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TECHNICAL BULLETINS—MORTARS

 

The following are design tips for the use of mortars when setting cast stone material.  Specifications are based upon the requirements of ASTM C270, Type N mortar. Although proportions may vary depending on the specific application, the recommended mixture, measured by volume, for Portland cement and lime mortars is:

The correct mixture of mortars must have good bond strength, be durable, resist rain penetration as much as possible, be weather resistant, accommodate movement by being flexible, and have a moderate compressive strength. The mixture is one of the most important factors when installing masonry walls. It is the glue which holds the puzzle pieces together while being flexible and durable enough to withstand expansion and contraction of masonry materials.

 

Proper mixing procedures must be adhered to as follows:

Note that mortar that is older than ninety minutes should be discarded. Mortar will dry faster on hotter days. You may want to keep it moist with a damp cloth on extremely hot days.

 

More wet mortar should be used for head joints in most hand set stones and in setting brick and block. Stiffer mortar should be used when setting larger stones and shims, and all pieces that are 300 pounds or greater.

 

Dowel holes, anchor slots, and any type of anchor pocket should be completely filled with mortar unless non–shrinking grout or anchoring cement is recommended for dowel connections. Since the stone needs to bond with the masonry wall below, it is recommended that you avoid placing mortar on a full bed of flashing.

 

Only the ends of lug window sills and stair treads should be set in mortar as this prevents the stone from cracking due to loading and settlement.

 

Wetting head and bed joints will protect them from joint shrinkage.

 

Rake all stone to stone joints to a depth of three–quarter inch for pointing later. Stone to brick joints are usually struck and tooled to a slight concave.

 

During application, be sure to protect the cast stone pieces from mortar and grout staining by sponging the face with clean water. Should removal of mortar be a problem, first try washing the cast stone and masonry units with soap and water. Commercial masonry cleaners, such as SureKleen™ No. 600 can be used with a Tampico™ Acid Brush or equivalent. Do not use metal tools as they can permanently scrape and damage the face of the cast stone. Additionally, do not use power washers or sand blasters to clean the stone.

 

Once the project is complete, you will want to wash down the entire surface. Make sure that you monitor the collection of water, especially any acidic solutions and cleaner mixes that can puddle. Proper water drainage is important. After final inspection of the project, you will want to consider the use of water repellents.

 

Remember to review our bulletin regarding the use of water repellents, and recommended sealants when used to with pointed joints.

It is important to note that careful planning at the start will assist in eliminating disappointment for any homeowner or commercial designer at the completion of the project.

 

DESIGN TIPS — MORTARS (PDF)

 

The information within this and all our bulletins has been provided as a guideline and based upon statistical data and prior uses. We always suggest that you consult with your engineer, architect or contractor for the best design and use of cast stone for your project. Our design team is always available to answer any of your questions. We do not accept any liability from damages resulting from your interpretation of the data contained within.