14 Aug West Townshend Stone Arch Bridge: Week 6 & 7
Posted at 15:49h
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The sixth week of progress on the stone arch renovation began with the lengthy process of "repointing" all of the mortar seams of the original arch span.
Repointing is the process of removing any of the original mortar that may have been damaged by the ravages of time and environment and applying new mortar to help seal and strengthen the joints between stones.
Due to the time necessary to repoint the mortar and the time it takes for the mortar to cure, the first step was to build a tent-like structure over the entire bridge and work area.
The tent structure will help keep any rain from pooling on the arch, thus weakening the mortar joints (and there were some strong storms that week), but it also keeps direct sunlight off of those joints which can cause damage by causing the mortar to cure to quickly, as well.
Check out the Week 6 & 7 Recap and Time-Lapse YouTube videos below to see the work in progress!
The photograph to the left shows how time-worn and damaged the original mortar joints were when the team exposed them all after the site was excavated.
In the photographs below, you can see the team working on the mortar joints on the top and underside of the arch span. The first order of business was to chip away any loose pieces of existing mortar to ensure a strong bond when the new mortar is applied. This was achieved by using hammer drills and good old fashioned hand-held hammers and chisels.
Once all of the existing mortar joints are cleaned and prepared, the process of repointing can begin in earnest.
To maintain the integrity of the original building processes from the early twentieth century, NHL-5.0 Natural Hydraulic Line Mortar was used. This type of mortar is the closest to what would have been utilized in those times. For visual esthetics and remain true to the original vision of the bridge, the new mortar was color matched to blend in seamlessly with the existing mortar.
The repointing process is a very meticulous and time consuming one, but it was a challenge that the team handled adroitly. The photographs below demonstrate the difficult conditions that the team had to perform the repointing work in...but the final outcome was amazing.
At the end of the sixth week, the entire arch span was covered in wet burlap to help during the curing process for the mortar. It is crucial for hydraulic mortar to dry slowly, the burlap is essential for retaining the moisture that will allow the drying process to occur in that slow manner. Week seven was a down-time week at the job site as nothing could be worked on around the arch span during the curing process. The only activity was a daily check of the burlap and to spray it down to maintain moisture as necessary.
More Photos of the Work In Progress!
