Q: I have an old brownstone house and some of the stone have been falling off, what can I do to prevent further damage and fix the damage that has already occurred?
A: When you have brownstone deterioration or any form of stone deterioration and want it to stop, you have to first identify the root cause. Sometimes it’s as simple as replacing downspouts or replacing roof flashing, to prevent further damage to the stone. Other times it can be a long complicated series of tests and empirical analysis. Depending on the cause of the deterioration of the brownstone, a number of solutions can be applied.
If the stone is only sugaring or sanding with light deterioration, then perhaps doing nothing for a maybe a year and watching the stone for further deterioration is sufficient. However, if the stone is in much worse shape with possibly a ¼ inch or more of stone loss, then some could be some very serious problems with the integrity of the stone.
Brownstone as with many different types of sandstone has bedding planes. These bedding planes in the stone tend to detach from one and other depending on how the stone was laid in the wall. Imagine a layered cake as the stone, with each layer on top of one and other. If the stone cake is put on its side there is a greater chance that moisture can get between the layers and cause delimitation and or exfoliation. This being a common problem associated with sandstone, a more detailed resource for classifying the type of stone loss you may have can be found here.
It is always recommended that when fixing damage to stone that a qualified professional be brought out to see what the damage is and come up with an appropriate course of action. There are many different ways to approach fixing a stone like whether consolidation is appropriate is an appropriate first step or not. In my eyes, it is always best to honor the original detail of the stone and artisan who created it by only fixing what is broken. When patching stonework an important approach is to make sure that appropriate sympathetic patching materials are used. (Lithomex) The use of impermeable materials can cause further deterioration of the stone by trapping moisture. This will result in a faulty patch that can accelerate deterioration to the adjacent stone.
We got an email back in 2011 with some amazing photos of Ian Cramb. These photos are from 1958 in Iona, Scotland. Ian was working on the cloisters of Iona Abbey at the time. Iona is a small island off the west coast of Scotland near Oban. These photos came from another Ian, Ian Taylor who spent a month living in Iona as a student in 1958 where he captured these photos during his stay on the island.
Also, in the recording below Ian talks about the apron he is wearing in the photo. He only wore that apron during his time in Iona and every morning it was blessed before he began the day’s work at the Abbey.
Q: Could I perhaps use cement and sand? What is the advantage of using lime on old stone structures
A: You should not use only cement and sand for a variety of reasons, the first being that in today’s mortars, lime adds workability and plasticity to the Portland cement mortars. Without lime in the mix or proprietary additives, the cement and sand mortar will have extremely poor workability. Secondly, modern-day cement is much different than early cement or lime, it is very hard, dense, vapor impermeable, and brittle. Cement can trap moisture inside the wall and erode the mortar behind the repair mortar, this can cause further unseen deterioration and masonry unit (stone, brick, terracotta) deterioration, thus resulting in a delayed and much larger/costly masonry repair.
The advantage of using an appropriate lime mortar on old stone structures deals with compatibility. There is a rule of thumb when approaching a restoration project and that is to repair in kind with like materials. By following this approach an individual can avoid unforeseen problems associated with trying something “new and improved” when there is such a well over 2,000 years of lime building history. There have been a number of studies done around the world on historic structures that conclude that even a small amount of Portland cement added to a lime mortar mix, can cause detrimental damage to the adjacent masonry and historic bedding mortar.