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Old 21-08-2015, 12:46   #16
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Re: Lewmar Hatch Crazed Finish Repair

If your gonna try polishing, get the Micromesh kit, but if it's crazing, that is internal, it amounts to stress cracks in the plastic.
But yes, many chemicals will apparently accelerate crazing, one of them being Ammonia contained in window cleaners, for this reason you'll find aircraft window cleaner is ammonia free. Best thing to clean plastic windows aircraft or not is plastic polish, this after flushing the window with clean / clear water and your bare hand to remove anything that could scratch the window when you polish it, like sand or salt crystals.
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Old 21-08-2015, 12:50   #17
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Lewmar Hatch Crazed Finish Repair

Digression - cesium oxide will dissolve the skin on your fingers! We used cerium oxide, optical quality, for final polish of telescope mirrors just before putting the reflective layer on them. Fast cutting and, correctly prepared, very uniform particle size so as not to add new scratches. Iron III oxide is used for polishing silverware so it ought to be hard enough for plastic and probably cheaper. Just change clothes to something old before. The stains from it never go away! Remember - optical quality preparation.


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Old 21-08-2015, 12:50   #18
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Re: Lewmar Hatch Crazed Finish Repair

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Originally Posted by Charlie View Post
How about some before and after photos Ken.
Will do.... Good idea
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Old 21-08-2015, 13:18   #19
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Re: Lewmar Hatch Crazed Finish Repair

Untreated acrylic gets a milky surface in under five years, particularly in a sunny climate. Untreatd polycarbonate even faster. I don't know if acrylic is available with a UV-protection layer but polycarbonate definitely is. They use it for windows for earthmovers. That surface is also much more scratch resistant, almost like gorilla glass. I got the advice however to sand away the protective layer where it will meet sealants. Otherwise not even sikaflex 291 will stick to it. The added cost for the UV-treated quality is quickly regained in longer service-/replacement intervals.


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Old 21-08-2015, 13:22   #20
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Re: Lewmar Hatch Crazed Finish Repair

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Originally Posted by a64pilot View Post
If your gonna try polishing, get the Micromesh kit, but if it's crazing, that is internal, it amounts to stress cracks in the plastic.
But yes, many chemicals will apparently accelerate crazing, one of them being Ammonia contained in window cleaners, for this reason you'll find aircraft window cleaner is ammonia free. Best thing to clean plastic windows aircraft or not is plastic polish, this after flushing the window with clean / clear water and your bare hand to remove anything that could scratch the window when you polish it, like sand or salt crystals.
This is a common misconeception as the "cracks" look deep. Its an optical illusion, the cracks/crazing is usually on a few thou deep. Sanding and polishing will bring it back.

The only worry is that you remove too much material that the hardware no longer fits correctly. However, there are tolerances built into the hardware so you can remove quite a bit before that point.
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Old 21-08-2015, 14:40   #21
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Re: Lewmar Hatch Crazed Finish Repair

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I'm going to try polishing one of them just like when I did the hull a couple of months ago. Sand paper then polishing compound, and see how it turns out. How can I harm them? They're already dead... Kinda like doing CPR on a dead guy... Really, I can't hurt them.
Just a couple thoughts:
-Be careful you don't start with too aggressive a grit or you may be causing yourself a lot of work.
-Plastic fills normal paper very quickly, I would try specific use media. for plastic
-Be VERY careful you don't get into the frame anodizing with sanding or you will damage it's anti corrosive qualities. Right now you have good frames.
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Old 21-08-2015, 14:52   #22
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Re: Lewmar Hatch Crazed Finish Repair

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Just a couple thoughts:
-Be careful you don't start with too aggressive a grit or you may be causing yourself a lot of work.
-Plastic fills normal paper very quickly, I would try specific use media. for plastic
-Be VERY careful you don't get into the frame anodizing with sanding or you will damage it's anti corrosive qualities. Right now you have good frames.
- This is one common problem when people try. They start with a grit that is NOT course enough (like 300 or 600). You must get to the bottom of the crazing cracks for it to be sucessful. Its better to start with 220 and take it slow, using your eyes to verify when you are there.

- Wet sanding takes care of the plugging problem.

- I have those exact hatches and the acrylic can be completely removed from the frame and hardware. I would recommend doing this before you start sanding.

Finally... If you have access to micro-mesh discs you can get a little better result. Its not really required, but you will need to spend more time with the polishing compound.
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Old 21-08-2015, 15:09   #23
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Re: Lewmar Hatch Crazed Finish Repair

I dunno. While I don't dispute that they can be not vey deep, mine were on the range of .080" to .100" deep. Far more then I would ever want to try to polish out, but like Ken says can't hurt to try.

I am curious though, if you went through the trouble to dismount the lenses from the frames, why wouldn't you just replace them with new? Mine were thirty years old and I expect the new ones to last at least as long.

Here's another thought, when I was messing around with my hatches I put some acrylic solvent glue (methylene chloride) on a spot to see what would happen. It didn't make them disappear completely but it certainly minimalized their appearance, just not enough to make me not want to replace them.
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Old 21-08-2015, 15:53   #24
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Re: Lewmar Hatch Crazed Finish Repair

I have just replaced the lens in a Lewmar ocean 70 hatch.
Just cut around the lens with a razor knife and carefully lever out the lens.
The time consuming part is cleaning of the silicone from the hatch. Use a sharp plastic blade or wood and scrape and use a 3m scrubbing pad. it took me about 4 hours. There is no solvent that works. I then layed down 3/4" x 1/8" buytl tape on the inside of the hatch. Tape the outside top of the hatch and the replacement CAST ACRYLIC lens. Place the lens on a raised base and lift the hatch up to the lens. Easier to center the lens in the hatch. Press down the lens into the tape to get a good bond. Use black Dow Corning 795 sealant to fill in the gap. Run your finger around to get a smooth finish, then remove the tape from the hatch and the lens. Let it sit for a couple of days.
Cost
Tape $12
DC 795 $8
Cast Acrylic from American Plastics $130
Cutting to shape $140
My time $?

Select Plastics quote about $400 plus shipping each way.
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Old 21-08-2015, 16:10   #25
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Re: Lewmar Hatch Crazed Finish Repair

What about those kits in auto supply to refinish headlights ?

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Old 21-08-2015, 16:11   #26
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Re: Lewmar Hatch Crazed Finish Repair

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What about those kits in auto supply to refinish headlights ?

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They only work on very light crazing, more like hazing! For deep crazing they do nothing..
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Old 21-08-2015, 16:19   #27
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Re: Lewmar Hatch Crazed Finish Repair

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There is no solvent that works .
You might try a product called "Marine Debonder". It debonds silicone and 3M 5200. I have used it and works great. I have also loaned it to people on the dock, everyone that has tried it ordered their own can. In the case of 5200 it takes roughly 15-30 minutes to work.

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Old 21-08-2015, 18:35   #28
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Re: Lewmar Hatch Crazed Finish Repair

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I dunno. While I don't dispute that they can be not vey deep, mine were on the range of .080" to .100" deep. Far more then I would ever want to try to polish out, but like Ken says can't hurt to try.
At .80 to .100 deep that acrylic is structurally compromised and that solvent cement could make it worse. Time for new.

Getting cast acrylic and cutting it to size is not that big a deal with some basic shop tools. A table saw with a good blade works great.

I have used these guys for acrylic in the past. Good pricing and reasonable shipping. They sell only cast.

https://www.estreetplastics.com/Sear...lts.asp?Cat=80
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Old 23-08-2015, 09:27   #29
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Re: Lewmar Hatch Crazed Finish Repair

How has this shaken out Ken?
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Old 23-08-2015, 09:36   #30
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Re: Lewmar Hatch Crazed Finish Repair

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How has this shaken out Ken?
I haven't done anything yet. Waiting for Oyster to get back with the hatch replacement quotes, which will probably motivate me to start. I'll do at least one hatch prior to the end of my season, just to know where I stand for next season.

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