A calcium chloride test is used to determine the emission of water vapour by concrete slabs in order to establish whether the slabs lie within acceptable moisture limits. Concrete slabs emitting high levels of water vapour are likely to damage overlying flooring materials. The calcium chloride test kit is applied to a slab where it absorbs water vapour, and the change in mass will indicate the level of vapour emission. Vapour emission is expressed in pounds per 1,000 square feet per 24 hours.
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Things you need
- Wire brush
- Vapour emission test kits
- High-quality gram scale
- Protective cone
Ensure the conditions are suitable for carrying out the test. A slab should ideally have been at a temperature of 18.3 to 29.4 degrees Celsius and humidity between 40 and 60 per cent for at least 48 hours prior to the test.
Prepare the test site by grinding the area clean or using a wire brush and thoroughly removing all dust. Ensure there are no cracks in the test site and that it does not fall in direct sunlight. Test at least three sites in the first 1,000 square feet and one site for each subsequent 1,000 square feet.
Remove the test kit from its packaging and measure and record its starting weight.
Apply the kit to the test area of the concrete slab following the manufacturer's instructions. This usually involves placing the dish containing calcium chloride on the slab and sealing a dome over the test site to ensure water vapour does not enter the test from other areas.
Place a safety cone over the test site to mark it and prevent disturbance. Leave the test kit sealed in position on the concrete slab for the correct time as indicated by the manufacturer. This will expose the calcium chloride to any water vapour emitted by the concrete. Leaving the kit in position for an incorrect period of time will result in an inaccurate calculation.
Remove the dome after exposure and retrieve the dish of calcium chloride. Re-seal it using the original tape and weigh the whole test kit again. The increase in mass represents the amount of water vapour emitted during the test procedure.
Use the manufacturer's guidance to calculate the vapour emission of the slab from the increase in mass of the test kit. Vapour emission is acceptable if the results show it is less than 1.36 Kilogram per 1,000 square feet in 24 hours.
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