No-fines home - insulating

[cwhaley]

I'm going to insulate one wall of the mother-in-law's home (the outside wall of the living room).

Plan is to strip the plaster, batten out and fill with 25mm insulation, then overlay that with 25mm insulation and cover with plasterboard/skim.

Are there any special considerations to take into account? I know the general composition of the concrete substance of these homes and when I saw one knocked down locally, it seemed like two skins of concrete filled with pebbles. If I remove all of the render/plaster, what will I see below?

I do have a decent Bosch SDS drill with DeWalt bits.

 

[^woody^]

Celotex type insulation would be better than any old insulation at that thickness.

 

[endecotp]

You're proposing to insulate the interior of the wall, right? Have you considered external wall insulation?

I think when you remove the plaster you'll find pebbles held together with cement. You can fit insulation boards to that.
A membrane of some sort may be required. Maybe someone else will comment on that.
I'd suggest not battening, but instead dot-and-dab insulated plasterboard. Fixing into the no fines will be unpleasant; glueing to it with d&d adhesive should be much easier.

Think about how to deal with windows and sockets.

Not that I've ever done anything like this....

 

[cwhaley]

Yes this is internal wall insulation (I did the same in my upstairs North-facing rooms). External insulation has been done to many homes in her area but is far, far more expensive and beyond her price range unfortunately.

No sockets on the wall, just one light switch so I'll be careful taking plaster off around the line of the wire.

Would an adhesive hold the weight of 50mm of insulation and 12.5mm of plasterboard? I only ask because I've never used the 'dot and dab' method before. I don't mind drilling into the walls as I've done before, but would happily take an alternative!

Thanks for the replies.

 

[Mr Chibs]

I've batten'd mine, with 25x50mm battens, then 50mm celotex, then plasterboard.
Board adhesive bags say it is ideal for fixing thermal boards... but I'm a bit sceptical as insulation board (5kg) & plasterboard (25kg) is quite heavy per 8x4.
Battens also make it fairly easy when dealing with sockets etc.
D&D is quicker though!

 

[cwhaley]

The weight of the boards is what's concerning me here. 50mm deep battens are a good idea too - I only suggested 25mm insulation as I have tons of 25mm x 25mm lengths of treated timber.

If the only downside is the pain of drilling into the concrete, I'll take this and ask for a new set of drill bits for my birthday Not a huge wall anyway (14' long by 8' high).

 

[Mr Chibs]

The battens only stick out 25mm from the wall, I used concrete screws to fix them to brick wall.
I wouldn't bother with only 25mm insulation... 50mm would be the minimum to make a difference.
SDS and Bosch drill bits will make mincemeat of the process.

60mm concrete screw, for batten, then 50mm celotex on top, 60/70mm screw for celotex, then 80/90mm for plasterboard.

 

[cwhaley]

By 25mm I meant 25mm between the battens as I already have these, then overlaid with 25mm over the top (written in my first post), but I see you're proposing an air gap behind which sounds like a good idea. I didn't have the gap on mine and haven't had problems, but this wall is much more open to the elements than ours' (370 ft. above sea level in damp mid-Derbyshire)

Thank you for the ideas. Will be starting in the spring so gives me some thoughts!

 

[^woody^]

Air gaps are not a good idea and are unnecessary.

 

[cwhaley]

Air gaps are not a good idea and are unnecessary.

Why aren't they? Genuine question as it has been recommended to me before.

When I did upstairs at my own home, I took everything to bare brick, battened out and filled between the battens with 25mm insulation, then covered that with 25mm insulation and then screwed foil-backed plasterboard over the top. Had no problems but the idea of an air gap behind has got me thinking.

 

[motorbiking]

Don't batten, that just increases the U-value - Just buy Celotex PL4065 (or similar) and fix directly to the stripped brick, using frame fixers or dot n dab etc. Then tape and skim the joints. The only downside is a need for longer screws when fixing items to the wall.

You don't need an air gap where there is a vapour barrier and no chance of warm air touching the cold surface. If you create an air gap then you increase the risk of condensation.

Question: before you do any of this: - what kind of wall is it. Have you considered the heat loss might be the windows, doors, floors chimney etc?

see video on how to here:

 

[cwhaley]

those are expensive! I do like the idea of them to be fair with everything all in one, thanks for suggesting. Thing is though I've not had any problem with the battening I've done and I know others who did it when Celotex was being sold cheaply by a building contractor a few years back.

The heat loss is through the wall which is why I want to insulate it. As the post title and earlier posts say, it's a no-fines house with completely un-insulated concrete walls.

 

[^woody^]

Why aren't they? Genuine question as it has been recommended to me before

Because air is not as good an insulator as celotex, so you are wasting the space for no gain.

Plus an unvented air cavity with a cold surface increases the condensation risk - in your case the consequences are not that significant, but the principle remains that its not a good idea.

 

[cwhaley]

Thank you for the answer; makes perfect sense. Initially I was told the air cap "lets the air flow".

I'll do it as I did mine then -- with Celotex pressed against the wall and foil tape over all the joints before putting the plasterboard up.

 

[endecotp]

Dot-and-dab is an absolutely standard method for attaching plasterboard (insulated or not) to walls and has no trouble at all with the weight.
Another option is to use sticky foam. I've done this once and it is also rock solid. In this case you're encouraged to also use a small number of mechanical fixings, but I think that's a fire safety thing and not related to its normal strength.