In an upcoming remodeling project, we will be uncovering a section of hidden stonework that will need to be repointed to match the existing exposed stonework.
How do we go about matching the color of the mortar?
A.Tony Jucewicz responds: When matching existing mortar, I first try to decide whether a match can be achieved using "standard" mixing ingredients. The pointing mix I use consists of one part Portland cement and three parts sand. Portland cement is available in gray or white, and sand in my area is available in white, yellow, or brown. When gray cement is used in the pointing mix, the color of the sand has little effect on the final color of the mortar. When using white cement, you can control the color with the sand used in the mix. White sand will produce a white mortar, yellow sand a beige mortar, and brown sand a light brown mortar with a reddish tint.
In my area of Pennsylvania, I’ve had the best success matching the mortar found in older stonework by using white Portland cement and a mixture of brown and yellow sand. Before I begin pointing, I premix all the sand needed for the job. The premixed sand can then be mixed 3 to 1 with the cement.
If you can’t match the mortar using readily available materials, you’ll have to use solid-color dyes. These are packaged dry and must be mixed in thoroughly when the sand and cement are dry-mixed. You’ll need to make numerous test batches and allow them to dry for about two days before comparing them with the existing mortar. However, after the dry materials for each test batch are thoroughly mixed (and before any water is added), you’ll have a close indication of the final color.
Dry dyes tend to be very concentrated: A one- or two-pound bag will tint a full 94-pound bag of cement. If only one or two masons are pointing, a full bag mix is too much mortar to mix at one time. When making smaller batches, you’ll need to carefully control the amounts used in the mix to maintain a consistent color. It’s important to finish your test samples the same way you’ll be finishing the final work: A brushed joint will have a different color than a smooth troweled joint.
Tony Jucewicz is a stonemason in Riegelsville,Pa.