Repointing

Repointing is the process of renewing the pointing, which is the external part of mortar joints, in masonry construction.

Over time, weathering and decay cause voids in the joints between masonry units, usually in bricks, allowing the undesirable entrance of water.

Water entering through these voids can cause significant damage through frost weathering and from salt dissolution and deposition.

[2] Before starting any actual work, building owners examine the masonry units, mortar, and the techniques used in the original construction.

If a historic structure needs repointing, building owners usually hire an architectural historian or conservator to help pinpoint the issues.

[3] It is common to see cracking along old repairs because of the shrinkage of hard mortar and the seasonal flexing along the joint.

[3] Examining the structure before working will also help establish the strength and permeability of the original mortar in order to match the new.

[2] Such performance characteristics include permeability, compressive strength, and coefficient of thermal expansion.

Rather than the mortar relieving the stress, the masonry units will, thus suffering further damage such as cracking or spalling.

The first is called "wet chemical" in which a sample of mortar is crushed and mixed with a dilute acid.

[2] Another form of "wet chemical" analysis is the same process but the carbon dioxide gas that is given off by the digestion will be collected and the type of mortar will be determined by its volume.

Other examples of instrumental analysis are scanning electron microscopy, X-ray diffraction, and atomic absorption spectroscopy.

There are important performances of mortar that can not be determined in a lab: original water content, rate of curing, weather conditions during original construction, method of mixing and placing the mortar, and cleanliness of sand.

Extremely high or low temperatures can cause rapid drying which can have negative effects on the mortar, masonry units, and the structure itself.

[2] Removal of old mortar between joints is done carefully to avoid damage to masonry units.

On buildings with soft materials, such as under-fired brick, lime mortar, or terra cotta, removal by hand is often the most effective to avoid damage.

[5] Caulking cutters with diamond blades are an acceptable power tool to remove mortar in wide horizontal joints.

After vacuuming, the remaining debris is removed with a water jet from the top of the masonry area down.