Technique for Rubber Restoration

[midcenturyfrogman]

I just wanted to share something I was made aware of recently. I was always under the impression that dried out, perished rubber is essentially analogous to trash, and that there is nothing you can do to even begin to return it to its previous elastic state. Well, I stumbled onto a process that seems to do exactly that, and I'm interested to know if anyone else has ever heard of this or anything similar.

The background into the process is that some older Japanese motorcycles use rubber air intake boots that can become very hard and dried out from the constant heat cycles, and apparently there was/is no good source for high quality replacements. So, necessity always being the mother of invention, some Japanese bike enthusiast with a chemistry background came up with an easy method for rubber replastication.

You submerge the rubber in a solution of 1 part wintergreen oil to 3 parts 91+% isopropyl alcohol, and that's it. You leave it in the solution for 24-72 hours until your rubber reaches its desired plasticity and pliability. So far I have only tested this method one time, but with really good results. I tested it on what was a completely perished and totally rock hard Healthways Aqua-Champ swim mask from the 1950s. I felt this mask was a really good candidate because it was essentially new old stock, still in the box and without any wear or damage that could hinder the success of the process. The biggest thing I was watching out for as far as for the test piece is cracked rubber. If the dried rubber has cracks that run the whole way through the piece then it will like just separate when it is restored. Luckily with the Aqua-Champ mask cracking was minimal.

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The mask ended up being submerged in the solution for around 80 hours, with most of the change happening between the 2nd and 3rd days. The solution very quickly took on the aqua green color of the rubber, but it did not seem to have any effect on the color of the mask itself. I would urge caution to anyone wanting to try this on anything that has other plastics or materials in addition to the rubber being treated attached to it. In the case of this mask there was the lucite lense and the two steel strap attachment points on either side. The metal strap attachment points were completely unaffected by the rubber treatment, but unfortunately the lucite lense was surface etched and ruined by the solution and had to be replaced. It's for this reason that I recommend caution with any item that has plastic pieces which cannot be removed.

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But despite any draw backs, I am beyond pleased with the results here. After treatment the mask is essentially as elastic and pliable as it would have been 65-70 years ago. I can even put it on and get a good seal! This process took a rock hard little curio piece mask and returned it to a literally usable state! I'm definitely interested in hearing some feedback on this, or if anyone has similar processes/experiences they'd like to add.

[nikeajax]

Hi Nick! Yes, for the most part, I did know about this I have yet to try it though...

I didn't know about the alcohol though: I've heard you can use just straight methyl salicylate too (oil of wintergreen). I've often wondered if I could spray it on the outside of old HW hoses that have set.

Before the Scuba came out, there was the L.G. Arpin, Divair which was distributed by Healthways: the early hoses were flavored/scented with wintergreen, kinda makes ya wonder, don't it!

JB

[midcenturyfrogman]

Jun 29, 2023 10:45:35 GMT -8 nikeajax said:

Hi Nick! Yes, for the most part, I did know about this I have yet to try it though...

I didn't know about the alcohol though: I've heard you can use just straight methyl salicylate too (oil of wintergreen). I've often wondered if I could spray it on the outside of old HW hoses that have set.

Before the Scuba came out, there was the L.G. Arpin, Divair which was distributed by Healthways: the early hoses were flavored/scented with wintergreen, kinda makes ya wonder, don't it!

JB

Hey JB,

So as far as I can tell, wintergreen oil appears as a main ingredient in several commercially produced rubber restore products. Most of these products are intended to be sprayed on the affected rubber, so topical application probably does work to some degree. The wintergreen oil is essentially your replacement plasticising agent that is going in and taking the place of the original plasticising agent that either broke down or evaporated away and left the rubber dry and brittle. The isopropyl alcohol is acting as a solvent. It not only diffuses the wintergreen into the solution, but it also saturates the rubber.

I think this is the key to why this method works so well. The alcohol (or solvent) provides the means for the wintergreen oil (or plasticising agent) to make its way deep into the rubber and completely restore it. It should also be noted that isopropyl alcohol is not the only solvent with which people have had reported success. Supposedly Xylene is a contender for the solvent which produces the best results in this method, however I was worried that it could be a bit too strong to use on 60+ year old rubber of unknown composition, so I went with the isopropyl alcohol as a milder alternative.

Lastly, that's super cool and interesting to hear that original Divair hoses had a wintergreen scent! Makes me wonder if they actually used wintergreen oil as the plasticising agent in their rubber. It would stand to reason that they might have, because the main reason wintergreen is used in the restoration technique is that it is a good, stable, not toxic, plasticising agent.

[nikeajax]

Daaaang son, you can write, can'cha?

It's my thought that perhaps the Divairs were using hoses not intended for the purposed used and that they might have been repurposing them and reconditioning them with the oil: this is only my theory though!

If you ever get a chance, you should watch this film:

en.wikipedia.org/wiki/The_Monster_That_Challenged_the_World

See it for a few things, the women in it are reallllly nice to look at The monster while a bit stiff, is genuinely-creepy looking, nightmarishly so. But then, then there's the Divairs with Medusa-masks: the hoses are perversely long, like maybe four-feet long, EACH! Holy smokes their long, you'll laugh when you see them jiggling around like tentacles... Oh, the dry suits are super-boss too!

JB

[SeaRat]

Midcentryfrogman,

'Love the descriptions you have provided. And, getting that mask back into shape is great. There aren't many of those still around.

I've had several (three) Scubapro three-window masks melt off my face (yes, I've been diving that long). So now I use the same mask, but made of silicone. Those will last forever.

Concerning the neoprene that many of these masks are made of, my understanding is that it isn't just drying out, it is the ozone that they are exposed to that actually chemically interacts with the neoprene to make it "melt." I saved the glass from one of my favorite Scubapro masks, and replaced the silicone mask's front glass with the one that had no front valve for expelling water. Here's me with that neoprene mask:

Winchester Dam028 by John Ratliff, on Flickr

And here's the silicone mask with the older front lens.

John with Scubapro's Supervision silicone mask. by John Ratliff, on Flickr

So for my neoprene masks, I use a light coating of silicone grease to try to hold off the ozone effect on the rubber. I'm curious whether your use of wintergreen oil would also help them out? Here's a website that explains the effects of ozone on rubber:

www.applerubber.com/hot-topics-for-engineers/understanding-the-link-between-ozone-and-rubber-deterioration/

John