Thermal Shock – Why I don’t clean windows on Frosty Days

Double glazed cracked window

In brief, thermal shock is where a sheet of glass either expands or contracts very quickly due to hot expansion and damage happens as a result.

Most often the problem is rapid expansion, from very cold glass getting hot water put on it. Why would this happen? Well, have you never heard that if you put water on a car windscreen to defrost it on a frosty morning, that you should never use ‘hot’ water, just warm/tepid water. Otherwise you can break the windscreen? That is the most common form of thermal shock in day to day life – Frozen glass + Hot water = Thermal Shock

The problem is made worse if there are any little cracks or imperfections in the glass already. If so, these will crack open faster than a perfect sheet of glass.

Vehicle windscreens are a special type of glass, made to withstand a lot of flexing and movement. So, if glass like this can crack with thermal shock, just imagine what glass that doesn’t have this ‘flexibility’ treatment can do. Glass such as ‘architectural glass’ for instance, the glass that your household windows are made from. That type of glass is even more prone to breaking with thermal shock.

Though the imperfection can occur anywhere, the most confusing for homeowners, is when the imperfection is on the glass edge, usually behind the frame and thus, it cannot be seen. So, the owner believes that there was nothing wrong with his/her window and that someone has broken it. Actually, impact damage and stress or shock damage looks different, but I am not going into that right now. Except to say that you can normally see the point of impact with impact damage and the crack pattern it often different with more cracks outward from the point of impact. Look at the photograph of the double glazed window, it is an obvious stress crack from the edge behind the frame. The origin is hard to see in this photograph, but it is clearly a stress crack rather than an impact crack.

We are interested in stress or shock damage, which is often, though not always, leading from an imperfection in the glass.

There are various reasons for imperfections in window glass, such as:

    • Edge Damage from poor handling by the factory, transport, fitter or anyone else with any contact with the glass from the moment it comes to the end of the production line.


    • Poor cutting technique or tool. Can leave a slight imperfection that isn’t noticed at the edge of the glass.


    • Wrong glazing sizes. Not enough clearance has been left for the glass moment within the fame. (Glass needs to move, contract and expand in the frame under normal conditions)


    • Poor frame design can result in the same problem as wrong glazing sizes.


    • Frame debris when glazing. Bits of dirt, stone, glass, nails etc left in the frame to rest against the edge of the glass. (Glass needs to contract and expand in the frame so increased pressure can damage the edge if it expands against a hard/sharp object)


    • Warped frame. A frame that is not totally straight can warp the glass within causing stress damage.


    • Poor fitting blocks. Glass is set on special blocks, the wrong size of block or even the wrong type/material of block can lead to glass edge damage.


    • Damage from site works. Glass is easily damage from the slightest thing. When glass is being put in, sawing, cutting drilling, moving, hammering, metal cutting, stone cutting is also often done around the glass. Any of this can cause slight or not so slight, damage. I have see this a lot.


    • Previous thermal stresses. Glass can flex too much under strong thermal conditions e.g. a very hot day, something amplified the suns rays (the same was as a magnifying glass can, many forest fires are stared like this). Previous stresses like this cause damage that can’t bee seen yet. Actually a very sunny day alone can crack and break a window.


    • Solar Glass (Low E etc. coated glass to retain heat). The very nature of this glass can cause the glass to heat more and result in thermal stress damage.


    • Normal impact damage. Day to day life takes it toll on everything. It’s easy for a window to get impact damage and you not notice it. Every impact does not result in a very obvious crack, some are microscopic in size.


    • Glass can contain nickel sulfide impurities at the manufacturing stage. This is a risk in glass production that can result in glass damage a number of years after the glass has been fitted. It’s a little ‘ticking time bomb’. The crystals can change and re-shape in the glass resulting in stresses and damage. This can even e the the cause of spontaneous breakage for no apparent reason that can be seen in glass.
      Other manufacturing error. Glass production is complex, and even though the largest, most reputable companies have good quality control, imperfections can get through.


  • Cheap glass. If the glass is a cheap glass, a common problem in today’s society of competitive pricing, money saving etc there are likely to be more imperfections in the glass at production level. A cheaper glass company cannot afford to be as selective about the glass it sends out to market. They also cannot afford to spend as much money on high end production equipment, or quality inspection equipment.


Single Glazed Cracked Window
On this single glazed cracked window. You can clearly see how the crack started at the edge, behind the frame to the right. Then spread from that point of damage. This is a stress/shock crack, not an impact crack from something hitting the window.

As you can see, there are many reasons why glass can get imperfections and damage. This damage can lead to breakage all on it’s own. Or cause the sort of minor damage that is the start of a crack from thermal shock damage.

Thermal shock is a problem for window cleaners still, especially water fed pole cleaners. We use hot water (well some of us use hot water most use cold water, which is useless in the cold weather). The hot/warm water hits the frozen glass and any imperfections will simply crack open. Not what you want, nor what the window cleaner wants.

So, quite often, a water fed pole window cleaner just doesn’t clean windows on frosty mornings.


If you are interested, you can get some more information on glass breakage from a few more sources:

  1. Wikipedia – Spontaneous Glass Breakage
  2. UK Centre For Window And Cladding Technology
  3. Windows Online UK


Spiders Web on Window Surround & Frames

Spiders Web on Window FrameYes, you can tell the seasons on the year in this part of the country by what needs cleaned off window frames, sills and window surround. As I clean all this as well as the glass, I am always aware what the most prolific type of dirt / debris is at any point in the year as it changes season by season.

I clean my customers windows regularly, so the things that need cleaned off change as we go through the year. There is less and less mould and algae accumulating on the sills now, so less work with the scrubbing brush round the sills for me. But, the spiders webs are appearing more and more. The fine webs are no problem, but the blobs of web in the corners of the window surround and jammed between the top of the frame and the surround are starting to accumulate.


The spider’s web blobs occur for 2 main reasons:

  1. Primarily, because spiders feed on smaller insects that get trapped in their web. The spider then wraps up the insect in web in preparation, stores it close by and keeps it for consumption later.
  2. Spiders webs don’t really like water. They are fine with morning dew and light showers etc, but not good in bad weather. Rain and wind destroy the web, often resulting in a shapeless blob of destroyed web sticking to something near the site of the original web.


Getting the fine webs off (such as the spider’s web photo at the top of this page) is no problem, though the blobs do cause take a bit more work (see photos below). They are very sticky, and are usually well jammed into a corner. Since I clean these off all my customers windows, I have become rather practised at it, and have even designed my own tool for removing them safely and cleanly. I have had to do this as none of the usual window cleaners tools are really up to the job – we have a bigger spider blob issue in this part of the country than elsewhere it seems.

The only good thing for me is that spiders generally don’t go above the ground floor windows. Yes, you do get a few, but as a rule, I only have to remove the mess on the ground floor windows, though that mess does gets very bad as we get into better weather and the insect population increases.

Anyway, the spiders are back out of hibernation or wherever the go in the winter, and my spider’s web removal tools are out on nearly every job these days, and we are only just at the start of spring!

My customers can be assured that I take pride in my work, and my company tag line “The ‘Complete window’ cleaner” is not just some marketing label claim, but I do clean the complete window – spiders webs and all.


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Here is an example of spiders web I cleaned from a window the other day:

Spiders Web on Window Surround & Frames
Spiders Web Cleaned Off Window Surround & Frames


Spiders Webs Removed As Standard by Warrenpoint Window Cleaning


Sahara DesertThe Sahara Sand that blew in, has been leaving a film of grime on the windows of many of the houses and businesses I clean the windows for. Funny enough, in Warrenpoint, the properties nearest the sea appear to be the worst affected. It actually looks like the film of sea salt that can be seen on windows here when the storms blow up, so pale and fine is the sand deposited on the glass.

Thankfully, the purified water cleaning method that I use cleans this sand off beautifully, and does it without scratching the sand across the glass as other window cleaning techniques can. The cleaning method I use, lifts the sand off the glass with purified water, and the suspended sand is then agitated off the glass. Finally the glass is rinsed with more purified water before finishing.

The sand has blown in across the UK and Ireland, leaving it’s mark everywhere it has gone:



Though I have stated in another article on this site (Rain Water Is Excellent For Window Cleaning), that rain water is generally not dirty. That s not the case on this occasion. The sand is in suspension in the rain water and has dropped onto windows and everything else, carried in the rain that fell overnight in this part of the country.

I guess that I am going to be pretty busy cleaning sand off windows in the immediate future.

Man Falling Off Ladders

Man Falling Off Ladders Believe it or not, window cleaning can actually be a very dangerous task.

For too many years, it has been expected that a window cleaner will go places and take risks on ladders and window sills that no one in their right mind would normally do as part of their job. I still find it amazing what home owners expect a window cleaner to do. And many on the owners who expect the most dangerous climbs, expect to pay the least! I suppose that this is a throwback from many years of old style window cleaners making these dangerous climbs in the past day after day – until they fell off. They did this because they needed to make a living, so if they didn’t clean that window – someone else would, and would get the job for that house or business. In the UK and Ireland, we are also known for our windy weather – some places more than others. How may people will go up a ladder with no support in gusts of 45mph? Well, I can tell you that this is done day after day by window cleaners – until they fall off.

Today, many people hate the sound of “Health & Safety” it speaks of restrictions and not being allowed to get the job done. Though, in the window cleaning business, the H&S executive had to make changes as too many window cleaners where either dying or getting seriously damaged. They brought in restrictions like how high you could go up a ladder and how it had to be secured etc. These decisions were based of the outcome of many accident investigations, they are designed to keep more people safe when up ladders. One of the regulation they brought in was that you couldn’t use a ladder if a safer alternative was available to you. This is where the water fed pole system started really taking off.

The Water Fed Pole (WFP) cleaning method had been around, but not widely adopted as it was expensive – certainly many times more expensive than the traditional tools – a ladder, squeegee and applicator.

Today, more and more window cleaners are using the WFP cleaning method. There are a number of real advantages, such as getting a better clean in my opinion and getting the frames cleaned as well, but the thing that really pushed it into the forefront was safety. You can clean just about any household or low-rise commercial window from the ground, so no more ladders to fall off, or walking along dangerous window sills, walls etc. I still carry ladders on my van, but only occasionally have to use them. With a carbon fibre water fed pole, I can clean 3 storey houses and roof windows all from the ground. I also clean multi storey office buildings and factories – all from the safety of the ground with a water fed pole.


 Window Cleaner's Ladder Right On The Edge Of A Wall Over A Drop This is a window cleaner’s ladder sitting on the edge of a wall over a drop with stone steps at the bottom. If the ladder slipped on the green mould or accidentally knocked by a passer-by, the window cleaner would have very little chance of survival. This was done in the UK Feb 2014 – not years ago. The window cleaner risked his life to clean one window. He admitted that if he had a water fed pole system, then he would not have needed to do this.



Here are a few reports of some of the many accidents that still happen from traditional window cleaning. Most, if not all of these accidents happened because the H&S working at height regulations were not observed:


Hot Water Window Cleaning

Hot Water Window Cleaning from Warrenpoint Window Cleaning

Hot Water Window CleaningIt’s January, and we are well into the winter now with temperatures dropping sub zero. So, I have installed a hot water system into my window cleaning van. From now on, all the pure water window cleaning will be ‘hot’ purified water.

I have already been using hot water for cleaning internal windows during this cold weather, even though the specialist cleaning products that I use are design to be used with hot or cold water, I simply find that the hot water gives me that edge, especially with food or body oil based marks. Now I am also using hot water for the outside of the windows.

Hot water window cleaning cleans the glass and window frames more effectively than cold water because it softens and absorbs dirt much faster. The purified water I use is already excellent at absorbing dirt, now I have improved the system even better by making the water hot. In the winter months, windows get dirtier than the summer as the bad weather lifts more dirt and sea salt and deposits it on your windows (any everything else that wind and rain lands on). So, having hot purified water to clean windows and frames in the winter is very advantageous.

The water is purified (removing all disolved impurities – minerals, salts, metals etc), then heated in the van, then piped to my water fed pole through an extension hose. This means that the whole system is still entirely self contained in the window cleaning van, and I have a continuous supply of hot purified water all day long.


 Hot water window cleaning is not standard for most window cleaners

Did you know that the majority of window cleaners using purified water systems do not use hot water? In fact, I don’t know of any that heat the water that operate in the same areas as I do. Most don’t use it due to the expense involved in both the initial set up costs and ongoing heating costs. Even many of the traditional window cleaners don’t use hot water. With so many people being out during the working day, even the traditonal window cleaner has problems getting a new bucket of hot water every couple of houses. So, cold water has become the norm for window cleaning these day.


 The best service that I can offer

Right from the start, I have always wanted to provide the best cleaning service that I can at a competitive price. This new hot, purified water window cleaning system is simply a continuation of this policy of doing the very best I can for my customers.


Smear free clean windows & even cleaner PVC frames

Cleaning windows with cold water in the cold weather doesn’t clean as well as hot water window cleaning. My customers won’t really have noticed this in the past, as I have simply worked harder to get the windows and frames clean. Now, even those ‘hard to see’ marks and smears that contain body oil from fingers, hands and pets etc, will be eliminated with hot purified water.

PVC is notoriously hard to clean and I can already do a pretty good job of getting rid of dirt and algae etc from the window frames when I am cleaning customer’s windows. With the hot purified water, I expect to be able to clean even more dirt and grime from PVC window frames, making the overall imression of clean windows much better.

The winter does give some other problems. Some colder days I have even had to stop working as the cold water I was using to clean the windows, simply froze on contact with the glass!

The water is now heated ‘on the fly’ just as I am using it, and I can control the temperature as needed. So, there will not be any problems with water getting too hot for the glass, or cooling down too much as the working day progresses. I will have a constant supply of hot water straight out of my van all day long.

I hope that this new hot water window cleaning system will be of noticeable benefit to my customers.