Cast-In-Place Concrete
General
Cast-in-place concrete as a permanent wearing surface over a waterproofing membrane presents a number of potential difficulties. Special care and precautions are to be taken. Derbigum recommends that this method of providing a wearing surface be considered a last resort, and then only in close consultation with Derbigum.
Some of the difficulties to be considered are:
- Damage to the waterproofing membrane during the concrete casting process.
- Steel reinforcing fixing methods.
- The membrane is subject to excessive stresses caused by expansion and contraction both through the curing process and subsequent thermal fluctuations
- Extreme difficulty in accessing the waterproofing system at a later stage in order to effect repairs, alterations or additions.
When it is necessary to use this system, the concrete is to be laid on a protective sand/cement screed (approx. 1:6 or 1:8) which in turn is laid on an isolating double layer of 250 micron polyethylene sheeting. Concrete paving is to be cast in panels (generally not exceeding 10m²) creating movement joints which are to be filled with a jointing compound. The size of the joints is to be determined by the Engineer.
Abutments and Edges
The waterproofing membrane is to be turned up at edges to a level higher than the finished concrete level. A soft-joint is to be formed at all abutments so as to accommodate movement in the mass concrete and avoid damage to the waterproofing membrane.
Specification
| Specification |
| One layer Derbigum CG4 on one layer Derbigum CG3 waterproofing membrane with 75mm side laps and 100mm end laps, sealed to primed surfaces by “torch-fusion”, followed by a layer of 250 micron plastic sheeting with 50mm laps loose laid on waterproofing as isolation/protection layer followed by a 40 mm thick protective screed (by others) to receive cast-in-place concrete (elsewhere specified). Waterproofing to be installed by an Approved Derbigum Contractor. |
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Flood Test
The integrity of the waterproofing should be established by means of a flood-test of 48hrs – 72hrs duration, prior to handing over to the contractor. A certificate is to be obtained from the professional team recording the date and time-period of the test and that the waterproof treatment was handed over in a clean, proper and watertight condition.
