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It's become a fairly common occurrence in shops to be faced with a tubeless wheel that was doing fine, slowly started having issues, and hasn't had a sealant re-up in a while or ever, but what sealant was used is either lost information or one you don't have handy. If unknown, maybe you could figure it out if you pull the tire, but that's sometimes easier said than done these days, and you can always clean out what's in there and start over, but what you really want to do if possible is just shoot some fresh sealant into the valve and move on.

Every sealant manufacturers says not to mix brands, yet experience bears out that usually if you just do it, it's fine. But what possible exceptions are there, and why? Are there any sealants out there that are particularly bad for the purpose of possibly mixing with unknown prior sealants? Any that are particularly good? Any hidden compatibility rules that might allow a shop to responsibly only have a small number of bottles around yet still be able to handle anything that comes in the door?

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    I would surmise that mixing different latex sealants should be fine, but avoid mixing a non-latex sealant with a latex sealant. – Rider_X Nov 30 '18 at 7:56
  • I'm guessing it has a lot to do with the solvents used -- you don't want to mix solvents. – Daniel R Hicks Nov 30 '18 at 22:46
  • I guess there's an extension sub question - can you mix two sealants when one is dried up or do you have to clean out the old one first ? – Criggie Dec 1 '18 at 1:53
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    @Criggie you can just add more unless you are worried about a few added grams of the old sealant. Usually you can guess/estimate when the sealant is getting low and just remove the valve core and add some more. If you break the bead/rim seal you may have to clean the tire bead to get a clean seal again, but typically you can get away without cleaning the tire bead. – Rider_X Dec 1 '18 at 5:46
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If your tire has begun to lose air slowly (loses 10 PSI over 2 days), it has lost the liquid carrier in your sealant. The remainder of the sealant is dry or lumpy and can't travel to the new thorn. It was ammonia or environmentally friendly antifreeze (not ethelene glycol) that evaporated. Like the original liquid is pretty much gone.

Our riding club carries Orange seal and Stan's in portable 3 ounce bottles. We use it interchangeably any time a member gets a low tire on the trail. Never had an issue.

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    Stan's and Orange in particular are pretty well known to play nice. The problem for a shop is there are now literally over a dozen sealants – Nathan Knutson Dec 13 '18 at 20:20
  • Nathan - I am far, far from a content expert. I have been interested for a long time because living in the desert causes sealant to dry quickly. "I believe" that most of the many brands are using an antifreeze equivalent to reduce evaporation and "I believe" Stan's used to use ammonia as a liquid but does not any more. It too. It doesn't stink anymore. – Cliff Dec 13 '18 at 21:00
  • Two little tricks I used with high school racing team (riders didn't want rotating weight added by adding unnecessary sealant) 1. let bike sit in a stand for 5 minutes with valve at the bottom. 2. pull tubeless core out. 3. measure depth of fluid with the little red spray wand from WD-40 spray can. 4 if less than 1/4 inch - add one ounce of windshield washer antifreeze. It will remix with the existing latex and chips to retain function for months. If the dipstick is barely wet or is dry add sealant instead. It is too late to remix with the solids. – Cliff Dec 13 '18 at 21:14

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