What Really Happens When You Use Flex Seal To 'Fix' A Tire

Using a tire sealant in your tires is a simple tip to maintain tire pressure. That said, not all sealants are built the same or function in the same way. Flex Seal is a great example; while it's great for some household sealing projects or waterproofing projects on materials like metal, wood, and concrete, the manufacturer cautions against using it for repairing a tire.

Flex Seal is easy to apply, which can make it good to use on an RV roof sometimes, but that doesn't mean it's an instant roadside fix. The issue is that full curing can take up to 48 hours, meaning it may not fully seal a puncture until two days after it's applied. But even after fully cured, just because a tire appears to be retaining air doesn't mean it's safely repaired. A proper puncture repair fills the area with a rubber stem and then seals the inner liner with a patch. Spraying the exterior with a coating is a much less secure solution.

Even if Flex Seal does provide a temporary fix for smaller punctures, it's unlikely to work on larger openings or more significant damage. "Temporary" is also doing a lot of work there: Flex Seal may appear to hold in the short term, but can degrade over time, leading to another leak or even a blowout.

Much like applying Flex Seal to your gutters, long term durability can be a real issue. But even in many cases where Flex Seal may initially appear to be effective, it's often not addressing more significant damage to the tire underneath. For a proper repair, a tire needs to come off the wheel and a full check of the inner lining is a must.

Also, for most road tires, the USMTA only recommends attempting a repair on the tread area, and no larger than a quarter inch in diameter. The issue with using Flex Seal as a temporary fix is that it can obscure the actual size of a puncture. If you've used Flex Seal, but intend to bring your vehicle/tire in for a longer term solution, make sure you let the mechanic or technician know that you've applied Flex Seal. They should then be able to assess whether a tire qualifies for repair or needs to be replaced and, if possible, install a proper stem and patch.