Construction Methods of Red Brick & Lime Mortar

Lime Mortar Basics

• Traditional lime mortar commonly contains 1 part lime putty to 3 parts sand and dries by reacting to the air. Lime mortar is softer than mortar containing cement and more able to adjust to shifts in the building. The exterior of the mortar may crumble in time and need to be resurfaced for cosmetic reasons.

Other Lime Mortars

• Lime mortar dries slowly. To make it dry faster you can add what are called Pollozans, named for the Pozzuoli region of southern Italy. Pollozans include dust sieved from crushed bricks or China clay or trass, volcanic ash. The lime in hydraulic lime mortar, which also dries faster, is made from limestone that contains clay and other impurities. Water makes these impurities form solid crystals. Gauged lime mortar contains Portland cement. The cement makes the mortar turn solid, not the lime.To restore historic masonry using gauged lime mortar, the U.S. General Services Administration recommends 1 part Portland cement to 3 parts of lime and 8 to 12 parts sand as needed to match the existing mortar.

Reconstructing Brick Walls

• You can more easily match the looks of an original wall if you mix the mortar yourself instead of buying commercial mixes. Do not apply lime mortar within a month of freezing temperature unless it contains cement. Keep the wall damp for several days after you apply lime mortar. If it dries too quickly it may be weak and subject to winter erosion. If you use hydrated lime, mix it to the consistency of thick cream and let it stand two days before you use it.

Repointing Joints

• Do not fill out the joints by adding lime mortar to make 3/8-inch mortar joint like a ¾-inch joint. Either carefully add a thin layer of lime mortar to maintain the original depth or use a grinder to remove the surface of the old mortar before you apply a finishing layer. If you grind it, use a blade smaller than the width of the joint so you don’t damage the edges of the bricks.