Cutting holes before or after skimming?

[MJNewton]

The question as to whether to cut downlight holes before or after skimming seems such a commonly asked question on the Internet, but with a seemingly 50:50 split response this doesn't sit well with someone like me that prefers a right and a wrong way!

 

I have just finished plasterboarding our new extension ceiling with 12.5mm square edge board on resilient bars at 400mm centres. As my (bad) luck would have it, 3 of the 5 downlights (for worktop task lighting) look like they're going to end up slap bang on unsupported board edges/joins (paper edged of course) and so I am getting nervous about what consequence that might have in terms of causing cracks, either during installation (if I drill the holes after the ceiling has been skimmed) or just long-term due to a compromise of board strength.

 

I was thinking I might cut the holes before I get the boards skimmed then any movement during cutting won't be an issue. I could also then feed some adhesive-backed timber/plasterboard up through the hole and position them across the board edges/joins adjacent to the holes just to give a but more support.

 

Does drilling holes beforehand make life hard for the plasterer? Will it inevitably compromise the finish he can achieve? I did ask him when he quoted (pre-lockdown) and I seem to recall him just saying he prefers no holes - mentioned something about plaster falling out - but I didn't really push him as at that stage I didn't realise I'd be wanting to drill on some joins. I also didn't realise what a maze of joists and resilient bars I'd be up against, and typically how nearly all of my desired downlight positions seem to be really near some sort of obstacle so if I screw up I'd rather do that before it's skimmed (to allow an easy repair) than after.

 

I might be worrying over nothing... I do that. A lot. But if you can honestly tell me a plasterer won't have any issue with five 70mm holes (okay, and three 125mm holes for my MVHR vents too) over a 35m² ceiling that'll set my mind at rest.

[ProDave]

Before every time for me. Means you can see from the screws where all the joists and noggins are, and you can be SURE once you have cut the hole you can reach the cable (and if there is a problem pop a board off and investigate.  Then leave the cables coiled up just next to the hole so you can fish them out.

 

If the spread grumbles, he will still get on and do it.

 

Anything else, unless you are VERY careful and take LOTS of measurments, you risk drilling into a joist, or not finding a cable where you expect one.

[CC45]

I'd adjust the position of the boards to avoid downlights on an edge.  I took a lot of careful measurements and then cut them after skimming.  Worked fine.  You could use a plumb line and mark the position on the floor.

[nod]

1 hour ago, ProDave said:

Before every time for me. Means you can see from the screws where all the joists and noggins are, and you can be SURE once you have cut the hole you can reach the cable (and if there is a problem pop a board off and investigate.  Then leave the cables coiled up just next to the hole so you can fish them out.

 

If the spread grumbles, he will still get on and do it.

 

Anything else, unless you are VERY careful and take LOTS of measurments, you risk drilling into a joist, or not finding a cable where you expect one.

As a plasterer it pains me to say 

Before 

Much easier to skim without them cut 

But if you loose a wire or trap one when boarding its only five minutes to take a board down 

 

Pictures where taken two weeks ago

After skimming one plot the electrician realized he had placed a row of Dow lights on a RSJ 

Expensive mistake 

Four other plots we where able to remove a few boards for him 

No real drama 

[joth]

This is good news! I was planning to use trimless plaster-in downlighters and worrying about the grumbling this would cause, but if the grumbling is expected even for normal downlighters I think we should be fine

 

https://www.mr-resistor.co.uk/item.aspx?i=15768

 

 

[ProDave]

39 minutes ago, joth said:

This is good news! I was planning to use trimless plaster-in downlighters and worrying about the grumbling this would cause, but if the grumbling is expected even for normal downlighters I think we should be fine

 

https://www.mr-resistor.co.uk/item.aspx?i=15768

 

 

I will be interested to see how you get on with those.  My expectation, from all the plasterers I have seen, I you will spend ages clearing out all the muck that has got into the fitting, and then patching up the plastering around the edge of the fitting (based on a simple thing like making good a light switch back box after the spread has been)

[MJNewton]

Thanks everyone for the input - all really useful. Following up on a couple of points:

 

14 hours ago, ProDave said:

Before every time for me. Means you can see from the screws where all the joists and noggins are, and you can be SURE once you have cut the hole you can reach the cable (and if there is a problem pop a board off and investigate.  Then leave the cables coiled up just next to the hole so you can fish them out.

 

If the spread grumbles, he will still get on and do it.

 

Anything else, unless you are VERY careful and take LOTS of measurments, you risk drilling into a joist, or not finding a cable where you expect one.

 

Yes, that's what's concerning me. Even more so that I might screw up a hole and have to perform a repair of some sort. Doing that on a beautifully finished skimmed ceiling would make me weep!

 

13 hours ago, CC45 said:

I'd adjust the position of the boards to avoid downlights on an edge.

 

It's a bit of a complicated room shape, with a lantern cutout and numerous corners to accommodate, and moving the boards round on my board plan didn't give me many options without resulting in thin slithers or another joint-related problem (e.g. MVHR vent holes) somewhere. The problem join is the bottom row of boards below (where 7 and 8 run alongside 19 and 20) above the worktop beneath.

 

 

More to the point though; the boards are already up! 

 

13 hours ago, nod said:

As a plasterer it pains me to say 

Before 

Much easier to skim without them cut 

But if you loose a wire or trap one when boarding its only five minutes to take a board down 

 

That's good to hear. As long as the plasterer can cope with it (i.e. it's not a showstopper - just a preference) then I'm a bit more content. I could always bung him £20 or something as a token gesture for any grief these holes cause him!

Edited June 22, 2020 by MJNewton

[MJNewton]

1 hour ago, ProDave said:

My expectation, from all the plasterers I have seen, I you will spend ages clearing out all the muck that has got into the fitting, and then patching up the plastering around the edge of the fitting (based on a simple thing like making good a light switch back box after the spread has been)

 

On that point I was myself concerned about my clean backboxes ending up full of plaster so I've shoved in some pieces of cardboard to at least cover the cables up and help keep it out. Perhaps this'll just mean the plasterer will really go for it and I'll be poking around looking where my holes are!

 

 

I might put a little piece of tape over the screw lugs too.

Edited June 22, 2020 by MJNewton

[CC45]

I'd cut boards 7 & 8 in half lengthways and then move 19 & 20 up the room and put the 1st two offcuts back where 19 & 20 were = lights now in the middle of a board.  Now their up, I'm not sure I could be bothered.

 

Don't bother with the cardboard, a good skimmer will give them a rough clean out for you, wait for it to dry 24hrs and then use your PB knife / file to finish the job off properly.  poke some wire into threats that are blocked.  The bigger pain is polyfilling the boxes where the plasterer hasn't done close enough to the box...