Masonry
Overview
Mortar, made up primarily from lime and sand mixes, has been used in masonry structures for thousands of years. Historically, mortar was made from a mixture of lime putty to local sand by volume in a ratio of 1:3. Sometimes other materials were used as additives, such as crushed shells, brick dust, clay, natural cements, pigments, and even animal hair.
In 1824, Portland Cement was patented in Great Britain; however, while it was imported prior, it was not produced in the United States until 1871. It was not in common use throughout the country until the early 20th century. Therefore, most masonry structures built between 1871 and 1930 can contain a range of materials – from pure lime and sand mixtures to a variety of lime, portland cement, and sand combinations. It wasn’t until the 1930s that more standardized mortar products were available at a large scale.
Mortar Repointing
Factors of Consideration
COLOR AND TEXTURE MATCHING – Sand texture plays the biggest role in the aggregate of mortar. We match the original sand as close as possible to ensure that the color, as well as the aggregate size of the sand in our new mortar matches what was originally used. We take samples from the original mortar and carefully match our new mortar mix to ensure an accurate match.
POINT STYLE – We analyze the original construction to determine the appropriate tooling order and methods to use in order to replicate the joint profile used when the building was originally constructed.
MASONRY UNITS – We examine the original masonry units so that any replacement that is required will match the size, color, and texture of the original masonry unit. A single wall can include a variety of sizes and colors, especially with hand-cut brick or rough-cut, locally-quarried stone. We are careful to make sure that whatever replacements we make match the overall features of the original materials.
Joint Preparation
We remove old, deteriorated mortar from the joints to a depth of 2 – 2 1/2 times the width of the joint prior to repointing. Great care is taken at this stage to guard against damage occurring to the original masonry units. We use hand tools whenever possible to ensure that no damage is done to the masonry units themselves.
Filling the Joint
In cases where deteriorated mortar has been removed to a depth greater than 1 inch, we compact new mortar into these areas in several layers. We successively refill these areas in approximately 1/4 inch lifts. Once a lift is thumb-print dry we apply the next layer until the joint is filled flush with the surface of the original masonry unit. This process ensures that the mortar has enough time to shrink and harden between lift applications so that the repointed joint retains its structural integrity. Once the final, flush layer of new mortar is thumb-print dry we tool the joint to match the depth, profile, and texture of the original joint.
Aging the Mortar
Even after carefully matching the new mortar mix to the old mortar, sometimes color differences still occur. When this happens we are able to stain the new mortar to more closely match the original mortar surrounding it. This helps the repointed areas blend in consistently with the original joints.
Brick Restoration & Patching
Initial Inspection and Analysis
We perform a thorough inspection to identify any areas that have sustained damage or excessive aging. Anywhere that the brick units themselves have been damaged or compromised must be addressed. We restore where the original brick that has spall, cracked, broken, or missing. Spalling and cracking typically occurs in the face of a wall whereas bricks that have been broken or missing typically occur at corners and edges, such as washes, cornices, and parapets.
Surface Preparation
Where bricks have spall or cracked we use brick patch material to restore them. First, we carefully remove any loose or spalling pieces of brick and clean the surface to which we will be applying brick patch. We mix the dry patch material with liquid latex which cures to match the hardness of the original brick. We paint a thin coat of liquid latex on the affected area just prior to applying the patch material. This helps ensure solid adhesion of the patch material to the brick as it cures.
Color and Texture Matching
We carefully match the color of the patch material to the original brick color. In cases where multiple or a blend of colors occur in a single brick we are able to use a variety of pigments and washes to paint the patch material to match the existing brick after it has cured. We also carefully match the texture of the patch material to the original brick to ensure that the areas we have restored blend naturally into the surround area.
Limestone Restoration
Limestone restoration follows a very similar method to brick restoration and patching. We thoroughly inspect areas for damage and identify the best method to restore it to its original condition. We first clean the damaged area in preparation for applying the patch material. Again, as with bricks, we carefully match the color and texture of our limestone patch material to mimic the original condition.