Stages of Deterioration
Stage One: Over time, heat and direct sunlight removes the linseed oil from the putty, it becomes powdery and cracks in the putty appear on the external face of the window. This powdery putty is no longer water proof. Rain water seeps through the powered putty to the internal side of the window.
Stage Two : As this process continues over time, the linseed oil fails completely and the powdered putty washes out of the external lead channel or cracks out falling away in pieces. Grime and rain water come in though the gaps and makes the interior of the window dirty. This can be seen most easily from the inside of the building at night with the lights on. The window may being to buckle and bow or alternatively rattle in the wind. Wire ties that once held the panel to steel reinforcement bars may break making the window further unstable. Without the strength of the putty to hold the panel the malleable lead will warp, fatigue and break under the weight of the panel. These breaks in the lead will occur only at the stress points at first and may not be visible to the naked eye. If maintenance is carried out at this stage, the cost and labour is minimal, as usually maintenance can be carried out on-site. Unfortunately often stage 2 deterioration goes unnoticed by the custodians of the window, until major repairs are required.
Stage Three: This is when the lead has lost the vast majority of its putty, the lead matrix has become brittle due to expansion and contraction and is fatigued at the stress points, usually at or around the solder joints. The naked eye can clearly see the lead is cracked in numerous places. Daylight may be seen where the lead and glass have moved away from each other. Individual panels of glass may be falling out out the window. The forces of gravity and wind pressure may cause the entire window to collapse. This stage is avoidable and only occurs when no intervention at the earlier stages takes place. At this stage the only option is to carefully remove the window, partially or fully dismantle it and rebuild it, retaining the old glass, repainting or repairing the broken glass and replacing the perished lead. This late intervention is expensive. Repainting to match pieces of missing glass is time consuming and requires a highly skilled painter who can match the old painting techniques and sourcing old glass may be problematic.
Water has been seeping through this powered white putty leaving tell tale dirty watermarks on the inside of the window.
Hair line cracks are barely visible in this lead, if no action is taken, with time they will open up causing structure problems.
The lead cracks are clearly visible to the naked eye, if this issue is consistent throughout the lead, the window with be experiencing an alarming amount of movement and requires immediate attention.