Loctite testing (was: 1678 Robot Reveal 2022)

As promised, I tested several thread locking products on polycarbonate. Loctite products 243 (blue), 263 (red), 425 (plastic safe) and Vibra-Tite 122 (similar to Loctite 243) were applied to a 10-32 bolt that went thru a hole in the ~center of ~2" x 1.25" x .125" coupon made from Kirex polycarbonate. A washer and nut was then tightened onto that single coupon and remained clamped for at least 2 hours.

Vibra-Tite’s VC-6 is their polycarbonate safe thread locker. The other VC line of lockers did not specifically say they were polycarb safe, but were safe for a variety of listed plastics. Unfortunately, our search for VC-6 found 30ml bottles ranging from ~$92.00 to $128! Decision made to not test this product.

My goal for this test was to try and determine when the polycarb became adversely affected by the Loctite. For example, your bot broke Sunday morning near the end of Qual matches and you’re gonna be playing in Elims. Your team fixes the broken part and uses Loctite to help secure the fastener on the polycarb part. Is that piece safe to use in the next 3 hours? 5 hours? 10? Basically, can you depend on the polycarb not to craze/fracture/break before Finals match 3?

In the original test shown in this thread: https://www.chiefdelphi.com/t/1678-robot-reveal-2022/404113/83 Every coupon I made showed crazing/fracturing after ~6 weeks and when bent to simulate a part bending. e.g. A polycarb collector arm being hit or running into an object. Between this 6 wk test and the test below, I did some other “quick and dirty” testing to get an idea of how much I could reduce the clamp time.

One of the quick/dirty test with Loctite 243 showed a fracture/tear at ~2.5 hours! L 243 at 2.5 hours …The writing is “backwards” because I took the photo to show the tear, not the words.

At 48 hours, a coupon snapped in half while bending. L 243 at 48 hrs

The above two coupons are .062" thick, not the .125" material.

The 2.5 hour test provided some guidance on when I should begin bending the coupons and how frequently.

I made lots of coupons and planned for roughly a 2 hour interval between tests for 6 hours then increasing that interval to 4, 6, 8, 12 hours, etc. I sorta planned it on how long I was willing to stay up after a long day of testing!

All the test and control coupons except those from Loctite 425 were stored in a plastic box with the lid on. My rationale was that if there was any evaporation/outgassing, it may adversely affect the control groups. This was an attempt to replicate thread locking products on a bot and having nearby plastics cross contaminated. I didn’t put L-425 in the box because if there was cross contamination, I didn’t want the plastic safe group affected.

The testing process was as follows: Apply thread locker; tighten the nut down by hand using wrenches; wait the designated time period; remove nut and bolt from the coupon; visualize; photograph; clamp in a vise with the hole at the top of the jaws; bend >45° but <90° by hand; visualize and photograph again. Document observations.

Here’s the test results with notes/observations and links to photos of the coupons. I hope the spreadsheet is self explanatory enough.

Thread locker spreadsheet and notes

Comments and quick summary:

-Every coupon in the control groups, except one, had no crazing, fractures or tears that I could see. One had a small tear. n= approx. 14.

-Most of the test coupons (with thread locker applied) had tears/fractures that were visible after bending. Only two had no apparent damage ( with Loctite 243).

-Vibra-Tite 122 had a lot of crazing at 2 hours. I checked the remaining VT-122 test coupons and they all had significant crazing. I aborted that test and didn’t even bend one in a vise.

-Loctite 263 (red) testing was aborted after about 4.5 hours as crazing became apparent and the polycarb was tearing during the bending.

-Loctite 243 (blue) surprised me. It did not show the obvious crazing and fracturing like my quick and dirty test above at 2.5 and 48 hours. All the test coupons (except two) had tears when bent, but the damage was not as bad as previous testing.

The results were so different from earlier tests that I created another batch of five test coupons for L-243 and ran both groups simultaneously. Results were the same: no crazing seen before the bending. Tearing occured during bending.

Not sure why the two tests are so different. Notable differences are: different polycarb manufacturers and both are of unknown age. Likely different moisture content. Different production batches of Loctite. Different thicknesses of polycarb.

On test coupon #57, two small tears appeared during the bend. I bent it two more times in the same manner and, as expected, the tears increased in size and a new tear appeared at the edge.

I terminated this test plan early (only two more test coupons to go) because it didn’t seem like any new information was being learned. The test coupons were all showing damage and the tears were mostly smaller than with the other products.

-Loctite 425 (plastic safe) was the real shocker. Since this was intended to be a plastic safe product, I planned for my first bend at 24 hours then 48 hours, 72 hours, and then a week plus. At my 24 hour test, I saw a tear on the test coupon. I decided to shorten the 48 hour test to 36 hours. At 36 hours, I saw tiny crazing around the hole and the bend resulted in multiple tears! I checked the remaining L-425 coupons and they all had crazing and tore/fractured when bent. I aborted the test at ~36 hours. Loctite 425 does not appear to be safe for contact with polycarbonate.

L-425 is the only product tested that is a cyanoacrylate based locker. All the others are anaerobics.

Conclusion: The thread lockers tested all damaged the coupons. The control groups, with no thread locker applied, did not show any damage (except one). Do not allow the thread lock compounds tested to come in contact with polycarbonate.

Follow up: Test Vibra-Tite VC-6 and other products in the VC line.

Freebie: I also tested Dykem and a Sharpie marker on some of the thinner polycarb. No damage seen! Photos are in Thread Locker Test folder



I did a one piece test of VCC3 versus loctite 242, using 1/4-in polycarb with press fit nut pockets (and steel nuts) to preload the area under test. The loctite showed obvious cracking in 24hr, the VCC had not failed yet a week+ later. No photos on my phone, will follow up…


That’s annoying that 425 isn’t actually polycarb safe. Did you try just regular cyanoacrylate super glue?

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We’ll save that for another day :slight_smile:
…there are lots of “flavors” of cyano.

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Of note, Loctite says 425 is for use on metal and plastic fasteners. I can’t find a claim from them that it’s safe for use on polycarbonate or any other specific type of plastic.

Most plastic fasteners that I’m aware of are made of nylon.


Contact them. They’ll respond.

We did some much more informal testing on 243 and 425. First, we applied 243 and 425 to the surface of a strip of 1/4” poly, and let it dry for ~24 hours. We bent the sample strip and neither loctite significantly effected the poly. Next we heavily applied both loctites to #8 bolts tightened in a sample of 1/4” polycarb. In this case, the 243 created spiderwebbing, but the 425 didn’t. Based on this, I concluded that neither loctite would harm polycarb after the solvents flashed off, but if you put any stress (including tighting bolts) on the polycarb while the 243 is wet it can fracture easily.

We started this when we had polycarb links on our intake cracked at their mounting bolts using 243. When we switched to 425 we were able to assemble and use the intakes for a while without any cracking. The links do typically crack at the bolts eventually, but we have not tested a loctite free assembly to compare longevity.

TLDR: In our testing loctite 425 can be used with polycarb, but may cause minor weakening.


Thanks Patrick. Did you tighten the 8 bolt into threaded polycarb or into a nut via a thru hole?

My understanding of 243, and the other anaerobics thread lockers, is they remain wet until they’re not in the presence of air (in a nut/bolt thread) and in contact with metal. At that time, the compound hardens.

When I disassembled the nut from the bolt (after clamping for a time period), the 243 was usually still wet between the washer and coupon, but not on the threads where the nut was tightened on the bolt. I wiped off the wet 243 with a paper towel.
Similar results with 263. I don’t recall if 425 stayed wet, but I doubt it since it’s a cyano.

Interestingly, the Vibra-Tite 122 was not wet. It actually appeared to stain(?) the polycarb. See the photos in the folders. The 122 bottle says “Competes with Loctite 243…”

I agree that tightening a bolt would create stress on the plastic. In the control groups, the tightened nut/bolt did not show any crazing or fracturing.

I couldn’t figure out how to link multiple photos with each coupon, but in the folders, for each coupon, there is a before bending and after bending photo. Most of the before bend photos in the 243 folder do not show crazing (spiderwebbing). The crazing and tears happen after a large stress is applied (bending).

Thinking about this, would the damage be worse if the bend stress occurred while the nut was still tight on the bolt and had that layer of stress (as in a real case scenario)? …What robot has a bolt removed and is then impacted?

Re: your observation that 425 was hard to apply due to the lack of viscosity and large tip opening - would highly suggest a luer lock needle tip. I use McM 75165A679 on all my loctite bottles at work (and sometimes an even smaller one for some CA adhesives).


@Skuke is it possible to add the thread sealant, Loctite 545, to future tests? It can be used like the teflon tape on the pneumatic fittings.

LOL! I am more than happy to support you, @philso, when you run the next set of tests!

Coincidentally, @Michael_Corsetto and I briefly discussed the thought of using regular 'ol Teflon tape on bolts touching polycarb.

Chemistry was never my strongest science, so apologies first to any chemistry majors I may upset if I butcher anything here. I encourage anyone with more knowledge to correct me here.

CYA glues should be “safe” to use around or on polycarbonate (including to intentionally bond polycarbonate) - but there is always going to be risk of crazing. Typically, the risks associated with adhesives and polycarbonate is that the solvent used in the adhesive will end up dissolving the polymers in the polycarbonate itself. But CYA glues are solvent-free. CYA glues function by bonding a bunch of Ethyl 2-Cyanoacrulate monomers into a polymer that fills gaps between the surfaces being bonded together, and tends not to care a whole lot about what those substances are as its essentially creating a mechanical locking bond.

But basically every source on adhesive interactions with polycarbonate warns that CYA glues have the potential to cause crazing in polycarbonate, particularly if used in excessive quantities and/or with longer curing times. I’m not entirely sure why this is.


Yes we tightened the bolt in through holes. Also I don’t know anything about the chemistry of thread lockers other than 425 some sort of CA glue, but both 425 and 243 will eventually dry/cure when left on the surface of polycarb.

I know this is suppose to be obvious, but, obvious is scary. How about doing the test dry, ie no thread locker?

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You’re right it wasn’t obvious! …I only read my original post a half dozen times (or so) before hitting “send” and I didn’t pick up on the fact that I didn’t define what a Control “coupon” was. I apologize, I should have been more clear.

A coupon is the piece of polycarb with a hole through it.
The Control coupons were the control group for each of the thread lockers tested. There was at least one Control for each Test coupon. Each Control had a 10-32 bolt, washer and nut tightened in the same manner as each Test coupon except there was NO thread locker applied.
All the Controls were stored in the same box as the Tests (except for 425 Control & Test) to try and determine if there was any contamination from chemicals evaporating/out gassing, etc.
When a Test coupon had the nut/bolt removed, was bent in a vise, and examined, I also did the same to with a Control coupon.
With some of the tests, I did not bend more of the Control coupons because the damage was so obvious to Test group. Remember, my goal was to test thread lockers. Also, I knew there would be further bending of Control coupons from other test groups.

Of the 14 Control coupons that were bent, all but one showed no damage whatsoever. There was no crazing, tearing, fracturing, etc. It looked like a piece of polycarb that got bent.
The one Control coupon that showed damage had a small tear propagating from the hole edge.

I still have a bunch (10+) Control coupons in the box. They can be used for some future testing or a thread locker, albeit limited quantity. Or just to bend after sitting for a few weeks to see if the stress from a tightened nut has any effect over a longer time period.


Hi Skuke
Great. Glad you did that. How about Elmers glue or RTV or latex caulking or even honey? They aren’t officially used for the application, but we aren’t building airplanes or spacecraft either or have to meet some kind of specification.

As noted similarly in an earlier post I wrote: I’m more than happy to support you, @kent, when you run the next set of tests!


I bent test coupon #58 this morning. It had Loctite 243 applied to the bolt/nut 10 days ago and has been sitting in the plastic box. Upon removing the hardware, there was no obvious crazing (even under a microscope). After bending, there was a moderate size tear at the hole and small tear at the edge.
There was some Loctite under the washer that was not hard or dry. I wouldn’t call it liquid, but it wiped off easily with a paper towel. It had, maybe, a peanut butter consistency. The Loctite on the bolt and under the nut was dry and does not wipe off. It turned to a white color and was flaky when scraped with an Exacto knife. It appeared just as you’ve probably seen. The Loctite within the area of the hole in the polycarb, and not in contact with the nut, remained blue in color. It had a hard Gummi Bear consistency.
Hmmm. I think I’m hungry.

I’ve been advised that I wasn’t very clear that before/after photos of all the Control and Test coupons, with quick notes about each, are at: Threadlocker test result Spreadsheet with photos and notes
Row 12 also has links to all the photo folders if you don’t want to click on each of the coupons individually.


I bent the last test coupon, #59, with Loctite 243 applied to it 65 days ago. I also bent Control coupon #9. Both have been sitting in the same plastic box this whole time.

Test coupon #59 had a very small amount of crazing around the hole but easily broke into two pieces when bent.
Control coupon #9 looked unaffected but the edges had a small tear during bending.

Also interesting that the nut was difficult to remove (Blue Loctite #243). Difficult to the point that I bent the bolt using the box ends of the two combination wrenches. Just seem weird to me that I would have struggled to bend the bolt so close to the head even if I wanted to, using only wrenches.

I have no test coupons remaining and the testing is concluded. I do have about a 10 control coupons with bolts and nuts tightend on them, but no plans to use them for anything. Thanks for your interest in testing.