MasterBuild Africa

How to build a Concrete Slab

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Concrete slabs are used to support everything from patio furniture, to foot traffic, to semi-trailer trucks. There is need to provide a firm and stable base for the concrete slab by compacting the subgrade properly. Read through for steps in building a strong concrete slab.

Step 1: Mark out rough area of slab using wooden stakes. Mark lowest point.

Constructing a Concrete Slab Foundation

Step 2: Break hard ground with a mattock. Starting from the lowest point, excavate the ground removing any vegetation, soft spots in soil and protruding rocks. To avoid a section from been slightly higher than the other, use 2 bricks on edge to check levels. Fill any depression with road base to obtain a flat area.


Step 3: Spread clean sharp sand over the prepared surface, then screed. Create a formboard using old timber to hold fluid concrete in place. Drive wooden stakes on the outside of formboard until top of each stake is just below the top edge of the frame.


Step 4: Measure both diagonals of the form board to ensure they are equal. Line form board with a membrane to prevent damp rising into slab. Overlap the material and seal with duct tape.


Step 5: Cut steel reinforcing mesh and position on the board, this helps to hold steel up from the bottom of the slab. Tie overlapping mesh together with wire and ensure the wire tails point into the concrete and will not be exposed.


Step 6: Pour concrete into formboard and spread into corners with a shovel. Keep spreading until concrete is 10mm above formboard.


Step 7: Screed, using a backward and forward chopping action to level concrete. Remove excess concrete as you work and feel up hollow areas and re-screed.


Step 8: Tap formboard with hammer to release trapped air bubbles, then fill any voids that may have appeared. Run concrete edging tool around perimeter to remove sharp and brittle edges. Cure concrete for at least a week so slab can gain strength, then remove formwork.







culled from Better Homes and Gardens

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