Windshield Crack Repair Experiment 1: Learning From My Mistakes

Key Takeaways

A standard windshield repair kit ($10-$13) contains glue and a suction cup, but the suction cup is only useful for small bull’s-eye chips — not long cracks
Do NOT drill a hole at the end of a crack to stop it from spreading — it can melt your drill bit, break it, and actually make the crack longer
Park in the shade when applying repair resin because UV light from sunlight will harden the glue before you finish applying it
Determine whether the crack is on the outside layer, inside layer, or the laminated sandwich layer before applying any repair resin
Use your fingernail to feel for a bump along the crack — if you can feel a ridge, the crack is on that side of the glass

Why I Tried DIY Windshield Crack Repair

Windshield replacement is expensive. Depending on your vehicle and insurance deductible, you could be looking at $200 to $400 out of pocket. So when a crack appeared on my Dodge Caravan windshield — originating from near the rearview mirror mount — I figured it was worth trying a $10 repair kit before spending hundreds on a full replacement.

This is Part 1 of a two-part experiment. I am going to share exactly what happened, including the mistakes I made, so you can learn from them. Check out Part 2 for the continuation where I apply the resin to both sides and cure it under sunlight.

What You Need: The Windshield Repair Kit

I picked up a standard windshield repair kit from Walmart for about $10. You can find the same type of kit on Amazon for around $12 or at auto parts stores for about $13. The kit typically includes:

Repair resin (UV-curing adhesive) in a small applicator bottle
Suction cup device with a center chamber for injecting resin into bull’s-eye chips
Curing strips (clear adhesive strips that hold the resin in place while it cures under UV light)
Razor blade for scraping off excess cured resin

When to Skip the Suction Cup

The suction cup device is designed for small, round damage — the kind of bull’s-eye or star-shaped chip you get when a rock hits your windshield. It creates a vacuum seal around the damaged area and forces resin into the impact point.

But for long cracks, the suction cup is useless. A crack is too long and narrow for the suction cup to cover. Instead, you apply the liquid resin directly along the length of the crack, which is what I did in this experiment. If your damage is a long crack rather than a small chip, you can save money by buying just the resin and curing strips without the suction cup assembly.

Understanding Windshield Glass Layers

Before you attempt any windshield repair, you need to understand how automotive glass is constructed. A windshield is not a single piece of glass — it is a laminated sandwich with three layers:

Outer glass layer — faces the outside elements and road debris
PVB interlayer — a plastic vinyl butyral layer that holds the glass together on impact
Inner glass layer — faces the vehicle interior

This three-layer construction is critical to know because the repair resin can only reach and fill a crack that is accessible from the surface you apply it to. If the crack is on the outer layer and you apply resin from the outside, it can seep into the crack and fill it. But if the crack is on the inner layer, applying resin to the outside will not work because the plastic interlayer blocks it.

How to Tell Which Side the Crack Is On

Run your fingernail across the crack on both the inside and outside surfaces of the windshield:

If you feel a slight bump or ridge on the outside, the crack is in the outer layer
If you feel it on the inside, the crack is in the inner layer
If you cannot feel anything on either side, the crack may be in the sandwich interlayer, which makes DIY repair very difficult

With your bare hand, you probably will not feel anything. The key is using your fingernail — it is sensitive enough to detect even a tiny ridge. In my case, at least part of the crack seemed to be on the outside layer, which gave me hope that the repair resin would work.

My Biggest Mistake: Drilling a Hole

Many car repair resources suggest drilling a small hole at the very tip of a crack to relieve stress and prevent the crack from spreading further. The theory makes sense from an engineering perspective — the tip of a crack is a stress concentration point (technically a singularity in fracture mechanics), and drilling a small hole redistributes that stress across a larger area.

In practice, however, this went terribly wrong for me. Here is what happened:

Attempt 1: Rotary Tool

I first tried using a rotary tool (like a Dremel) with a fine drill bit. The problem is that rotary tools spin at extremely high RPMs. The friction generated so much heat that the drill bit literally melted. I lost the tip entirely.

Attempt 2: Regular Drill Bit

Next, I tried a standard drill bit at a lower speed. This one did not melt, but the vibration and pressure snapped the drill bit clean in half. And worse — the stress from the drilling actually extended the crack. The crack grew longer right before my eyes.

My advice: Do not drill a hole in your windshield. Unless you have professional glass-working equipment and experience, the risk of making the crack worse far outweighs the potential benefit. I made the crack noticeably longer by trying this, which is exactly the opposite of what I wanted.

Applying the Repair Resin

After the drilling disaster, I moved on to applying the resin directly to the crack. Here is the process:

Cut the applicator tip — Use a razor blade to cut the tip of the resin tube at an angle for better control
Work in the shade — This is critical. The resin is UV-curing, meaning sunlight will harden it within minutes. You need working time to apply it evenly along the entire crack
Apply slowly and steadily — Run the applicator tip along the crack, squeezing gently to let the resin flow into the crack via capillary action
Do not rush — According to the instructions, you should move slowly to give the resin time to seep into the crack. I moved too fast and probably did not get full penetration

The resin is a thin, clear liquid that works by filling the air gap in the crack. Once cured by UV light, it hardens to a similar refractive index as the glass, making the crack less visible (though rarely invisible).

Lessons Learned in Part 1

This first experiment taught me several important lessons:

Skip the drilling — It made my crack significantly longer and did not help at all
Determine inside vs. outside first — This determines your entire repair strategy
Work slowly — The instructions are right about moving at a measured pace
Shade is essential — Find covered parking or work early in the morning before direct sunlight hits your windshield

The crack was not fully repaired after this first session, and I was not completely sure whether the resin penetrated the crack properly. So I continued the experiment in Part 2, where I applied resin to both the inside and outside of the windshield and moved the car into sunlight for UV curing.

Is DIY Windshield Crack Repair Worth It?

For a $10 to $13 investment, it is absolutely worth trying before paying for a full windshield replacement. Even if the repair is not perfect, it can slow or stop the crack from spreading, which buys you time. Just avoid the mistakes I made — especially the drilling — and you will have a much better first attempt than I did.

If the crack later caused other issues (like my rearview mirror falling off), you can address those problems separately with inexpensive repair solutions as well.