Using concrete/building blocks

[ChippyJoe]

Helping a friend build a 14' x 12' workshop at end of garden using concrete building blocks but never used these before in my very modest brickie work in the past ! He will use it to rebuild engines and wants to put a support beam across to use a hoist to lift them. Height of the walls will be about 8'.
My questions are:
1-Should we use high density blocks for the whole walls or just the first row, where I assume I should put a DPC. High density blocks are very heavy of course, but I can find very little info on the lighter ones usage.
2-Should we put a pier halfway along each wall for the support (hoist) beam ?
3-Should we consider 140mm thick blocks rather than 100mm for wall strength or is this over-engineering ?
4-Will whatever blocks we use be waterprrof or should they be masonary painted (guess we will be painting the outside anyway).
Thanks, Joe

 

[noseall]

The entire internal skin of most modern homes is built out of lightweight blocks and these, support the roof and floors. However, where steel beams etc bear onto the structure pad-stones are used directly beneath.

Use 7n dense concrete blocks and/or engineering bricks below dpc. Use 3.5n lightweight aggregate blocks above dpc if you are rendering or build the lot out of dense fellas if you want to show pointed block-work.

You can continue to use 3.5n light-weight fellas even if you are not rendering but they look like a dogs dinner.

From a strength point of view 100mm thick walls will be adequate however they will be very vulnerable to the elements and extremes of temperature. All depends how comfy you want to be and whether internal dampness is going to be an issue.

 

[ChippyJoe]

Many thanks for the reply which is most helpful. As a simple 'lay brickie' I'm not quite understanding the term 'structure pad-stones' - are these stronger ones or hard bricks ?
Not planning on rendering, probably painting. Am happy to use the 7n ones all the way up even though they appear to be quite heavy. I've seen some medium density blocks (by googling) that are a smoother 'paint finish', maybe we could consider these if easily available.
When you say 100mm will be adeqate but vulnerable, would 140mm add benefit here or would that be down to cladding or other ?
Again, as a lay brickie I have always wondered about dpc's (rubber/plastic roll) as being a breakline in the mortar ! Is it just the weight of the wall above that keeps it all safely in place ? (this may seem a really silly question !)

 

[noseall]

A pad-stone is a fancy name for a hard block which bears the impact of steel beams etc, particularly when softer 3.5n blocks are used. You can actually buy pad-stones in the form of a block sized (215mm x 440mm x 100mm) piece of cast concrete.

140mm will always be better than 100mm in the same way a cavity wall will be better than 140mm. A cladded 140mm structure in my opinion will be adequate for a workshop, however they are no fun to lay.

Medium density fair faced blocks sound ideal and a reasonable compromise.

Earth retaining walls aside, DPC's should always be fitted irrespective of their structural vulnerabilities.