Polycarbonate heat induced print through.

[Franziska]

Hi,


we have a number of large Polycarbonate windows.


Unfortunately they are not 100% clear anymore.
They are not scratched, the previous owner tells me that it's actual printhrough from some sunshade cloth he had over the windows when in very very hot summer weather in Mexico.


Is there anything we can try to fix this, apart from one day replacing them?


Anyone had similar issues with Polycarbonate?


Don't start a Plexi vs Polycarbonate discussion please.


It is what it is and in general I'm very happy that they are Polycarbonate.


Thanks for your help!

[jordanbettis]

If you're sure the damage is on the surface you could polish it off. This would be a big job especially if you try to do it on the boat. Polycarbonate will also fog up over time due to UV. The only solution to that is replacement.

[User 09]

No sadly. If its the print through pattern you are referring to, it cant be fixed. Technically, it can be, but the amount of effort and work would be well in excess (time/labor/materials/sanity) of what it would cost to just replace them.

If you have a random orbital sander with a velcro pad, you could get some polyester felt. Cut a disc of the felt a bit larger than the pad, stick it on and get yourself some Novus #2 polish. Apply a thin coating to a section of the polycard and buff off with the felt/sander. Its really the only reasonably easy/inexpensive way of trying to get a little clarity back into the polycarb if its even possible. It wont do anything for the surface texture though.

Side note: The Novus and felt are a great way to keep polycarb and plexi clear and prevent the cloudy/hazy appearance they get from being in the sun if done polished regularly. If you/anyone decides to do this with the Novus, its critical to carefully clean the surface first with soap and water to get any surface dust and grime off first, otherwise you can end up buffing the plexi or polycarb with what turns into a sanding pad.

[FuneSF]

Some of my polycarbonate dodger windows started to look like that this year. They're seven years old. Once they craze and film like that, they're shot.

I'm going to replace them this winter. I'm going to attempt it myself. It's cheaper to buy an industrial sewing machine than what the canvas shops are charging.

[Franziska]

Thanks. No crazing, no substantial haze either. After 14(!) years, but, the print through is clearly there.
Interesting, those panels who had & have no sunscreens are fine.


In my other boat we have some Polycarbonate windows as well. Also at least 12years old.
They are not crazed either, but slightly scratched and hazed.


The previous owner and ourselves don't polish the Polycarbonate, so that the surface protection does not suffer.
We just rinse it occasionally down.


So, I think unfortunately we need live with the print through for now.

[Iron E]

Here's the deal. That pattern might not be in the polycarbonate, but in the U/V protective coating (Used for windows) on the sheet.
You can most likely polish this out (Novus 3 system), but it may leave the window with no U/V or scratch resistant protection and may limit its useful life.

There are some vinyl overlaminates I've used that are optically clear which might be a yearly or every other year solution if you polish the coating off and need protection.

[Franziska]

Originally Posted by Iron E

Here's the deal. That pattern might not be in the polycarbonate, but in the U/V protective coating (Used for windows) on the sheet.
You can most likely polish this out (Novus 3 system), but it may leave the window with no U/V or scratch resistant protection and may limit its useful life.

There are some vinyl overlaminates I've used that are optically clear which might be a yearly or every other year solution if you polish the coating off and need protection.

That's interesting. Thanks.


I also heard one could spray paint clear two component polyurethane laquer on to reaply UV protection.


Not sure if that's true.

[Iron E]

Originally Posted by Franziska

That's interesting. Thanks.


I also heard one could spray paint clear two component polyurethane laquer on to reaply UV protection.


Not sure if that's true.

You probably can but I don't think it would be optically clear.

I would opt for optically clear vinyl with U/V protection - apply wet - squeegie out liquid. It's not very difficult

Tip - The key is "Optically Clear Vinyl" NOT "Clear Vinyl"
One you can see through (like a window) the film.
The other you can see what's underneath (Like a badge or decal) the film.

[s/v Jedi]

Ignore all comments about polishing, painting and adding films. The windows are end of life and must be replaced; everything else will fail.

I wish it wouldn’t but I tried it all.

[Franziska]

Originally Posted by s/v Jedi

Ignore all comments about polishing, painting and adding films. The windows are end of life and must be replaced; everything else will fail.

I wish it wouldn’t but I tried it all.

Thanks.


I can see through them fine except for the imprint.


Yes, the imprint is annoying and I think I need to live with it for now, but why would you consider them end of life?


No crazing and no significant haze or yellowing either.

[s/v Jedi]

Originally Posted by Franziska

Thanks.

I can see through them fine except for the imprint.

Yes, the imprint is annoying and I think I need to live with it for now, but why would you consider them end of life?

No crazing and no significant haze or yellowing either.

If you can live with the imprint then I recommend using a UV protective coating for cars, which is what we did for years.

It is end of life because the UV protective coating of the polycarbonate has deteriorated and is now ineffective. The imprint is that coating damaged by the canvas because it has become fragile.

At some point we gave that up because next thing is the haze. We then did wet sanding and polishing to bring it back to pure polycarbonate, then try every kind of UV coating that we could think of. All wasted effort; it helps for maybe a couple weeks but not more than slowing it down.

I have been studying this for many years (think 20 years or more) and found the biggest issue is the cut edges of windows when they are installed proud which is often the case. There’s no coating there of course and light that enters here is reflected back into the material by the outer surfaces again and again, deeply damaging it. Such proud edges must be protected, like with black paint or a frame.

And yes, acrylic does last much longer because the material itself is much more UV resistant. Glass is best of course.

[nfbr]

We had the same iimprint. My edges are covered by frame. Wet sanded and polished. Lasted 12mths then hazed. PC is much softer than acrylic. Tuffak AR has a coating. Once its gone they are vulnerable to abrasion. I do disagree with Jedi, I understand acrylic to be more UV suscetoble but less abrasion susceptible.
We ended up replacing with Tuffak AR. Worth it. I used the old ones as templates. Do read the Tuffak adhesives guide, it wont be what you expect. PC is different to Acrylic.

[s/v Jedi]

Originally Posted by nfbr

We had the same iimprint. My edges are covered by frame. Wet sanded and polished. Lasted 12mths then hazed. PC is much softer than acrylic. Tuffak AR has a coating. Once its gone they are vulnerable to abrasion. I do disagree with Jedi, I understand acrylic to be more UV suscetoble but less abrasion susceptible.
We ended up replacing with Tuffak AR. Worth it. I used the old ones as templates. Do read the Tuffak adhesives guide, it wont be what you expect. PC is different to Acrylic.

I hope the knowledge of the whole world is good enough to convince you?

ChatGPT 5 says:

Here’s a forum-ready explanation you can use, clear but with enough depth for boat owners comparing options:

⸻

Polycarbonate vs. Acrylic Windows on Boats – UV Resistance

When choosing glazing for a boat, one of the biggest factors (besides strength and clarity) is how the material handles UV exposure. Both polycarbonate (Lexan, Makrolon, etc.) and acrylic (Plexiglas, Perspex, etc.) are plastics that break down in sunlight, but they do so in different ways:

Acrylic (PMMA)
• UV stability: Acrylic is naturally much more resistant to UV. Standard marine-grade acrylic can last 10–15+ years in direct sun without yellowing or turning brittle.
• Appearance: It stays clear longer and resists that cloudy, amber discoloration.
• Surface: It is harder than polycarbonate, so it resists scratches a bit better.
• Downside: Acrylic is more brittle. A sharp impact (e.g. a winch handle or wave-tossed block) is more likely to crack or shatter it compared to polycarbonate.

Polycarbonate (PC)
• UV stability: Polycarbonate is inherently much less UV-resistant. Unprotected sheets can yellow, haze, and even become brittle in just a couple of years in marine sun.
• Treatments: To compensate, most marine polycarbonate is sold with a UV-resistant hard coating or co-extruded UV-blocking layer. With that treatment, lifespan can be extended to around 5–10 years, but usually still not as long as acrylic.
• Strength: The big advantage is toughness—polycarbonate is extremely impact-resistant, virtually unbreakable under normal boat use. That’s why it’s often chosen for storm panels, dodger windows, or places where a flying block might hit.
• Surface: It scratches more easily, especially uncoated. Hard-coated versions resist scratches better but cost more.

⸻

Bottom Line for Boats
• If you need clarity and UV stability (e.g. fixed windows, hatches, portlights), acrylic is usually the better long-term choice.
• If you need impact resistance and safety (e.g. storm shutters, companionway doors, high-impact areas), polycarbonate with a UV hard coat makes sense, but expect to replace it sooner.
• In practice:
• Acrylic = lasts longer, looks better over time.
• Polycarbonate = tougher, safer against impacts, but degrades faster unless specially coated.

⸻

Would you like me to also add a cost comparison section (price per sheet, coated vs. uncoated) so forum readers get a practical feel for what they’d be paying for each choice?

[sinnerman]

It actually looks "cool". It is what I see without my glasses...

[Shaneesprit]

Of course they are not shot lol.
They are plastic you can sand and polish, until clear.