Loc-tite vs Plexiglass

I need to use Loc-tite (or equal) on the screws that hold my rear window to the roll bar . I've read dire warnings on these pages about the problems associated with Loctite contacting Plexiglass. Some said basically "no way, no how" can you let Loctite contact Plexi. Well, I took a piece of scrap Plexi (heaven knows, there's enough of THAT lying around) and put on a blob of real Loctite and pseudo Loctite (cheapo stuff called "thread locker") ...and let it set on there for 1/2 hour. When I wiped it off, there was no evidence whatsoever ... no mark, no crazing, no stain ... nothing. Can anyone tell me why the warnings I've seen several times in the past? Anyone have another "'speriment" to counter my simple test?

At my former job I designed a heat exchanger with a Lexan (polycarbonate) piece bolted on. It had studs going through holes in the Lexan plate and nuts to hold it down. The mechanic who built it applied RTV to seal it off, but he had a few small leaks through the studs, so he simply reached for Loctite and wicked some in there. I didn't get to see it, but he claims within a minute, spiderweb cracks formed throughout the plate. I was amazed when I saw the cracks and that Loctite did it. Afterward, we read the bottle and it warned against use with polycarbonate and acrylic (Plexi)

I wonder if you were to apply the Loctite to a hole drilled in your test piece if you would see anything interesting. I also wonder if there is a big difference between how it would react with Lexan vs. Plexi.

Just my experience...

locktite

I used Locktite to do exactly what you are thinking of doing. Seemed like a good idea at the time.......It took 3 months but just about every screw hole in the roll bar starred and cracked. ( My 7a was in my garage the whole time) Van's said it was the Loctite. Had to get a new rear plexi section ( $450.00) plus freight. Never did fit as well as the first one. Yes, I had oversize drilled the holes, deburred etc. I have kept the baggage plexi as a reminder.

Rupester said:

I need to use Loc-tite (or equal) on the screws that hold my rear window to the roll bar . I've read dire warnings on these pages about the problems associated with Loctite contacting Plexiglass. Some said basically "no way, no how" can you let Loctite contact Plexi. Well, I took a piece of scrap Plexi (heaven knows, there's enough of THAT lying around) and put on a blob of real Loctite and pseudo Loctite (cheapo stuff called "thread locker") ...and let it set on there for 1/2 hour. When I wiped it off, there was no evidence whatsoever ... no mark, no crazing, no stain ... nothing. Can anyone tell me why the warnings I've seen several times in the past? Anyone have another "'speriment" to counter my simple test?

Click to expand...

Put the Loctite on a Plexiglass edge, and then inspect it under a microscope. Inevitably, you'll see microscopic cracking that may not be viewable with the naked eye. And those microscopic cracks will grow over time by "work of fracture" to become cracks that YOU REALLY WILL SEE.

I used Vibratite on all the threaded fasteners in my canopy... it's been sitting in the guest bedroom for a couple nears now (sigh) and no cracks.

I bought a bottle at the local Grainger outlet, but here's another place I found that will sell it to you: http://www.bigdboltandtool.com/vibratite.html

And an interesting article: http://www.adhesivesmag.com/CDA/Articles/Feature_Article/e7b0d50543a6d010VgnVCM100000f932a8c0____

For what it's worth, I believe this is the same stuff a certain large avionics company uses on the screws they use to assemble those fancy boxes...

good luck,
mcb

In the motorcycle world there are numerous warnings given about using loc-tite on windshield attachment fasteners. The screws on my beemer come with a small amount of loc-tite already applied to the threads so you don't have to use the liquid. If you do use the liquid it will seep onto the plastic and crack. Don't ask me how I know.

Bill:
What you see on the screws of your Beemer is not very likely Locktite. There are many fastener applications in industry where a nylon locking element is desirable, both on nuts and male fasteners. This nylon "patch" is applied to the fastener by induction heating the metal, then spraying the nylon onto a small area. Control of the spray allows the production of locking fasteners with very precise torque/tension and prevailing torque performance. Typically, fastener producers turn to companies such as "Nylok" to provide this service. Their production output is in the millions per month.
Terry

Ya'll are convincing ...

Thanks much for the responses. You've convinced me.
I may still try a drop of Loctite in a drilled hole and look under heavy magnification, just to see what it does.

Locktite on Plexi

I also found that Locktite does not get along well with plexiglass and I wanted a thread locker that I knew was compatible since my canopy is screwed down to the frame. Good ole Proseal worked fine. I dipped each screw into Proseal left over from tank construction prior to torquing down in tapped holes. We are at 300 hours and 5 years with no cracks so far and screws remain tite. Also used Proseal to bed the plexi windscreen and canopy into all the fairings to seal out water. Use isopropyl alcohol to safely clean the surplus off the plexi. It does not craze like MEK or lacquer thinner will but it does clean it off with a little effort.

Dick DeCramer
RV6 N500DD flying
RV8 fuselage
Northfield, MN