Is plasterer taking the piss?

[Sam9769]

We have hired a plasterer to insulate our kitchen ceiling with celotex and board and plaster it. He installed sheets of celotex but didn't tape up any seams or apply an expanding foam to the gaps and is proceeding to board it?

Is he taking the piss and cutting corners?
It seems to me that what he is doing is a waste of time if he isn't going to fill the gaps as the insulation won't be effective.

Can you tell me what you think please?

I think sealing up the gaps would be a really bad idea. There would be no ventilation and you’d probably get damp. However, I should caveat that I’m not in any trade so others may disagree! I do live in an old house and know the importance of ventilation though

From a quick google review the gaps need to be covered with aluminium tape and bigger gaps with expanding foam other wise the insulation won't be effective.

I have only seen it done on walls but they always tape and use expanding foam to stop cold bridging. Absolutely loads of videos on youtube of people insulating walls which is where I have seen it for research purposes for my own house.

I watch really knowledgeable people like Charlie DIYte. Edited to add Ali Dymock into the mix, loads of others though.

I think armed with that id ask him the reasoning behind not sealing it, to see if he comes up with anything that sounds reasonable?

Fair enough. Better than nothing though! It’s still providing insulation. Have you had a chat with the plasterer to see what his opinion is of doing it your way?

You don’t want the insulation to be so effective that it causes condensation.
perhaps have a chat with the chap and ask him his reasoning for leaving the gaps.

There coincidentally lots of people (on MN too) complaining about condensation and buying dehumidifiers to deal with it.

I'd repost this in Property rather than AIBU to get answers from people with relevant knowledge

Well, it's not really doing it my way. The aluminium tape is supplied for the purpose of sealing the gaps in addition to the expanding foam. He's charging us over £1K for the job. I don't want him to do it his way or my way, I want him to do it the right way. I'm not paying him over a grand for a job that's "better than nothing".

@KnickerlessParsons but is that because they are having their walls insulated? I mentioned Charlie DIYte because he has installed a lot of insulated plasterboard to his house as it is solid wall. He also didn't want to use dot and dab because it literally puts wet adhesive between the wall and the insulation.

Any time you cut a hole into insulated boards you break the vapour barrier and risk cold bridging. You have to dot and dab, or in his latest video use adhesive foam specifically for installing plasterboard/insulated plasterboard to create a seal around it. Therefore all gaps in insulation should be taped and expanding foam used. He references insulation websites to backup his reasoning. This is on other videos too, Restoration Couple being another.

Charlie's whole content is based on learning a lot about his projects with help from the professionals, showing you all his experiments before committing to the work he does. Saying he is very accomplished at DIY would be an understatement. He also talks dehumidifiers, mould and damp, extractor fans as well as insulation.

Thank you.

Why are you having it done? For warmth, or because you have condensation issues? What is above the ceiling - a simple roof, or a void space of the level above?

And what is the starting point? Are you insulating beneath the existing ceiling so you have a plaster/celotex/plasterboard sandwich, or replacing the entire ceiling? Is the existing ceiling plasterboard, or lath/plaster?

And what is the depth of the celotex? The boards vary from 1" thick upwards.

And how is the celotex and plasterboard attached?

And what things are going to penetrate the new ceiling (downlighters, fans, extractors, etc)

I'm presuming that you've had the original ceiling removed, in which case the celotex should be fitted within the joists. (Small gaps such as boards butting up to each other don't matter terribly).
There should then be a vapour barrier so no moisture can get to the cold side of the insulation otherwise you'll get mould/rot in the joists,
And then the plasterboards should be screwed into the joists, taped, and skimmed.

If the existing ceiling is in place, then the procedure is much the same but the insulation boards must be screwed into place with flat plates to stop the screws going through. Under no circumstance should this be done with dot/dab things like gripfill or expanding foam because the vapour barrier would then be the shear layer.

HTH

We have hired a plasterer to insulate our kitchen ceiling with celotex and board and plaster it.

Just to add, is this what you told him you wanted?

Or did you specify an outcome you wanted (warmth, limited condensation, etc)

If you told him the process to follow (celotex and board) then he's doing that and might just be doing exactly what you asked for.

If you gave him the desired outcome then he should be acting according to building control.

Thank you for your response.

The kitchen ceiling has been removed and 70mm celotex has been pushed in between the joists. There is a void above the ceiling.
The insulation is being installed for warmth as there is little insulation in the house. He has done nothing with the gaps between the celotex and joists and is proceeding to screw plasterboard over the celotex.

Should he have taped and foamed the gaps?

How do you create a vapour barrier?

Many thanks,