On interior walls and ceilings I do something similar leaving a gap between boads of around 5mm which then allows sufficient adhesive to go full depth with a roll over key to lock boards together much as an old lathe and lime plaster would have done. But I still embed tape into that just as industry and insurance companies require to prevent cracking. On the external wall if using insulated plasterboard then using foam to continue the insulation barrier is also the preferred way. If there are areas of movement the fibacryl from Toupret is very good.
IMO using a proper system (such as Optima) to create a hollow drylining is much better solution that either direct plastering or messing about with dot & dab, especially on an uneven wall.
It creates a space to properly insulate, & allows the easy running of services. Any electrical items in the new area can be installed in easily installed flush boxes.
I agree Badger for flat finishing of boards even on crooked walls and hiding services. Just dont use glass fibre no matter what St Gobain say it attracts moisture and sags over time. Rockwool OTH doesnt. If you use a membrane then the natural insulations can be use but are pricey compared to rockwool. Foams usually have higher insulation levels but shrink over time so gaps can leak heat. Air sealing tapes around socket boxes etc are a good idea.
I must admit to having an aversion to using expanding foam from an aerosol can. I find it to be both messy and expensive, especially as a part used can doesn’t keep long at all. I admit that it does have its uses though, especially with an extra long nozzle pipe to reach otherwise inaccessible areas.
Instead, I usually first glue 40mm thick plain polystyrene panels to the wall in such a position that the joints will be offset by half a panel from where the 10 + 40 plasterboard joints will be.
Where I know that heavy items such as radiators need to be attached to the wall, I hide a suitable piece of timber firmly attached to the wall underneath where the plasterboard surface will be, and then cut away the insulation from the back of the board to accommodate it.
Perhaps it’s not exactly a ‘best practice’ listed in building codes but it works a treat.
I think that when working with old buildings it is necessary to be willing to adapt to the existing situation, and also to consider how much space one can afford to lose from the interior dimensions of the room, as well as factors such as the inherent dampness of the wall, and the level of insulation required…
I think it just depends upon the prevailing situation as to what system is best to use, and that they all have their pros and cons.
I know folks who prefer to use the metal rail system to which to screw the plasterboard as they can leave a nice big space behind it into which to slide 200mm of insulation roll. However, you lose about 210 to 230mm of space from the interior of the room, have a relatively flimsy structure that vibrates if someone slams a door or a big truck rumbles by, and where every element of the metal structure is supposed to be electrically earthed.
Others prefer a 4 x 2 timber structure into which they can incorporate extra noggins that will subsequently hold heavy items such as radiators or wall cabinets. A damp-proof condensation shield can easily be stapled across the timber frame before the plasterboard is nailed on. In this way the wall only consumes about 110 to 130 mm of interior room space.
Myself, I prefer the glue it to the wall method, but then I always have an avid helper in the form of my good lady wife who just loves throwing the dollops of adhesive onto the wall. Jolly good fun she reckons.
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I’m no fan of fibreglass, mainly because of the nasty dust/fibres & consequent nasal irritation (yes, even if I wear a proper mask). However, it doesn’t sag behind placo if you get the right stuff, the more solid panels that are made for that very purpose. I have seen many bodge jobs where someone has used the softer stuff designed for ceilings/lofts where the sag is very apparent. Moisture should not be an issue if a proper vapour barrier has been used.
Exactly. I’m a fan of Steico wood insulation; not cheap but very good & the dust is a lot less problematic.
I can’t stand foams of any kind due to their use of petrochemicals, & I find them messy & inaccurate to work with, & solid sheets are a pain to transport & store.
Possibly, but that thickness isn’t necessary for external walls in mainland France. Also see other response further down.
Not is they ar properly specified & installed. There are many cowboys who don’t know how to use it.
That is untrue. Only metal structures that are exposed in the regulated ‘volumes’ of a salle d’eau need to have earth bonding. I’m wearing my pro electrician hat here.
Which would only apply if you were using less insulation than the metal rail argument you made above. With wood you’d still need,say, 150mm, to accommodate 150mm insulation, & you’d have to cut it to fit into the studwork. An Optima type system could use continuous 150mm insulation & then have the 16mm fourrures & vapour barrier in front of it i.e. only taking up a minimal bit extra compared to timber (which unless the walls are true will take up more space due to the need to make adjustments for that.)
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Badger, how are you on air sealing tapes around the electrical patresses, been watching some low carbon green builders and the mold you can get is quite alarming behind fittings.
Hiya,
All I can say is that the norm in this neck of the woods (Vendee 85), is that builders retro-fitting old houses with internal wall insulation put up a metal frame and then slide 200mm of glasswool in behind it. Whether it is necessary or not according to the applicable regs I wouldn’t know, but wherever one lives surely more insulation is better than less.
When using wooden stud framing it doesn’t necessarily mean that you end up with a lower R factor on the insulation. It depends what insulation material is used. For example; A Kingspan board 75mm thick gives an R factor of 3.4 compared to 2.5 for 100mm thick glasswool. Of course it is a lot more expensive than using glasswool which is why the latter tends to be used where there is sufficient sacrificial space.
Regarding the earthing of metal frames I accept entirely your expert word on the subject as I know full well that your knowledge of the regs is comprehensive. I wonder if you could spare some time to come and educate the vendors of the rail packs who will frequently tell folks that they all need to be earthed. No doubt it helps them to sell additional reels of earthing cable. To be fair, I doubt that it is realistic to expect the staff at a builders merchant or Brico shed to know all the current regs about electrics, plumbing, heating, drainage, insulation etc.
Overall, I think that whether one system is better than another is a bit of a subjective question. Each house is different, and what will work well in one will be inappropriate for another. Then there is also the question of personal preference. I note that you mentioned that you find glasswool unpleasant to work with whereas I don’t really have a problem with it.
Even different rooms in the same house will be better served by different systems. A small bedroom needs maximum space retained so glued 10 + 40 panels with additional 20mm panels underneath may be preferable, whereas for a large kitchen with wonky walls, 100 x 50 timber studwork enables the easy subsequent fixing of heavy wall cabinets. Also handy if you need additional support for the joists of the floor above.
Just a matter of horses for courses I reckon.
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If you have problem plaster, Zinsser is great stuff as an undercoat. Very good sealant. Shellac or water based variants.
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@Robert_Hodge - We (Stuart writing this) will be using the insulated board with a vapour barrier method. Do you have the name of the glue you use for this and ‘normal’ plasterboard. We will use the same method you described that’s carried out by your wife - throwing dollops of adhesive onto the wall 
We will be paying particular attention to the outside walls - some of them have mould and are ‘icy cold’ to the touch.
I may have mentioned before, but it’s an old farmhouse (the type with 3ft thick walls). Up until now I’ve been concentrating on our small fishing lake, our outside areas (about 2 acres of fields/paddocks) and general maintenance on a ‘need to do’ basis. We’ve been threatening to start on the interior of the house for years but we thought we’d start on the entrance hall - it’s a tiny room really, but it needs some major attention.
Thank you.
Placo is normal plaster board, doublage is insulated, pick your thickness. The adhesive is PM1 or you can use expanding foam for boards not the regular foam. If you are doing a bathroom later then using Wedi panel or similar means you can go thicker on insulation and forgo the placo especially if tiling but you can skim the boards as well if painting or papering.
Youll obviously need to treat the mold first.
Hi Stuart,
The powder adhesive is called ‘Mortier Adhesive’, or ‘Mortier Adhesive Placoplatre’, or sometimes just ‘MAP’. Much cheaper to buy it in 25kg bags from one of the larger Brico places. You’ll find it being stored undercover in the vicinity of the sacks of mortar, concrete, plaster etc.
Tip: Make the purchase online by means of one of the ‘Drive’ or ‘Click & Collect’ schemes and then when you go to collect it at the pre-arranged time, it will be brought to the back of your vehicle for loading - usually by forklift. Saves a lot of lifting.
Stored correctly it will keep for years and remain fully usable. Essential to keep it in a dry place.
Tip: I slide the unopened bag into an old dry plastic 50 litre compost / soil improver bag. Then store the bag upright on its end having first put some plastic sheeting down on the floor to stand it upon. In this way you can open the top of the bag, take out what you need by means of a scoop, and then fold the top of both the bags closed, and weigh down with a brick to keep it firmly shut.
If you wish, I can ‘PM’ you and talk you through the whole process if you haven’t previously worked with this method.
Robert.
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I’ve used both Action and Lidl paints, the Lidl wall paint us probably slightly better. Action wood paint is fantastic. We did our kitchen cabinets with it, 2 coats followed by their matt varnish and it is bomb proof. I got some on my plastic kitchen table cloth and 12 months on I still haven’t been able to get it off! Cost a fraction of the stuff from the bricos!
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Hi Robert
Some very useful tips especially about the click and collect. Thanks for the offer to PM me but I’m sure that I can get through this just fine.
I won’t actually be starting on it until the spring and the weather warms up. I need to wait for the warmer weather because I have two doors to hang and I don’t want to do that particular job in this weather.
But if I do feel I need some more advice, I will certainly contact you. You’ve been a real help with some very useful information. Thank you very much indeed.
All the best - Stuart
I (Stuart) just want to say thank you to everyone who has contributed to this posting. It’s been an interesting one to read, with some handy tips and tricks.
You really are all friendly and knowledgeable and don’t seem to mind sharing your knowledge.
I do have experience of most DIY things in the UK using their methods and products but it’s a bit different here knowing the same things I would have used so the tips and tricks that different people have come across is always useful.
Rachel has made a file for me with names of some of the items to be used and I’ve bookmarked the posting so I can refer to it when the time comes to actually do the work.
Out of interest, this was my last project in the UK. We had an abandoned farmhouse - it had been vacant for 25 years and this is a before and after picture of part of the property.
Thanks again - Stuart
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If you did that yourself, we’ll be asking you for advice 
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There’s no doubt that warmer and dryer weather will be helpful to the various drying stages that are involved in the process.
Well done re the UK farmhouse. Clearly you are not averse to taking on a challenge.