After the removal of the old windows and prior to the installation of the new replacements the cills in part needed to be replaced. It is usually the external component of the cill that needs to be replaced as this is the bit that is exposed to the elements.
There are occasions where the rot has travelled beyond this exposed part and continues under the window and into the internal components of a cill. This is often caused by ill fitting windows where the bottom rail sits on the cill and capillary action occurs.
Unless the window is opened on a regular basis the water sits and rot eventually takes hold.
The cills have a 4.5 degree fall from window to edge. Rot can also travel up to effect frames as was the case with the octagonal window. The glazing beads had to be removed as they had deteriorated. Broken putty being the cause of the rot in the glazing
beads as well as the frame itself. A timber flannel was introduced onto the frame and glazing beads replaced. A particular feature of Collins windows are the parliament hinges which allow the windows to be fully opened flush to the brickwork.
I spent considerable time searching on the internet for replacements but couldn’t find ones that were exact in design and more crucially size. I imagine that Collins must have had a job lot made specifically for these windows. Close inspection suggested that they were indeed made in a foundry rather than on a factory production line. So replacing one of the two hinges to any given window cannot be undertaken. I had to replace both as the projection on a modern replacement does not match the original. The original projection being 121mm ( 4 3/4″) . The closest projection I could find was 114mm ( 4″ ) . Original hinges appeared to be made from cast iron with a high percentage of steel although this may be a guess rather than a fact as this is not my area of expertise. Lime based mortar was then applied to the underneath of the cills and at the ends. Again this too had to be right. I found a supplier who matches colour in premixed lime mortar so that once it’s set it will marry into the rest of the property. Several properties close by had patched mortar that did not match and it did not look right.
Finally after 350 hours of manufacturing , replacement of cills , repairs and installation of replacement windows I could finally stand back and feel confident that these windows are good for another 70 years.