Building blocks - which density ?

4 May 2004
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United Kingdom
Hi All,
Can't get the search to work at the moment so I hope I'm not going over old ground!
I need to block off a doorway in an outside cavity wall which is brick and block construction - which type of building blocks should I use for the inner skin?
Also, could someone give a quick guide to the typical applications for each density of building block please ?
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Generally you should use the same blocks that were used in the origional construction if you can. This ensures that the strength of the new work matches the existing.

Blocks can be put into 2 general types ( this can be split further).

7 newton- Used in foundations, garage floors (block and beam floors) etc where strength is most important but not theremal requirements.

3.5 newton- Used for all walling work (unless extra strength is required). There are many different types and sizes also with different u- values.

This is generalising, it is alot more complex than this and as I have said, with many different types. For DIY, this knowledge should be sufficient.

Hope this helps.
Thanks Julio.

I'll be using these blocks to close off a doorway in a block and brick cavity wall - the lintel will remain in place, so I guess the lower spec blocks are the ones I need to use. How do the 7 Newton and 3.5 Newton blocks equate to the Medium and Low Density blocks that you see in the buidlers merchants / DIY shops ? Are 7 Newton blocks 'medium density" and 3.5Newton blocks "low density" ?

Thanks again,


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