Re-board or start from scratch

[mikepercival]

After 3 years of being in our house we've finally come to do up the dining room which is an extension built in the late 80s.

It's freezing in the winter because it's essentially got 4 external walls - 1 backs onto garage, 2 are external and the other one is the old external wall of the kitchen.

I want to insulate it to try and get it warmer and was planning on installing either dot and dab insulated board or batten, use insulation board and then standard plasterboard over it.

Trouble is, on taking off the old wallpaper, it looks like it's currently simply plaster on the turbo block of the internal leaf of the cavity wall. It's obviously had some shrinkage over the years and has been patched (badly). See the pics.

The question is, should I try and take the existing plaster off and back to the blocks (is that going to be a nightmare given how soft turbo blocks are?) or just take off any blown plaster areas and then batten/dot and dab as mentioned before?

My plasterer is saying i should take it all off, but just wanted to see other opinions before I decide.

Thanks in advance.

 

[JohnD]

You can copy and paste photos into your post.

 

[mikepercival]

Thanks John, I've added the images directly to the post!

 

[dontbelieveawordofit]

by turbo blocks i’m assuming you mean thermal blocks ?

 

[mikepercival]

Yeah, I'm just going off the name the architect put on the plans (we got the old plans when we bought the house) but yeah they're the grey thermal blocks.

It's these: https://www.forterra.co.uk/thermali...rcrete-block-detail/thermalite-aircrete-turbo

 

[mikepercival]

I put a link in the last post so its being moderated but the short answer is yes, they're the thermal blocks!

 

[dontbelieveawordofit]

thermals , my pet hate. i wouldnt go knocking it about too much.
they dont look like shrinkage cracks to me . you could take the plaster off and find those cracks go straight through the blockwork. i’d dot dab it .
others may disagree.

 

[mikepercival]

Hi benny, thanks for your thoughts on it and I agree on the thermal blocks, the house is full of them and they're nothing but trouble!

I had a structural engineer check the cracks out while he was here looking at other stuff and he wasn't concerned by the cracks (he said it was likely that the plaster was stronger than the block and as it dried/shrunk, it cracked and as you said, it would probably have cracked the block too). His recommendation was to dot and dab it too.

My only concern with dot and dab is how strong the current plaster is on the wall - it's obviously blown in a few places (around the cracking mostly but in other places too) so i can always hack those bits off but not sure if it bodes well for other bits blowing once they have more weight attached to them. That was why I was considering battening to fix to the block rather than the plaster.

It's a mine field!

 

[dontbelieveawordofit]

theres a few options . you wont get a great fix for a batten in a thermal block.
dot and dab will do it. everything holds everything else together.
just make sure to prep it soundly before trying to bond anything to it.
or
make a 2x2 timber frame screwed to the floor and ceiling joists and board and skim that.

 

[mikepercival]

Thanks mate, appreciate the help with this.

 

[mrrusty]

Personally as the walls are fairly flat I would use insulated PB and use a foam adhesive like instastik. D&D adhesive has the advantage when you need to adjust the dab thickness to position the boards accurately, but has the disadvantage you really need a paddle mixer to mix it. A bag of D&D adhesive will do 1 1/2 to 2 boards. The gun foam will also do about 1 1/2 - 2 boards /can so isn't much different in cost and no mixing. Either method you should stick a couple of screws and plugs in (technically) for building regs so that the boards don't drop off in a fire (!!)

 

[mikepercival]

Thanks mrrusty and good point on the screws and plugs, hadn't thought of that!