Good afternoon, colleagues. Does anyone have any idea how to restore these old hardboardknobs? They've been out in the elements for a long time. Perhaps soak them in vinyl glue and press them back together? Any help is welcome. Kind regards.
These old 'fibre' knobs were made from cellulose/paper, impregnated with some phenolic-formaldehyde resins and pressed molded under pressure and heat. Similar material to Pertinax material: Pertinax® - a traditional material with a new future. I think there are many ways and methods to restore it. It'll depend a lot on how you want to go about it. Either simpler home DIY styled or elaborate "professional" methods. DIY-styled examples:- 1. It must first be thoroughly cleaned and dried. Ensure no oils or remaining moisture. A variety of glues or adhesives can be used. Fastest would be the low-viscosity cynoacylates aka "Superglues"(further classed into general purpose to speciallized types):- Check if the fibre knob's degradation is just superficial or more extensive into its core. The above adhesives are usually very fast acting. Apply carefully to soak the surface. It might penetrate deeper if you immerse the knob completely in an air-tight container, slowing down the curing. Exposing to air and moisture might instantly cure the glue and makes it difficult to clean the mess, especially on the knob's "knurled or toothed" edge. Once lifted from immersion, immediately blow away the excess with compressed-air. Do not use a rag or paper towel to wipe (it'll stick to those instantly and cause another mess). Leave it to cure naturally. Heating can hasten it a little but not really necessary. You need fast hands to expedite this before the glue hardens.(expect the glue to stick your fingers and hands). 2. In a more forgiving method, you can also use Gasket Shellacs such as: Soak the wheel thoroughly in the shellac. Wipe-off the excess. Allow to dry slowly in the open. Do not heat it immediately(allow all the alcoholic solvents to evaporate first). After leaving it to thiroughly dry, for say a couple or so days, you can gently heat it to slightly harden it further. Touch up if necessary. 3. Using other adhesives like: epoxies, polyester resins for fibreglass repairs, acrylic adhesives, etc. Select any available that has: - very low viscosities for better penetration. - as slow curing as possible to allow more working and clean-up time and reducing the possible mess of cured adhesive on the knob's "knurled/toothed" side. "Professional"-styled: Might require speciallized equipment, fixtures and bonding agents/adhesives. Vacuum-Pressurized-Impregnation gives the most thorough penetration. Heat curing adhesives. Best to use phenol or resorcinol-formaldehyde adhesives and resins as used for forming the Pertinax material. There are more speciallized adhesives for cellulosic materials like paper, cotton, wood, etc (datasheet attached) such as: Once the adhesive/impregnation agent has cure, you can finish and polish the knob to make it look new.
Thank you very much MYN!!! This is not a help, this is a magister class!! The degradation is very deep, I will try some of this ideas, showing the results, best regards
@Leonardo Collares My compliments to @MYN for his comprehensive and informative insights. I had no opportunity to restore the fibre control wheel on this Pigeon Ignus naptha stove, because it was absent, so I’d to make one from scratch. I used the flexible sheet (Novus 30) that I punch heat-proof washers from for camp stove burner riser seals. Having made a steel spindle to fit the stove burner regulator I punched discs from the Novus sheet and bonded a laminate of them using two-part epoxy adhesive. John
@Leonardo Collares Use something that you are comfortable working with. Solvent-free adhesives are usually the best performing but it depends on availability too. You might need to touch-up the knob's side serrations. The look badly degraded as well. As long as it is not really crumbling apart, it can still be saved. Very ingenious, @presscall Fibrous gasket sheets make an excellent substitute. Bonded with epoxies. Epoxy adhesives do not require drying off any solvents, which can be limiting if you have non-porous materials involved. Once mixed, they will still cure and harden in enclosed space.
Very nice job @presscall!, no doubt it may be a very good solution in case the restoration dont work, thank you very much!!!
Thanks again @MYN, I am thinking in a water dilueted vinylic glue in order to penetrate as deep as possible, dry it under presure, and later cover it with some resin, thank you
@MYN @presscall You all are truly excellent craftsmen. I'm glad to hear some new information. @Leonardo Collares I hope it will be repaired successfully.
Intresting post old broken flaky control knobs are a problem. I make replacement out of a kind of fibre board called tufnol that can be had on ebay. You can work it just like metal its really tough and insulates you from burnt fingers Cheers pete
@MYN I have plenty of shellac. I mix it with ethanol for waterproofing cardboard boxes (see here). Do you think that soaking, then drying an old worn fibre control knob would in that solution? Tony
I think it would work pretty well. Shellac flakes used to be available from many hardware stores in my hometown when I was much younger. Unlike many resinous compounds found today, shellac is completely natural. The Permatex gasket shellac that I mentioned earlier is also similar although it has been modified. The solvents used are also alcohol-based. For the old worn-down fibre control knob, I suppose it depends on whether the degradation is superficial or deep down into its core. The shellac in alcohol would work especially well on the former. For deeper treatment, I think it might be better to melt the shellac flakes into a thin liquid without the alcohol. And then soak the fibre knob in the molten shellac instead. I think it doesn't require a high a temperature to melt pure shellac. Maybe around 80°C at most. Perhaps slightly lower. Just need to ensure the heating is slow and controlled to prevent it from boiling. Just like many other resins, boiling shellac can easily catch fire. A thick fibre knob that is thoroughly soaked with alcohol-dissolved shellac might take longer to dry completely. But I think it might still work. Unlike many paint lacquers, I think shellac with alcohol solvent won't form an impervious top film that prevents or greatly slows down further drying.
