Why stud/pipe finders don't work?

[feynman]

I have tried two different types, both Bosch, not cheap, but they gave very confusing results, so I returned them both and got my money back.

I've searched this forum and it would appear that newish-build dry walled housing such as mine might have a metal foil backing on the plaster board?, which seems to massively confuse the detector.

I can find studs using the tapping technique, but I need to find pipes and cables reliably too.

Any comments or tips?

Thanks.



Mods; Please move this post if neccessary, thanks.

 

[foxhole]

You can often see a screw or nail head under obtuse light giving away the location of a stud, can be confirmed by piercing the wall with a fine screwdriver blade then measurements with give the location of further studs.
Electrician tools will locate power cables and probing fixing locations with screwdriver blade will locate pipes. Power cables should have been protected behind plasterboard but can never be taken as a given.

 

[feynman]

Yeah, as I say, I can find the studs. I need to know why the detectors don't work reliably for pipes and electrics.

Anyone know about the foil backing in drywalling?

 

[freddiemercurystwin]

Anyone know about the foil backing in drywalling?

Do you mean why the foil backing or is the foil backing having an adverse effect on the gadgets?

 

[feynman]

OK. Let's start again.

I have bought two different Bosch stud/pipe/wire detectors; for use in my 14 year old drywalled house, and they both gave very confusing readings.

For example they would show live electrical cables over a distance of about 18 inches. Now I might have been following the cable run by chance, but when I went 18 inches at 90 degrees to that, I still got the live cable indication. Now a cable cannot cover an area 18 inches by 18 inches !

A similar thing happened when I was trying to detect pipe runs in the shower room wall. I got multiple positives which, when you mapped them out, could not possibly have been true, even if it had been plumbed by a spider on speed !

The readings were also not consistent - if I went over the same spot on the wall several times as recommended, the detectors would give different results, so I took each one back to Screwfix and got my money back.

My question is, why don't they work?

I believe there might be a metal foil backing to the plaster board?

Is this the case? and if so, is this what is confusing the detector?

Can anyone comment or offer advice?

 

[freddiemercurystwin]

They don't work because they're not very good. Search the forum for cable or stud detectors and you will see.

It depends on the construction as to whether the plasterboard has a foil backing, when there is one it acts as a vapour barrier, preventing any moisture from getting past the plasterboard.

 

[feynman]

OK, thanks.

So it's not anything I'm doing wrong necessarily, the detectors just aren't very good and/or are confused by the electric field from a cable being distributed by the metal foil backing?

That's what I suspected.

Think I will buy one of those handheld screens with a tiny camera on a goose neck to see where the pipes run etc.

Cheers.