This year's masonry students at Algonquin College prepared the voussoirs for the bridge in class from big slabs of Indiana Limestone. The dimensions have to be absolutely precise. The job of cutting and shaping the springers, then dressing them and giving them an interesting texture is time consuming, but the final look is worth it.
On the bridge we are building at the Perth Legacy Project during the festival, the other interior springers, the ones that won't be seen, are made on site out of the Madoc limestone material provided by Upper Canada Minerals. The angle of the springers (the first voussoirs that create the angle for the rest of the angled voussoirs to spring off of ) have to match the ones the students made. They are much rougher, but still will work to provide the right angle of support for rest of the stones we will be fitting over the arch
Menno Braam is sighting down the springers that we made. They have been laid between the dressed Indiana Limestone blocks that have already been carefully set in place. He is checking to see that ours line up with the student voussoirs that have already been lowered into place by machine onto the concrete abutments.
Once all the springers are set in place, beams are set on blocks sitting in the water to form a support 'crib' in preparation for the 12 foot wide wooden form to be set on. This form will temporarily support the huge dressed voussoir stones which are essentially laid vertical over the entire opening.
The heavy former was carried and lifted into place by six of the volunteer wallers at the festival yesterday afternoon. There is a good deal of adjusting to make sure it fits exactly at the right height and at the right orientation so that the Indiana Limestone voussoirs will all rest absolutely snug on the arch shape..
The tolerances that John Bland is working with here on the design he did in Sketchup, need to be within less than the width of an eighth of an inch, if all the voussoirs are to fit correctly.