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Beware Of Ghosts Of Fitters Past

I AM often asked whether a floor that has been installed for a number of years can still have moisture issues. The answer is very definitely yes!

I first came across this when working for Protimeter at Marlow before the company was acquired by GE. I was doing some demo work in a warehouse in Didcot with Ardex. The floor we were working on was over 10 years old and consisted of a power floated concrete slab 8in deep; a Visqueen membrane had been installed before the concrete was poured.

RF (radio frequency) search mode readings came up quite high at 600 to 700 on the Protimeter MMS 0 – 1000 scale. Measure mode pin readings on the surface were much lower as one might expect, reading as they did between 9.5 and 12.00, bearing in mind that the surface was contaminated by rubber (and carbon black) from forklift truck tyres.

Early in the day I set a surface hygrometer and also drilled and inserted a humidity sleeve. We returned in the afternoon and the results were instructive. The reading on the surface hygrometer was 60% RH (I did not abrade the surface prior to setting it in position). The reading in the sleeve was 94% RH, quite a surprise to me.
What this was illustrating was the way in which the power float finish had acted as an efficient DPM in its own right. The Visqueen sheet had allowed the concrete slab to dry from one surface only and that surface was a shiny smooth power float. Nevertheless a decade after installation and sub-surface moisture levels were still high enough to cause major problems with floor finishes should the surface of the slab be machined or damaged in anyway.

Earlier this year I examined a similar situation for a client where there had been an issue with large LVTs. The site in question had previously been a supermarket and the subfloor was terrazzo with 600 x 600mm LVT

fitted over.

I lifted a tile and located previously installed 16mm Protimeter humidity sleeve. Using the fast response Protimeter Psyclone hygrometer, I recorded a stable RH of 97.1%

at a temperature of 17.1degC. This indicates that the substrate below the sur face is wet (i.e. above 75% RH. Dr y is defined as at or below 75% RH).

Tests with a Protimeter MMS in both search (RF below sur face) and measure modes (pins on the surface) revealed figures of 273/1000 and WME of 8.7 to 16.8. This again is consistent with a sub-sur face moisture condition and illustrates the effect of both the terrazzo polished surface and the applied primer/ sealant acting as a par tial membrane.

The relevant standard is BS 8203:2001+A1:2009 Code of practice for installation of resilient floorcoverings, stating that the substrate must be dry as measured by a sur face hygrometer giving stable readings of 75% or lower at and after 24 hours.

I set a digital floor hygrometer on the substrate without abrading the sur face and two fur ther data logging floor/ambient hygrometers, one with the sur face abrasion and one without.

Hygrometer readings: Ambient – Protimeter Psyclone 63% RH Tramex Hygrohood On un-abraded Terrazzo 64% RH (after 24 hours in position) Search mode (RF) readings with both Protimeter MMS and Tramex Encounter Plus indicate high readings, even through unlifted tiles.

This further adds weight to the supposition that there was high moisture in the subfloor. Further tests with a Protimeter Hygrostick in the pre-installed sleeve gave a reading at equilibrium of 97% RH which confirms the high RF readings indicating moisture as opposed to spurious conductive elements within the

subfloor substrate.

Downloads of the Equilog data logger floor hygrometers revealed the following:


What this reveals is that where the surface is abraded or otherwise scabbled or scratched up, this allows the passage of moisture vapour to migrate upwards and to interact with materials attached to that surface. Old floors may have old moisture issues. Beware the ghosts of fitters past!

Peter Grant Consultancy & Contractor Services

T: 07885 221675


This article has been reproduced from the Contract Flooring Journal website. You can find them at