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Verdict: 
Offers reasonable puncture protection, but blowouts can be extremely messy
Weight: 
302g

Weldtite Dr Sludge tyre protection sealant does the job it's claimed to, sealing small holes up to 3mm with the minimum of fuss. If you're already running stout tyres and thorn-resistant tubes then it adds extra protection, but I'd suggest tougher tyres/tubes as first measures. Also, don't expect it to mend rips/punctures along seams or bigger holes – and do expect things to get messy in such scenarios.

The sealant has been around in this form for quite some time, although Weldtite has recently brought out a tubeless-ready version. This one is designed for inner tubes, including golf carts, wheelbarrows and so on, and is best suited to bikes with Schrader or Woods valves.

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Weldtite describes Dr Sludge as an 'environmentally friendly, water based formula'; judging by the smell, texture and consistency, I'd say it was some form of liquid latex. Its ability to fill cuts up to 3mm in diameter is quite impressive given most factory-filled tubes claim and seal those around 1mm. That said, they do all work to the same basic science. In the event of glass or similar sharps piercing the tube, centrifugal forces propel the goo, which, when exposed to air, cures on contact, with minimal loss of pressure.

There are some limitations, though. Specifically, tube seam punctures will mean a new tube, plus a big, sticky mess. I speak from previous experience, using a different brand's ready-filled tubes, in the middle of winter, with a small child cruising behind on the tag-along...

Fill your butes

Our 250ml test bottle is sufficient for two 700C or 26 inch tubes. While it can be delivered with the wheels in situ, I erred on the side of caution, introducing it to fresh tubes over the kitchen sink. Either way, give the bottle a brief shake and remove the top. This comes with a valve core remover, and you'll need to extract those from your tubes first.

Next, attach the flexible hose over the valve stem and squeeze the bottle gradually until you've released half the contents. Once the valve has 'burped', distribute the sealant evenly by simultaneously rotating and squeezing the inner tube.

Clean any excess from the valve stem, reintroduce the core, refit and inflate.

To evaluate the formula's prowess, I opted to share the bottle between my fixed-gear winter trainer and my mountain bike-derived rough stuff tourer, which was sporting some sprightly but puncture-prone rubber.

There's a slight weight penalty, which is noticeable during reinstatement and when running a lightweight folding tyre – but you wouldn't be running goo-filled tubes on a TT missile. It's quickly forgotten anyway, given a few miles, especially if you're running heavier duty touring/commuting rubber.

Performance

Since I was retiring the Univega's lightweight trail tyres I purposely delivered a stout tack through the front's casing. There was a brief pregnant pause then an audible hiss, but within a few rotations the goo did its thing. I checked using my SKS digital gauge and 6psi was the total loss, plus there was no further leakage or loss some 25 mixed terrain miles later.

With hedge-cutting season in full flow, lanes carpeted in vicious thorns, a couple struck lucky – the rear succumbing twice along the same stretch, demanding I stop, extract the offenders, and brush the casings again before continuing. This time 12psi bled out, but that's a minor inconvenience on a commute compared with flatting, especially at night and along unlit roads.

Using a decent quality middleweight butyl tube on my fixed gear winter trainer and alternating between Clement Xplor USH and Maxxis Roamer tyres, I've had a couple of flints pierce the casing, nicking the tube. Each time I lost 8psi, but again, provided you check and reinflate your tyres regularly, this isn't much of an impairment.

> Regular pre-ride checks

Tube quality is another factor to consider. I'm quite partial to bulk buying budget butyl, primarily as wedge pack staples, but the thinner walls mean they're trickier to patch. Bombing along a stretch of wet, silty unmade road on my tubby tourer, a flint became embedded in the shoulders and my ear-to-ear grin was displaced by that sinking feeling. Unfortunately, the seam had been nicked and Dr Sludge couldn't keep pace. Long story short, the clear-up was messy, involving foliage and a new tube.

By contrast, I've had no such problem on the fixed, although – in keeping with this genre – the sealant has tended to clog the valve, requiring occasional stripping and cleaning. This is also true of ready-prepared models, including BTwin's self-sealing tube, which is still going strong on my traditional road bike.

Conclusion

Ultimately, Dr Sludge genuinely does what it says and is reasonably priced. Big sharps at the right (wrong) angle can render them useless. Those seeking some additional protection on their winter training bikes might find something like the BTwin sealant-filled model mentioned above a more practical option, though.

I have to say, though, decent tyres with aramid casings are my first defence. Going the belt 'n' braces route with a cross/gravel build, I'd opt for something like Kenda thorn resistant inner tubes. These do add a fair bit of weight, relative to a standard or even sealant-filled model, but are ultra-dependable and easy to patch.

Verdict

Offers reasonable puncture protection, but blowouts can be extremely messy

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road.cc test report

Make and model: Weldtite Dr Sludge Puncture Protection Sealant

Size tested: 250ml

Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?

Weldtite says: "Protection sealant to provide ongoing prevention against punctures in tyres."

I'd say it's an old school sealant that works fairly well and with Schrader/Woods type valve cores, but those with Presta valves wanting to go this goo-filled route are better served by factory filled tubes.

Tell us some more about the technical aspects of the product?

Weldtite lists the following:

* Environmentally friendly water based formula

* Also for use on trailers, wheelbarrows, golf carts, etc.

* Suitable for Schrader type and other valves with removable cores

* Core removal tool included with easy applicator nozzle

Rate the product for quality of construction:
 
6/10
Rate the product for performance:
 
6/10

Does pretty much what it says on the tin and competently but there are limitations, and in keeping with any sealant type product, a bigger hole/blowout can prove very messy.

Rate the product for durability:
 
6/10
Rate the product for weight (if applicable)
 
5/10

There is a slight weight penalty, but this is unlikely to bother commuters, laden tourists or utility riders.

Rate the product for value:
 
6/10

Tell us how the product performed overall when used for its designed purpose

Overall, Dr Sludge has done what it says it's supposed to and will seal small holes with the minimum of fuss up to 3mm. However, should a sharp nick a seam, or the puncture is a big 'un, then you're left with a big sticky mess and needing a new tube.

Tell us what you particularly liked about the product

Does what it promises and is largely forgotten on a day-to-day basis.

Tell us what you particularly disliked about the product

Nothing, given the design brief. However, in keeping with this genre a seam cut or blowout can be very messy. Thorn-resistant tubes and more dependable tyres would be my first resort. Factory-filled tubes are better options for road-biased riders looking to take this route.

Did you enjoy using the product? Pleasantly indifferent.

Would you consider buying the product? Possibly

Would you recommend the product to a friend? If they were running stout tyres on their workhorse and wanted some additional protection, then worth a closer look.

Use this box to explain your score

Dr Sludge lives up to expectations, but does have its limitations. Stouter tyres/thorn resistant tubes would be my first choices.

Overall rating: 6/10

About the tester

Age: 43  Height: 1m 81cm  Weight: 70kg

I usually ride: Rough stuff tourer based around 4130 Univega mountain bike frameset  My best bike is: 1955 Holdsworth Road Path and several others including cross & traditional road

I've been riding for: Over 20 years  I ride: Most days  I would class myself as: Experienced

I regularly do the following types of riding: cyclo-cross, commuting, touring, fixed/singlespeed, mountain biking

Shaun Audane is a freelance writer/product tester with over twenty-eight years riding experience, the last twelve (120,000 miles) spent putting bikes and kit through their paces for a variety of publications. Previous generations of his family worked at manufacturing's sharp end, thus Shaun can weld, has a sound understanding of frame building practice and a preference for steel or titanium framesets.
Citing Richard Ballantine and an Au pair as his earliest cycling influences, he is presently writing a cycling book with particular focus upon women, families and disabled audiences (Having been a registered care manager and coached children at Herne Hill Velodrome in earlier careers)