After BAR editor Hershel Shanks criticized recent unsightly repairs to the Temple Mount walls in Jerusalem in his September/October 2010 First Person, archaeological architect Leen Ritmeyer wrote a letter in our January/February 2011 issue to explain how the improper use of cement in the repairs was causing some of the problems on the Temple Mount. This view is now echoed by Edward D. Johnson, the chief conservator of the Archaeological Architectural Field School run by USAID in Luxor, Egypt, who condemns the use of cement in archaeological restorations and explains the dangerous and devastating problems it can cause.

Being both an archaeologist and archaeological conservator whose practice emphasizes built heritage and having worked in many places around the world, principally in Egypt, for the last 22 years, I have repeatedly seen cement used on archaeological sites and structures with effects ranging from mildly damaging to completely disastrous. Simply put, cement has no place in the care and conservation of any archaeological site or structure. This is a basic principle of archaeological conservation that I have emphasized continually in my teaching of the subject, most recently in the Archaeological Architectural Field School run by USAID in Luxor, Egypt, where I was assistant director and chief conservator.

Cement damages ancient materials and structures in several ways, all of which work together to accelerate deterioration.

Cement in bulk has a different coefficient of expansion than ancient building materials, which are principally limestone and sandstone. Under warm, sunny conditions it will expand at about twice the rate of the original materials. When used on ancient structures, if put under ancient stone, or used to attach it to an underlying substrate, its expansion will tend to lift that stone off the surface to which it is attached, causing that surface to buckle, detach and slough off.

Cement is also loaded with soluble salts. These will leach out of the cement over time. They will migrate into the pores of the ancient building material, where they will be deposited by evaporation, forming salt crystals. Subsequent exposure to, or absorption of, moisture from the air will cause these crystals to dissolve and reform. This cycle of dissolution and recrystallization exerts immense pressure on the pores of the stone, causing their disruption and destruction. This leads to powdering, spalling off of decorated surfaces, and if not checked, complete disassociation of the stone into sand or powder which can cause larger structural failures in a monument.

Finally, cement is unsightly and always visually clashes with original stones and their patina of age as is dramatically revealed in the pictures in BAR.

Cement

David Philips PE — US (8/9/2011 4:34:56 PM)

It is unlikely salts LEACH from 'cement' repairs. Leaching is a process where water passing through or over a material dissolves and carries away some component of the material. An example is water flowing over limestone which leaches the salt calcium carbonate. What happens with cement is that the chemical hydration of the lime in the cement goes on for a long time and as it does water (with a high dissolved solids content) is forced out of the cementitious matrix of the concrete or mortar.

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Cement

David Philips PE — USA (8/9/2011 4:21:54 PM)

Actually the coefficients of thermal expansion of cement (and concrete and mortar), and limestone, and sandstone are not different. The data ranges for expansivity for all of these materials almost completely overlap. If there is a difference in how much the repairs expand vs. the original materials it is likely because the repairs are more massive, not more expansive.

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cement on Temple Mount

Jim Church — (7/13/2011 8:19:06 PM)

I imagine that if the Israeli Archeological Society had done the repairs with cement the hue and cry would have been heard around the world. Funny how in this day and age the world refuses to speak truthfully about such travesties and chastise those who have desecrated the sacred Mount.

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Preservation of ancient masonry

Tommy Simpson — USA (7/13/2011 2:44:10 PM)

Having been a mason for 40 years I had ocasions where I needed to repair erosion wear and etc. I had the best use with a method of my own design. It is not a long lasting repair, but it is easy to repair the patch. And another benefit is the ability to match the color for look. For the rock of course I used new rock. If the rock is the same type it will weather even with a sealer in just a few years. For mortar I used dyed bedding compound and applied a sealer over the whole masonry structure.

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The Trouble with Cement

Richard Andrews, Architect — USA (6/27/2011 6:46:14 PM)

Regarding the recent article on the destructive use of cement, I wish the article could have been more specific. Was it referring to Portland Cement, one of the components of concrete, or Portland Cement mortar? Either one can cause problems and both are destructive. For restoration projects with softer old brick, we use lime-based mortar, which was originally used. Obviously, each situation is different and any new applications should only be done with careful regard to the original ones.

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The Trouble with Cement

Brian Macdonald — USA (6/22/2011 2:58:17 PM)

I have to agree with Dr. Johnson's declaration that cement should and must be rejected in any archaeological restoration project. In my opinion, two things should happen: first, if such a restoration is to be undertaken then the binding agent between the stones must be made of the same material the original builders used; nothing modern at all. The second thing is also the least costly and most effective: just leave the site as it is!

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