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Discuss Best method to find joists ? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

L

Lofty

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Ok, so you have a customer who's ceilings are boarded using foil backed plasterboard which effectively screws a lot of the electronic detectors and they DO NOT want loads of holes made in it so that 'it looks like a second-hand dart board'. What's the best way of locating the joists so they can have downlighters fitted ?.:confused:
 
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L

Lofty

  • Thread Starter Thread Starter
  • #3
Hi Cirrus,
Could do. But they have laminate flooring up there. So I suppose they either pay us to do it or they do it themselves and we come back.

Best regards,
Lofty
 
U

U Jay

  • Thread Starter Thread Starter
  • #4
Could try tapping on the ceiling with a screwdriver handle, I know it's primative but the tone changes when you hit a joist. Sorry best I can do this time of night.:eek:
 
J

Jurassic Spark

  • Thread Starter Thread Starter
  • #5
I normally tap the ceiling with the knuckle of my index finger and listen to the sound it makes. When it becomes a dull thud instead of a hollow noise you've found or are pretty near to the joist.

I use a laser line fixed to the ceiling to mark out the positions of the downlights, fixing it in a position to give suitable clearance away from the joist. I then make a pilot hole where the centre of the downlight is going to be and then stick a wire from a coat-hanger into the hole pointing it in four directions to make sure the joist is far enough away.
 
U

U Jay

  • Thread Starter Thread Starter
  • #6
I like the laser idea, keep 'em nice and straight. btw if ever you can't find a cable in a downlighter hole when the plasterers have chucked everything out of sight, try sticking your mobile phone up there and take some pics...works a treat!
 

Des 56

-
Arms
Esteemed
A joist finder (also refered to by its other name Hammer )
will soon let you know where its located
:)
 
L

Lofty

  • Thread Starter Thread Starter
  • #8
Actually did it using the knuckle method and my laser line. Took some time but victorious in the end. Mind you the plumber wasn't happy about having the radio off so we could here the different 'tones'.
 
L

London Luke

  • Thread Starter Thread Starter
  • #9
Once you have found 2-3 and worked out the "Spacing" etc it should be easier.

I have seen a very unusual method a few years ago !!
the plasterboard was held up with nails. this guy using some timber went around banging the ceiling until the little bits of plaster fell off the nails !!!. I must admit he did a good job and it took him very little time to make good after (decorator painting anyway)
 
J

jibtech

  • Thread Starter Thread Starter
  • #10
nice thinking with the nails and the mobile phone and the wire to check for clearance from the pilot hole

arent laser lines ace!

i want an endoscope they look brilliant and you can check out your own poop chute or a friends:p
 
L

linzilou72

  • Thread Starter Thread Starter
  • #11
That's hilarious jibtech, do you live in Brighton by any chance??
 
L

London Luke

  • Thread Starter Thread Starter
  • #14
ɹoɯnɥ ʎɹp pǝllɐɔ sʇı
 
J

jibtech

  • Thread Starter Thread Starter
  • #15
could put it on the van underneath fault finding and above rewires endoscopys? endoscopies? bum inspections??

hahah lol sorry im a kid but not from brighton how dare you!!

im a good welsh lad :)

and that means im tight(with money) and if im gonna buy something im gonna exploit all its uses now bend over free inspections for all forum members luke is paying.. and first up! he requested on pm!!
 
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A

alancp

  • Thread Starter Thread Starter
  • #16
wot about the old faithfull tool, the spreads hammer, it wont find where the joists are, just a lot of places where they are not!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
S

spark-doctor

  • Thread Starter Thread Starter
  • #17
I use a rare earth magnet, you can get them on Ebay. It is only the size of a 2 pound coin but very very strong. Use it to find the nails or screws in one joist and push in a board pin then the next joist and then you can work out the spacing of the joists.

You can also drop it in a paper or plastic coffee cup that has been left on a metal surface and laugh your arse of when your mate trys to pick it up.
 
W

wattsup

  • Thread Starter Thread Starter
  • #18
They are normally 16" or 400mm centres if load bearing(floor above)

Sometimes 18" if not load bearing, upstairs ceiling etc..
 
S

sparkyork

i use a dewalt self levelling one. does horizontal and vertical and shines for miles and miles and miles and miles and miles, proper good, not cheap but you pays your money you get what you pay for!!
 
M

mdshunk

  • Thread Starter Thread Starter
  • #21
I got a thermal imaging camera a while back for another reason, and it has the side benefit of finding the joists in a ceiling when you're fitting recessed lighting fixtures. It's the closest thing to having X-ray vision. Shows each and every joist very clearly, and also shows any additional blocking that you might not have expected if you only found the joists.

Here's the one I have:
FLIR ThermaCAM B-CAM Infrared Thermal Imaging Camera - Mfg# 27801-0202



 
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M

mdshunk

  • Thread Starter Thread Starter
  • #23
yeah baby im liking that, bet that was a pretty penny tho?
$5000 US, so I'm guessing that's about 10,000 pounds maybe? Not something you'd leave lay around while you went on your lunch break.
 
S

sparkyork

blimey! thats more than i thought it would be! suppose you'd have a job pricing one of these in with 10 downlighters! looks great tho, its like something off that arnie film "eraser"
 
M

mdshunk

  • Thread Starter Thread Starter
  • #25
blimey! thats more than i thought it would be! suppose you'd have a job pricing one of these in with 10 downlighters!
Yes, it would be pretty difficult to hide that in the price of a job like that, unless your customer was rich and suffered from Alzheimer's.
 
J

jibtech

  • Thread Starter Thread Starter
  • #26
thats ace does it see through clothes?

seriously tho i have done surveys with one of these in industrial applications looking for hot spots never thought of looking for joists with one though

and the de walt laser line with auto levelling is the one i used couldnt fault it

oh and not 10000 more like 2500 you went the wrong way :D
 
M

mdshunk

  • Thread Starter Thread Starter
  • #27
oh and not 10000 more like 2500 you went the wrong way :D
Oh, sorry. Yeah, that makes a big difference.

After that whole Boston Tea Party thing, when we ran you all out, you not only forgot to leave behind your dictionary, but a dollars to pounds calculator would have been nice. ;)
 
W

wayne

  • Thread Starter Thread Starter
  • #28
i thought the usa was trying to turn the dollar into The global currency??
 
M

mdshunk

  • Thread Starter Thread Starter
  • #30
great piece of equipment, you got any other gadgets to show us?
Beats me. I'm not sure what I might use that you'd find interesting that you don't already use. I've got so many gadgets for stuff, but many of them are peculiar to US wiring methods.

i thought the usa was trying to turn the dollar into The global currency??
We're saving that for after we take over the world. :D
 
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W

wattsup

  • Thread Starter Thread Starter
  • #32
>>thats ace does it see through clothes? <<
I hope not, my vault stick ain't what it once was, well and truley battered, needs attention.. Any apprentice females out there know how to repair it? In fact it ought to be an exam question -:)
 
G

greekislandlover

  • Thread Starter Thread Starter
  • #33
Sorry if I'm missing something here, but after you have found the joists, how are you going to get a cable through them if the punter doesn't want you to lift the laminate, and doesn't want the ceiling peppered with holes? Are you planning to put all the downlighters within the same joist and point them in random directions, or is the ceiling suspended with some space above the joists to run cables?

My tip for looking in tight spaces is a bit of broken mirror tile and a head torch. If you shine the torch on the mirror and angle just right you can see what you need to. Not sure the "Elf N Safety" nazi's would necessarily approve of carrying broken mirrors in the toolbox though. I like the thermal imaging camera and endoscope ideas though :)
 
M

mdshunk

  • Thread Starter Thread Starter
  • #34
Are you planning to put all the downlighters within the same joist and point them in random directions, or is the ceiling suspended with some space above the joists to run cables?
I guess you can drill holes in the UK, same as we can in the US? :p

I use these long, flexi bits if I need to drill through several joists, from one down lighter location to another. They're between 3 and 6 feet long, and they bend a bit so that you can get them in the ceiling cavity. Maybe you all have those available to you already?

 
M

montybaber

  • Thread Starter Thread Starter
  • #35
you lot have got everything over there :(
 
M

mdshunk

  • Thread Starter Thread Starter
  • #36
you lot have got everything over there :(
Hey, brother, eBay is everywhere. My wall chaser was shipped from the UK. Didn't cost much at all for shipping. Maybe you have to pay an import duty for stuff from the US?
 
S

sparkyork

with reference to that looooong drill bit! im not sure that would work over here, for one i dont know if you could get that through a 65mm downlight hole without destroying the cieling around the hole, 2ndly, dont know what the regs are like over there but we've gotta drill a certain depth in the actual joist, must be a bit of guess work involved in using one of these and also not knowing what your about to drill through!! (pipes, soil pipes, cables) it'd be one of them hope theres nothing there moments where you close your eyes and pray!
 
M

mdshunk

  • Thread Starter Thread Starter
  • #38
with reference to that looooong drill bit! im not sure that would work over here, for one i dont know if you could get that through a 65mm downlight hole without destroying the cieling around the hole,
Probably not. My typical recessed lighting cans take either a 4-3/8" (110mm) hole or a 6-5/8" (168mm) hole. They work well for that. There is a placement tool that holds the bit "bent" so that you can effectively drill "dead centered" in the timber if you're skilled. No way to prove it to an inspector, obviously. Here's another nifty gadget you might like, along the lines of the broken mirror and head torch. It's called a "wall eye periscope". Works good in ceilings too. It's basically just a mirror with a little LED lamp built in.



 
T

tony.towa

  • Thread Starter Thread Starter
  • #39
They say the simplest ideas are the best.

That wall eye periscope is a superb idea, the number of times I've tried to make my neck double jointed to try and see if there is a way round a hidden noggin. Ebay here I come.
 
C

Carter

  • Thread Starter Thread Starter
  • #40
Whenever I get conned into a domestic job and need to find the ceiling joists my first option is to get up close and look for any rippling that coincides with the 16 inch spacing.
If that doesnt reveal anything, next port of call is to drop the pendant and locate the joist it's usually fixed to. Then apply 16 in centres.

Loving the mobile phone camera wheeze though, kudos for that one. And that little periscope doodad is just an excellent bit of bling for the toolbox! :cool:
 
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