Why is the putty on my window breaking away?

The quality of the putty used determines how long it will last without cracking. PHOTO/xidiosstuff

What you need to know:

A few years after their installation, the putty used to hold the glass in the window (glazing) and door frames started cracking and falling away, leaving parts of the glass exposed. What could be the cause of this?


Although all putty eventually cracks and or breaks over time, Samuel Kungu, a builder and a glazer, shares a  few other reasons why putty may start cracking and breaking away.

To start with, Kungu shares that the quality of the putty used while glazing is an important factor in how long it will last without cracking.

He shares that there are a number of low quality products on the market that are also cheaper and often, customers are enticed into buying them only to last for a short time and crack.

“Sometimes, some sellers mix the putty with other substances which may lower its quality and strength making it crack and fall away within a short period of time after glazing,” Kungu notes.

Another of the reasons why your putty might be breaking or cracking is having it exposed (without paint) to conditions outside; including water, sunshine and other conditions. These weaken the putty by absorbing the elements that help it to bond strongly for a long time, Andrew Muhwezi a metal fabricator, shares.

He also notes that the use of paraffin to soften the putty while glazing makes it easy to crack faster.


As mentioned earlier, all putty is susceptible to cracking over time and so, unless it cracks and begins to fall away or if it is too cracked especially due to time, then the option to replace it can be considered.

For putty that has mild cracks or just a few parts that have fallen away, having a refill of these gaps/ cracks can be done, especially if the rest of the putty is still intact.

“This can be done by scraping away the old putty, cleaning the area and applying new putty. This should be painted after the putty dries.

“To fix gaps between cracked putty, more space can be created to give the old putty a more smooth finish and then new putty can be inserted in between the gaps and given a smooth finish,” Muhwezi explains.      

If the putty is beyond repair, then having it totally replaced is the solution, Solomon Kwagala, a builder, says.

“This needs to be done by a professional who knows what they are doing and can be able to save the glass without damaging it in the process, unless the owner needs it replaced as well,” he explains.

To do this, one needs to first remove the old putty by using a sharp blade to scrape it off. One can also chop the putty out to remove it.

After this, the place where the previous putty sat needs to be cleaned thoroughly before the new putty is installed and given a good finish.

“After drying, the new putty should be painted to protect it from early cracking. Alternatively, if one has a big budget or is looking at serious renovation, they can replace affected old windows, doors with new ones that have modern rubber glazing,” Kwagala says.


Never add paraffin to the putty to speed up the drying time as this will cause it to crack sooner.

Putty takes between seven to 14 days to dry. Leave it to dry completely before painting. Do not leave the putty unpainted for longer than 17 days.


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