What are these spots on my windshield?

[Tommy]

Tiny specks on the windshield visible only when sun is shining at a particular angle.

What are they? 

Cheers

Tom 

[Guest]

They are the beginning of windshield replacement, called Crazing.

Clarence

[Tommy]

How bad do they need to be before needing replacement (ie. How much time do I have, Doc)? Is this a normal aging process of a plexiglass? And is there any way of slowing the process down or even repair it?

 

Thanks Clarence 

Edited November 1, 2017 by Tommy

[rbridges]

I don't think you're windshield is suddenly going to explode, but it will probably start being an esthetic/visibility issue.

[TTaylor]

No way to slow it down except to minimize the windshield exposure to sunlight.  Keep the plane in a hangar or with a good cover over the windshield when possible.  Time to start saving for a nice Solar Gray (Grey depending on your country) windshield.   The Oz sun is very harmful on plastic. 

[bradp]

When it becomes difficult to see other aircraft or land at a well lit airport at night it's time to throw in the towel.

You can use micromesh to take off some of the oxidized material as a stop gap in the mean time - see if you can get a bit more out of it.  Micro mesh is a very specific process.  If you want to DIY the kits are probably worth it. If you want your A&P to go at it, at some point you should just put your funds into a new wind shield.

Don't know how this works for Oz, but chief aircraft gives wholesale pricing for LP aero and mine did not need any additional trimming.  Of all the windows I replaced two side windows needed trimming.

One of the gotcha's with windshield replacement is that the retaining strip for the modern mooneys can be corroded if the sealant has become brittle and allowed water in.  Another is that you may find little flecks of old sealant that drop down from who knows where for about a year after a new windshield goes in.

[Guest]

9 hours ago, Tommy said:

How bad do they need to be before needing replacement (ie. How much time do I have, Doc)? Is this a normal aging process of a plexiglass? And is there any way of slowing the process down or even repair it?

 

Thanks Clarence 

It's not fatal.  As others have pointed out it comes down to visibility and aesthetics, when you or your AME can't stand it, it's time.

Clarence

[Andy95W]

3 hours ago, M20Doc said:

It's not fatal.  As others have pointed out it comes down to visibility and aesthetics, when you or your AME can't stand it, it's time.

Clarence

Yup.

+1.

[carusoam]

You can see it’s progression....

Every time you fly into the sun.  If you can't see through the windshield, it’s time.. 

you can use some plastic treatments, like lemon pledge... that puts an oily material on the surface... solves the first problem of crazing and light diffraction, but causes other challenge like a dirty looking window...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Bob_Belville]

I found Great Lakes Aero Products very good to work with. FWIW, I debated going 1/4" on the windshield but am happy I settled on 3/16" solar grey all around. Not a terrible project but be sure to thoroughly clean old sealant and use the proper 2 part products for the install. If you do the side windows you might want to opt for a vent window pre installed in the door. Nice for cross ventilation.   

http://www.glapinc.com/

[glenn reynolds]

I take this crazing much more seriously than I used to.  My prior plane had a pair of sunroof windows, which always saw the sun, didn't get hangered or covered by the windshield cover.  I was flying along when my kids asked about the crazing and I said "we will probably need to replace these soon"  and I gave one of the skylights a tap to emphasize my point.  Bad idea.  At this point I should interject that the plane was current for it's annual inspection, my mechanic simply said I could change the windows when it bothered me.  So there is this fairly loud bang and we are flying at 5,000 feet with a missing skylight!  The kids were pretty scared, so I put on my best dr science voice and explained how the bernoulli effect which was the same effect that made our wings work was currently making the sucking sound in the cabin, and look, how cool, it would suck trail mix right out of mid cabin and and out the missing skylight!!  very cool effect, kids calmed down and my heart returned to my chest and I focused on entering a busy pattern, spotting planes on two concurrent downwind legs, getting in sequence and landing.  Oh so good.  I turn around to see how the kids are doing and learned that we had "venturi'd" the foam ear plugs, they had shredded my charts "they were out of date daddy", The trail mix and popcorn all gone as were the tissue, windshield wipes and heavens knows what else.  You can be assured we flew home with 120 knot tape.  But there is no doubt that crazing weakens the plastic and frankly I wouldn't want to be sitting behind weak plastic.  just a thought. Besides it's hard enough to make a landing into a setting sun on a west facing runway, buy a new windshield.  

[Hector]

Crazing which is essentially micro cracking of the acrylic. The vast majority is on the surface typically most of it no more that .010 inch deep. UV exposure and certain chemicals can accelerate the process. Micromesh kit can be used to remove damage but if you don’t know what you are doing you will end up with optical distortion caused by abrupt change in thickness. Not sure it is even worth attempting on our windscreen. Better off plan to get it replaced when it becomes annoying. No real safety issue here.


Sent from my iPad using Tapatalk

[carusoam]

Acrylic cracks will propagate... tap, tap, whoosh! (Great explanation, Glenn!)

Similar to a glass automotive windshield... automotive glass is two layers with a plastic film in between.  Helps to hold the glass in place after a crack has extended across the whole way...

Best regards,

-a-

[Sean S]

5 hours ago, Bob_Belville said:

I found Great Lakes Aero Products very good to work with. FWIW, I debated going 1/4" on the windshield but am happy I settled on 3/16" solar grey all around. Not a terrible project but be sure to thoroughly clean old sealant and use the proper 2 part products for the install. If you do the side windows you might want to opt for a vent window pre installed in the door. Nice for cross ventilation.   

http://www.glapinc.com/

GLAP is definitely a good product! I would stay with the factory thickness. Going to a thicker glass adds labor time to modify the clips and hardware. Personal experience. Plus, I added the 1/4 glass to my F and did not notice a reduction in cabin noise.

[m20j]

Also -- solvents!  Both acrylic and polycarbonate windows are each very susceptible to crazing and damage from certain solvents, in particular where there are stress points from installation or the original forming process.  Perhaps even more so than UV.

The safest cleaner to use is an acrylic safe polish or cleaner.  I've never understood the variety of stuff people use instead of buying the right product for the application.  It's not even that much more expensive.

Having been in the manufacturing industry with these materials, I have seen variations on the video below inadvertently demonstrated too many times, with either crazing or cracking as the end result.

 

 

There are many sources of compatibility charts.

http://www.holophane.com/hlp_library/brochures/HL-2445.pdf

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwjrwpS1nKDXAhVE34MKHQ1YBxQQFghIMAU&url=https%3A%2F%2Fwww.allplastics.com.au%2Fcomponent%2Fdocman%2Fdoc_download%2F173-allplastics-perspex-chemical-resistance-pdf%3FItemid%3D&usg=AOvVaw2li7k6D2MN0UzRlPeCwCz9

And data from our window manufacturers:

http://www.lpaero.com/careins.html

Why risk some untested product on our expensive windows?  And if you can't find a local source for Aircraft window cleaners, motorcycles and boats also have the same acrylic.

 

 

Edited November 2, 2017 by m20j

[jetdriven]

I see people all the time recommending Home Depot products to clean the windshield and a lot of them contain alcohol and ammonia. This stuff is terible for Plexiglass.  Having changed out a windshield it's not fun.  It's a whole days labor or more and the part itself is 500$. Ours was 747$ shipped.  Plus touhave to drill the 50 rivets out to get the retainer strip off and I have seen very few that went back together with -4 Cherry max rivets in standard size, and fewer that laid flat when re-installed. I've seen rivets in figure-8 holes, bashed and warped retainer strips with rivet set marks and lifted edges all over, dome rivets, and even truss head philips screws. Anyway let's just say it's likely to look like crap when it's redone, better to not force the job to be done. Use proper plexiglass cleaner. 

[Stephen]

Had right rear PA-28 window (admittedly much thinner) go "kaboom" .....gone .

Windshield much more robust....but I would recommend replacing it. 

[ArtVandelay]

Mine is the same way, and it’s the thicker version that was replaced back in 94, which means I have cherry rivits which are apparently hard to remove.  It’s going to have to get a lot worse before I change it out.