Wilco do a translucent heavy-duty vinyl tape for outdoor repairs, get a roll, clean up the outer surface with something like lighter fuel, or washing-up liquid, to degrease it, push the crack together, or better still get someone else to do it and lay a strip of the tape over the crack, then reinforce the inside with anything that’ll hold it, ideally having cleaned out any crap, like P.38 body filler over some sort of mesh, even wire netting, just to help support it.
It doesn’t have to be pretty, just functional to prevent it getting worse.
This is the stuff, a quid a roll: http://www.wilko.com/multi-purpose-diy-tape/wilko-all-weather-tape-50mm-x-10m/invt/0437151
Reinforcing the inside is key to making it last as long as possible, though, but that can be any old stuff to hold it together, it ain’t needed to win prizes!
Is it a crack? I’ve just bumped the corner of my bumber at the weekend, the paint cracked and chipped off but he actual bumper underneath is perfectly fine and undamaged. The paint (or whatever it is) looks quite thick – like 3mm or so. Almost like a shell over the plastic bumper, so will need filling and re-painting but no need for any repairs to the actual bumper underneath. Is that really a ‘crack’ or just a crack in the surface paint layer.
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