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We repair historical lime mortar chimneys. Lime is still being used as a mix in mortar even today. However, it is mixed with portland cement, giving it far greater strength and longevity. Chimneys built in the eighteen hundreds typically were constructed with mortar made just of lime. It was before portland cement was invented. The problem is when prolonged moisture penetrates lime mortar it loses its strength. It slowly turns into a dusty sandy mix that builds up behind the brick or stone, pushing it out as it builds. When you remove a brick it all flows out like a waterfall. It is quite a sight to be seen. It doesn't impact people until they see it for themselves. Then they realize just how fragile their chimney is.
A lot of times people do not realize how damaged their chimney is because it often has been tuckpointed on the outside using portland cement sometime in the past. Tuckpointing usually involves only the outer 1/2 inch of material, meaning all the rest of the lime mortar is still lurking inside. This outer layer camouflages the real situation making everyone think the chimney is stable when it is not. Sometimes it is just a good windstorm away from falling over.
We, at Detroit Steeplejack, are very experienced at restoring lime-pointed mortar. We follow a system of removing old deteriorated mortar and then filling it in with new portland cement.
The exact mix for replacing lime mortar is extremely important. It can not be too
hard, or it risks the chance of splitting or cracking the old brick or stone. We can craft just the right mix for your historical chimney project.