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Anne Marie Helmenstine, Ph.D.

How Can You De-Ice Your Windshield?

By January 29, 2014

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Do you have tips and tricks for removing ice ice from your car's windshield or preventing it from forming in the first place? Recently I was asked if science can be applied to defrost a car windshield more quickly than waiting for the car's defroster to warm up and melt the ice. Here are a few different ways you can defrost your windshield quickly.

Warm water works if it's not super-cold outside. You can pour warm water over your windshield and use the wipers to clear it off. If it's really cold outside, all you are going to accomplish is adding a thick layer of ice to your windshield (best case) or cracking your windshield from the temperature difference (worst case).

Saltwater works for the same reason salt works as a de-icing agent (and warm saltwater would be your best bet). The ions in the salt lower the freezing point of water, so a little ice will be melted by the saltwater. This water will attempt to re-freeze, but the temperature will need to be colder than 32°F for that to occur. All salts aren't created equal for de-icing. Normal table salt works when it isn't really cold. Road salt, which has a different chemical composition, works better when the temperature is very low. Salt exposure isn't great for your car, so keep that in mind. Actually any chemical that you add to water acts as impurity and lowers the freezing point of water, so wiper fluid would melt the ice more quickly than pure water, too.

A quicker way to melt the ice on your windshield is you already know... placing your bare hand against the windshield. This works because (a) your hand is warm and (b) your hand is solid. Warm solids contain more particles per unit area to convey heat to the windshield than you would get from warm air (molecules in air are very far apart). So, any warm solid will de-ice the windshield better than air. Any warm liquid will de-ice better than air for the same reason (ice melts faster in water than in does in air of the same temperature).

You don't have to use your hand. The base of a warm shoe would work; so would a warm book. The more dense the object is, the more effective it will be. Therefore, you'll get more de-icing power from your shoe than you would from.. say... your sock. The heat capacity of the material matters too, which is part of why your hand is such a great defrosting tool.

If it's not too cold, I'd probably go with a warm, damp towel on the windshield. If it's bitterly cold, the ice scraper is still your best bet. If you have a garage and live in a warm climate, you can prevent the frost from forming in the first place by parking inside.

What are your best tips for de-icing a windshield?


October 22, 2009 at 2:04 pm
(1) Dave says:

What about giving your windshield a good coating of something like Rain-X before it gets cold and precipitates?


December 4, 2009 at 11:08 am
(2) Keba says:

The best and quickest way that I have found is to run cold water over the windshield. Works every time.

December 5, 2012 at 11:29 pm
(3) snowplow says:

Here is my process for de-icing my windows:

Start your car and crank the defrost and heat.Next, warm up some water on the stove and then add two cups of salt and stir. Pour the hot saltwater over the windows’ exteriors. This will have the effect of warming up the glass as well as melting the ice. Work in small sections and soak up the excess water immediately with a towel. You may be left with a very thin layer of ice. Scrape the rest off with ease!

Be careful when applying hot water to your windows. If you dump buckets of water on the windows and ignore the towel, you can easily freeze your doors and other mechanisms. Respect saltwater as the powerful tool it is and be patient.

December 15, 2012 at 3:00 am
(4) Phil Dhingra says:

I keep reading online that pouring warm water over a frozen windshield will also break the glass due to the extreme temperature change.

February 5, 2013 at 6:22 am
(5) casey says:

I have used half pint of boiled water in a kettle mixed together with one and a half pints of cold .Slowly trickling it down all the screens .Then get in and imediately drive.
I have done this for 40 years of motoring .No problem.

February 20, 2013 at 8:46 am
(6) NOICE says:

It is a good article, and I will like to inform you that now there is a new Swiss made product, NOICE: with only one application (It takes just 15 min), your windshield will be clean in just 10 seconds for all winter.

February 20, 2013 at 8:49 am
(7) NOICE says:

It is a good article, so I will like to inform you that now there is a new Swiss made product, NOICE, that with only one application (It takes just 15 min), your windshield will be clean in just 10 seconds for all winter. You can watch the demonstration in this video:

February 27, 2013 at 8:36 am
(8) cole says:

Move to Key West Fl. Good food! Good fishing!
disclaimer: this is not a paid advertisment

November 20, 2013 at 11:20 am
(9) Megan says:

what about vinegar water? helpful or harmful?

November 23, 2013 at 12:21 pm
(10) Nimkee says:

an old cab driver told me one time and i always do this during storms …put a thermos of hot water under the seat ,, by thye time youre ready to use the temp is just right and hey if its too hott put a bit of snow in the thermos ….gently pour over windshield …works great on frozen door locks too just remember its water so leave the car run for a bit with the heat on full ..

December 6, 2013 at 7:22 pm
(11) Mo says:

I have been using warm water on my cars since the 80′s and so far I’ve not encountered problems. I used to use quite warm water but now I tend to go for warm. I fill a watering can with it. This has the volume and enough heat capacity not to freeze up. Before ice melts and the temperature rises you have to supply latent heat of cooling. I go all round the car and get all the windows clean and ice free. I then use a squeegee to wipe of the excess water and wipers to wipe the front and rear screen. Try not to get water into the mechanism (flexi hinges) of the wiper blades. I have had these refreeze so preventing the rubber blades following the glass contour, which can be dangerous! If I go away I have a large collapsible water bag in the boot in case I need to get warm water. I also have dicer!

December 21, 2013 at 11:48 pm
(12) Jnaet says:

Keep a bottle of 91% alcohol in squeeze or spray bottle. Apply it to the windshield. The ice will thaw

January 9, 2014 at 12:52 am
(13) Greg S. - Chicago says:

Impatient drivers trying to remove ice from windshields often discover creative ways to break the glass. Glass Doctor busts the top five vehicle de-icing myths:

1. Pour hot water on the vehicle’s windshield and windows to melt the ice. Make sure it melts the ice completely so the frozen glass will shatter due to the extreme temperature change.

2. Tap the ice on the car windshield with a hammer to break the ice into pieces to pick off the glass. If that doesn’t work, hammer on a screwdriver or ice pick. This usually results in an impact hole or a large crack.

3. Scrape the ice off the truck windshield with a metal ice scraper, key, spatula, utility knife or crowbar. The metal either scratches or cuts grooves in the glass.

4. Use a propane torch to melt the ice. Not only is this dangerous to the torchbearer, but this also can unintentionally melt the glass.

5. Pour a mixture of vinegar and water on the windshield so that it freezes to the glass before the rain does, thereby preventing ice. Unfortunately, vinegar eats pits into the windshield glass.

“These ideas may be creative, but they can be hazardous to your health,” Glass Doctor Franchisee of the Year, Ed Sieber of Glass Doctor of Charlotte, N.C., said. “There is a better way to safely remove ice from windshields and auto glass. Gradually heat the glass from the inside while scraping and brushing ice from the outside.”

February 3, 2014 at 10:56 am
(14) Tauseef Ahmad malik says:

i think Raoult’s law works here .. Depression in freezing point of water when salt is added to it .. i have read it some 10 years ago in my higher secondary education. besides, the other applications of raoult’s law are Relative lowering of vapour pressure and Elevation of boiling point

February 3, 2014 at 12:54 pm
(15) Barb H says:

Get out there 15 minutes you have to leave and let the car run with the heat & defrosters at full blast. Everything will defrost in time and you can forego the hot water & scrapers.

February 4, 2014 at 5:41 pm
(16) Rose says:

What if you are getting frost inside your car on the front windsheild

February 6, 2014 at 1:10 pm
(17) Matthew says:

Sometimes the heater in your car can create condensation on the inside if the temp is right outside . If your heater works and this still happens turn on the AC – no not on cold – it is an air ” conditioner ” it will remove the moisture from the air even when the heater is used .

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