How to De-Ice a Windshield

Why the order is the whole trick

Ice on a windshield is not a slab sitting on glass, it is a layer bonded to it, and everything about clearing it quickly comes down to breaking that bond rather than removing the volume. The defroster attacks the bond from the warm side, de-icer attacks it from the cold side, and the scraper removes what is already loose. Doing them in that order takes about four minutes on a hard frost. Doing them in any other order is how people spend fifteen minutes and scratch something.

The wipers, first, because this is the expensive mistake

The single most common piece of winter damage is not glass, it is wiper blades. A blade frozen to the windshield will tear along its edge the moment the motor pulls it, and a blade with a torn edge chatters and streaks for the rest of its life. In the worst case the motor or the linkage takes the load instead.

So before anything else: look at the blades and do not touch the stalk. If they are stuck, they will release on their own once the defroster has run for a couple of minutes. The same applies to a washer system you have filled with summer fluid — press the washer on frozen lines and nothing comes out, which is the point at which Prestone AS253 at $15.85 a gallon, published to -34F, stops being an optional purchase.

Where to spray, and how little you need

Ice is thickest at the base of the windshield, where meltwater ran down and refroze, and that is also where the wipers are buried. Spray there and into the cowl rather than across the whole screen: the chemical’s job is to break the bond at the edge so the sheet lifts, not to melt an inch of ice.

CRC Ice-Off at $7.18 is the pick for this because CRC publish what is in the can and what it is safe on — plastic safe stated in the spec table, harmless to car finishes, and frozen locks named as an application, which matters on an older car with a key barrel. Prestone’s 17 oz AS244 at $18.36 is the bigger can with a scraper cap, and publishes no figures at all. The de-icer roundup has the full comparison.

Scraping without marking the glass

Glass is around 5.5 on the Mohs scale. Brass is softer, so a brass blade wears before the windshield does — which is the reason Snow Joe give for using it on the Snow Joe Edge, $9.97, with a published 4.8 inch blade and a two-year warranty. What is harder than glass is the grit that blows onto a car in a salt-treated town, so brush the loose material away before the blade goes anywhere near the surface.

Scrape in overlapping passes in one direction, from the top down, so the debris falls away from the area you are working on. Keep the blade off paint and trim entirely: brass is softer than glass and considerably harder than clear coat. The scraper roundup covers the cone and the long-reach options, and the snow brush roundup is what to use on bodywork.

The four things not to do

• Hot or boiling water. Thermal shock can crack laminated glass, especially where there is already a chip, and the water refreezes in the cowl and around the door seals.
• Running the wipers to break the ice. It tears the blade edge and loads the motor.
• A credit card, a spatula or a key. Hard plastic and steel are both harder than you think, and none of them have a straight edge.
• Hacking at thick ice with a scraper before any heat or chemical. You will be there a while and the grit under the blade is doing the damage.

What the salt leaves behind

Everything you clear off the glass ends up in the cowl, the door shuts and the carpet, and brine is the part that does lasting harm. Winter washing covers what to do about the underside on the days you get one, salt stains on carpet is the interior half, and door seals is the five-minute job that stops a door freezing shut in the first place.