How to repair a windshield yourself : The Dos and Don’ts of DIY windshield repair

8 months ago

We’ve all seen all sorts of homemade solutions to auto glass repair on the wild wild Web. Well, as you know, not everything you see or read on the Internet is worth trying in real life (remember the “putting your phone in the microwave will recharge it” thing?). We decided to demystify some popular windshield repair hacks, and explain to you why they do or don’t work.

 

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But first, a little windshield science.

It’s no secret, a mere scratch or chip can quickly lead to a big crack or break, compromising the safety of your windshield not only by impairing your view, but also by weakening the glass that is supposed to stop the roof of your car from crushing you and your passengers in case of rollovers.

Your windshield can hold 1,5 times the weight of your entire car, displaying a tensile strength (ability of a material to withstand a pulling force) of around 10,000 psi. A surprisingly small crack in the glass can weaken it greatly, putting your safety at risk.

The types of impacts and nature of risk
Depending on how the crack or break spreads, the nature of the risk to your windshield’s integrity and solidity varies. A larger crack or hit than those listed here generally lead to full windshield replacement.

 

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This chart from UniglassPlus/Ziebart’s website can come in handy to evaluate the risk:

  • Green: This is a minor crack, but there is still risk. You have some time to act before it becomes yellow or red, but don’t wait too long.
  • Yellow: This needs quick action. If it spreads, it could become unrepairable. You can avoid high and unnecessary cost by acting now. 
  • Red: Emergency! No time to lose with this one, it’s a serious safety hazard. If it’s repairable, it must be taken care of without delay.

 

DIY Windshield Repair Methods Overview

The most popular search engine queries about windshield repair basics mainly revolve around 4 homemade solutions : 

  1. Nail polish
  2. Bug spray, salt and rubbing alcohol solution 
  3. Superglue
  4. Tape

 

Nail polish 

As much as nail polish might visually resemble windshield repair resin, it is not, at all, the same thing. Nail polish doesn’t harden nearly as much as resin and won’t stick either. Remember how we talked about the tensile strength of your windshield earlier? Well, logically, the material used to repair it should hold the same strength.

Tensile strength is calculated according to two factors: adhesive strength (ability to adhere, to stick to the glass) and cohesive strength (ability to hold itself together). The adhesive strength of nail polish averages around 21 psi (let’s not forget the total tensile strength of your windshield averages 10,000 psi).

While we don’t have exact numbers about its cohesive strength on hand, let’s just say it’s an actual issue in the nail polish industry… between the base coat and the top coat. So should we consider it for auto glass repair? No. We shouldn’t.

Plus, just as every other homemade solutions listed above, it can’t be applied with enough pressure to fill all the little gaps the crack properly, letting in air bubbles that will further weaken the repair.

 

Bug spray solution

A solution of bug spray, salt and rubbing alcohol stays completely liquid and won’t harden, dismissing its usefulness as windshield repair material right away. In fact, it leaves a thin salty and sticky bright white film on the windshield and inside the crack, impairing the driver’s view even more than the break alone. Hundreds of people tried it on YouTube, it simply doesn’t work.

 

Superglue

To begin with, the superglue method requires someone to push on the crack from inside the car to “fill the crack more thoroughly”, putting it at great risk of expanding.

If the tensile strength of superglue varies from 1000 to, let’s be generous, 5000 psi, making it stronger than nail polish (shocking, isn’t it?), it still holds less than half the tensile strength of your windshield. 

And since you can’t apply it with enough pressure, nor can you pull out air and moisture from the chip to begin with, you’ll be sure to seal in air bubbles, not only making the auto glass repair weak, but also preventing a further repair, since it’s practically impossible to remove the glue from the crack.

Bottom line: superglue is a one way ticket to windshield replacement.

 

Tape

Do we really have to go over this one?

Although tape is clearly not an option for windshield repair, it can temporarily protect a chip from getting filled with dust, dirt or water before repairing it. We’re not talking about duct tape here, just clear and not-so-sticky tape you can remove easily.

 

So… What now?

Well, most car insurance programs cover 100% of the fees of a professional windshield repair. In most places, you get a free warranty (depending on the company, it can even be a lifetime warranty) on the job, and you get it done properly.

Some windshield repair kits are on sale, but they also have their pros and cons. They’re well-known for working wonders on minor scratches, but also for worsening bigger impacts and making the job of the expert who will eventually have to repair it very difficult. 

 

How would a pro do it then?

Well, the technician starts by vacuuming the air and moisture out of the crack or chip, something that is nearly impossible to do without buying more expensive tools than those included in a basic repair kit. 

He then applies resin (with proper tensile strength, refractive index and flexibility level) with plenty of pressure to fill every tiny part of the crack. He also has a UV lamp to speed up the drying process, allowing the resin to dry perfectly in place before removing the pressure. 

Then, to even the excess resin on the glass, he shaves it flat and polishes your windshield clean.

 

Bottom line

Although it’s not rocket science, windshield repair is still trickier than it looks. Be very careful if you decide to use a windshield repair kit on your own, and be sure to ask a pro for any major repair!
 

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