An unexpected property of Blu-Tack

[Michael GilliganParticipant @michaelgilligan61133]

About three years ago … as a ‘temporary lash-up’ I installed a nice little USB-powered LED lamp under the translucent stage of my stereo microscope.

It has proved very useful … but part of its temporary status was my use of a generous lump of Blu-Tack to serve as a strain-relief bushing.

Today, that was revealed as a mistake !

The majority of the USB cable has remained flexible, but for a length of about 60mm the [white PVC] sheath has hardened, and has actually fractured at the point of maximum stress.

Lesson learned … and shared

MichaelG.

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[OldironParticipant @oldiron]

I use it for many purposes but have never seen it do anything like that. Must have some kind of acidic reaction with the cable material. Thanks for the tip Michael.

[Steve Skelton 1Participant @steveskelton1]

I suspect that the Blu-Tack has absorbed the plasticiser from the PVC cable in a similar manner that polystyrene will.

[Tim StevensParticipant @timstevens64731]

There is a general problem with soft PVC in all sorts of applications. The plasticiser is leached out far too readily, hardening the PVC, and sometimes softening whatever it is in contact with.

My worst experiences with this have been with older vehicle tyres and inner tubes. If there is no rim-tape handy, the temptation is to use (PVC) insulating tape, which seems ideal, but … the plasticiser moves from the tape to the inner tube, hardening the (sharp) plastic, and softening the rubber, so part A cuts through part B. Not at all pleasant especially in a foreign country eg the Pyrenees.

What to use instead? I have found duct tape to be OK, as it has polythene as its plastic, not PVC. Polythene does not include plasticiser (I think!), and if you rip it lengthways, rather than cut it, the strength is not sacrificed.

Tim Stevens

[John HaineParticipant @johnhaine32865]

I use Sugru for making cable strain reliefs and similar.  It isn’t flexible but you can mould it round sleeving to anchor it, running the cable through the sleeving.

[jaCK HobsonParticipant @jackhobson50760]

Also watch out for expanded polystyrene – it eats insulation.

[John Doe 2Participant @johndoe2]

Something in Blu-tack leeches out – ask any university student ! Blu-tack is often banned in student digs, because whatever it is soaks into the plaster in the wall and can’t be removed. It has to be dug out and the hole filled.

[Michael GilliganParticipant @michaelgilligan61133]

True … but the ‘unexpected property’ was that it also appears to draw-in the plasticisers from other material.

There is presumably something akin to osmosis going-on

MichaelG.

[Matt TParticipant @mattt]

As a well versed member of student digs I’ve never heard of this rule, but I can confirm, blue-tac often stains the wall. In my experience a good landlord will simply paint over it, as they will with light switches, plug sockets and anything else they can lay a paint brush on. If a student landlord ever went to the bother of digging out and replastering for a simple blue tac mark I would like their number!

[Rod RenshawParticipant @rodrenshaw28584]

What a horrible thing to happen.

I have found a lump of BluTack useful for putting on the end of boring bars to reduce chatter. I think its mass changes the natural frequency of vibration of the boring bar. I have been keeping the lump in a plastic box but after reading this thread I am going to find a metal tin to keep it in!

Rod

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