A Driving Instructor's Blog

Apologies to anyone who has followed the Jennychem links and been met with a 404 error. They updated their website, and it wasn’t until I came to place a new order that I realised. The links are fixed now.


The problem of smeared windscreens in the rain has driven me nuts ever since I started driving, but it became a major headache when I became a driving instructor.Smearing windscreen in rain

We’ve all experienced it. You get a few spots of rain, and when the wipers wipe you get a mosaic pattern left behind for a few seconds. In heavy rain it’s like someone poured chip fat on the screen and you just can’t see properly. I’ve had varying levels of success removing it – scrunched up newspaper (no good), sodium lauryl sulphate (not bad), various solvents (fair), Clearalex (quite good) – but things came to a head when my lease company replaced my car a few years ago. In rain you couldn’t see anything, and absolutely nothing would get rid of whatever it was on the windscreen. I was so bad, I seriously thought that the glass must have been damaged in some way.

Essentially, what causes it is oil, or something related to oil (grease, wax, and so on). Virtually every vehicle on the road leaves deposits behind. Some of it is dusty, some is gritty – but a lot of it is oily or greasy. That’s why when it rains after a period of dry weather we’re advised to take care, because the road can be very slippery as oil sits on top of the wet tarmac before being eventually washed away. Obviously, any road spray is also going to be mixture of dirt, oil, and water, and when this gets on to your windscreen you start to get smears. Now, up to a point, your screen wash can deal with it, but eventually the oil seems to bond to the screen such that removing it is no longer easy.

Strangely, washing your car can also lead to the same sort of problem – especially if you use a car wash (hand or automatic). Any wax on the rags or brushes will transfer to your windscreen, and if you’ve ever noticed how a single greasy fingerprint is capable of smearing across the whole windscreen (unless you use something that lifts it off), it doesn’t need much to cause smearing on the outside when the glass gets wet. It also gets on to the rubber of your wipers, and collects underneath them when they’re off, so even if you manage to clean the glass the wax is smeared back again from the rubber as it dips into the stuff in the gutter, just like a pen dipped in ink.

The particular problem with my lease car this time around turned out to be, as far as I can tell, the result of a manufacturing residue. Something gets on the glass during manufacture, and it’s still there when you get hold of the car.

How can you get it off?

Most detergents and surfactants will remove the normal deposits of wax and oil with varying degrees of success, though car wax is particularly stubborn. Even Fairy Liquid works up to a point. Some cleaners are more powerful – for reasons of chemistry – and are much more effective. Clearalex can be purchased (these days it’s a liquid, but you used to be able to buy it in sachets in powder form), and you add it to your screenwash. The problem with it is that it leaves a horrible white residue when it dries. I have had some success with Sodium Lauryl Sulphate (SLS), which is an anionic surfactant used in many household products. It removes quite a lot of windscreen gunk, but it didn’t seem to touch wax (it also leaves a slight residue at the concentration you have to use it at).

Then I came across sugar soap. I’d not heard about this before, but it is used by decorators and builders to remove grease and dirt from surfaces prior to painting. Sugar Soap - from Screwfix

Wikipedia describes it thus:

Sugar soap as typically found in Commonwealth countries is a cleaning material of variable composition sold for use on surfaces affected by greasy or tarry deposits which are not easily removed with routine domestic cleaning materials. When in dry powder form it looks like table sugar thus causing the name.

The solution is alkaline and its uses include cleaning paintwork in preparation for repainting.

It looks exactly like Clearalex powder, and I suspect that there may be some similarities in chemical composition. However, compared to Clearalex, sugar soap is dirt cheap – one 5g sachet of Clearalex costs about £1.50, but sugar soap is about £2 for nearly half a kilo from Screwfix. I bought some and made up a batch. I soaked some soft cloths in it, gave the windscreen a good scrub and rinse, then took the car out for a run in the rain.

Initially, I thought it hadn’t worked, but with each wiper pass the glass was getting noticeably clearer. The sugar soap appeared to have softened whatever it was on the glass and it was gradually coming off. So when I got back home I made up another batch and soaked some rags in it, then left them covering the windscreen (including the bit at the bottom) for about half an hour. I also cleaned the blades with it. This time the windscreen was absolutely crystal clear.

Sugar soap is great for one-off cleaning, and it got rid of the residue I’d had trouble with, but it leaves the same horrible residue if you put it in your screenwash for normal use.

Not long after this I stopped using my local ESSO garage because the new management had added 5p to their fuel prices (they used to match Asda, but overnight became one of the most expensive in Nottingham). I shifted from using their Tiger Wash machine to a hand car wash, and I was intrigued at how clean they could get the car just using some small garden hand pumps and a power spray. The next time I was in, I did a bit of snooping around the bulk containers of the concentrates they were using, and discovered “TFR” – which is “traffic film remover”.

After reading up on this, I bought some TFR from a company called JennyChem. They also supply the mysterious cherry-smelling shampoo the hand car washes use. In a nutshell, a 1-2% TFR solution gets all the oil/wax film off a windscreen in one go, and it also seems to also attack the residue I’d been plagued with on my lease cars since that first one that had it, though sugar soap is still best for this. The same concentration in your wash bottle keeps it off, and it doesn’t leave much residue.

As time has gone by, I have started using the TFR in a small spray bottle to clean my alloys and bodywork in between visits to the hand car wash when I have an upcoming test. It removes brake dust from alloys like all get out, as well as summer tree gum and bird crap (especially when the little sods have been eating blackberries and insist on sitting on the telephone wire right above my driveway).

As a footnote, my hand car wash has just started using what I am assuming is a liquid wax (I haven’t yet identified it) that makes water bead very easily (and very impressively) when it rains. The problem is that it gets on the windscreen, and it is a sod to get off (two sugar soap treatments did it).

Does TFR damage the windscreen?

No.

Does TFR damage paintwork?

If it is the non-caustic type, and if it is used at the manufacturer’s recommended concentration, no. But remember that TFR will remove any wax you have applied, so you will need to re-wax after using it on painted surfaces. However, removing wax is exactly what you want if it’s on your windows.

Strongly caustic types – which are cheaper and harsher, and often used to shift several centimetres of crap off the undersides of lorries – could damage painted surfaces if used at high strengths and if left on for too long.

The stuff supplied by JennyChem (linked to earlier) is not strongly caustic as far as I am aware, and is specifically designed for use on cars.

Does TFR leave a residue?

The stuff I use doesn’t – well, no more than normal windscreen washer solution does. You’ve got to remember that when you use your windscreen washers, you’re doing it to remove dirt on the windscreen. That dirt is visible, so when you wash it off it will leave visible streaks outside the wiper area when it dries. It’s like when a bird drops a load on the screen – when you wipe it off there’s a good chance it will sit on the screen at the edge until you scrape it off by hand. There’s not much you can do about that.

Is there a non-chemical solution?

A reader (from Australia) wrote to me to tell me that he had had success removing that new-windscreen film using Cerium Oxide paste. You can buy it easily from various places (including Amazon) in various forms – powder, paste, or block – and it is specifically used for polishing glass. If you buy it, make sure you get the finest grade possible – ideally, one which is specifically sold for the intended purpose.

Can you put oil on the windscreen to prevent smearing?

Or, as it was put to find the blog, “can u put oil on wind screen 2 prfent rain”? NO. It will make it worse. It’s oil (and suchlike) you are trying to remove. Put it on deliberately and you could end up killing yourself – you won’t be able to see properly.

You can buy things like Rain-X, which are intended to make water bead up and roll off more easily, but those who use it often complain that it is patchy in coverage and leads to worse problems with smearing when the wipers pass over the glass, especially as it starts to wear off. I nearly tried this, once, but the risk of it causing more problems put me off. I’m not saying it doesn’t work, just that not all reports about it are as positive as the advertising is.

My windscreen is smearing when it snows

That’s probably a different thing, and not “smearing” at all.

When the windscreen wiper rubbers get cold, they also get stiff. As a result, instead of flexing to the windscreen contours and bending forwards an backwards on each stroke of the wiper, they snag and bounce across. They may even not touch parts of the screen properly on the wipe. All of this is often accompanied by a horrible grunting sound, and it leaves behind a trail of smeared water.

Also, if there are remnants of snow on the blades, this can leave a trail of melt water as the blades wipe.

There’s not much you can do if it’s really cold except put up with it, or let them warm up as the windscreen warms up (a cold windscreen will also smear until it warms up). But scrape off any snow or ice and at least you won’t get melt water (and they’ll warm up quicker if they’re going to).

I see rain spots after my wipers wipe

You’ve got wax or some other coating on your screen. I get it after I’ve been to the car wash, and I get it off using TFR and/or sugar soap. I would guess that you also have a visible line where the wipers stop at the end of their wipe span – that’s where they pull wax or oil residues from the bottom of the screen and leave it behind as they change direction. Like I say, TFR gets it off.

Don’t forget that the wiper blades must also be cleaned. There’s no point cleaning the glass of wax if the rubber still has it on it. The wipers will put the wax back as soon as you use them.

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