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T he days when a stone thrown up off the road
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by the vehicle in front could result in a shattered windscreen are long gone. Today's screens are laminated rather than toughened and are more likely to crack or have a lump gouged out of the surface— Sometimes referred to as a bullseye. In many cases minor damage can be repaired for a modest cost.
However, even the most robust of screens can occasionally need replacing and with modern windscreens increasingly bonded into place rather than gasket glazed (held in place by a rubber surround) this can be a complex exercise. It can sometimes take as long as twoand-a-half hours to cut out all the old glass, remove various bits of trim that later have to be put back. apply the bonding agent and put in the new glass.What's more, the vehicle has to stand idle while the bonding agent cures sufficiently to allow it to be driven away safely.
"We'd recommend that the job is done late afternoon and the truck left to stand overnight," saysJeff Brett, a senior executive at replacement glass specialist Silver Shield. Based in St Ives, Cambridgeshire, and with a branch in Norwich, the firm covers East Anglia and has close ties with a group of independent glazing specialists offering nationwide coverage.
Bonding agents that cure more rapidly and offer drive-away times of as little as one hour are available —National Mobile Windscreens director and general manager Phil Lomas says the high-quality agents he buys from chemical giant Dow are among them. But there is considerable debate over the wisdom of using them on trucks..
Based in Bristol, and with 34 branches, National Mobile Windscreens covers the Home Counties, the West Midlands and the South Coast. It is a member of the National Windscreens Consortium which has 125 depots throughout the country.
Standing time
"With any agent, though, a lot depends on the rake of the screen that's being fitted and its weight," says Finn Sunde, managing director of bonding agent distributor Winbond. He points out that while car and many van screens slope, truck screens are usually almost vertical, placing a lot more stress on the urethane bond. "What's more, they're heavy when compared with car and van screens, which tend to be paper-thin," he says. "As a consequence I would tend to favour letting a truck with a newly-installed bonded screen stand for three to six hours before being driven away, and preferably overnight." Lomas reports:"The one-hour-drive-awaytime agents we use are suitable for typical truck screens weighing up to 39kg. Remember though that we're talking about drive-away times here. It can be two days or even a week before the urethane is completely cured." Driving away a van that's been left to stand for no more than an hour might be ill-advised if it's fitted with an airbag; a standard feature on light commercials these days. "If you have a bump, and the airbag goes off, then the odds are that it will blow the screen straight out of the vehicle," warns Esprit marketing manager Neil Skidmore. Esprit markets windscreen repair kits that hauliers can use themselves.
Fitting conditions
What is not under debate is the need for the screen to be replaced in dry conditions — preferably undercover— because of the requirements of the bonding agent.That is not the only reason why screens should be swapped in a workshop. Because they are heavy and positioned high off the ground it takes two people to lift them into place; not the sort of task to be undertaken at the side of a motorway in a howling gale.
If the truck has Lobe left standing, then don't make the mistake of deciding to service it and tilt the cab-with only a semi-cured bonding agent holding it in place, the screen is likely to fallout. Even with a one-hour-driveaway agent, the screen should be left to cure for at least five hours before any attempt is made to raise the cab. Some operators take the view that, in effect, this means the truck will have to remain idle for five hours even if a onehour bonding urethane is used to avoid the risk of losing the new windscreen.
Screen costs inevitably vary, with the installed price of a bonded new one for a tractor unit liable to be between £1/5 and £250. Sometimes the mouldings around a bonded screen, destroyed when the old screen was chopped out, also have to be replaced, adding as much as £200 to the bill if it's a part that has to be sourced from a truck dealer.
So why bond glass in place to begin with? As well as being aesthetically pleasing it helps to stiffen the cab, and the urethane can be applied and the glazing put in place by robots on the production line.
Heater elements,coatings that reflect heat, and moisture sensors that work in conjunction with the wipers are all appearing on windscreens — especially on vans — which adds to the cost of replacement. 'Screens featuring them can cost £100 more than a standard screen.so operators usually opt for the latter if they break,says Brett.
However. RAC Auto Windscreens takes a different view.According to a spokesman: "Customers tend not to downgrade, despite the expense."
Hauliers are always anxious to save cash and Lomas is concerned about what he claims is a growing amount of cheap Chinese-made glass appearing in the UK. "I'm not talking about glass produced as part of joint ventures between Western companies and Chinese organisations, but inaccurate copies of Western products," he says.
Lomas warns that one of the big difficulties with these screens is that they do not always fit properly.As a consequence whoever has installed them may have tO come back a few days later to put the problem right, leading to an increase in downtime for the operator.
Screens look easy "Remember t hal while some screens look easy to make I'm thinking of screens for R Series Scanias and Daf CFs for instance they are in fact extraordinarily difficult for even the most proficient manufacturers to get consistently right," says Lomas.
Repairing cracks or bullseyes is considerably cheaper than purchasing a new screen made by an established manufacturer such as Pilkington. It involves injecting the damaged area with a clear liquid acrylic resin. "Properly executed, all a repair will leave is a tiny, faint, shadow because the resin refracts light in a different way to glass," says Brett. A British Standard Code of Practice BS AU 242a:1998advises on how big an area can be repaired depending on where the damage is on a truck's windscreen. If, for example, it's within a 350mm-wide area centred on the steering column that extends from the bottom of the screen to the top of the swept area (ie within the driver's immediate line of vision) the damage repaired should be no longer than I Omm at any point. However, if the damage is up in the far corner of the screen on the passenger side, it can be up to 40mm.
In practice much larger areas of damage are regularly repaired successfully. While that may not be a problem so far as the driver's vision is concerned, whether such a repair would result in MoT failure is at the tester's discretion. "Many repairs to truck screens take place just prior to an MoT," says Lomas.
"Truck testers tend to take a tough line over screen damage and I suspect that they don't always understand how a laminated screen actually works," says Brett. 'A repair certainly won't weaken a screen if that's what they're worried about because the resin is likely to he tougher than the original glass."
DIY repair option
Ask a specialist to carry out a repair and you may be looking at a £30 to £45 bill.There is no reason why hauliers should not do the repair work themselves if they are willing to invest in the necessary equipment and have their technicians trained.
Esprit markets repair kits at either £399 or £569.They come with the necessary tools; the former kits is suitable for up to 18 repairs and the latter for up to 36 before the supply of resin is exhausted.Thereafter all the operator needs to do is periodically buy a pack of Esprit resin at £11.95; that will be enough for up to 10 repairs. If looked after, the tools themselves will last for ages, says Skidmore. Recently. the firm took back in part-exchange a kit that had been in use for 25 years."We're willing to offer anybody who wants to part-exchange an old kit £200 off the price of a new one," he says. "The old one doesn't have to be one of our kits either, although we do draw the line at accepting a £14.95 DIY kit bought from an accessory shop!
"All we usually ask is for the old kit to be at least three-quarters intact. It doesn't even have lobe clean."
Buy a new kit and Esprit will train your technicians to use it free of charge, says Skidmore: "We run courses on the second Wednesday of each month at our headquarters in Newcastle-under-Lyme. Free training will also be offered to somebody who bought a kit ages ago, has never used it, but wants to put it into action."
The company can dispatch a trainer to an operator's premises, but there will be a charge based on the distance travelled. If staff cannot be spared for training they can download a 29-page manual as a pdf file from Esprit's website or obtain a training DVD from the firm. Both are available free.
Skidmore argues that repairing a screen is more environmentally friendly than replacing it because making glass uses so much energy. "Extremely high temperatures are needed to manufacture it, bend it, and eventually melt it down when it comes time for it to be recycled," he points out. Dispatching a pack of repair resin has far less impact: "The repairs made using our kit are permanent and the vehicle can be washed or driven immediately afterwards. Heated screens can be repaired in exactly the same manner as ordinary windscreens.
Tinted screens Tinted screens and top band areas can be repaired in the same way as plain screens because the colour is in the layer between the inner and outer sheets of glass. 'Plain or tinted, you're talking about 20 minutes downtime and less than £2 for the resin,says Skidmore. "Don't forget either that if your truck fleet's windscreens happen to be covered under your insurance policy, and you make several claims for replacements during the course of a year rather than having them repaired, your premium will go up."
Esprit also markets special tools for removing bonded glazing. Cab door glass is toughened, and can be smashed by a flying stone, or by thieves. "Some cab windows can take up to an hour to replace, some will take up to two," says Brett. Simply removing all the little bits of shattered glazing can take ages, but he adds: "All of our vans -we run a total of 15 are equipped with vacuum cleaners," With cab door glass more likely to be in need of emergency replacement than laminated windscreens, it's worth noting that National Windscreens, RAC Auto Windscreens, Silver Shield and Autoglass all have 24/7 numbers that can be called to summon assistance.
Security film can be applied to the inner surface of cab windows to stop them disintegrating if they are hit with a mkt, hammer, but at a typical bill of £300 per cab, this does not come cheap.
How about heavily tinting your windows stretch-limo style? "It'll cost you £50 a time,," says Brett.
But remember that you are not permitted to tint the windscreen or the glass in the driver or front passenger doors." •