Homemade boiler gaskets?

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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Postby CoffeeBeetle » Nov 20, 2018, 11:15 am

Hey all

I'm working on restoring a Conti Prestina and I will soon have to figure out a solution for my lack of a boiler gasket. Researching this forum I've found a couple of different suggestions for what material to use for gasket making and most of them seem to recommend fiber or something similar. I also found mentions of a material/manufacturer called Klinger who produces a product called "Klinger-chem" which seems perfect for this case.

You might be wondering why I'm writing this post then if I already found two suitable solutions for my problem? Well, it seems like those solutions aren't really available to a regular guy in Denmark who lacks connections in the highly secretive world of European custom gasket manufacturing.
All the fiber sheets I can find online are paper thin and most of them don't mention much of food grade or max temp, leading me to believe that they would be bad choices. I found "Klinger-chem" gasket sheets at the lovely price of well over 300USD per sheet, which just seems ridiculous to me.

The two options that I seem left with(unless someone here knows where to get good fiber gaskets in Europe) are PTFE sheets and silicone.

So my real question to you guys is: Would a home cut gasket of PTFE, silicone or both somehow combined be a suitable gasket for a boiler where the flanges are made of cast copper and aren't perfectly flat?


Postby Sw1ssdude » Nov 20, 2018, 5:13 pm

Klinger sounds familiar. They made the boiler glass gauge of my olympia (which holds up to 300bar, just in case...)
I didnt know that they also make gaskets.

What i'd recommend is silicone. Most silicones are safe for use in food processing machines, because its super inert, just like the teflon coating in your frying pan.

Teflon is also an option, but its way stiffer than a sheet of silicone. If you have a badly uneven meeting surface, go for silicone, since it will squeeze into the scratches.

If you have the machine apart, you could grind the surfaces perfectly flat and smooth.

Silicone should be easy to obtain, just make sure its foodsafe and temperature proof, get a stencil from your boiler and a exacto knife and start cutting. For screw holes you'd best use a hole puncher. Same goes for teflon. Most gaskets i use are about a millimeter thick. If you use thicker or thinner material than the old gasket, be sure that your boiler screws are not too long (boiler wont be tight if they reach the end of the receptive hole) or too short (not enough thread engaged, danger of messing up the thread).

Don't know about fiber or cork gaskets.... i use those for engines. You can get them at the garage you trust working on your car. Whole other situation there, those are oil proof and most likely NOT foodsafe, but a good option to stop your on/off switch from wiggling, or similar. But i bet there are also foodsafe fiber gaskets.

If you are not so fond of dodgy hand-carved gaskets, make an EXACT drawing of your stencil, buy some material and a case of craft beer and drop all of it off at the next architecture bureau or another place where they have most likely a laser plotter. They can cut you a perfect shape.
Silicone and fiber is easy for lasercutting, teflon i dont know, but DO NOT cut PVC or unknown material on Laserplotters, nor have it cut by other people, the fumes are causing cancer.

Another thing i found that might help:

Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed)

Good luck!
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Postby Sw1ssdude » Nov 20, 2018, 5:31 pm

Hmm, just saw the topology of a pristina boiler...

The boiler flange you can grind flat on some grinding paper that you laid on a very flat table (marble coffeetable, glass surface, mirror), but the lid with its lip is tricky. That should be most likely turned on a lathe... but if you didnt screw up your lid surface while removing the gasket, you should be in the clear...

I learned that gaskets 'seat in' a long time ago, so be sure to regularly check for leaks and retighten if necessary.

Good luck! Take some pictures if you have the time....
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Postby samuellaw178 » Nov 20, 2018, 6:10 pm

Excellent response by Nino above!

To share my personal experience, I have used silicone sheets to make a 'temporary' boiler-to-lever-grouphead gasket, only to have it stay on the machine permanently. I am impressed how well it did and how it is almost-indefinitely reusable - it doesn't leave any annoying residue on the metal surface upon removal, and even after 1.5 year it is still completely pliable. I think it should work well for the boiler as well. In contrast, the factory fiber/paper gasket cracks after being in commission for a few months, and left some residues that're almost impossible to clean.

As to PTFE, the potential downside is it requires a more perfect surface for sealing and retightening after initial installation. Also, PTFE may creep over time from what I understand. It may be an issue if you have steel bolts that are prone to rusting.

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Postby CoffeeBeetle » Nov 20, 2018, 6:22 pm

Thanks for the response guys, sounds like silicone is the option I should look closer at.

The flanges have been cleaned and sanded with fine sandpaper to get the last bit of fiber gasket off(that sh** just absolutely will not get off older machines). It's not completely flat(as in machine made) both because of the remnants of gasket/discoloration after gasket and because the flanges are cast copper. The technique with sanding the flange on something flat would only work on the boiler flange and not the lid as Swissdude pointed out.
I could, of course, get it professionally made but I would rather wait and check if there are other options. There aren't many places where I live that could handle that and it is likely going to be rather expensive so it's the last resort.

As a student, I might actually have access to a laser plotter through my university. If that could make me an exact cut then that would be worth checking out instead of playing around with knives and hole punches I suppose.

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Postby drgary » Nov 22, 2018, 3:23 am

Hi Magnus,

Doug Garrott of Orphan Espresso restored many espresso machines before they launched their grinder business. In my thread on restoring my Conti Prestina, Doug offered this advice on specs for rubber gasket material.

orphanespresso wrote:HNBR and NBR sound a lot like designations for BUNA rubber. The lowest temp rating available. The material should be at least EPDM, HSEPDM, Viton is best (silicone has a higher temp rating but is often too soft for some applications). I have never seen BUNA used on an espresso machine unless it was sourced at the Home Despot by someone who did not know any better.

His recommendation was Viton sheet. That advantage of a rubber gasket material over PTFE is that it will do better filling imperfections on the boiler flange. Also keep in mind you'll be tightening the boiler bolts to the metric equivalent of 15 foot pounds using a torque wrench. I ended up sourcing a fiber gasket from new old stock for the Prestina and may eventually regret that when it's time for a gasket change. For now it holds up, and you know this is as Doug would say "unobtainium."

A quick search on eBay shows Viton sheet of 1/16" thickness and 12 inches by 12 inches would be $33.50. (Rich Goodin recommended 1/16 or 1/8 inch thick gaskets in your liquid gasket thread.) So, translate that to your measurements and Euros. The mistake I made in cutting my Viton sheet was to not be careful enough in creating a template I could lay on the sheet. Also the Viton I bought may have been too thick to work easily.

If you are going to use silicone, another good choice, you will need to make sure it is firm enough that you're not getting the type that is used in gel sole shoe inserts. I did some brief online research and found that there is a rating scale called Shore hardness that you can look up online. I found a 20" by 20" by 2mm silicone sheet on eBay for under $21 free shipping at Shore hardness A scale of 60, which translates to about the hardness of a rubber tire tread. Shore A 40 would be as hard as a pencil eraser, which should also be suitable for a gasket. The seller of the 60 hardness sheet is in China, so you may want a seller with local or EU stock.

If I were to do it again I would carefully measure the inside and outside diameter of the boiler flange. Then I would mount thick, stiff paper on a wooden workbench and make the template with a large and accurate circle cutter. I have found drywall circle cutters for less than $10 that easily extend to the size you would need. You can mark the flange with non-toxic material, lay the template on it and that would accurately locate your bolt holes. The advantage of a template is you can make sure it fits before using it as a guide to cut your gasket out of expensive material. I would very carefully use a very sharp hobby knife to cut the gasket edges so they'll fit. Once you've accurately marked your bolt holes with the template you can use an inexpensive leather punch to create the holes in the gasket.

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Postby CoffeeBeetle » Nov 22, 2018, 4:44 am

Thanks for the informative post Gary, I was a bit nervous about making my own gasket after seeing the challenges you faced trying it but I might have found a way to avoid this problem altogether. Just about every university here has an "entrepreneur/startup area" that is supposed to help people with prototyping ideas for projects and such things. I found one such place that offers free use of a laser cutter so if all goes well I will just draw up a plan for the gasket and have the machine cut it accurately, it should save me the trouble and it might also come in handy later if I have to make another smaller custom gasket.
I also found a few offers from China about different rubber materials but the price and "google translate" postings lead me to believe that it would be a recipe for trouble down the line if I went with that material.
Checking the hardness scale I can see that the Viton I have available for buying is rated at 70: https://www.ebay.co.uk/itm/VITON-RUBBER ... 0505.m3226

But I can get a considerably cheaper silicone that is rated at 60: https://www.polymax.co.uk/silicone/sili ... olid-sheet

If 60 is the hardness of tire then that should be more than enough I assume, and the second offer is FDA approved. From what I could find Viton is a trademarked name so I'm thinking that the price difference might be more about the name than any actual difference in quality? Don't know much about silicone but does anyone know if the increased price on the Viton sheet is worth it in this case?

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Postby civ » Nov 22, 2018, 6:27 am


According to Paul Pratt, the best and most durable 'o' rings for vacuum breakers are made from silicone, not from Viton.
His opinion is based on his experience maintaining commercial espresso machines, where silicone orings would outlast the less expensive viton ones (which would last only 6 months) by far.

His site is down at this moment, but this is the link:
See the 'O-rings revisited Feb 05' section.

I followed his advice for the vacuum breaker in my Cimbali Junior D/1 and it has worked flawlessly ever since, the silicone 'o'rings last around 18 months before they start to degrade.

The boiler seal ring in my ca. 1969 La Pavoni is made from silicone also and it works great.
Not one issue even though I've had to open it up at least two times, it is always as new.

The problem is cutting it: I had a fellow who makes gaskets and rings for a living do me the favour of cutting one for me with one of his jigs. He uses special circular cutters made from sheet metal to do it (think cookie cutters). It was not the exact size but stretching it a bit made it work.

There are circular cutting tools in the market that you can use to try to make one:


The real trick here is to be able to immobilize the sheet so that it will maintain a stable dimension and not stretch while you are cutting it.
Being silicone it is not an easy task but I'm sure there's a way to get it done.



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Postby CoffeeBeetle » Nov 22, 2018, 7:43 am

Is silicone considered the more expensive option, or am I reading something wrong? Perhaps it is just the sources I've found but silicone sheet that is both food safe and rated to the proper temp is considerably cheaper than viton.
I always assumed that viton was the more "luxurious" option and silicone was the store brand of the gasket world.

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Postby civ » Nov 22, 2018, 8:34 am

CoffeeBeetle wrote:Is silicone considered the more expensive option ...

That's what I recall reading from Paul Pratt's website.

CoffeeBeetle wrote:... assumed that viton was the more "luxurious" option ...

That could be for a number of reasons, depending on what the intended use is and manufacturing costs.
And then there may be many different qualities of silicone and viton, really can't say.

But if anyone knows about this it's Pratt and he uses silicone o'rings when changing the seals on vacuum breakers in the commercial machines he services. I think he also produces/sells (?) red silicone gaskets for vintage/modern lever pistons and groups.

The group gasket on my Cimbali D/1 is also made from red silicone, it's been in use for more than five years now.
I just give it a throrough cleaning and 'turn it over' everytime I do maintenance.