CWCT FACETS

01.03 Testing

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Categories: Envelope Sealing

Introduction
Cladding systems and components are routinely tested to determine properties such as resistance to wind load, airtightness and watertightness.  However, the pressures used for these tests are often different, and it is easy to become confused as to the purpose of these tests.

This Section aims to explain the normal procedure for determining test pressures, and to give guidance on the methods of test and applicability of test results.
 


Site wind loading
The key performance criteria for designing any cladding system is the windloading that is likely to be experienced at the particular location.  Windload is determined by following the procedures in BS 6399: Part 2.  Normal practice is to determine the wind load based on a 5m diagonal dimension (a typical distance between cladding fixings), that will occur just once, on average, in any 50 year period.  This wind load is then often rounded up, typically to the nearest 400Pa, and a minimum wind load of 800Pa is required by CWCT (CWCT, 1996).  Further guidance on wind loading is given in Section 04.04.

Rounding-up of wind load is aimed at manufacturers of standard components or systems, such as windows, which are more cost-effective if they are designed and tested to some target value.

Stating the actual site wind load, and testing at pressures other than 800, 1200, 1600 and 2000Pa, is usually only cost effective where the majority of the cladding system is being tailored to the particular building (bespoke cladding) and design savings can be made.

In either case the wind load stated by the specifier is the design wind load, i.e. that value which the cladding must be designed to resist.
 


Wind load testing
Testing for resistance to wind load is divided into two basic elements - serviceability testing and safety testing.  Separate positive and negative wind load test pressures can be applied if the design wind load has different positive and negative magnitudes (negative wind pressure is normally the greatest).  This (again) is particularly appropriate when testing bespoke cladding.
 


Serviceability wind load testing
For a serviceability wind load test a component or sample of the cladding is subjected to both positive and negative pressure differentials equal to the design wind load, to ensure that when the 1-in-50-year wind load occurs the cladding system or component neither fails (by moving too much - this assessment is usually deflection limited) nor ceases to be weathertight.

The deflection of parts of the component or system are monitored and compared to pre-defined limits.  An excessive deflection may lead to damage to fixtures and fittings, failure of joints, or may simply be unnerving for the occupants of the building.

The serviceability test is always followed by a repeat of the tests for air and watertightness, to ensure that the cladding will perform after experiencing the 1-in-50-year wind load (this wind load may occur in the first or fiftieth year of the life of the cladding, may never occur, or may occur on successive days - it is a statistical measure).
 


Safety wind load testing
For a safety test the objective is to determine whether the cladding has a factor of safety beyond the design wind load.  This test is usually only performed for flexible cladding systems, where stress limits may be exceeded and permanent deformation occur.  The test sample is subjected to positive and negative application of 50 per cent above the design wind load.  A limit is placed on the residual deformation of the cladding system.

It is important to note that the designer of a cladding system may alter the design of structural members and fixings to ensure that the elastic limit of materials is not quite reached at the design wind load - this will often allow the minimum use of materials.  The 50 per cent overload will cause the elastic limit to be exceeded, but should not cause the system to fail, or components to become detached.  It is important that fixings are capable of passing this test, as the cladding should not fail structurally during this test.

Weathertightness tests are not repeated following the safety test, as the sample is expected to have deformed permanently.  This test is also not applied to components such as windows which are only to be mounted in rigid walls - the hazards associated with structural failure are much less, and the number of fixings is greater (they are also generally over-designed).

The wind load tests are structural, and are related to issues of health and safety, and so must be performed to the full wind load (and beyond for safety) Wind loading is covered in detail in Section 04.04.
 


Air and watertightness testing
Air and watertightness testing may be required for a number of reasons.  Airtightness affects occupier comfort (draughts), energy usage (mass transfer) and watertightness (water droplets entrained in air flows).  Watertightness is essential to avoid damage to the cladding system and to the contents of the building, and failure of watertightness must be accommodated in terms of provision for drainage.
 


Airtightness testing for energy usage
Energy usage is important on a day-to-day basis.  Assessing the airtightness of the cladding as it relates to energy use must therefore be based on a sensible day-to-day average pressure difference.  Moreover, the test may also be performed for positive and negative pressure differentials, as both lead to energy wastage.  Negative test pressure is required for, say, stairwells.

As stated above the design wind load is based on a single gust of wind, occurring once in 50 years on average.  However, on a day-to-day basis the average wind load on a cladding system is much less.  Typical values for pressure differential when assessing energy usage are 25, 50 or 75Pa.  A 50Pa dynamic pressure corresponds to a site wind speed of 9m/s (assuming a difference of 1.0 in external and internal pressure coefficients) - this is about 20 miles per hour, and probably represents a windy day for many UK sites.  A 75Pa dynamic pressure similarly corresponds to a site wind speed of 11 m/s (about 25 miles per hour).

Systems which rely on a sealing action under pressure may not perform as well at low pressures as at high pressures.
The selection of either 25, 50 or 75Pa is left to the specifier.  The 50Pa difference is preferred as it is a normal step in the airtightness testing procedure defined in BS 5368: Part 1.
 


Airtightness testing for occupier comfort
Occupier comfort will be affected by the occurrence of draughts.  If a draught occurs every time there is a gust of wind then the occupier could have reasonable cause to protest about the performance of the cladding system or component.

However, to understand the factors which govern the occurrence of draughts it is necessary to understand how wind behaves other than the 1-in-50 year peak wind load.  The voluntary European wind load standard, ENV-1991-2-4 includes a calculation of the number of gusts (Appendix B, Figure 1), image.  This graph indicates the number of times, in a 50 year period, that a gust occurs at some proportion of the peak wind load.  For example, a gust at 75 per cent of the peak wind load will occur, on average, 101.6 times in a fifty year period (about 40 times).  Similarly a gust at 50 per cent of peak wind load will occur 103.3 times, or about 2000 times in a 50 year period (40 times per year, on average).  Neither of these could be considered enough to cause a problem.

A gust at 25 per cent of peak wind load will occur about 105.4 times - this is an average of 5000 per year, or about 10 per week.  This is much more likely to be noticed and would cause a discomfort problem.

Sensibly then, airtightness should be assessed at a pressure somewhere around 25 per cent of the peak wind load.  For convenience, test pressures are banded into the classes 300 and 600Pa for walls; lower values are sometimes used for windows.

Guidance on selecting between these pressures is a little more difficult to find.  The designer could simply take 25 per cent of the peak wind load and round up to the nearest of 300 or 600Pa.  Air-tightness test pressure is normally chosen purely on how airtight a building is required to be regardless of the wind load; for prestige or air-conditioned buildings it is often advisable to take the highest classification.
 


Curtain walls
For fixed panels air leakage rate per unit area is measured at pressures up to a specified pressure, 300 Pa or 600Pa. For opening lights air leakage rate per unit length is measured.  The peak pressure and acceptable leakage rates for curtain walling and windows in curtain walls are set in the CWCT standard.  The air leakage must be no greater than the allowable value for all pressures up to the maximum.  The peak pressure is taken to be 600Pa for low energy or air conditioned buildings and 300 Pa for all others. Permitted leakage rates are available here for fixed panels and here opening lights.
 


Windows
BS 6375 part 1 allows three classes of performance: Curves A, B and C for opening lights, image. For fixed lights the permitted air leakage rate is 1 m3/hr/m.  Curve A is used for windows with a design wind pressure below 1201Pa while curve B is used for design wind pressures of 1600Pa or more.  Curve C is provided for the specification of higher grade windows when less air leakage is required.
 


Doors
Air leakage rates through doors are invariably greater than those through a window with the same joint length and area.  This arises mainly because of the physical difficulty of arranging a good seal at the threshold.  For commercial doors that are frequently opened the air leakage associated with repeated opening may dominate the effective air leakage rate.  Acceptable air leakage rates through doors are not given in any British Standards.
 


Calculating air leakage
Total air leakage is calculated either:

  • by measuring the air leakage per metre length for each type of joint and total length of each type of joint and caclculating the resultant air leakage
  • by measuring the air leakage per unit area for each type of wall or screen and calculating the resultant air leakage

In the first case it is necessary to measure air leakage for every type of joint.  In the second case it is necessary to measure air leakage through representative areas of wall.
 


Overall air leakage
It is important that the permitted air leakage is not exceeded at each pressure. If air leakage is too great at the peak pressures then there may be excessive drafts and it will not be possible to heat the building on the coldest windiest days. If the air leakage is too great at lower pressures then air leakage will be too great on many days of the year when there is a gentle breeze. This will have a serious impact on heating bills.

Many specifiers now set an overall air leakage rate for the whole building. This is usually set at some pressure lower than the peak pressure recognising that energy losses and hence fuel costs are governed by typical overall air leakage. The lower pressure is taken as 25Pa, 50Pa or 75Pa in different countries. The recommended value for use in the UK is 50Pa. BSRIA recommend that all buildings should achieve an overall air leakage of 10 m3/hr/m2 at 50Pa and that the air leakage should be 5 m3/hr/m2 at 50Pa for low energy or air conditioned buildings.
 


Watertightness testing
Watertightness is important to the occupant of a building.  Significant water penetration may cause visible damage to soft furnishings and carpets, and if undetected could also lead to the breakdown of glazing or glass unit seals or even structural damage within the cladding system.

Determining a suitable test pressure for watertightness testing is a little more complex as the watertightness test is not undertaken at the design wind pressure - the positive wind pressure.  A particular issue is that a short term gust has little relevance to water penetration - the quantity of water that can be blown into an opening in a few seconds is very small, and unlikely to cause problems.

Moreover, peak rainfall does not correspond to the highest wind speeds - indeed driving rain is often variable in direction, due to the vortices caused by strong air flows around a building.  The greater problem is that peak rainfall occurs for long durations at lower wind speeds.  Windows are tested with the pressure applied for periods of 5 minutes at lower pressures and this has been found in practice to be an appropriate test.

Again it is sensible to use standard values, and common values with the airtightness test also have some merit - for this reason watertightness is typically assessed at 300 or 600Pa.  For curtain walling a 450Pa value has been added. This image shows the watertightness test pressures recommended for different levels of design wind pressure.  The step function approximates to a slope of 0.25.  Interestingly, the North American practice adopts a slope of 0.2, image.
 


Water penetration through facades, windows and doors
It is a primary function of the facade to prevent water from entering the building.  The CWCT 'Standard and guide to good practice for curtain walls specifies:

  • The curtain wall, and any incorporated opening lights, shall be designed to prevent leakage of water onto the internal face of the curtain wall, (Clause 2.11.1.1)
  • The curtain wall, and any incorporated opening lights, shall be designed to prevent water entry into those parts of the curtain wall that would be adversely affected by the presence of water. (Clause 2.11.1.2)

These requirements hold good for all windows and wall elements.

The assembled wall should meet this specification throughout its design life and in all weather conditions.  Risk of water penetration is related to the exposure of the site, the building and the wall.  All tests for water penetration resistance spray water onto a test panel or window while a pressure difference is maintained across it.

It is recognised that no test for water penetration resistance exactly represents the air and rain movement on and around a facade.  However, experience has shown that successful performance under test is a reasonable measure of successful performance in use.
 


Curtain walls
Curtain walls may be constructed as face sealed walls (with a primary water seal at the outer face) or rainscreen walls (with a ventilated outer face).

The water penetration resistance of a face sealed curtain wall depends on the integrity of all the joints in the wall. These may be damaged by movement of the wall unless the wall is correctly designed to accommodate thermal movement, cladding movement, structural movement and so on.  For this reason curtain walls should be tested as large panels representative of the final construction and the panels should be tested for water penetration resistance after all of the movements have taken place.

Curtain walls comprise large impervious surfaces from which rain water freely drains.  Large volumes of water may flow across a curtain wall and for this reason water is sprayed onto test panels at a rate of 3.4 l/min/m2.  This is more intense than for window testing to BS 6375 Pt 1.  Opening lights in curtain walling should be tested to the same standard as the whole curtain wall.

Face sealed curtain walls may be tested under a constant pressure difference (static test) or a fluctuating pressure difference (dynamic test).  The pressure differences for curtain walling are in the range 300Pa upward and are related to the design wind pressure for the wall, a measure of site exposure, and are given here. Dynamic testing is usually only specified for exposed sites or for walls that are being tested to a static pressure of 600Pa.
 


Ventilated rainscreens
Water penetration of walls with ventilated rainscreens is dealt with in Section 02.01.
 


Windows
Windows are tested with a water spray intensity of 2.0 l/min/m2 and a static pressure difference across them of 50Pa to 300Pa depending on the exposure category (wind pressure) of the site.  Windows may be specified by reference to BS 6375 Pt 1 provided that an exposure category is included in the specification.

Windows included in curtain walls will have a greater flow of water across them and will experience greater deflections than those fixed into a masonry opening.  Windows for use in curtain walling should be tested as part of the curtain wall.
 


Doors
Water penetration through doors is invariably a greater risk than water penetration through windows.  This arises mainly because of the physical difficulty of arranging a good seal at the threshold. No tests for water penetration through doors are given in any British Standards although the test methods in BS 5368 Pt 2  'Methods for testing windows - watertightness test under static pressure' may be used.
 


Testing procedures
Testing is performed to check air leakage, water penetration and also wind resistance. Tests may be conducted on components such as windows and doors or on complete panels of wall.

Components should only be tested separately when they are to be built into an opening with rigidity similar to that of the test box to be used.  Large relatively flexible constructions such as curtain walling have to be tested at large size so that the box does not impart stiffness to any component.  Typically this requires a specimen two storeys high and several metres wide. The CWCT has defined a standard test panel for stick curtain walls here. Windows to be incorporated in a curtain wall should be tested within the curtain wall not a rigid box which may improve their apparent performance.
 


Windows and doors
Windows, doors and othe components are commonly tested to to BS6375 pt1 and similar standards exist in other countries.  The test apparatus comprises a box which can be pressurised and to which a window is fixed, image. The outer face of the window faces into the box.  water is then sprayed on to this face at a rate of 2.0 l/min/m2  while a pressure difference is applied across the window to check for water leakage. Peak test pressures are 100, 200 or 300 Pa and the pressure rises as steps 50, 100, 200, 300 Pa and higher pressures may be used. Air leakage is measured at increasing pressures upto 200 or 300 Pa in steps 50, 100, 150, 200, 300 Pa.
 


Curtain walling
Test specimens are much larger than single components and are attached to a support frame representative of the building structure.  A box, usually of plywood, is built behind the specimen and negative pressures are created in the box to provide the pressure difference across the wall, image. A static water test is run by spraying water onto the face at a rate of 3.4 l/min/m2.  The complete cycle of wetting and applied pressure differences is shown in the image.  Peak pressure is 300, 450, 600 Pa or 0.25 of design wind pressure.  Dynamic water tests are run by forcing air on to the face of cladding using an aeroplane engine, image. This is adjusted to give deflections equivalent to those measured in the static test.

Air leakage tests are conducted in the same way as for testing windows to BS6375 pt1.  Air leakage through particular components or joints can be achieved by taping over the joints that are not to be included in the test.  The test regime is shown in this image.

Wind testing servicability tests are conducted using the test pressure squence shown in this image.

The sequence of tests performed on the sample wall is;

  • Air permeability/draughts
  • Watertightness - static
  • Watertightness - dynamic (if required)
  • Wind resistance - servicability
  • Air permeability/draughts
  • Watertightness - static
  • Building movement regime (if required)
  • Air permeability/draughts
  • Watertightness static
  • Thermal cycling regime (if required)
  • Air permeability/draughts
  • Watertightness - static
  • Watertightness - dynamic (if required)
  • Hose test (if necessary)
  • Wind resistance safety
  • Ultimate strength test (if required)
  • Dismantle inspect and record

Tests are run in this sequence to allow proper inspection and interpretation of the results as the tests progress.

The discretionary tests are run if required and are followed by air and water tests to discover whether they have caused a deterioration in performance.  The movement and thermal tests are run to ensure that the wall is servicable and maintains its integrity throughout its service life.
 


Site testing
Although many cladding components and systems can be tested for watertightness in the laboratory or on a large-scale mock-up, these tests neglect a critical issue with watertightness - the impact of site workmanship.

The fabricator and installer of a cladding system are relied upon to ensure that the joined surfaces of components are cut straight, gaskets properly fitted, and sealants properly installed.  However, the installer is often left to resolve intersections between joints, overcome inaccuracies in the as-built structure and ensure proper sealing to adjacent cladding systems.

For this reason it is often appropriate to test a small part of the installed cladding system, to ensure that fabrication and installation have not in any way reduced the performance of the system, and to check the performance of interfaces with adjacent systems that did not form part of the laboratory test.  However, site testing itself can also be poorly applied, and this Section aims to identify some of the key issues of which the site test specialist and specifier should be aware.
 


The frame of reference
An important requirement before carrying out site testing is to have a frame of reference - the assessor must know whether certain parts of a component or system are capable of passing the specified test when properly fabricated and installed.  This is simple to define when a component or large-scale specimen has been successfully tested in the laboratory.  The site testing procedure can then be applied at the laboratory to determine if the test is suitable.

This approach will also generate a second piece of important information - which components or parts of the system will not pass the test.  It is known, for example, that the hose test generates a strong jet of water with a penetrating power far in excess of normal driven rain; this test will usually fail joints which are intended to be opened (for example around doors and opening lights of windows), unless a modification to the test procedure is made.  It is often possible, on a test mock-up, to modify the parameters for a site hose test to determine the condition under which an opening joint will pass the test with the agreement of all parties.
 


Specifying and witnessing site tests
Non-specialist specifiers should seek advice from a UKAS accredited test laboratory or cladding consultant on how to specify and witness site tests.
 


Site tests
Watertightness can be assessed on site using three distinct approaches:

  • The hose test,
  • The spray bar test,
  • The cabinet test.



Hose testing
This test is defined in Test Methods for Curtain Walling (CWCT, 1996) and the AAMA standard 501-94.  The CWCT hose test varies from the AAMA test only in that joints within 120mm of each other can be tested in one pass, providing there are no projections/obstructions that shield the joint.

Hose testing uses a compressor to drive a flow of water through a nozzle, forming a strong jet of water droplets.  The nozzle is defined, as is the pressure of water entering the nozzle and the flow rate of water through the nozzle.  The water jet is always aimed perpendicular to the plane of the cladding system, and at a fixed distance from it.

Hose testing is primarily intended for the testing of permanently sealed joints.  The high pressure water spray should not dislodge gaskets or wet-applied sealants unless they have been poorly installed or not been allowed to cure.  Water will be forced through small gaps in these types of seal, and will find its way through unsealed joints between framing components.

Hose testing may not be suitable, in its unmodified form, for use on open joints (even if baffled, the flow of water from the nozzle may overwhelm many open joints) or joints which are intended to open.  Weatherseals around doors and opening lights of windows are made of softer rubber compounds, in part, to ensure that the door or window can be operated comfortably - these softer seals are intended to prevent penetration of run-off water but are easily pushed aside by the jet from a hose.  However, the spray bar test is usually more applicable to this type of joint.

If the hose test is used on open or opening joints the normal procedure is to reduce the pressure of water entering the nozzle appropriate for the joint under test, and to maintain the distance from the nozzle to the joint.  This will ensure a meaningful test and is preferable to holding the nozzle further away from the joint as it does not require any change of action on the part of the operator.

Where it is not possible to obtain this frame of reference at the time of laboratory testing, the following procedure can be followed.
All parties should agree on a good quality window in terms of both fabrication and installation, and this is used to determine the frame of reference.

Where this benchmarking process results in a very low nozzle pressure, say below 150kPa, or one party considers the results to be questionable, or the component selected for benchmarking to be unacceptable, it is recommended that a cabinet test be carried out to determine if the selected component/area can achieve the specified performance.  If the results are successful, the hose test can be carried out on that area to determine the frame of reference for further testing.’

When testing joints at an internal corner the hose should be positioned 0.3m from both walls (rather than 0.3m from the joint) to take account of the water re-directed off the walls and towards the joint.

The hose test is also suitable for use on sloped claddings, providing the jet is aimed perpendicular to the joint.  If a volume flow of water is required simply to observe its flow and drainage from the cladding/roofing the spray bar test is more suitable.
 


Apparatus for hose testing and method of test
A typical set of apparatus for hose testing is shown in this image.  Note that no connections (e.g. quick-clip connections) should be placed between the pressure gauge and the nozzle as these can dramatically reduce the water pressure.  The recommended nozzle is the Monarch Type B-25, #6.030 nozzle. Note that the nominal water pressure is 220 +/- 20kPa, which gives a water flow of 22 +/- 2 litres/minute through the standard nozzle, with a cone angle of 30o.  The standard distance from nozzle to joint is 0.3m, and the joint is tested in 1.5m steps.

Wetting of the test area begins at the lowest horizontal joint, rising progressively upwards via the intersecting vertical joints to the next horizontal joint.  If water leakage occurs but is not easily located, an additional procedure is recommended: all joints to be tested are sealed with masking tape and progressively exposed and tested by working the hose back and forth across the stretch of joint for a period of five minutes.  Once the source(s) of leakage have been found and rectified the area is re-tested.

One parameter which is not defined in the test procedure is the rate at which the hose should be played along the joint - a 30 second period for the specified 1.5 metre test length is comfortably achieved, such that there are ten passes during the five minute test.

A specimen that has been successfully tested in the laboratory can be used to calibrate the site hose test: a window of acceptable workmanship is tested with the hosepipe and the flowrate is gradually increased until water leakage occurs.  A slightly reduced flowrate is then used on site to distinguish between windows of acceptable workmanship and those of unacceptable workmanship.

However, the results are only comparative and do not absolutely guarantee weathertightness.
 


Spray bar testing
Spray bar testing is not yet standardised, although a draft European standard is in preparation.  A spray bar is a long pipe fitted with holes or nozzles at regular intervals, to provide a spray of water over the face of a cladding system.  A single line of nozzles should be used, and water allowed to run down the face of the cladding system.

This test is suitable for open-jointed systems (e.g. rainscreen cladding and unsealed patent glazing) and opening joints, as water is not forced into the joint.  Moreover, the test is useful for assessing water flow around penetrations through systems - a penetration may redirect the run-off flow onto a joint, or perhaps onto a drainage opening.
 


Apparatus for spray bar testing
The basic apparatus for spray bar testing is shown in this image.  From the draft European standard prEN 13051, the nozzles should each give a water flow of 2 litres/minute with a 3 bar water pressure per nozzle, and have a spray angle of 120o.  The nozzles are spaced 400mm apart and mounted 400mm from the face of the cladding system.

The area of cladding to be tested should be agreed.  Essentially the spray bar test is a test for runoff.  Therefore, the position of the grid of spray bar nozzles in relation to open and protected joints (e.g. under projections) should be properly considered.  The nozzles can be directed at a joint, but it is preferable that they are directed at a point above the joint, so that the run-off flow runs down over the joint or area under test.

It should not be necessary to alter the water pressure or flow rate for the spray bar (5 litres/minute/metre length of spray bar), although the position of the spray bar on the cladding system is open to some adjustment.  As stated above, the spray bar should generally be located above the area of cladding to be tested, and at the ridge, with water running down one slope, when testing roofs.
 


Cabinet testing
Cabinet testing is based on the procedure outlined in standards such as BS 5368: Part 2.  The basic apparatus comprises a cabinet which can be sealed to the cladding system, a means for pressurising or de-pressurising the cabinet and a spray system (usually a spray bar or grid of nozzles).

The basis of cabinet testing is to create a positive pressure difference on the cladding system, whilst spraying water onto the external face.  This technique is suited to the testing of doors or windows after installation.  However, there are several problems associated with this test:

  • The first problem is where to fit the cabinet.  If the cabinet is mounted on the external face it is necessary to pressurise the cabinet, which will tend to push the cabinet off the cladding system.  External fitting is also costly when many storeys above ground level because of the reliance on access equipment.  If mounted on the internal face the cabinet must be de-pressurised, which will help to hold it in place, but this will limit access to the surface of the cladding system to look for signs of leakage.
  • The next problem is how to prevent lateral air movement through the wall - pressurising or de-pressurising a section of wall may draw air in from the sides, rather than directly through the part of the wall under investigation.
  • Finally, the finished surface of a wall may not permit easy attachment or sealing of the test cabinet - many cabinets are built in-situ and are specific to one part of the cladding system.

These limitations make cabinet testing costly, and it may be easier to remove a window or door for testing in a conventional test rig.  The interface between a window and a wall is more suited to hose or spray bar testing.
 


Apparatus for cabinet testing
The operation of the cabinet is generally based on a Standard such as BS 5368: Part 2, which defines parameters such as water flow rate and nozzle position and spacing.

A cabinet may be constructed of plywood inside or outside of the wall as for a laboratory test. However, a simplified method of cabinet testing is to seal the test area internally with polythene and to de-pressurise the enclosure with an industrial vacuum cleaner, measured with a gauge, image.

If this simplified method is used the polythene sheet must not come into contact with any of the sample area on the inside of the wall to ensure that air is drawn through the joints.  However, the results are not comparable with the cabinet test unless the full net pressure across the wall is developed and the true deflections of the wall or component occur.

Whilst cabinet tests are perceived to require rigid test cabinets similar to those used in laboratories it is possible to construct a cabinet from polythene sheet and a frame of scaffold tubes or similar.  If this approach is used the frame should be braced against the building structure and transmit no loads to the wall which should carry only the pressure difference generated by the cabinet.
 


General issues for site watertightness testing
The following are general issues which apply to all of the methods described above:

Surface cleaning
Before testing, the test area should always be washed with a mild detergent and rinsed with clean water.  This prevents dirt from being forced into the system and clogging normal drainage paths, and the detergent also helps to break surface tension (water can otherwise be prevented from entering a small opening by surface tension effects).

Internal finishes
Site testing should always be carried out before internal finishes are applied - internal finishes prevent observation of the internal surface of the cladding, and would have to be removed anyway if remedial work is necessary.

Test location
It is very easy with hose and spray bar testing for the observer on the inside of the building to be looking at a section of cladding remote from that where the hose or spray bar is actually applied.  Good co-ordination is required, and radio communication between assessor and observer is essential.
 


Summary of site testing procedure
The following steps are required if the site test is to provide genuine results:

  • Determine which site testing techniques are to be used and, if they allow fine tuning, what form/modification to the standard sequence is to be used;
  • ‘Site’ test a laboratory mock-up of the sample which has already passed all other specified tests;
  • Armed with a knowledge of the expected site performance of the component or system agree which parts of the installed system are to be tested;
  • Agree a suitable procedure for remedial action should problems be found;
  • Consider how water runoff will be managed to prevent flooding or damage to elements not designed to be wetted;
  • Proceed with site testing.

Summary of tests suitable for various components/systems

  • Permanent (fixed) joints - hose test, spray bar test, cabinet test
  • Opening joints - spray bar test, cabinet test
  • Open joints - spray bar test, cabinet test