Block strength in External Wall/Ground Floor Construction

[patp]

Our brickie, who comes highly recommended, is pricing up our job. We gave him the detailed drawings to work from.

The architect has specified, on the drawings, that the Durox Supablocs are 3.6Nmm2. Our brickie says that they haven't used that spec for years and always use 7.3Nmm2 now. I have queried with the architect over who is right and his answer is that either is fine but we should only need 3.6mm2 as we are only building a bungalow.

 

Firstly what is the difference? I assume it is density and strength?

 

What do others think?

 

I haven't checked the difference in price by the way.

[epsilonGreedy]

On 09/08/2019 at 12:49, patp said:

Firstly what is the difference? I assume it is density and strength?

 

 

Strictly speaking the difference is strength though within any particular manufacturing process/block ingredients recipe, then density increases with strength. A 7.3N hemelite weights about 15kg, whereas a 7.3N thermolite type block with an internal structure that looks like the inside of a Cadburys whisper bar will be much lighter.

 

On 09/08/2019 at 12:49, patp said:

What do others think?

 

 

I have come to realize there are regional/team conventions, in any area tradesmen like to stick with what they know. In my part of the world Plasmor 3.6n Fibolites are the block of choice for inner two story walls, these straddle the light/medium block categories at 9kg per block.

 

What weather proof cladding will you use? I ask because aerated blocks suffer from freeze/thaw cycles when wet.

 

I assume your questions relates to above dpc?

Edited September 1, 2019 by epsilonGreedy

[PeterW]

Neither will matter, it’s a minimum spec. Just check the design spec for the block against the SAP DER/TER as you need to make sure the thermal performance isn’t affected by a different block. 

[Oz07]

I thought 3.6n ok for 2 storeys

[PeterW]

50 minutes ago, Oz07 said:

I thought 3.6n ok for 2 storeys

 

It is - but a lot of sites are using 7N throughout as it means only having one block type on site as 7N have been traditionally a below DPC block (well round here they are ..!)