Plasterer's Request Ceiling Holes

My plasterer has requested I do not make holes in the ceiling for down lights until ceiling is plastered. Issue is I cannot get into the ceiling void as upstairs floor has underfloor heating. ( Ceiling is not yet boarded out). Is there an easy way of finding the cable terminations.? I have thought of taking a reference point and measuring position of each location but on a 40 sq mt ceiling divided into 3 banks of lighting this could be a long job and possibly prone to error. Other thought was to fix a clout clout nail at the location and use metal detector, but as the ceiling has resilient bars I guess the detector will be fooled. Does anyone have a neat solution to this issue?

Thank you

measuring carefully can work, provided you don't lose the numbers. If joists aren't in the way, then plenty of slack in the cables and a downlighter big enough to get your haand through gives some room for error. You can also get downlighters with a fixed ceiling plate that you fit before plastering.  I have also heard of a new product, a sticker you fix to the plasterboard that when skimmed over 'bleeds' a stain through the plaster to show where to drill

Mark the walls, all four of them, pull a chalk line across, you then have a grid of the hole positions,

Can you mark your grid on the floor using duct tape or marker pen and when the plasterer has finished use a vertical laser to transfer the points to the ceiling for drilling the downlight holes

i always take measurements and drill the holes myself. plasterers cannot be trusted to get them in the right place

just make sure that when you go back for 2nd fix, the wall you take your measurements from hasnt been built out by 120mm

UNG said:

Can you mark your grid on the floor using duct tape or marker pen and when the plasterer has finished use a vertical laser to transfer the points to the ceiling for drilling the downlight holes

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Posher way of what I was thinking

I was going to say mark floor and use a plumb bob to transfer marks

I take measurements before the ceiling is boarded out. Once it has been boarded I cut holes before plasterer has skimmed. Mistakes do happen - these can easily be fixed before skimming - not so easy afterwards.

The plasterer is just trying to make things easier for himself - which isn't necessarily the best approach for the job as whole. The ceiling can be skimmed after holes are cut easily enough - indeed one plasterer I work with prefers the downlights to be half in BEFORE he skims so that he has enough light - he is skilled enough to do this, not all are.

Take accurate measurements AND photo's before the ceiling goes up.

I try and run all down lights from a single piece of cable and leave a decent loop at each light position, often with a loose clip holding the cable away from the board, so it doesn't get trapped between the joists and the ceiling when the boarding goes up. Drill holes and fish cable down  - then do continuity and IR tests on the new cable from the switch before I start my 2nd fix

this is what happens when a plasterer marks the ceiling for you...

Could you stick a screw in where the whole will need to be drilled and let him plaster around the screw. 

I've only ever measured from a fixed reference afterwards or drilled before skimming. Never had any major issues, most plasterers I work with prefer me to drill beforehand so I am not putting holes in the wrong spot on their new ceiling, those that want me to do it afterwards have to accept that it can be hit and miss, but usually if you measure carefully it should be fine. I've done huge ceilings with loads of lights after the event, did one the other day where the first fix was done by someone else and there were nowhere enar enough lights and the kitchen was rearranged anyway. Just worked out where the joists were, marked the ceiling out and then drilled the first hole and rechecked the others. All fine, everything where it should be, no drama.

Basically, measure twice drill once if you are doing it afterwards.

Paint spray marks on floor plumbed from light position. Spray a big circle with cross in middle, ping up,from laser. Take pics

never failed me yet.....tricky when Carpet is down, paint can be such a stubborn stain :facepalm:

If floor is wood drop a plumb line from the light location & push a drawing pin in the floor, do the reverse after he has plastered...............works a treat.

M107 said:

If floor is wood drop a plumb line from the light location & push a drawing pin in the floor, do the reverse after he has plastered...............works a treat.

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That's so bloody obvious I had never thought of it.

I've measured them for years .  Set out where the lights come in relation to the joists ,  this usually means some jigging about to make sure they all miss a joist.

Check with builder on final finish of walls.

Make drawing , give to builder , keep copy.

Return when plasterer has gone.

The other method I do is measure where the joists sit  ( with builder)  leave cables in approx. position ....then set it all out & drill  after plastering .

However , the plumbline & pin method I like the sound of.

( I was caught out once when , unknown to me , a partition wall was taken down & resited ....started drilling at outer wall ...didn't realise till I got to the other end . )

Gosh what a great response thank you all. Not sure what option I will take they are all good ideas, could end up with a combination of them. However as have not yet decided exactly where the fittings will be and need to decide on the location I like the idea from Steptoe, as that will help me with the location, I can move the lines so as to get the gaps between the joists and the resilient bars (which run in the opposite direction) and the references will be there afterwards for drilling post plastering. My plasterer is very good and I try to make it as easy for him to do as good a job as possible which is why I try and accommodate his request. For me it would be better if the holes were predrilled but given the comment by Heffler about the lighting I will try and sell it to him that he can have some lights to work with as the room is quite dark but I am not sure he will favour this as the lighting will be into his eyes. I am fortunate that as I am doing the build myself there is only me and the plasterer in the loop so no one else to get it wrong. Thank you again a brilliant response.

i dont understand how it can be anything but measured?

I put the cable up to a measured point.

Someone plasterboards it.

I drill a hole to the measured point i put the cable at

Unless you plan to stab holes through while someone boards it, which has to be harder then measurement.