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Old 03-05-2013, 04:07 PM   #1
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Small cracks in Rock Guards

Just noticed that we have several small cracks on the rock guard on the curb side front wrap around window. The cracks are not visible from the outside but we just noticed them today when opening the inside window drape. We do not believe the cracks were caused by rocks because they are too numerous and we have Rock Tamers on our tow vehicle. They are on the lower side of the window that faces the afternoon sun (we have been in Florida nearly four weeks).

Has anyone experienced cracking caused by sun exposure? Except when on the road our Airstream has always been garaged.
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Old 03-05-2013, 04:17 PM   #2
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I believe the rock guards are made from vacuum formed acrylic sheet. Most of the stress is relieved by the heat during forming but some residual is still there. Acrylic can craze when exposed to some chemicals when it is under internal or external stress. The craze will be more apparent when looking outward. The craze cracks will be perpendicular to the direction of the stress. There is nothing you can do about them but if the break all the way through the plastic, the progression of the crack can be stopped by drilling a small hole at the end of where the crack is progressing.
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Old 03-05-2013, 04:25 PM   #3
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Question Cracks or crazing?

Give this a read see if it applies.....I have seen it on AS rock guards.

Bob
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Old 03-05-2013, 04:58 PM   #4
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Originally Posted by ROBERT CROSS View Post
Give this a read see if it applies.....I have seen it on AS rock guards.

Bob
There are so many small cracks that appear to be caused more by the sun than any stress. Most of the cracks are less than a quarter of inch and are widely scattered. There are only two larger cracks a little more than one inch long and more than two dozen 1/8" or less widely scattered in a one square foot area. I may call the factory tomorrow to see if anyone has heard about cracks caused by the afternoon sun--it's really weird.
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Old 03-05-2013, 05:49 PM   #5
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We also are in Fla. I noticed a crack on the curved stone guard. It's about 3" long and vertical. I when I get home I was planning to drill a small hole at each end and try some nylon mesh and epoxy in an effort to stabilize it. With the smoked finish I think it will be barely visible. Open to any other suggestions along the way.

Thanks all.
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Old 03-11-2013, 07:43 AM   #6
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When there are many small cracks that do not go through the total thickness of the plastic that is called "crazing" You can not do much about crazing. As stated before, It is usually caused by chemical exposure to stressed acrylic plastic. The chemicals could be anything from bug spray to some polishes or cleaners. Once you have it, there is no fix. If the cracks extend all the way through the plastic, drilling the holes will stop it from getting worse.
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Old 03-11-2013, 08:21 AM   #7
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We noticed this on our '05 last year, lots of tiny cracks/crazing on both sides of the curved stone guards.

Our trailer is stored inside, so I don't think it has excess UV exposure, but then again, we did have to replace the front skylight that was cracked and leaking this past year.

I used a Rain X spray on wax a couple times, it could be that. Also use formula 303 on the seals.
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Old 03-12-2013, 01:08 AM   #8
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Originally Posted by redeagle313 View Post
We noticed this on our '05 last year, lots of tiny cracks/crazing on both sides of the curved stone guards.

Our trailer is stored inside, so I don't think it has excess UV exposure, but then again, we did have to replace the front skylight that was cracked and leaking this past year.

I used a Rain X spray on wax a couple times, it could be that. Also use formula 303 on the seals.
Your experience sounds very similar to ours. I did clean the windows with Rain X before we left on our trip so that could have been the culprit. We had three days of heavy rain in Florida and we had a small leak in our front skylight. After researching this on the Forum I learned that this is a common problem on OEM skylights and plan to replace both of our skylights when we get home with Maxim skylights recommended as superior by several Forum members, Thanks for your feedback!
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Old 03-12-2013, 02:36 AM   #9
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I use this on the acrylic hatches on our boat. Plexus
It seems to have staved off the usual crazing that happens to all boat hatches eventually for 8 years now and the lenses still look very good!

I began using it on the curved stone guards as soon as our Airstream was home. not only does it protect but it cleans and makes them look new....
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Old 03-12-2013, 04:30 AM   #10
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Rainex is a silicone dispersed in a solvent. Both of these components are likely to cause crazing in an acrylic or polycarbonate stressed plastic. Rainex is great for glass windshields and I use it all the time for that, but I would never put it on any plastic parts.
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Old 03-12-2013, 09:46 PM   #11
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After you stop drill the cracks you can carefully infuse an acrylic glue like Crazy Glue to help strengthen the plexi.
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Old 03-12-2013, 11:22 PM   #12
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Dan and Liz's technique has worked for us for years ... standard fix.
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Old 03-12-2013, 11:39 PM   #13
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One thing to remember about acrylic (or plexiglass) is that it will craze and crack when exposed to alcohol. A typical source of alcohol exposure is window cleaner such as Windex.

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Old 03-12-2013, 11:57 PM   #14
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Plexiglass reacts to Acetone. I removed the curved stone guards on our Excella, put them inside up on a table and applied acetone to the cracks using a syringe with a very fine needle along the cracks. There was also inside damage due to hits on the outside of the guards. Applying acetone seems to have stopped the spreading of that damage.

If you know someone who is diabetic, the disposable syringes they use are perfect for applying acetone for many plastic repairs. The syringes are also plastic, however they do not react to the acetone.

Care must be taken not to smear the wet acetone away from the cracks. If you do damage the inside of the guard in this manner, it may be polished out with tooth paste after all is dry and hard.

This trick was passed on to me by a tech at Vintage Air, a company that makes aftermarket A/C systems for Street Rods and other cars. Their plastic Heat and A/C cases are bonded together using acetone.
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