Knowledge Base

Moisture Measurement in Solid Floors

 

(Article by Philip Leach, Protimeter Technical Manager)

 

(Simplifying moisture measurement in solid floors is something which concerns everyone involved in building and construction).

Building and flooring contractors are very aware of the problems posed by excessive moisture levels in solid floors. Excessive moisture in slabs and screeds can lead to the failure of decorative floor coverings, a time consuming and expensive problem to rectify.

The conflicting requirements of fast track building programmes and drying rates of concrete exacerbate the issue; slabs are usually the slowest element of a new building to dry out to safe levels. BS8203:1996 section 3 emphasises the importance of eliminating construction moisture as far as possible and draws attention to the time taken for slabs to dry. Under ideal drying conditions a 150mm concrete slab may take over 12 months to dry from one surface.

Moisture Levels – who needs to know?

Fundamentally, specifiers, contractors and suppliers have to be confident that a floor covering will not fail in service due to residual moisture levels in the substrate. Usually they will measure the ERH of the substrate using an embedded humidity sensor such as a Protimeter Hygromaster with hygrostick or humidity box or Concretemaster III with humidity box, in accordance with BSI recommendations. Some adhesive manufacturer’s use Protimeter instruments to assess moisture levels in slabs to ensure they recommend the most appropriate adhesive systems to their customers.

ERH measurements are the most valid for assessing if substrates are Dry (less than or equal to 75%ERH), Borderline (76-80%ERH) or Damp (over 81%ERH). Principally, this is because ERH measurements are material independent and unambiguous. See also AS 1884, AS 2455 & ASTM F2170-11.

How are ERH measurements made?

The most reliable rh readings of substrates are obtained from embedded humidity sensors that measure the humidity within the material, rather than at the surface. Inherently, temperature stability is better within the substrate and equilibrium conditions are reached more quickly than at the surface, especially if power float or power trowel finishing methods have been employed.

The Protimeter humidity sleeve is now familiar to many professionals involved with slab moisture measurement. This convenient device - that is virtually flush with the surface - is placed into 16mm diameter clearance holes that have been drilled at the specified points of measurement. After allowing sufficient time for equilibration, the user removes the cap of the humidity sleeve and inserts a Hygrostick or Concretemaster III probe. This is connected to the relevant Protimeter instrument and the ERH value is recorded. Once the measurement has been taken, the humidity sleeve is re-capped and left in place. Repeat measurement can be made at any time if there is a requirement to monitor the drying rate.

Taking moisture measurements – Speed is the key.

Regrettably, ERH readings are not instantaneous, as humidity sensors require time to equilibrate with the substrate under investigation. The Protimeter MMS is very useful to the flooring sector as it enables the user to assess the general moisture condition of a substrate and to identify local damp spots quickly and non destructively in addition to measuring its ERH.

The MMS is both a moisture meter and hygrometer in one. Rapid assessment is obtained by using the instrument in Search Mode whereby the meter is held against the surface and a radio wave is emitted into the substrate. The user can map the moisture profile of the slab in this way and identify areas that should be more rigorously investigated. The MMS can be then be used as a hygrometer to measure the ERH of the substrate at these points.

MOISTURE IN SUB-FLOORS

To get the best from floor covering, or applied finish the subfloor must not be neglected. This means keeping an eye on moisture. Explanation of the methodology for industrial floors.

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