Which Blocks 3.6Kn or 7KN

[glangri2]

I am about to embark on my 2 storey extension.

The wall is going to be a very conventional cavity one, with Bricks on the Outside, Blocks on the inside, and insulation in the cavity.

My question is, what sort of blocks should I be using on the inner skin?

Concrete or 'Aircrete' , and 3.6Kn or 7.0Kn?

When is one chosen over the other?

I am assuming that Aircrete blocks are easier to work with than Concrete ones, but when do you need to go for 7.0Kn over 3.6Kn..

Cheers
Gary

 

[noseall]

7n (dense) concrete blocks are used below dpc. Some builders use them where block work will be visible i.e. where there is to be no plastering.

3.5n (aerated) blocks will be ideal. These will afford you the necessary thermal performance as well as being easier to lay and transport.

A piecework brickie would not be pleased to see a pallet or ten of 7n blocks i can tell you!

 

[Chukka63]

ditto nosey,lol.i built a large extension in concrete blocks,not a nice job i can tell you.

 

[noseall]

ditto nosey,lol.i built a large extension in concrete blocks,not a nice job i can tell you.

Aye Chuck. Bet you only laid about 5 courses high before you had to move to another corner for fear of slump.

Imagine laying 'em in the winter, in the wet, with lousy muck.

 

[Chukka63]

correctomundo

 

[garyo]

7n (dense) concrete blocks are used below dpc. Some builders use them where block work will be visible i.e. where there is to be no plastering.

How come you can buy thermalite trench blocks though?

Gary

 

[noseall]

Because they are specifically 'trench' blocks.

 

[garyo]

Ah!

 

[drnail]

concrete blocks below ground ????????

 

[noseall]

concrete blocks below ground ????????

Care to elaborate?

 

[glangri2]

7n (dense) concrete blocks are used below dpc. ...........

......3.5n (aerated) blocks will be ideal. These will afford you the necessary thermal performance as well as being easier to lay and transport.

Cool, that is the answer I had hoped for.

I need about 40 blocks to get from the top of the foundation up to DPC. so will probably just order 1 full pallet of 7Kn concrete ones, use them until they run out and then get aerated ones for the rest of the build.

Cheers
Gary

 

[Chukka63]

its advisable not to mix the blocks above DPC if youre rendering or plastering them as the render/plaster will have differing drying/curing times and could result in cracking.

 

[The-brickie]

You can get 'aerated' 7.3n celcons (hi-sevens)... we have been building an extension and have had to use these under load bearing steels.

 

[Richie866]

Sorry to hijack the thread guys, but on a similar note - I'm hoping to soon get a large garage and conservatory built and it will be rendered. I have heard that aircreate blocks are crap to render so go for concrete.

Can anyone give an opinion.

Cheers

 

[glangri2]

Richie

Start a new thread!

This one is 18 months old !

For what it's worth though Aircrete blocks are no where near as weather resistant as concrete blocks, and they pull the moisture out of plaster/render very quickly so I should imaging that they are harder to render and that the render would be weaker/more brittle as well.

Cheers
Gary