A Driving Instructor's Blog

Smearing windscreen in rain

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.

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 can’t see properly.

Just to clarify, but there are two separate situations involved here. The normal everyday situation is that muck gets on to your windscreen, and you need to get it off. You do that by squirting some of your screen wash on to the glass, and the wipers wipe the muck away. I’ve talked about how to do that in the article about making your own screen wash. However, over time you get oil and wax bound to the screen which is very difficult to get off, and that is the second situation, and the subject of his article.

Things came to a head some years ago when my lease company replaced my car. From the first day I owned it, in rain you couldn’t see anything. All the previously tried methods, which had given various levels of success, failed completely. Scrunched up newspaper was no good, sodium lauryl sulphate had a minor effect, various solvents also minor, and Clearalex was probably the best but still far from perfect.

The problem was so bad that I seriously thought that the glass must have been damaged in some way.

Normal smearing is caused by gunk on the road loosely binding to the glass. All you need is a bit of water and detergent and it comes straight off. But wax is a totally different matter. A tiny amount of it can affect the entire surface of the glass, and is does not come off with normal detergents. In fact, the process of washing the car can be a major culprit – sponges and rags get wax on them from any waxing process you use, and if you go near the glass with them it gets on there, too. It’s even worse if you use hand car washes regularly (as I do).

The other thing to remember is that your wiper blades can also get wax on them. Even if you get your glass sparkling clean, a few wipes of contaminated blades can mess it up again almost immediately. Furthermore, if you clean the glass and the blades, but leave any wax in the well where the wipers sit, they pick it up and spread it around again.

That lease car – and several others since – appears to have had some manufacturing residue still on the glass, because I was also having problem inside with misting and hazy marks with certain sun angles.

So how can you get it off?

Clearalex is available as a liquid, but you used to be able to buy it in sachets in powder form. It is intended to be added to your screen wash, and it cleans quite well, but the drawback 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 or my residue, and it also leaves annoying white marks on the glass when it dries.

However, I eventually came across Sugar Soap. I’d not heard about it before, but it is used by decorators and builders to remove grease and dirt from surfaces prior to painting, and it occurred to me that that was precisely what I was trying to achieve with my apparently permanently gunked windscreen.

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.

The powder form looks exactly like Clearalex powder, and I suspect that there may be some similarities in chemical composition. But you can get liquid and trigger spray variants of it. The main difference between Clearalex and sugar soap is that the latter is dirt cheap, whereas the former comes at a premium price. You simply make up a bucket of the stuff with warm water and give your windscreen a good going over with a clean rag or sponge.

In the case of my ‘damaged’ windscreen, I soaked some cloths in the solution and gave my windscreen a good scrub. Then I 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 became clearer and clearer. The sugar soap appeared to have softened whatever it was on the glass and it was gradually coming off. When I got back home I soaked the rags again and this time left them covering the windscreen for about half an hour (not forgetting the bit under the wipers). I also cleaned the blades with it. This time the windscreen was absolutely crystal clear.

In conclusion, Sugar Soap is great for one-off cleaning. However, it leaves a nasty  white residue when it dries if you try to include it in normal screen wash.

Traffic Film Remover (TFR)

Not long after all this, I stopped using the Tiger Wash (drive thru) at my local garage and started using a local hand car wash – partly as a result of the garage hiking fuel prices, and partly because the hand car wash also did a damned good vacuum clean of the inside of the car. I was intrigued at how clean they could get the car just using some small hand pumps and a power spray. The next time I was in, I did a bit of snooping around and discovered ‘TFR’ – or ‘traffic film remover’.

After reading up on the subject, I bought some TFR from a company called JennyChem. If you use the code BAYJC8628 you will get a discount. They also supply the mysterious cherry-smelling shampoo the hand car washes use, along with a range of other treatments used by car washes. 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.

Right now, you can get a 5% discount at JennyChem using the following code at checkout.


I use 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, 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).

And a final note. You can make your own screenwash using TFR. But be advised this does still leave a slight residue.

Does TFR damage the windscreen?


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, which is ultimately why I use it.

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. However, the stuff supplied by JennyChem is not strongly caustic, and is specifically designed for use on cars.

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.

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 and 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 water streaks.

Also, if there are remnants of snow on the blades, this can leave a trail of melt water as the blades wipe. You get similar effects if a leaf or small piece of blossom gets stuck on your blades.

I see rain spots after my wipers wipe

Then you’ve got wax or some other coating on your screen. I get it after I’ve been to the car wash, and I remove it using TFR and/or sugar soap.

Don’t forget that the wiper blades must also be cleaned (as well as the space below the blades when they are in their parked position). 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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