How to Complete Foundations

How to Complete Foundations

Once you have completed the brickwork for your foundations, they need to be backfilled and waterproofed (USB) before you lay a slab to complete the foundations and start building. Here is your step-by-step guide.

Your tools:

• Spirit level
• Spade
• Square
• Compactor
• Wooden or aluminium Straight Edge
• Wheelbarrow
• Pick


When foundation walls are set, start backfilling with rubble and sand. Make sure the fill is compacted and does not contain vegetation. Use water to ensure compaction. Backfill to 120mm below wall level.

Laying USB

Lay a 20mm layer of sand (sifted) over backfill before laying USB.
Note: If foundation filling needs to be treated for termites, it must be done at this stage. Start laying USB over sand layer.

USB must cover the sides and go halfway over the foundation wall. Tuck USB into corners, hold into position with bricks. All overlaps must be 300mm and should be folded and sealed with jointing tape.

Preparing to lay the slab

Any electrical conducting or plumbing must be put into position before the slab is poured. Consult the electrician or plumber. Plug ends of all piping to ensure concrete cannot get in. All fabric reinforcement must be set above USB before the concrete is poured.

Laying the slab

Mix concrete for the slab and pour onto the USB, starting furthest from the mixing point. Level the concrete to the top of the walls using a straight board as shown. Clean excess concrete off the top of the foundation wall, ready to receive the DPC layer.

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