PROTIMETER REVISITED FOR LARGE SCALE DAMP … · thus potentially pose an issue for expert...
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Corrosion & Prevention 2014 Paper 136 - Page 1
PROTIMETER REVISITED FOR LARGE SCALE
DAMP INVESTIGATIONS
A. L. Airey1
1Airey Taylor Consulting, Perth, Australia
SUMMARY: Damp in structures precedes eventual rusting. “Protimeter Surveymaster” is a non-
destructive testing instrument favoured by building inspectors assessing bathroom leaks and the like.
The Protimeter measures the reflected radiofrequency signal some 10-19 millimetres into concrete or
other substrates, providing a dimensionless result for moisture that is dependent on the calibration
supplied by the manufacturer. The proprietary nature of the instrument’s operation and calibration can
thus potentially pose an issue for expert witnesses. Case studies herein comprise housing, commercial
and community structures that were investigated with firstly a hand held combined
moisture/temperature/surface relative humidity meter, the Protimeter, and by means of in-slab relative
humidity tests. The investigations in Perth’s summer of 40 percent relative humidity confirmed that
moisture transiting slabs and walls can be primarily gaseous and registering as “dry” in either surface
moisture content or surface relative humidity tests, but with the aid of the Protimeter easily diagnosed.
The results of the modern case studies suggests sub-slab vapour barriers are generally both designed
and constructed but there is a tendency to overlook the need to wrap the vapour barrier around the
edges of slabs and footings, causing a modern chapter of 19th
century rising damp problems to recur.
Keywords: Rising Damp, Concrete, Vinyl, Footing Design
1. INTRODUCTION
1.1 A brief history of Rising Damp in Structures
The NSW Heritage Association [1] reports that before the development of brick cavity walls, in 19th century historic
masonry structures “rising damp is caused by capillary action (or suction) drawing water from the ground through the
network of pores in a permeable masonry material….until the upward suction is balanced by the downward pull of gravity”.
The height of the damp related to the size of the pores; the smaller the pores the more elevated the damp. Once reaching the
maximum extent of suction the moisture then evaporates. A typical height for such evaporation is in the 300millimetre
(mm)-1 metre mark allowing a “tide line” of exfoliating paint, fretting brick and deposited salts on the walls of the structure.
The damage from damp was most often, limited to the walls owing to an understanding even in the 19th
century that the sub-
floor areas must be well ventilated; and that if this was not in place wood rot of the floorboards and toxic mould growth
could occur. It was soon identified that a flashing (damp proof course) could be added to the wall prevented the rising
damp and the National Construction Code of Australia [2] provides excellent guidance on sub-floor circulation required in
such structures. Retrospective remedial solutions for heritage structures are available in the form of silicone-injected
dampcourses, electro-osmotic systems and mechanical ventilation [1].
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Figure 1: Historic footing detail
In the progression towards modern slab-on-grade structures, slabs were traditionally cast between walls set on strip footings
as an independent member and the double brick walls formed a vapour space (Figure 2). In due course the design was
simplified to thickenings of the slab in place of separate footings as a structurally dependent member (Figure 3). Such
designs lowered the height of the floor to be in direct contact with the ground. This was a significant development since the
floor was no longer benefiting from the circulation of air beneath and the solution is dependent on a membrane to prevent
damp rising through the concrete pores. In the case of a missing or dysfunctional membrane, a far greater area could be
affected by damp than in 19th
century structures with reasonable sub-floor ventilation. It is important to note that in modern
design the membrane must be wrapped either, around the edge of the slab up into the base of the internal wall; or around the
footing as detailed in AS 2870 [3].
Figure 2: Independent slab - strip footing with infill slab Figure 3: Dependent structure
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1.2 Gaseous vs. Liquid Water
A misconception is that the vapour barrier is solely in place to “keep the water table out”. Many properties around Australia
are naturally well separated from the water table and are just as likely to experience damp problems as those with high water
tables. Whilst it is well understood that water turns to steam at 100 degrees Celsius (°C), gaseous moisture at room
temperature is not very well understood. It is invisible, but exists in the soil, in porous objects such as concrete, and the
atmosphere.
When water is in liquid state, it is held together by relatively strong intermolecular forces known as hydrogen bonding. This
gives the material a much higher boiling point than it would otherwise have owing to molecular size alone [4]. Liquid water
is a viscous liquid able to bead. Once in the gaseous state, water is subject to much weaker forces (van der Waal’s forces)
and becomes significantly more mobile.
When a structure is placed onto the surface of the earth, the process of moisture equilibration of the water table with the
atmosphere, is still in train with the movement of moisture into the atmosphere creating an upwards flow of gaseous
moisture.1 In concrete, the American Concrete Institute has defined this flow as the “moisture vapour emission rate” MVER
in units pounds per one thousand square feet per day (lb/1000 ft2/24 h) [5]. It is important to realise that this flow, is not the
same measurement as either moisture content (which is a static measure of total water available at the point of measurement,
as a proportion of the solid measured) or spot tests of relative humidity (RH (%); a static measure of the ratio of partial
pressure of water vapor in an air-water mixture to the saturated vapor pressure of water at a prescribed temperature).
The concurrent development of the plastics and concrete industries in the 20th
century led to a solution for rising damp in
concrete floors and footings/walls – extruded polyethylene plastic sheet commonly known as polythene or builder’s black
plastic. This seemingly flimsy sheet has a tight polymeric structure capable of excluding gaseous (as well as liquid)
moisture. Thus, membranes which are able to contain water, such as geotextiles, are not necessarily suitable for retarding
gaseous flow of moisture. This office has tested and reported the performance of geotextiles with comparison to polythene
finding although “watertight” to liquid water the performance of other polymers insufficient to prevent moisture vapour
transmission [6].
1.3 Moisture Vapour Flow Through Slabs
For this reason of gaseous moisture flow a subfloor vapour barrier is required by AS 2870 [3] and normally is placed prior
to the laying of a slab, to prevent this invisible rising damp through the slab, such that habitable structures have a room
moisture content < 60 % RH. Below this RH the probability of floor swelling, adhesive rot, and of mould or bacterial
growth is vastly reduced.
Moisture from the earth is not the only possible source of flow. The actual drying of newly cast slabs, flooding (either top
side applied water or sideways ingress) or a combination, can cause the slab to be saturated and the process of “drying out”
is a similar phenomenon if the slab is young; however is of fixed rather than perpetual duration.
1.4 Factors Affecting Slab Dry-Out Times
The diagnosis of whether slab moisture is rising damp, a “green slab” or has been subject to inundation is confounded by
inherent slab drying times.
Dry-out times for slabs following casting relate to slab thickness. Whereas a 100 mm slab-on-grade when first cast requires
a minimum 3 months to dry, a 150 mm slab requires 6 months and a 200 mm slab, 12 months to dry [5,7,8].
A number of other factors relating to concrete composition affect drying times [7]. Some can be measured directly from
core samples. Concretes have two main types of pores; microscopic “gel pores” in the nanometre scale and capilliary pores
which are generally much larger. During the reaction of cement with water at a low water:cement ratio (e.g. 0.4) hydrates
form and these hydrates tend to block up the capillary pores. This traps water within but overall allows more rapid drying. If
more water is added than is needed during the cement reaction, this tends to exit via bleed water to the surface. There is
usually insufficient cement to form the volume of hydrates required to block the pores and so fewer discontinuities form. A
high:water cement ratio is indicative of a likely continuity of the pores. A broad indication of the porosity of concrete is
given by compressive strength (an inverse relationship exists). Capillary porosity testing reflects on the total volume of
pores present.
1 Another misconception is that vapour pressure of liquids is only “up”; these are exerted in all directions but constrained by
solids.
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1.5 Development of Methods to Test Moisture
Moisture within apparently dry concrete slabs is primarily in gaseous form and tends to vary between 2% and 5-6%
however up until the dew point being reached, liquid water is not observed. The relationship between moisture content and
relative humidity of the pores is outlined in a “sorption isotherm”. The sorption isotherm below (Figure 4) is based on one
originally researched by Straube [9] published in the year 2000 for various building industry products. Following this
landmark publication and that of Hedenblad [8] on slab drying times, the information prompted further research and a
revolution in international guidelines and standards [5, 7, 10, 11].
Figure 4 Sorption Isotherms for common building products based on that of
Straube [9]
As can be seen from the above graph, the response curve for concrete is ostensibly flat until the relative humidity starts to
rise above 70%.
The delamination of flooring such as vinyl from concrete, is such a problematic issue that this is the subject of an American
Concrete Institute publication 302.2 R “Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials” [5].
First published in 2006 this provides four qualitative and five quantitative tests for the evaluation of moisture in concrete.
These include a calcium chloride test, where a weight of absorbent material in a container with only the bottom face
exposed is placed on the surface for a specified length of time then the final weight, which includes the moisture absorbed,
is weighed. This can be back calculated to the flow, and as such provides good data on the nature of the problem, but
presently is not in use in Australia. Two of the other quantitative tests recommended are in-slab relative humidity (ASTM
F2170, [11]) and the hooded relative humidity (ASTM F2170, [12]) which is the testing of accumulated humidity in the
area above the slab; the former is more widely used.
An Australian Standard was published in 2012: AS 1884 Resilient sheet and tile – Installation practices” [13], which drops
references to use of moisture contents as an acceptable method and adopts ASTM F2170 and F2170.
It is critical to assess whether slabs are in a suitable state to receive floor coverings. Problems we are aware of include:
Peaking, swelling and subsequent shrinkage (gaps) of wood, floating wood and laminate flooring
Warping of structural acoustic floors incorporating particleboards or compressed fibreboards
Delamination of vinyl floor coverings.
No less importantly in the placement of flooring materials are all other aspects of application outlined in AS 1884 [13] and
manufacturer’s instructions with regard to adhesive and the vinyl.
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1.6 Test Methods Used in this Study
1.61 TESTO 606-2
Moisture contents may be measured most accurately by driving heat off a concrete sample (“core”) and determining
gravimetrically. On site measurements, however, such as those taken with the testo 606-2, are actually a measure of the
electrical resistivity (or impedance) of the slab. The principle is that the resistance is measured between two probes, the
moisture content is then derived from a calibration curve which is provided by the manufacturer, which relates the electrical
signal to what is likely to have been achieved had a core been removed and the moisture measured gravimetrically.
This instrument also measures relative humidity via a small capacitive humidity sensor and temperature via a thermocouple
at the top end of the instrument. A disadvantage of this equipment is that unless the probes can penetrate into the surface the
moisture contents are reflective of only the very top surface. Surface relative humidity information can often prove more
useful.
1.6.2 In-slab relative humidity (ASTM F2170 [11])
In brief, a hole is drilled into the slab at 40% of its depth, a sleeve with cap inserted and the air in the sleeve allowed to
equilibrate (≥ 3 days). A measurement probe is then used to determine the relative humidity. This is the ratio of the amount
of water vapour actually in the air of the slab compared to the amount of water vapour required for saturation at that
particular temperature and pressure, expressed as a %age (%). Most devices require the input of pressure (i.e. do not include
a barometer). Modern probes contain a material that transmits at a particular dielectric constant when dry, which changes
when wet, and house a temperature gauge. Two types of gauges were used in this study. One, a Proceq Hygropin utilises a
narrow 7 mm diameter hole and in which a capped sleeve was fitted. After the equilibration period the probe is inserted to
obtain the reading. The other, a Tramex Hygro-i used a 19 mm diameter hole in which an electronic device is left to
equilibrate under the cap, which is later connected to the instrument for the reading.
1.6.3 Protimeter Surveymaster
The Protimeter provides an indication of “in-slab moisture” a distance 10-19 mm below the surface using a radiofrequency
signal and measuring the response generated. The scale of the instrument is dimensionless but has been calibrated by the
manufacturer as follows:
0 - 16 “green” (safe air-dry, likely to be <75% Equilibrium Relative Humidity)
16-20 “orange” (marginal, likely to be 75-80% Equilibrium Relative Humidity)
21 – 100 “red” (moist through damp, likely to be >80% Equilibrium Relative Humidity).
1.7 Classic Hypothesis Testing Challenges for the Inspector
In walls, it must be considered that damp can be rising, descending, bridging or horizontally ingessing into basements; and
that in slabs, damp can be temporarily rising (“green” slab; or a slab saturated by flooding) or permanently rising (long term
rising damp). A useful publication, albeit dealing with heritage structures, is that of the NSW Heritage Association [1].
Thus, testing strategies must be designed to differentiate which hypothesis is correct before proceeding towards a remedial
solution.
2. CASE STUDY ONE – HERITAGE STRUCTURE
This case study illustrates a classic response for rising damp response when using a moisture meter in the summer months of
Perth, where relative humidities are regularly 40 % or less.
Sub-floor measurements for wood moisture content were above 20 % and relative humidities 70-80 % relating to the wood
rot observed (Figure 5). The moisture measurements of the wall using the manufacturer’s “lime mortar” calibration curve
are shown in Table 1. A peaking of the moisture content is seen at 750 mm however the absolute values are dry; and the
variation between them not large owing to the slope of the sorption isotherm (Figure 4).
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Table 1. Moisture Content readings of wall exhibiting peeling paint
Height Above
Floor Level (mm) Moisture (%) Relative Humidity (%) Temperature (◦C)
350 1.7 58.8 23.9
550 1.8 58.0 23.7
750 1.9 57.6 23.6
950 1.6 57.6 23.7
1150 1.0 57.6 23.6
1350 1.0 57.4 23.7
1750 0.9 60.0 23.9
Figure 5 Sub-floor joist registering damp conditions Figure 6 Classic “rising damp” signature –
yet moisture readings “dry”
3. CASE STUDY TWO – MOULD IN POORLY VENTILATED BASEMENT
In a recently constructed basement the only ventilation was the entry stair (Figure 7). This had developed an overwhelming
odour with oppressive humidity approaching 80% (Table 2). The level above the basement was also fairly humid, at 70%.
In the basement however, there were no signs of disturbance (e.g. delamination or peeling) by water of the paintwork of the
walls which were in good condition and assumed to be concrete. Evidence of mould was limited to a small section of
particleboard cabinetry.
Basement moisture issues are reasonably common, particularly associated with inadequate tanking (waterproofing of the
walls). However, in the basement of this address, the structure was clearly not leaking. This suggested issues that were of a
gaseous nature associated with humidity, rather than liquid water.
A rising damp problem was suspected and moisture measurements taken in a corner of the room and in the wall behind the
stairs (Tables 2 and 3). It had been noted at this and other occasions that the “wood” calibration gave better separation of
results as the variation in concrete results was close to the limits of reporting; however this was not ultimately likely to
satisfy a critical audience so measures calibrated to concrete were also taken. The data indicate a peaking of moisture
contents at about 100 mm above the floor.
A further examination of the drawings of the structure found that a membrane was absent from beneath the footing, and that
the wall structure was in fact concrete infilled brick (that had been plastered), allowing a route for moisture to accumulate
(Figures 8 and 9). The odour was ascribed to mould likely to be growing in the cavity exuding waste gases into the
basement.
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Table 2. Moisture Content readings of wall next to corner opposite stairs
Height above Floor
(mm)
Moisture Meter
Setting
Moisture Content
(%)
Relative Humidity
(%)
Temperature
(°C)
100 Wood 28.6 75.8 23.0
300 Wood 13.1 77.0 23.2
600 Wood 16.8 77.1 23.3
900 Wood 15.1 76.5 23.4
1200 Wood 16.9 75.1 23.5
100 Concrete 1.3 76.4 23.0
300 Concrete 1.1 76.9 23.2
600 Concrete 1.1 76.9 23.2
900 Concrete 1.1 76.9 23.4
1200 Concrete 1.2 75.4 23.5
Figure 7 Odorous humid basement Figure 8 Mechanism “rising damp” of
retaining wall
Figure 9 Mechanism “rising damp”
wall beneath stairs
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Table 3: Moisture content readings on wall beneath stairs
Height above Floor (mm) Moisture Meter Setting Moisture Content (%) Relative Humidity (%) Temperature (°C)
0 Wood 12.8 74.3 23.7
100 Wood 31.0 74.1 23.7
300 Wood 16.8 74.2 23.5
600 Wood 16.7 76.0 23.6
900 Wood 12.4 77.0 23.7
1200 Wood 13.0 77.0 23.6
0 Concrete 1.0 74.6 23.7
100 Concrete 1.2 74.2 23.7
300 Concrete 1.2 74.6 23.5
600 Concrete 1.1 75.8 23.5
900 Concrete 1.1 77.0 23.7
1200 Concrete 1.1 77.0 23.6
4. CASE STUDY THREE – BASEMENT GARAGE/GYMNASIUM
This case study illustrates how the Protimeter was first usefully employed by us in another summer investigation.
A residence incorporated a basement garage. The garage retained soil to full height at the back wall which then stepped
down in a pathway to the east side to a level equal to that of the garage door. A substantial gymnasium and a downstairs
bathroom area were present in the garage. The entry to the house was above the level of the front wall of the basement.
Efflorescence and peeling of paint at the back retaining wall had been evident and had been extensively investigated by the
Builder and this office. Investigations included chasing out routes of stormwater drainage to check for the presence of a
leaking soakwell. No obvious defects of tanking or causes in the rear yard behind the full depth retaining wall were found.
The property was re-inspected and despite the efflorescence and peeling paint, absolute moisture contents were low and
within the range of the precision of the instrument, with the exception of the corner of the gymnasium (Figure 11) where a
surprise jump to 1.9 % moisture was found at 600 mm height (Table 4).
Figure 10 Internal wall (left of corner) and rear retaining wall
(right of corner) of basement gymnasium
Figure 11 Corner of gymnasium
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Figure 12 Wall backing garden bed Figure 13 Retaining wall backing yard stair
Table 4. Measurements with “Testo 606-2” of Basement Car Park/Gymnasium
(relative humidity (RH, %)/moisture content (%)/temperature C)
The area was revisited with a Protimeter. The absolute results are shown in Table 5, coloured with the manufacturer’s
assignments being green (dry) yellow (medium) and red (moist) as described in the introduction. As rapid progress was
being made with the measurements, two further areas of efflorescence and peeling paint were investigated being an area of
wall retaining the external stairs on grade (Figure 13) and an area of the front wall beneath the entry stairs (Figure 14).
Location On driveway
Rear corner gym
wall – internal
(Figure 10)
Rear corner gym
wall – retaining
(Figure 10)
Corner of gym
(Figure 11)
Wall backing
garden bed
(Figure 12)
1 m above
driveway 47.5 RH/30.3 °C
Slab at wall 59.1 RH/1.1
%/23.9°C 58.9 RH/1.1%/24°C 54.5 RH/1.1 % 59.6 RH/1.1%/23.4 °C
Wall - 0 51.2 RH/1.2 %
Wall - 150 61.6 RH/1.1% 59.7 RH/1.1%/24°C 58.4 RH/1.1%
Wall - 300 58.7RH/1.2% 59.3 RH/1.1%/24.3°C 44.9 RH/1.0% 58.4 RH/1.09%
Wall - 600 60.6RH/1.1%/24.3°C 51.0 RH/1.9%
Wall - 1200 60.2 RH/1.1%/24.2°C 48.5 RH/0.9%
Wall - 2 m 60.8RH/1.1%/24.3°C
Corrosion & Prevention 2014 Paper 136 - Page 10
Figure 14 Front wall
Table 5. Protimeter Measurements of Basement Garage/Gymnasium
Location
Rear corner
gym wall –
internal
(Figure 10)
Rear corner
gym wall –
retaining
(Figure 10)
Corner of
gym
(Figure 11)
Wall
backing
garden bed
(Figure 12)
Behind
table
(Figure 13)
Front wall
(Figure 14)
Slab - 1 m from
wall 18
Slab - 300 mm
from wall 22 18
Slab adjacent to
wall 22 18 20 22 22
Wall – 0 in joint 27
Wall + 150 mm 22 25 27 22 22
Wall + 300 mm 25 25 13-15 20 20 45
Wall + 600 mm 25 20 8-11 18 36
Wall + 1200 mm 21 16 13-15 11-13 16
Wall + 2 m 20 20 11-13 11
The results indicate an overall response in the red zone at distances above 150-300 mm. The exceptions were:
• Rear corner gym internal – showing higher humidity up the wall to 1.2 metres
• Front wall – high readings to 600 mm.
All results were characteristic of rising damp. Most slabs adjacent to the wall were also “red”.
An investigation of the drawings revealed that the areas tested all had the potential for rising damp owing to the polythene
absent beneath the footings and also, no apparent damp proof course into the wall (Figures 15-18).
Section F 2.2.2 of the Building Code of Australia Volume 2 “Class 1 and Class 10 Buildings” [2] observes:
A building is to be constructed to provide resistance to moisture from the outside and moisture rising from the ground
Limitation: F2.2.2 does not apply to a Class 10 building except where its construction contributes to the weatherproofing
of the Class 1 building.
In this case, the basement had been constructed to reflect a Class 10 building. Whilst a garage could be considered a non-
habitable structure, it is part of a class 1 building, being a detached house above. This highlights an issue we are seeing
more frequently with garages, where the usage is extended given the large areas allocated to them.
Corrosion & Prevention 2014 Paper 136 - Page 11
Figure 15 Detail at rear corner gym wall - internal Figure 16 Detail at rear corner gym wall - retaining
Figure 17 Wall backing garden bed Figure 18 Retaining wall backing yard stair
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5. CASE STUDY FOUR – SPORTING FACILITY
A slab at a 2 year old sporting facility (comprising a slab on grade, precast tilt-up panels and a steel roof) had experienced
some top-side flooding of vinyl flooring from outdoor sprinklers. The vinyl had been removed, however the slab had not
dried over the course of a year (Figure 19) despite cross ventilation enabled by windows and roller doors at the west and
east sides of the facility. A concern was that moisture had migrated a great distance into a neighbouring amenity “mini
gym” joined only via a single door. The Owners sought advice as to the reasons and a solution to dry out the slab.
Figure 19. Slab monitoring of relative humidity according to ASTM F2170
A grid of 32 measuring points of the slab, infill piece and wall in both the main gymnasium and adjacent “mini gym” were
investigated with the testo-602 and the Protimeter. The testo results for surface moisture contents were uniformly 1.0 to 1.1
% moisture content. The outdoor temperature was 32 °C and indoor temperatures varied little from this, 31.0 – 32.0 °C.
The outdoor relative humidity was 39.9 %, and internal relative humidities at the top of concrete or wall surface were at
37.5 – 40.1 % in the main gymnasium and 40.0 – 46.0 % in the smaller “mini” gym which was not benefiting from cross
ventilation.
The first Protimeter results are compared to the relative humidity readings taken by others at the closest date (Table 6).
Owing to the uniformity of high protimeter readings in the mini gym, it was hypothesised there may be some construction
defect present such as a missing membrane.
Table 6. ASTM F2170 Relative Humidity Measurements vs. Protimeter results 20/1/14
Location on slab closest to RH measurement
point(refer Figure 20)
Relative
humidity meter
20/1/14
ASTM F2170
Protimeter
raw reading
30/1/14
Protimeter interpreted
RH % reading
40 mm below
surface
10-19 mm below surface
(Near west wall) 86% 45 (red zone) >80%
(Mid-north wall) 86% 35-45 (red zone) >80%
(South-east corner) 72% 35-45 (red zone) >80%
Small gym mid-south wall 74% 25-27 (red zone) >80%
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An examination of the design showed the membrane to be present. The construction photographs were examined, and it
was determined that doubt existed as to whether the membrane had been extended over the infill piece, as photographically,
there was no evidence of it.
A core survey was undertaken finding that the membrane was present under the main slab but not present in the infill piece
(Figure 20). Testing of the cores sampled showed these to be of strength 31-38 MPa with a core from the main gymnasium
slab reporting a capillary porosity of 7% and water:cement ratio of 0.65. This suggests that although the connectivity of the
pores was likely to be high, the total volume of capillaries was not more than one would expect for a reasonably high
strength concrete, thus concrete chemistry was not the reason for long drying times. The mechanism of moisture infiltration
is shown in Figure 20 whereby moisture penetrating the gap is then able to percolate into the concrete. This would cause the
refreshment of the slab relative humidities shown in Figure 19.
To gain an understanding of Protimeter vs relative humidity results, the slab was re-measured on the 2nd
May at the location
of the relative humidity points. Four readings were taken of the surface of the concrete with the Protimeter around each RH
tube, the high and low of the range and the mean result reported below. The results suggest that the mean to upper of the
range at 19 mm depth correlated well with the relative humidities at 40 mm depth on this occasion.
Table 7: ASTM F2170 Relative Humidity Measurements vs. Protimeter results 2/5/14
Location on Slab
Protimeter raw reading
(mean; range of 4
measurements)
2/5/14
Protimeter
interpreted RH %
reading
RH ASTM
F2170
2/5/14
10-19 mm below surface 10-19 mm below
surface
40 mm
below
surface*
Near west wall 85; 70 – 100 (red zone)
zone)
>80% 86%
Mid-north wall 82.5; 70 – 90 (red zone) >80% 83%
South-east corner 57; 45 – 70 (red zone) >80% 74%
Small gym mid-south wall 66; 56 – 80 (red zone) >80% 71%
The Protimeter results are noted to vary seasonally. In January 2014, the raw results (Table 6) were lower than in May
2014 (Table 7). The results point to a seasonal recharge of the upper slab humidity. The manufacturer’s rating for both
dates however is the same i.e. being in the “red zone” implies moist through damp condition > 80% RH.
Figure 20. Missing membrane in delayed pour strip
.
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6. CASE STUDY FIVE – GREEN SLAB IN WAREHOUSE
A warehouse was inspected where the delamination upon impact of a trafficable coating was being investigated.
Spot measurements using the Protimeter on 3rd
February on bare concrete in delaminated area with results ranging 22-27
suggested the slab to be either “green” or suffering from rising damp. There were no signs of rising damp in the walls. A
further survey of the floor of 43 grid points was conducted on 26th February with Protimeter results ranging 22-45
suggesting that this was the case throughout. The survey took approximately 2 hours without difficulty through the coating,
which was up to 600 microns thick.
In due course it was decided to remove the coating in which case it became important to discover whether the sub-floor
vapour barrier was present. No construction records were identified thus in due course relative humidity sample points were
installed at four points associated with the original four concrete slab pours, and cores sampled at this time to check for the
presence or absence of a sub-floor membrane.
A membrane was found present with all four cores. The relative humidity results were measured 3 days later with a Proceq
Hygropin. This took a significant amount of time to equilibrate, about 20 minutes per location. At each location four
measurements were made with the Protimeter around the location of the relative humidity probe. The results are shown in
Table 8.
Table 8: ASTM F2170 Relative Humidity Measurements vs. Protimeter results 2/5/14
Location on
Slab
Protimeter raw reading
(mean; range of 4
measurements)
Protimeter
interpreted RH
% reading
RH
ASTM
F2170
Compressive
Strength (MPa)
Capillary
Porosity (%)
Water:
Cement
Ratio
Distance below
the surface
10-19 mm 10-19 mm 50 mm
Pour Area 1 40; 35-56 (red zone)
zone)
>80% 90% 23 NT NT
Pour Area 2 63; 45-70 (red zone) >80% 90% 34 9.7 0.8
Pour Area 3 40; 35-56 (red zone) >80% 86% 28.5 NT NT
Pour Area 4 40; 35-45 (red zone) >80% 94% NT NT NT
The results confirmed the coating had been applied before the relative humidity had dropped below 80 % (although
manufacturer’s advice stipulated a timeframe, rather than a target relative humidity). This is a consideration in the
replacement of the coating as further slab drying time is required. The water:cement ratio of 0.8 and porosity of 9.7%
indicate a rather porous concrete which would tend to favour long drying times.
When the Protimeter absolute results are considered, the range had increased from the initial series of measurements in
February, to those taken in May.
7. DISCUSSION
A design trend that appears to be occurring is use of garages for gymnasiums and workshops, i.e. as a multi-purpose
habitable space. Naturally, clients wish to install trafficable flooring products that do not delaminate, and do not wish their
wall finishes to degrade through rising damp. The provision of a sub-floor vapour barrier by itself is inadequate to meet
these expectations. It is also not clear whether it is adviseable to have a sub-floor membrane when top side wetting may
occur on a regular basis through the doors, causing encapsulated humidity. The design of such “outdoor rooms” requires
careful consideration of footing design, tanking and outdoor paths to prevent ingress of moisture through the walls.
There exists an understandable amount of confusion in the industry regarding terminology, with products offered for “rising
damp” actually often only suitable to address “green slabs”. Caveats on “long term rising damp” are often relegated to the
back pages of technical data sheets. Even the colour coding on the Protimeter is confusing in this respect with a “green slab”
registering in the “red zone”.
Water has a vapour pressure that is not constrained by gravity. It can move “sideways”. Australian Standard 1884 for floor
coverings [13] could be improved by providing stronger guidance that it is not only the slab which requires a sub-floor
vapour retarding barrier but the footings; and the classes of building to which moisture sensitive coverings such as vinyl can
be successfully applied.
Corrosion & Prevention 2014 Paper 136 - Page 15
Australia has moved on from the generally unsuccessful surface moisture checking to a more reliable relative humidity
checking, but is yet to adopt the approach taken by the US of measuring “dry flow” through slabs. It is not only conceivable
but reported that low humidity can occur but with high flow rates likely to delaminate vinyl and paints. These circumstances
are extremely relevant in Australia where atmospheric humidity can be sub-40% for extended periods. By measuring flow
(an assumptionless, outcome-based measurement), a useful feedback loop has been provided for the American flooring
installers and product suppliers that does not rely upon assumptions of the presence or absence of sufficient vapour
retardation.
8. CONCLUSIONS
In these examples the Protimeter Surveymaster provided valuable feedback to non-destructively confirm the extent of rising
damp, particularly in warm weather when surface moisture contents provided no guide. For walls, there is no critical
measurement required (establishing a rising damp flow is sufficient to diagnose damp problems) and the Protimeter
demonstrated superior performance to a hand held Testo-602 moisture meter. Such measurements provided a basis on
which clients can proceed to action remedial work when a property is under warranty.
For slabs, relative measurements were useful in determining whether saturation of a slab was uniform. For critical
decisionmaking regarding floor coverings further confirmatory information is required. Additionally, when a vapour barrier
is suspected to be absent, drilling to check is the only method we have found adequate to date.
Protimeter absolute results varied seasonally. It is noteworthy that the Protimeter does not measure to the same depth as
relative humidity probes. In winter there appeared a better relationship between relative humidity and Protimeter absolute
values. Whilst tempting to ascribe this to evaporation from the top of the slab, the case study involving a coated slab
suggests otherwise. It is most likely that the drop in temperature in winter time lowers the dew point, and the instrument
responds more vigorously to liquid water. The uncertainty in this respect is a downside of this “black box” technology.
Nevertheless, the broad categorisation of dry through saturated has proved remarkably accurate to date.
An important part of the further diagnostics of rising damp was obtaining the structural drawings and in some cases
conducting a core sample to check if a membrane was present. In most cases there was actually, a membrane present under
structural slabs however the detailing around the base of the wall, at the footing or infill area did not provide a barrier to
rising damp. This omission coupled with vinyl flooring in particular, provides opportunity for moisture to rise into walls and
percolate more generally across the body of the slab.
9. ACKNOWLEDGMENTS
Mr Scott Purnell of Airey Taylor Consulting, for drafting the footing details; SGS Australia Pty Ltd for core testing and
PNM Superior Floors for the relative humidity data of case study four.
10. REFERENCES
1. Technical Guide: Salt Attack and Rising Damp, Young D for Heritage Council of NSW, Heritage Victoria Department
of Planning and Community Development, South Australian Department for Environment and Heritage; Adelaide City
Council, November 2008. Available from http://www.environment.nsw.gov.au/heritage/publications/index.htm#S-U last
accessed 4th
June 2014.
2. National Construction Code Series, Volume Two, Part 3.4.1 Sub-Floor Ventilation, p 193, 2012.
3. AS 2870:2011 Residential Slabs and Footings, Standards Australia, Sydney, 2011.
4. Cotton FA and Wilkinson G, The Hydrogen Bond (In) Advanced Inorganic Chemistry, 4th
Edn, John Wiley & Sons, New
York, Sydney, 1980, p. 219.
5. American Concrete Institute, The Guide of Concrete Slabs that Receive Moisture-Sensitive Flooring Materials, ACI
302.2 R-06, 2006.
6. Airey PG and Airey AL, Restoration of Old Farm House, Strawberry Hill Albany – Use of RetroClay System, ICOMOS
(International Council on Monuments and Sites); Engineers Australia, 20 April 2009.
7. Cement, Concrete and Aggregates Association Australia, Moisture in concrete and moisture sensitive finishes and
coatings, 2007.
8. Hedenbald, G, Drying of Construction Water in Concrete, Swedish Council for Building Research, Stockholm, Sweden,
1997.
9. Straube J, Moisture Properties of Plaster and Stucco for Strawbale Buildings, Canada Mortgage and Housing
Corporation, Research Report, 00–132, 2000.
Corrosion & Prevention 2014 Paper 136 - Page 16
10. The Australian Timber Flooring Association, Timber Flooring, Version 2, 2009.
11. ASTM F170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes,
ASTM International, 2009.
12. ASTM F 2420 Standard Test Method for Determining Relative Humidity on the Surface of Concrete Floor Slabs Using
Relative Humidity Probe Measurement and Insulated Hood, ASTM International, 2011.
13. AS 1884:2012 Floor Coverings - Resilient sheet and tiles – Installation practices. Standards Australia, Sydney 2012.
11. AUTHOR DETAILS
Dr Anthea Airey is the Project Leader – Scientific Services at Airey Taylor
Consulting (ATC). Joining ATC in 2005 she has led the scientific effort in
corrosion, environmental and product-related investigations. Anthea is interested
in how pollution and natural atmospheric chemistry affects structures and human
health. Anthea has presented papers at IUAPPA, ACA and CIA conferences on the
effects of fluoride, carbon dioxide and chloride attack, and the corrosion of plant
rooms. Anthea is an ACA member, an immediate past President of the WA branch
of the Concrete Institute of Australia and presently a national councillor of same.