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85% of complaints are as a result of moisture, Source: FITA
If a subfloor/substrate has not reached the required level of dryness before a floor covering is laid then residual moisture held between the aggregate and cement (or other binder) will slowly be released, reaching the subfloor/substrate preparation and the floor covering causing damage from beneath.
Testing the moisture of a subfloor/substrate can be relatively straightforward, providing you know what you are assessing and have the appropriate equipment. British Standards are in place and subfloors/substrates should be tested in accordance with the British Codes of Practice BS 8203, BS 5325 and BS 8201. A BS hygrometer box should be used. This will provide a Relative Humidity (RH) reading. A reading above 75%RH is higher than is recommended to lay floors without a surface DPM.
If a moisture reading taken is greater than 75%RH then the subfloor/substrate is considered wet (when laying textile/resilient floor coverings, 65%RH for wood). Provided the subfloor/substrate is suitable to receive moisture protection products either a DPM or a MVS can be used. If using either UltraFloor DPM IT or UltraFloor Suppress IT, follow the product’s respective usage instructions as detailed on the datasheet.
Only as a two coat application, UltraFloor DPM IT may be used on subfloors/substrates where there is an absence of a constructional base DPM provided there is no hydrostatic pressure. UltraFloor DPM IT should not be used in projects where hydrostatic pressure is a concern. In such cases the use of pressure relief drainage and/or external tanking systems must be the primary method of protection against moisture.