stable pigments and then preblending them into the formula to ensure color consistency throughout the project. The SPEC MIX standard colored mortar line is available in Building Stone Mortar formulations and consists of a collection of 25 colors that are available throughout North America. When building owners and designers want a unique color that supports their vision for a project, the options for custom SPEC MIX colored mortars are endless and consistent from batch to batch.

A sample of the proposed product will be provided by the manufacturer for architectural approval and testing, if required. Preparation of a sample panel with all materials and masonry systems employed in the final project is imperative. Retain the mock-up or field sample through the completion of the project.

Allow mortar to cure a minimum of 7 days but no more than 28 days before cleaning. Consult manufacturer of the units and cleaning chemicals for further instructions to ensure proper washing procedures. Clean masonry only with a national proprietary cleaning agent (following the manufacturer’s instructions) or potable water. SPEC MIX products must be kept dry, covered and protected from weather and other damage.

Sizes and Equipment

SPEC MIX Building Stone Mortars are available in 80 lb (36.2 kg) packages for easy hand loading or in 3,000 lb (1,360.7 kg) reusable bulk bags to be used with the various SPEC MIX silo systems. When using the silo system, once the bulk bags of mortar are delivered to the project site, the portable silo is loaded with a job site forklift and the product is dispensed into a mechanical batch mixer.

Estimated Yields

Determining the actual square foot yield per 80 lb (36.2 kg) or 3,000 lb (1,360.7 kg) bulk bag of SPEC MIX Building Stone Mortar is dependent on the cut of the stone and mortar joint profile. Each 80 lb (36.2 kg) bag of Building Stone Mortar will produce approximately 0.75 cubic feet (21 L) of wet masonry mortar while a 3,000 lb (1,360.7 kg) bulk bag of Building Stone Mortar will yield approximately 28 cubic feet (793 L) of wet mortar

Building Stone Mortar Mixing Instructions

WEAR IMPERVIOUS GLOVES, such as nitrile.
1. Mixing is best accomplished by using a mechanical mixer to ensure optimal workability and performance.
2. Use clean, potable water; add the amount of water consistent with optimum workability which provides adequate water to satisfy the initial rate of absorption of the masonry units.
3. Mixing times are four to five minutes when using a mechanical batch mixer and should be held consistent from batch to batch.
4. Maintain the same mixing procedures to maintain consistency throughout the project.
5. Tool mortar joints when the surface is thumbprint hard. Keep tooling times consistent.
6. Hand mix mortar only with written approval by the specifier who should outline procedures.
7. Use mortar within 2.5 hours after initial mixing.
8. Retemper mortar only when mixing water is lost due to evaporation.
9. Whenever possible, do not retemper colored SPEC MIX masonry mortars by adding additional water; retempering may affect color consistency.