What is minimum compressive strength of domestic mortar?

[desperateofderby]

Building inspector has just been round & it turns out that the builder who knocked thru' our kitchen/diner has not sat the RSJ on a "padstone" (engineering bricks would suffice according to the inspector) as per the engineer's specification.

The stress under the beam is very low = 0.66 N/mm2

My husband is a civil engineer, but does not deal with domestic materials.

He reckons that it could be reasoned that the steel beam bearing on a suitable mortar layer will be sufficient. Whilst we do not know exactly how strong average building mortar should be, we think it should be stronger than 1MPa?

 

[jeds]

Bricklaying mortar is in the range 3.6 to 6.5 MPa (28 day strength) so it would have to be pretty poor to be 1MPa.

 

[desperateofderby]

I am extremely relieved/grateful to read that range of figures. My house sale could fall thru' if I don't have this work signed off pronto.

 

[tony1851]

If the factored load gives a stress as low as 0.66N/mm^2, you wouldn't need a padstone, even with the lowest-strength brick in rubbish mortar. The beam can't be supporting very much.

 

[garyo]

The padstones for the RSJ that supported the firstfloor on my knockthrough was specified as 'no padstone' - the idea being that it could bear directly on to 3.6N lightweight block. I put it on a couple of 7N blocks just to make sure anyway, but the point being, no padstones isn't necessarily a disaster.