Windscreens used to be attached to the car with a rubberised gasket seal. Now however, they are bonded to the body aperture of the vehicle with a strong polyurethane adhesive.
That's why the outer perimeter of a windscreen is printed with a black shading to make it opaque. It's ceramically printed on the glass and both hides the adhesive and protects it from UV degradation.
At some point, most car owners will have a windscreen replaced because of a stone-chip or crack or will have to replace a side window when some low-life smashes it to liberate a radio, sat-nav, mobile, laptop, etc.
If you are dealing with a reputable company the technician will put seat protectors on your seats and a cover on your car's bonnet. Then they will remove your windscreen wipers, tax disc, rear view mirror and some of your vehicle trim (the trim around the windscreen and where it meets the bonnet).
Next, if you have a modern vehicle with bonded-in glass, they will use a special tool to cut round the windscreen, slicing through the polyurethane adhesive which bonds the windscreen to the vehicle's windscreen aperture, freeing the windscreen ready for disposal. They will then cut off any excess old adhesive and make sure the aperature is clean and smooth.
The technician may apply primer to the windscreen aperature before he prepares the replacement windscreen. This depends on the individual company and the vehicle, I believe. Next he will apply adhesive to the new screen before offering it up to the aperture and fitting it in place.
You have to wait for the windscreen adhesive to dry. This can take an hour or so (depending on the company - some use a quicker drying adhesive).
This is especially important if you have a passenger airbag. Drivers' airbags use the steering wheel for support if they are triggered. The passenger airbag uses the windscreen. If your windscreen adhesive is not dry when the airbag goes off, the exploding airbag could simply push the screen out, affecting your and your passenger's safety.
If your windscreen is badly cracked it will need to be replaced, but if it only has a small chip then you can usually get it repaired.
If you have a fully comprehensive motor insurance policy then you'll probably be able to claim on your insurance and just have to pay the excess (about ££50 - £60 unless anyone knows different). And, it shouldn't affect your no-claims discount but check with your insurance company first to make sure.
If you are only covered for third party, fire and theft or just third party, then it will cost you more. The car glass companies like Autoglass don't publish prices online - you have to call them and they'll give you a price.
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