Techniques > Briefs > Repointing Mortar Joints > Execution of the Work >



• building up, introducing with tools
• tools for pointing
• rat-tail for strikign joint, other tools
• joint profiles
• recessed joints
• over-filled joints
• illustration: good, bad
• brushes

Filling the Joint

Where existing mortar has been removed to a depth of greater than one (1) inch, these deeper areas should be filled first, compacting the new mortar in several layers.

The back of the entire joint should be filled successively by applying approximately 1/4 inch of mortar, packing it well into the back corners. This application may extend along the wall for several feet.

As soon as the mortar has reached thumb-print hardness, another 1/4 inch layer of mortar — approximately the same thickness — may be applied.

Several layers will be needed to fill the joint flush with the outer surface of the masonry.

It is important to allow each layer time to harden before the next layer is applied; most of the mortar shrinkage occurs during the hardening process and layering thus minimizes overall shrinkage.

When the final layer of mortar is thumb-print hard, the joint should be tooled to match the historic joint. Proper timing of the tooling is important for uniform color and appearance. If tooled when too soft, the color will be lighter than expected, and hairline cracks may occur; if tooled when too hard, there may be dark streaks called "tool burning," and good closure of the mortar against the masonry units will not be achieved.

If the old bricks or stones have worn, rounded edges, it is best to recess the final mortar slightly from the face of the masonry. This treatment will help avoid a joint which is visually wider than the actual joint; it also will avoid creation of a large, thin featheredge which is easily damaged, thus admitting water.

After tooling, excess mortar can be removed from the edge of the joint by brushing with a natural bristle or nylon brush. Metal bristle brushes should never be used on historic masonry.