Portlight Crazing Repair ?

[DennisM]

Does anyone know if it there is a product that will remove the crazing that is just beginning to develop in my portlights? Or is it time to replace the acrylic (at least, I think it's acrylic)?

[Troubadour52993]

I replaced mine, but they were pretty bad. If it's only on the surface, you can sand it down and then power buff the sanding scratches with Novus plastic polish to get it clear again.

[donradcliffe]

Its time for replacement. Make sure that the new portlights never see anything like windex or paint thinner, which will both hasten their eventural crazing.

[DennisM]

Thanks, Troubadour. Unfortunately, it doesn't look like mere surface crazing.

Thanks to you too, Don. Ugggg.

[Troubadour52993]

And make sure you bed them in a commercial glazing caulk like Dow 719. I had to try and remove all the 5200 on a previously repaired leaky portlight. Uggg squared! Don Casey's book has a good chapter in it on replacing portlight acrylic. I've rebedded some and replaced some with (so far, knock knock) good results.

[DennisM]

Thanks again, Troubadour. I have that book. I'll look it up.

[Minggat]

Originally Posted by donradcliffe

Its time for replacement. Make sure that the new portlights never see anything like windex or paint thinner, which will both hasten their eventural crazing.

The word that jumps out at me is EVENTUAL. Here's what I learned right here on CF.

After replacing all my vinatage portlights and adding a couple of hatches with what I got a "great deal" on, I learned EVENTUALLY, (about 4 years with no windex, thinner ect contact, and in spite of covers) is that if I'd had not gotten such a good deal on EXTRUDED acrylic, and had know that CAST acrylic existed, I would not have ever asked the same question you are asking now. Let's not talk about the price of my education.

If you replace them, do yourself a favor and make sure that you get CAST acrylic. People here were showing photos of hatches with decades of use that looked like new.

[DennisM]

Woww, thanks Minggat. I had no idea the two types even existed.

[Rou-Coo]

I have been told that toothpaste is a temporary fix - but I've never tried it myself.

[Minggat]

Originally Posted by DennisM

Woww, thanks Minggat. I had no idea the two types even existed.

You're welcome.

Go here and watch me get my education.

http://www.cruisersforum.com/forums/...ing-24956.html

Warning: My exploding head my be inappropriate for sensitive viewers.

[barnakiel]

The product is called a new glass.

If original part not available, you can cut your own from a sheet of material.

b.

[hellosailor]

Toothpaste--not gels but "white" paste like old Crest--is what used to be called "tooth polish" and the polish is fuller's earth (diatomaceous earth) which is actually mined and sold as a mild abrasive. No miracle or mystery there.

Crazing isn't a surface condition, it refers to cracks that extend into the thickness of the plastic. They're caused by stresses and since they are physical CRACKS in the plastic, there is no way to repair them or polish them out.

Crazing is caused by UV exposure, chemical exposure, and mainly by unrelieved stresses from improper mounting. If you're not going blue water and not worried about spinnaker poles dropping into your hatches...you can ignore crazing for a long time. If you need to rely on the strength of the glazing--it needs to be replaced.

[Minggat]

Originally Posted by hellosailor

Crazing is caused by UV exposure, chemical exposure, and mainly by unrelieved stresses from improper mounting.

The trouble I have with that comment is that opening hatches are mounted in a factory frame, which is then hinged.

I'd leave off the part about improper mounting, or just change the "and mainly" to "or".

[hellosailor]

"The trouble I have with that comment is that opening hatches are mounted in a factory frame, which is then hinged."

First, the hinge is a straw man. Doesn't matter. Only the frame or surround that the glazing has been bolted/screwed/tape/compressed into matters. If that glazing is not free to MOVE, free to expand and contract without restriction, it will craze.

I haven't paid a great deal of attention to tearing down hatches to see who left proper clearance and who didn't, but I'd bet an awful lot of what's out there was "built to a price" like most other free market goods, and "built to a price" often means built wrong for the long run, since the first owner and the warranty will be long gone before the problems hit the next one.

The folks who make the glazing (like GE, Rohm & Haas) all say crazing comes from the same sources, and all claim it can be delayed--or prevented--if the causes are addressed up front. But let's face it, "doing it right" is often not cost effective or even feasible at all. So a 25 year old boat may need new glazing. File under "s*** happens", right? <G>

[Pblais]

I have 8 Atkins and Hoyle ports. All 19 years old. The cast acrylic ports are all crystal clear. The frames are Al Mag and have been rebedded twice since installation. Never use 5200 to bed anything. Metal frames in fibergalss need the abilty to flex a lot. 5200 sucks at flexing and why it will fail in this application every time. Best to check with the manufacturer on glazing. Glazing isn't bedding. Very different coefficent of expansions. The difference in rates of expansion is the key to getting the right caluk.

The only bad thing about cast acrylic is it is really expensive. You won't have to deal with it down the road.
Cast acrylic really is the best choice over anything else. Amazingly strong and very UV friendly.