PROTIMETER REVISITED FOR LARGE SCALE DAMP … · thus potentially pose an issue for expert...

Corrosion & Prevention 2014 Paper 136 -

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].


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


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.


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.


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).


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.


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


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


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


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.


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


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%


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

.


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.


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.

http://www.environment.nsw.gov.au/heritage/publications/index.htm#S-U


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.

PROTIMETER REVISITED FOR LARGE SCALE DAMP … · thus potentially pose an issue for expert...

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