Trained Eye


Plastic Block Window Caulking


This past winter has been extra unusual with our imitation glass block, or plastic block, bathroom windows doing a lot of noisy adjustments to themselves, particularly at night. While there is no breakage evident, some of the caulking is separating.  Are there any special repairs we should take now, other than re-caulking the areas which have come loose? Our house is in Headingley and was built in 2000.


Repairs and general maintenance to windows in a home should be a regular item on a homeowner’s to-do list, but is often neglected.  This time of year is perfect to do minor repairs, caulking, & painting.  Re-caulking and painting is ideally done in the Spring or Fall, when daytime temperatures are warm, but not too hot.  Also, dealing with the mid-Summer infestation of insects can be avoided.  It may be difficult to determine if you have any major concerns with your block window, from the limited description you have provided, but I will offer some suggestions for the problems.

Since your home is already 7 years old, it is unlikely that there is a major defect or problem with the plastic, imitation glass block windows in your bathroom.  If that were the case, you would likely have noticed leakage or damage in the first few years.  I am not sure what the true cause of the noises is, but it may not be coming from the window, at all.  I am assuming that this is a fixed window, and there should be little movement to cause such noises, other than that caused by thermal expansion and contraction.  The window should have sufficient built-in allowances for such movement, unless it is not designed for our climate. 

  If there actually is excessive movement in the fixed, plastic block window there may be one of two causes for this noisy problem.  First, the window may not have been installed with enough of a gap between the window frame and the wooden studs in the wall.  Normally, there should be at least a 6mm to 12 mm gap all around the window to allow for levelling and movement caused by expansion and contraction.  This gap is normally filled with polyurethane, blown-in foam designed for windows and doors.  Once this foam insulation is cured, the exterior wall siding can be finished and the interior covered with drywall.  If the wrong type of foam was installed, it may be exerting excess pressure on the window frame, possibly causing the noises you are hearing as the window heats up and cools down with daily fluctuations in temperature.  In this situation, you may be able to see a bowed window frame from the interior.  Placing a straight edge on the inside of the frame may show this bowing, which will confirm this suspicion.  If this is seen, removal of the interior window casing, cutting out excess foam and re-insulation with low-expansion foam may help with the issue.

  The second scenario is that the windows were bought from a manufacturer who designed the units to be installed in homes in a more moderate climate.  This is quite likely, as I have seen this issue in the past with imitation glass block windows.  In my case, I was involved in a couple of service repairs to these types of units for a local window manufacturer, several years ago.  Despite our best efforts, including replacing the entire units, the windows continued to provide the homeowners with grief, including leakage.  The final conclusion was that the plastic block components of the windows, manufactured in the southern United States , were not compatible with our cold winters.  I believe that the manufacturer discontinued using this product in their windows, for this reason.

  That brings me to my next suggestion.  I would contact the window manufacturer, directly, and ask them to send a service representative to inspect your bathroom windows.  This may only be possible if the manufacturer is a local company, or has a local service depot.  Most window glazing and sealed units have a warranty of around ten years, so you should be well within this timeframe.  You may even discover that there have been several other similar complaints, from other homeowners, and the manufacturer may have a solution.  If not, they should be able to determine if you have a significant problem or just normal deterioration to the caulking.

Since you noted that the caulking is deteriorated, this should be high up on your priority list for general maintenance repairs.  The plastic block windows that I have seen are mainly sealed with the caulking or sealant installed between the individual blocks and inside the frame.  If this becomes deteriorated, or shrinks significantly, leakage and damage is likely.  If this has occurred, snow and ice may seep into the cracks between the blocks. This may be the source of the noises, as the plastic expands and contracts against the ice in between the blocks.  If you are successful in getting a service inspection scheduled with the manufacturer, I would not touch the windows until after that service call.  If the service call is not possible, immediate repairs to the caulking is critical.  Ensure that you use a caulking compatible with the plastic block, and seal the gaps as soon as possible.  Again, checking with the window manufacturer or the owners manual, if one has been provided, for the proper window sealant material is a must.




P.O. Box 69021
#110-2025 Corydon Ave
Winnipeg, MB
R3P 2G9