Conservatory Wall Foundation and Base

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I have searched all over but cant seem to get any solid answer. Much of what is written either ends in arguing or completely opposite opinions so I though I would post my own circumstances.

I have dug strip foundations for my dwarf wall and part filled with concrete which has now been curing for some time. The next step is to raise this up too ground level. For this I wanted to use Thermalite Blocks for both skins for speed, ease and cost. Currently I need to come up about 300mm to hit ground level.

So my questions are:

1. Can I use my thermalite blocks for both skins (outside is to be rendered)
2. There is about 2inch of water in the trench which may come obviously return so I guess I must infill the cavity to ground level - what would be best for this?
3. If using the thermalite blocks on the outer skin I would want to render the course that enters the ground to protect from frost. What method do I use to avoid DPC bridging.
4. What stops the wall being very weak at the dpc level? does the cement bond well to dpc?

Obviously if you think there is a better way of doing it please say but I already have the block and I am on a really tight budget. I understand courses of engineering brick would be better outside but I am trying to avoid that.

Many thanks in advance to anyone who can help with solid advice. Please don't add any replies where you are not sure because its certain to go off topic quickly.

Thanks

James
 
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1/ Yes
2/ concrete
3/ Definitely go with the engineering brick
4/ The weight of the walls will overcome any weakness.
 
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Thermalite (any aerated block) can be rendered but they are the worst choice for rendering. They crack easily, absorb water too fast (poor resistance to expansion/contraction, poor render adhesion), and the pattern bleeds through the render prominently.

You should not use thermalite blocks at or just below ground level on the outside skin because frost will attack them. Use dense concrete or better still engineering brick 225mm below ground and 150mm above.

Stop the render 150mm above ground (or at DPC level if higher) to avoid splashing and damp issues, and frost attack.

Friction holds a building to the DPC, and the DPC allows the structure above ground to move with expansion

You should not build your walls now to ground level, but build them up to floor level
 
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Thanks for the replies guys. I guess I will put a few quid in then and get my self some dense block for the first couple of courses of the outside skin. I appreciate I should really use Eng brick but I am going to do the bricking myself and its probably easier for me to do with the bigger blocks.

In terms of the base slab is it a good idea to try and lap it on to the foundation?
 
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Do I need to do it or is it not really worth it?
 
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It's a design consideration, based on need rather than whether its worth it or not.
 
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