Looking for the perfect mortar recipe.October 18, 2011
Preparing the right mortar for a historic building requires the skill of a craftsman, the persistence of a detective, and the “sixth sense” of a great chef.
The color and texture of new mortar in a historic building are vitally important to restore a once-handsome building to its earlier glory. But restoration is only one of our goals. Our mission is historic preservation, which considers both the past and the future. Our challenge is to restore the historic appearance of a building and preserve it for many years to come.
The physical properties of mortar are just as important as its appearance. That’s because the mortar and masonry respond together to changes in temperature and moisture. They’re a system, and the mortar acts like an expansion joint. Especially when the masonry is as soft as the sandstone in the Avery Building, the mortar must also be soft – even more so. Under the normal stresses of expansion, contraction and moisture migration, we have to be sure the mortar will be the material to “give,” not the masonry!
If you look at a number of older buildings, you will easily recognize the ones that were repaired with a mismatched mortar. If the mortar used is too hard for the brick or stone in the building, under seasonal stresses the mortar will not “give.” Instead, the masonry will chip, delaminate, or “spall” under pressure.
On the other hand, if the mortar used was too soft, the only penalty is that the owner will have to repoint more often. So, it’s always best to lean toward the softer side for the mortar.
The mortar must also be at least as permeable as the surrounding brick or stone. As moisture evaporates, it will follow the path of least resistance – departing through the mortar or the masonry. Once again, we want the mortar to do the work and provide an easy path for the escaping moisture. This will help prevent damage to the masonry and retain the building’s appearance for many years.
|
> Avery Restoration
Partners
> Avery Restoration
Blog Index
Avery History
> Franklin C. Avery
> Avery Block Building
> Life on the corner
of Main & Main
> Avery Murder Trial
> Battle of the Banks
> Preserving
Fort Collins |
