Asbestos Window Putty / Glazing Compound

Asbestos window putty, also called glazing compound, is a linseed oil or synthetic-based sealant that was formulated with chrysotile asbestos fibres to improve its plasticity, durability, weather resistance, and adhesion. Applied to bed glass panes into wooden, steel, or aluminium window frames, this product was used on residential, commercial, and institutional buildings from the 1930s through the late 1970s. While each individual window contains only a small quantity of putty, the sheer number of windows on which it was used makes it one of the most widespread asbestos-containing materials in the built environment.

The asbestos content in glazing compounds varied by manufacturer and era, typically ranging from 2 to 10 per cent chrysotile by weight. The fibres gave the putty improved resistance to cracking, better adhesion to glass and frame surfaces, and longer service life compared to plain linseed oil putty. Some formulations also included other mineral fillers alongside the asbestos, making laboratory analysis necessary for definitive identification.

The primary health hazard from asbestos window putty arises during disturbance, specifically during window replacement, re-glazing, or renovation work. When putty is fresh, it is soft and pliable, and the asbestos fibres are well encapsulated within the oil-based matrix. As putty ages, however, it hardens, becomes brittle, and eventually cracks and separates from the glass and frame. Removing old, hardened putty requires chiselling, scraping, or heating, all of which can generate dust and debris containing respirable asbestos fibres. OSHA has issued citations to contractors for asbestos exposure during window replacement projects where old glazing putty was scraped without proper controls.

The risk is compounded by the fact that window putty is rarely suspected as an asbestos-containing material. Many window replacement contractors, glaziers, and homeowners remove old putty without any awareness that it may contain asbestos. Because the putty is scraped in close proximity to the worker's breathing zone, and the scraping generates fine, easily inhaled particles, the exposure can be significant even from relatively small quantities of material.

Before any window replacement or re-glazing project on a building constructed before approximately 1980, the existing glazing putty should be sampled and tested for asbestos. A licensed asbestos inspector can collect small samples from multiple windows for laboratory analysis. If asbestos is confirmed, putty removal must be conducted with appropriate controls including respiratory protection, wet methods to suppress dust, collection of all debris, and disposal as asbestos waste. Some window replacement contractors are trained and equipped to handle asbestos putty, but verification of their credentials is essential.