Do NOT use strong stuff on acrylic (Plexiglass)

[Jim Willis]

Acrylic (plexiglass, perspex) is very clear (more transparent than glass) can be heat0mould inot complex shapes like aircraft canopies, but it is HARD and BRITTLE. It is very like metal in that it can form little stress-rise surface cracks when stressed by multiple heat and cold cycles (=expansion and contraction). ALthough plate plexiglass is not stressed, such older acrylic or acrylica that has been heat formed and not annealed will eventuall form little "stars" or crazing.This can be accentuated by any strong, undiluted solvent or cleaner. This includes Xylene, paint thinner etc even IG cleaners (that are gentle) can do this if left on the surface.If you have acrylic portlights, expecially older ones, NEVER use anything stronger than soap and water (or copioulsy water-diluted pink). Even be careful with polishes if they have any amount of solvent in them (particlularly metal polishes).IG's Celar horizons will cause no harm and will protect. Meguires plexiglass polish is also OK but be careful.Clear vinyl (isenglass) and lexan (softer, bendy, never goes brittle) are dufferent and age by going yellow on the surface , THis can be removed by abrasive polishes OR by IG cleaners.KNOW your plastic. If in doubt, contact us or the boat maker.ThanksJim W

 

[Mark]

Thanks Jim

For a great article.The Plexiglass sliding hatch on our Hunter has a lot of very very fine scratches on it from when it slides under the fixed hatch.I have tried car polish and a few other things but have resigned to the fact (I think) that nothing can be done.Any ideas Jim?

 

[Jim Rushing]

Plexiglass

Plexiglass can be buffed out to remove surface scratches. However, Lexan is another matter. I made the mistake of using some excess Lexan for some of the side windows on a airplane that I restored. Just the normal cleaning has left small scratches and there is nothing that can be done except replace them. Also Lexan will craze if under stress of any kind. My biggest Plexoglass problem is after eight years I am getting star bursts in the companion way cover.

 

[Jim Willis]

How to tell plexigalss from lexan.

Jim= you can polish our scratches in acrylic (plexiglass. but of course if they are deep, then you have to remove a lot of surface- best to leave sleeping dogs lie? An alternative is to try filling in the scratches. I am looking into this possibility on my own boat where my hatch also has some scratches.I really LIKE lexan becuase it is so soft and non-brittle. THis does not get "craze marks" and it is soft enough to shape and polish. It oxidizes on the surface though (unlike acrylic) forming a yellowish coating that be be posished off or removed by IG cleaners (I like sea glow because of the extra UV protection.How can you tell lexan (polycarbonate) from acrylic (plexiglass, perspex). Tap a piece of lexan and it tends to make a "thud" rather than sharp click of acrylic and it will bend easily. A thin pieceof lexan can be bent almost double and back with out fatigue. Older lexan often is slighly yellowed but this is mainly on the surface (see above).Acrylic is very clear (even more light transparent that glass) and is hard. If you you have a piece that is (about quarter inch thick) it is very hard, does not bend and can shatter if hit by a hammer (not a good idea for testing?). When you tap it with a metal tool, you it has the "click" sound of something hard. Plexiglass CAN be bent when it is heated, but unless properly annealed it is internally stressed and will start to craze at the bending point by hot/cold cycles or BY SOLVENTS (stay away from strong cleaners- just use soapy water). If not bent you and still quite new (picture covers etc) you can remeove tape residue and paint overspray with IG lceaner (pink is the gentlest, but NOT xylene etc. I have not tried WD40 which can be used to take off tape residue of other surfaces and has a kerosene-type base.Plexiglass will always end up with little "stars" or stress cracks around fittings if not protected from heat and sunlight.Personally I would replace all of my plexi with thicker lexan. On my pilot house Gulf 32 the quarter inch plex windows would never keep out green water so I covered them with half inch lexan storm windows (should stop a .22 bullett!).Hope these experiences are are some use. Incidentlly polycarbonate (seemingly a harder grade than on my windows) is used to make ultracentrifuge tubes that do not break at 100,000 rpM.ThanksJim W