Sludge is a tyre and tube sealant from South Africa that is specifically designed to deal with the high inflation pressures of narrow road bike tyres.

It is also formulated for tubes with Presta valves. As the box says, it is a tube sealant for roadies. Application naturally requires injection of the fluid through the valve. Not only is the sealant formulated to go through the orifice of a Presta valve, but this part of the valve must be greased prior to application. This we did using the recommended petroleum jelly.

The bottle has a moulded plastic top designed to fit a Presta valve. Once the very tip has been sliced off, the nozzle can be threaded on to the valve until it covers the non-threaded bit beyond. This gives a decent seal, although it is worth having a kitchen wipe handy for the small dribble than will inevitably appear.

There is enough for two road tyres in the 100ml bottle. We put ours in a pair of tyres that seemed ideally suited to the stuff. Tufo, makes of innovative tubulars and tubular clinchers, offer their own sealant fluid, since repair of their tyres is otherwise impossible. We used Sludge instead.

Squirting the stuff in took about two minutes per tyre, and thanks to the petroleum jelly the valve nozzle remained unclogged and easy to screw closed once the tyre had been inflated. Other than the fact that the tyre inflated to 120psi (the rider is our 115kg subject)without fuss, there is nothing more to report. Ride sensation is unchanged.

So far, so good; we can report no punctures. Some readers might ask why we don’t simply inflate a tyre and stick a pin in it to find out what happens. Two answers: the makers have probably done so already, or they wouldn’t sell it, and some element of faith is required that might be lost should we try the above experiment and find it to fail. So, it’s a question of waiting to see how well the two tyres go…

Full fitment instructions are provided on the box. One 100ml tube will treat two tyres, and costs £7.99. A 200ml ‘mtb’ bottle is available for £9.99. Watch for further news…