Internal Walls - Marmox Thermoblocks & Concrete Blocks

[Mr Punter]

13 hours ago, Dave Jones said:

 

doesnt work like that.

 

It works like this:

 

	Height (m)	Lambda (W/mK)	R-value (m²K/W)	U value
Thermoblock	0.065	0.05	1.30	0.77
Aircrete 7.3N	0.215	0.18	1.19	0.84

[Kelvin]

On 27/09/2024 at 09:44, JohnMo said:

That was the way I calculated it all out also.

 

I used engineered brick on top of thermolite, good for fixing too. Our screed is 100mm concrete, so the thermolite block starts above the screed to insulation interface. So the no thermal bridges. All our internal walls are wood stud walls. We left an air gap either side of the acoustic insulation before the plasterboard. 

I calculated it that way too largely informed by one of your posts on one of my threads. 

[Dave Jones]

On 28/09/2024 at 09:43, Mr Punter said:

 

It works like this:

 

	Height (m)	Lambda (W/mK)	R-value (m²K/W)	U value
Thermoblock	0.065	0.05	1.30	0.77
Aircrete 7.3N	0.215	0.18	1.19	0.84

 

until the aircrete gets slightly damp or even worse wet then they are horriffic.

 

[DannyT]

On 27/09/2024 at 11:35, Mulberry View said:

This has all been very helpful, thanks to everyone who has contributed.

 

Just a couple of points I need to clear up...

 

So, Medium-dense Concrete blocks for the ground floor walls are a good choice?

How high to block up the ground floor walls in terms of the Posi floor above?

Take your internal walls up to the underside of joist height. Even if they aren’t load bearing walls I’d still have them so the joists are sitting on them to take some bounce out of the floors.

If your joists are not on yet, string a tight line from the outer exterior walls at each end at joist height and run your interior walls in to that height. 
when you eye through then from one end, all your walls should be same height through out the building.

medium dense blocks are fine for internal walls. We use both medium and thermalite, just depends on the developers preference.

[Mr Punter]

2 hours ago, Dave Jones said:

 

until the aircrete gets slightly damp or even worse wet then they are horriffic.

 

 

Yes when wet they are probably as thermally inefficient as solid concrete but these are internal walls so should not apply.

[Mulberry View]

5 hours ago, DannyT said:

Take your internal walls up to the underside of joist height. Even if they aren’t load bearing walls I’d still have them so the joists are sitting on them to take some bounce out of the floors.

If your joists are not on yet, string a tight line from the outer exterior walls at each end at joist height and run your interior walls in to that height. 
when you eye through then from one end, all your walls should be same height through out the building.

medium dense blocks are fine for internal walls. We use both medium and thermalite, just depends on the developers preference.

 

My First-Floor Posis are in already. My main focus is in trying to get the level right for the doorway openings so I can drop the lintels straight on top of a course, then work out the remaining blockwork after that (probably 2 courses). Planning on making the doorways 2100 high, but should I take this from FFL or top of actual finishes?

 

I have about 275mm left on the floor build-up above the B&B floor, so I need to achieve 2375mm in blockwork for the lintels to work out.

 

I've just received my Marmox Thermoblocks, they sent me 100mm thick blocks instead of 65mm by mistake, fine by me and nearly courses (2360mm with a 10mm bed under the Marmox), so I guess I can just fatten the courses up a little and get to 2375mm without too much trouble.

[DannyT]

I go 2100mm off FFL. A little thing I sometimes do is pick the frames up the thickness of the tile, wood floor etc so you can slip it under rather than cut around frames, architrave etc. I also lay wood and tile floors before skirting and again leave a 10mm gap between skirting and concrete for carpets to slip under.

Are you using wall starters to tie in to exterior walls or have ties been left out to tie into?

If the later your best following block courses best can. I’d also run some 100mm dpc under first course.

Off FFL should be 9 block and a brick to box lintel. Upto FFL you could do your course of 100mm marmox and 2 course of brick bedded up slightly to get to FFL.

[Russell griffiths]

Do you know about profiles for your blockwork ends/ corners. 
if your 1st floor is in it’s easy to make some 4x2 upright at the exact location of the wall ends, simple screw into some scrap timber and plumb up and fix to the floor joists. 
you can then mark your blockwork gauge or height on this timber and slide your string line up a course as you go. 

[Mulberry View]

1 hour ago, Russell griffiths said:

Do you know about profiles for your blockwork ends/ corners. 
if your 1st floor is in it’s easy to make some 4x2 upright at the exact location of the wall ends, simple screw into some scrap timber and plumb up and fix to the floor joists. 
you can then mark your blockwork gauge or height on this timber and slide your string line up a course as you go. 

 

Brilliant suggestion, thanks for this.

[Mulberry View]

1 hour ago, DannyT said:

I go 2100mm off FFL. A little thing I sometimes do is pick the frames up the thickness of the tile, wood floor etc so you can slip it under rather than cut around frames, architrave etc. I also lay wood and tile floors before skirting and again leave a 10mm gap between skirting and concrete for carpets to slip under.

Are you using wall starters to tie in to exterior walls or have ties been left out to tie into?

If the later your best following block courses best can. I’d also run some 100mm dpc under first course.

Off FFL should be 9 block and a brick to box lintel. Upto FFL you could do your course of 100mm marmox and 2 course of brick bedded up slightly to get to FFL.

 

That's all very helpful, but why 2 courses of bricks at the bottom and 1 at the top if that could be dealt with in a 10th block course as both a block and 3 course amount to 225?

 

Mines an ICF build, I'm not a huge fan of starter bars and am probably going to go with Owletts that I can plug into the concrete. I have time on my side with this, I'm not in a rush.

[DannyT]

42 minutes ago, Mulberry View said:

 

That's all very helpful, but why 2 courses of bricks at the bottom and 1 at the top if that could be dealt with in a 10th block course as both a block and 3 course amount to 225?

 

Mines an ICF build, I'm not a huge fan of starter bars and am probably going to go with Owletts that I can plug into the concrete. I have time on my side with this, I'm not in a rush.

If it’s a ICF then make it 10 block. Only brick courses required if exterior walls were block build and you was keeping courses with that for example photo below

 

[Mulberry View]

10 minutes ago, DannyT said:

If it’s a ICF then make it 10 block. Only brick courses required if exterior walls were block build and you was keeping courses with that for example photo below

 

 

Aaaah, yes of course. Nice one, you've been a great help.

[Dave Jones]

19 hours ago, Mr Punter said:

 

Yes when wet they are probably as thermally inefficient as solid concrete but these are internal walls so should not apply.

 

dont be silly. its a bodge, marmox are designed to eliminate this cold bridge. 

 

Nothing stopping using blocks as every house has done for years it will save a few pennies but its wrong and is still a cold bridge.

[Mulberry View]

I'm still at it with these internal walls, I'll post some pics when I get a minute. But what lintels for the internal doorways now that I'm using medium-dense concrete blocks?

 

My merchant has suggested the right-angled external ones like this...

 

[Iceverge]

 

Can you not get precast concrete lintels easily in the UK? 

 

[Mulberry View]

4 minutes ago, Iceverge said:

 

Can you not get precast concrete lintels easily in the UK? 

 

 

Ah, perhaps I can. I'll check. You think its definitely strong enough @Iceverge?

Edited Thursday at 10:46 by Mulberry View

[Russell griffiths]

Concrete lintel, but go up a size they are about 150 deep. 

[Mulberry View]

1 minute ago, Russell griffiths said:

Concrete lintel, but go up a size they are about 150 deep. 

 

So not this then?

 

[Russell griffiths]

Depends what it’s holding up

if it’s just two courses of block until you hit ceiling level then your fine with those, if it’s a wall taking uppperfloor joists then go bigger, or consult your drawings. 

[Mulberry View]

1 hour ago, Russell griffiths said:

Depends what it’s holding up

if it’s just two courses of block until you hit ceiling level then your fine with those, if it’s a wall taking uppperfloor joists then go bigger, or consult your drawings. 

 

Just the two courses.

 

While I'm here. I have two solid walls that align with a first floor Posi (no openings in either), should I pack the gap between the top of the blocks and the Posi to add strength to the floor? If so, is any protection needed between the joist and the mortar?

[Russell griffiths]

Don’t use mortar, it will crumble under the constant deflection of the joists, just a tiny amount of movement magnified many times a day times days a week will result in the mortar wearing or crumbling ever so slightly leading to the gap increasing. 
either slate packing or a nice timber to spread the load. 
work out your wall courses, you could get a nice 4x1 fitted to the joists sitting on top of the blockwork, or an equivalent depending on the gap. 
buy it a bit bigger and run a plane over it until you get a snug fit.