Jointing mortar for old bricks: how to choose the right mix

Which jointing mortar should you use for old bricks?

The right jointing mortar for old bricks consists of a mix in which hydraulic lime, white cement, and sand are matched to the softness and porosity of the original material. A commonly used base composition is 200 kilograms of CEM I 42.5 cement mixed with 100 kilograms of hydraulic lime per cubic meter of sand. If you are working with very soft, handmade bricks, the lime content may be increased and the cement content reduced.

Why does old masonry require a different jointing mortar?

Old bricks are more porous and softer than modern factory-made material. They were fired at lower temperatures and contain more air channels. This structure allows moisture to move through the brick more easily. A hard, cement-rich jointing mortar blocks that natural moisture balance. What happens then? Moisture cannot escape, remains trapped in the brick, and causes internal damage during frost. The brick crumbles at the edges, cracks, or loses its surface layer. This is known as frost damage.

The rule of thumb is therefore: the jointing mortar must always be softer than the brick. When masonry expands and contracts with temperature changes, the joint absorbs that movement. The brick itself stays intact. This principle applies to all types of masonry bond, whether it is stretcher bond, cross bond, or another historic pattern. A soft mortar functions as a sacrificial layer: the joint may wear, but the brick remains preserved.

Which sand should you use for jointing mortar with reclaimed bricks?

The color and texture of the joint are largely determined by the type of sand you choose. Rhine sand with a grain size of 0/1 millimeter produces a grey tone. This suits dark grey or purple-brown facades. Dune sand gives a cream to light-yellow color that harmonizes with old brick in pink, orange, or salmon tones. White sand creates a pale, almost lime-like joint that lets the brick stand out visually and works well on facades where you want to emphasize the relief of the masonry. When working with reclaimed antique bricks, the goal is to preserve the natural colors rather than disturb them with the color of the jointing mortar.

How do you make sure the jointing mortar cures properly?

The quality of your jointing is determined as much by aftercare as by the mix. Jointing mortar needs moisture to cure. If it dries too quickly, the joint becomes porous and powdery and will not provide durable protection. Keep the fresh joints moist for the first two to three days by lightly misting them with water regularly. This prevents the mortar from losing its binding strength. Full curing takes about 28 days. Only then does the joint reach its final strength and weather resistance.

The ideal temperature for applying jointing mortar is between 15 and 20 degrees Celsius. Frost during application or curing damages the structure of the mortar. The same applies to extreme heat: at temperatures above 25 degrees, the joint dries too quickly. Protect fresh jointing from heavy rain with a cover, while ensuring enough ventilation. Covered masonry that remains wet without air circulation can develop mold or discoloration. For larger surfaces or complex historic facades, it is wise to call in a craftsman experienced with authentic masonry. That prevents costly repairs later and preserves the value of your investment in old building materials.