2018 Propping Guide

Part One

Raising Safety Awareness

All masonry alterations are high-risk tasks and the safe execution is complex and technical, which is why expertise is vital.

The main cause of collapse during masonry alterations is from overloading equipment due to underestimating the weight of the load and over extending Strongboy’s from the wall to avoid internal 1st floor wall damage and/or to gain more fitting work space.

The Maximum Safe Working Loads

(S.W.L)

A correctly used Acrow prop, maximum safe working load, 3,400Kg.

An Acrow prop used within the props and needles method, maximum 1,700Kg.

Without any warning a Strongboy or any similar designed product misuses the Acrow prop and the safe working load is severely reduced by at least 90%, from 3,400kg down to a maximum of 340kg and can even reduce down to 0kg of which depends on the size & the working height of the Acrow prop, how plumb, how tightly fitted and how far the Acrow prop is positioned from the centre of the wall and is fully explained within this guide.

Strangely, the marketing theory behind a Strongboy is to use fewer Acrow props and to reduce masonry damage which certainly is not the case when the maximum safe working load is only 1/5 of the correct propping and needling method and if maintaining the 340kg safe working load the hole within both sides of a cavity wall or a 9″ wall is the same size required to fit a needle, if not larger, as seen below.

As seen in the drawing below, a Strongboy misuses the Acrow prop due to the severe eccentricity of the load and because the web of the Strongboy sends the load onto the side of the Acrow props inner tube which is designed for loads from the head plate down to the foot plate only.

The Acrow props inner tube curves and loses height when overloaded or over tightened which is the legal duty of the user not to overload and to work with an Acrow prop fitted with a Strongboy in a professional and competent manner.

A full 360 degree turn raises an Acrow props adjustable working height by 8mm, jacking or over tightening can dangerously overload an Acrow prop especially when eccentrically propping with a Strongboy as the measurement from masonry to the solid base will not change, only the Acrow prop or the Strongboy will dangerously deflect and alter.

When the inner tube of the Acrow prop is raised over half-way from the outer tube, the safe working load decreases even further and increases the risk of curving the inner tube, ensure to use the correct sized Acrow prop for the task at hand, see the graph in part 3 for further Acrow prop guidance.

When eccentrically propping masonry, plumb and concentrically loaded Acrow props should always be used to support roof timbers, joists and beams separately due to the different live/static loads they may be carrying. Always check the condition of joists and beams before propping, where in an unsatisfactory condition replace or repair before continuing.

When used correctly upon small openings, a Strongboy can be a useful piece of temporary support equipment but when misused or overloaded through not knowing the weight of the load or over extending from the wall to gain further fitting work space, a task isn’t safe.

TWO  SECTIONS OF THE OLD STRONGBOY INSTRUCTIONS

(Correct)

On normal cavity walls the maximum distance from the centre line of the Acrow prop to centre line of the cavity wall is 215mm ( 9″ inches) or using the leading edge of the hammer plate as a guide, measure 150mm to the centre of the cavity. As drawn below.

(Misleading)

For a wider hole on stable walls the Strongboy’s should be positioned a maximum of 900mm apart.

TWO SECTIONS OF THE NEW COINCIDING STRONGBOY INSTRUCTIONS

(updated November 2015)

(Misleading)

A Strongboy can be used on single or double skin walls where each leaf is up to 4 ½” (112mm) thick. If double skin, the maximum cavity is 2” (50mm). Ensure the blade of the Strongboy is fully supporting the second skin.

(Correct)

The distance between props should be calculated from the assessment of the loading but in any case it should not exceed 900mm.

The misleading instructions have increased the risk of the Strongboy user to overload and to underestimate the weight of the load and also suppresses the true level of knowledge required to tackle masonry alterations safely and correctly.

Examples

A

9″ brickwork can weigh in excess of 600kg per square metre, (120 bricks plus mortar) which would require at least five Strongboy’s per linear metre (at 167mm centre’s) on a larger opening on a typical two storey residential property, weighing 1,440kg per linear metre without roof loads and making the use of Strongboy’s unsuitable & obsolete for the task.

B

A Strongboy was designed in the mid 1980’s when the typical cavity size was only 50mm but due to changes in construction design a cavity size has now doubled to 100mm. Attempting tasks which require wider steels with welded top/bottom plates for wider cavities and still only using Strongboy’s is where further problems of overloading from over extending from the wall arise.

C

The new misleading instructions (updated Nov 2015) suggest that propping a cavity wall or a 9″ wall by over 300mm eccentricity from the centre line of the wall to the centre line of the Acrow prop is acceptable even when the safe working load is dangerously reduced to an unknown level, as seen below.

D

Within the new misleading instructions there is no mention of the maximum eccentricity of 215mm. Strangely, all measurements are taken from the end of the bendable and over sized tongue, “If” this was a correct method of measuring eccentric loads it is actually safer to support a 100mm cavity wall which is not permitted than a 50mm cavity wall which is permitted as the measurement from the centre of the Acrow prop is 25mm less eccentric.

To change the instructions to suit the design of an existing product after twenty five years with no explanation or without any further research or testing can not be lawful when it dangerously reduces the S.W.L to an unknown quantity and endorses further misuse of which causes a higher risk of collapse during masonry alterations.

A Strongboy is designed to be misused and it’s not possible for the Strongboy to offer the correct fitting/work access for every task without dangerously overloading itself.

(The Up-dated but flawed new Strongboy instructions are available to view in part Five)

 

We recently asked the institute of structural engineers:

“How is it possible for a structural engineer to design a task safely with Strongboy’s when the safe working load varies from 340kg down to 0kg and depends on the size of the Acrow prop used, which pin-hole height is used, how tightly the Acrow prop is fitted, how plumb and how far the Acrow prop is fitted from the centre of the wall”?

THEIR RESPONSE

“The Health and Safety Panel has discussed in great detail and over many e-mails the comments that you have raised. The Panel has taken the time to discuss the situation and the position of the Institution. With that the Panel thanks you for your query.

As a learned society the Institution exists to promote the art and science of structural engineering and does not comment on the efficacy of proprietary products.”

The H.S.E also refuse to answer any of our questions.

Not commenting on the efficacy of a Strongboy is why collapse is such
a reoccurring theme on site. Endorsing and promoting the Strongboy by designing temporary works with a Strongboy and without correct procedures and misleading instructions is far from an art form, only dangerous and so nineteen eighties.

A qualified structural engineer didn’t attend university to design
inferior temporary support works so why have IstructE and the H.S.E made it strangely acceptable to prop the rear of a property on a number of over loaded mild steel bendable tongues that sit eccentrically upon a misused Acrow prop and when the obvious accident’s continue to reoccur it’s only ever the contractor that’s at fault and fined or maybe imprisoned for corporate manslaughter if collapse causes fatality?

 In their own words, the role of the H.S.E is to provide advice, information and guidance, to raise safety awareness, to Inspect, investigate and to take enforcement actions.

 Conflict of Interest!

“Over £69,000000 worth of fines were collected by the H.S.E between 2016-2017”

Something is amiss when a government organisation is in control of raising safety awareness and can also benefit from handing out fines to builders that aren’t safety aware due to inadequate information, misleading marketing & incorrect instructions.

To prevent/reduce the risk of accidents there are approximately 20 H.S.E leaflets available for the “busy builder” which provide up to date guidance from ground excavations to avoiding overhead power lines, however there is”still” no H.S.E guidance available for masonry alterations which is the most difficult and dangerous task within the Construction industry. 

Why do the H.S.E think this is acceptable behaviour when they have improved the vast majority of simple work procedures and other construction industry sectors immensely, is it due to their inability to correct the situation without accepting the responsibility of the fault of which they helped create in the first instance by allowing incorrect procedures, misleading instructions and insufficient warnings, tests & guidance for over 25 years?

Future generations are also only one lesson away from misusing Strongboy’s as they are taught by misleading instructions and by the majority of structural engineers and builders that think Strongboy misuse is acceptable due to the incompetence of the H.S.E in this field.

H.S.E “busy builder” leaflets website link;

http://www.hse.gov.uk/construction/areyou/builder.htm

Part Two

 –

Every task of masonry alterations is totally different! 

A variety of temporary support equipment is required to tackle every different task safely and correctly.

 

CHECK LIST

1

What is the nature of the task, is it remedial works or fitting a permanent support? Is it forming a new opening or increasing the size of an existing opening? Is the opening in a 4″single skin of masonry, two skins or more? Is the opening in the outer or inner leaf of a cavity wall or in both skins? Do both skins require support at the same time or can it be split into two tasks with two separate & suitable permanent supports to half the risk?

2. What is the age and condition of the masonry and what is the masonry material? What design (cavity or solid)? What is the size of the cavity? What thickness is the wall? Which bond is the masonry and which mortar mix, cement or lime?

3. What are the existing ceiling heights? What are the size and direction of floor/joists, are they load bearing onto the wall or are they non load bearing? Does the existing floor impede the internal fitting access?

 4. What height is the opening, ground floor, first floor or higher? Is a permanent support fitted underneath joists? Are the existing joists fitted within the web of the permanent support or is the permanent support fitted at the same height or below non load bearing joists?

5. What masonry opening size (including bearings) is required? Is a load-point intact? What is the total weight of the load that requires support? Which variety of lintel/s or steel/s are most suitable? What’s the length, depth, width, thickness and weight of the permanent support/s?

6. Which variety of temporary support equipment is designed to support the masonry and the weight of the load safely and also provides a safe and sufficient fitting work space without over extending and dangerously overloading itself?

It’s not possible for a Strongboy or any similar designed product to give the correct fitting work access for every task without dangerously overloading itself, which is why we created the non intrusive Brick Brace Safety Tool and Safety System.

The more methods known, the safer and easier the different tasks of supporting masonry become.

Temporary support equipment options in alphabetical order, Acrow props, Brick Brace, Needles, Prop-Wise and Strongboy’s?

Using a mixed variety of temporary support equipment safely reduces the repair time and supports all of the masonry in between props and also improves the unknown variable safe working load of all the existing propping methods.

Brick Brace with Acrow props, Brick Brace with Needles, Brick Brace with Prop-Wise or Brick Brace with Strongboy’s and depends on the task at hand of which variety is most suitable.

C.R.O.S.S.

Confidential Reporting On Structural Safety.

When carrying out temporary needling and propping one of the most important aspects is to ensure that the props are concentrically loaded and plumb.

The use of a steel bracket on top of the prop giving a minimum eccentricity of 200 mm would not seem to be such a good idea?

Interestingly such a product does exist and has proved very popular with builders who see it an advantage to prop only one side of a wall.

The prop is sold and hired from builders’ merchants with minimal safety instructions and is potentially unsafe due to bending moments being introduced by this product into Acrow props designed only for axial compression. Any device that modifies the behaviour of props by introducing bending moments is potentially hazardous.

Another reporter has come across these in use and in his view they must only be used in the case of limited openings where the masonry can arch over leaving only a small triangle of masonry below the arching that can potentially break away.

All in all these are for light use only and never for heavy shoring. The reporter thinks that the manufacturers, and possibly the hire companies, would be negligent if they did not provide some guidance on the use of such props.

Another reporter has frequently seen builders using props with cantilevering head-plates which cause the supporting props to bend. Some years ago he photographed a set of such props which had very noticeable curvatures. The wall above had dropped in consequence causing damage to the building and resulting in a substantial claim against the builder. The reporter generally advises builders not to use such head-plates.

Correct propping is essential and temporary works failures are a recurrent theme on site. It appears that this type of prop should only be used in specific low risk circumstances.

Part Three

ACROW PROP GUIDANCE

As seen in the graph below, a size no1 to a size no3 Acrow prop have a maximum safe working load of approximately 3,400kg with a size no3 reducing down to approximately 600kg when the adjustable working height is fully raised at four metres.

Between the height’s of 2.2 metres to 3 metres, a size 3 Acrow prop (purple) has a far superior safe working load than a size 1 or size 2 Acrow prop (red and green), ensure to use the correct sized Acrow prop for the task at hand.

Using a Strongboy with the inner tube of the Acrow prop raised over 50% from the outer tube reduces the safe working load and increases the risk of curving the inner tube.

A Strongboy has a maximum safe working height of three metres from a permanent solid base.

The tongue of a Strongboy is designed to support two skins and is too long to support only the outer skin of a cavity wall when the internal skin of masonry impedes, the safe working load is severely reduced when the tongue bends and should be avoided as there are safer options available.

We do not endorse the misuse of any temporary support equipment but anyone that continues to overload Strongboy’s through over extending from the wall, we highly recommend bracing the brickwork over the opening when possible to reduce the risk of collapse.

Acrow Props exhibiting any of the following defects should not be used;

A tube with a bend, a tube with more than superficial corrosion, a prop with a bent head or base plate, an incorrect or a damaged pin or a pin not properly attached to the prop by the correct chain or wire.

Install props vertical to ensure that it can support its specified load. Props must never be used more than 50mm out of true vertical for every 1.8m in height as this severely decreases the S.W.L.

Ensure the base of the prop is bearing directly onto the surface and that the surface is capable of supporting the weight that will be placed upon it. Screw props to surfaces and spreader plates where possible to reduce the risk of collapse through accidental knocks & movement.

Fork head prop attachments should be used to reduce eccentric loads and to ensure a superior safe working load when using needles.

When fitting a permanent support within active living accommodation ensure the rooms above are vacated and closed.

Do not attempt a task in severe wet, gusty or windy conditions due to further dynamic loads.

Lime mortar masonry acts differently than cement mortar masonry during alterations which is why the Brick Brace should also be used when possible where propping lime mortar masonry.

 —-

Part Four

What is a Load-Point?

A 35 degree angle in a stretcher bond and a 25 degree angle in a Flemish bond from both ends of the opening, carrying up to the central perpendicular joint where both angles meet is the load-point.

When an opening is made within an existing wall and a load point is intact, the triangle of brickwork above the opening is the only masonry that could collapse and therefore the only masonry that requires support.

This small triangle of masonry is what Strongboy’s were designed to support when fitted 900mm apart.

Upon larger openings when any of the 3 points of the triangle do not remain, this law changes and the weight of the whole storey height will rest back over the length of the opening (including roof loads when they apply) due to the masonry above not having the correct arching effect.

On a typical two storey residential property this can weigh up to 10 times more than the smaller triangle and is why Strongboy’s are so easily overloaded upon wider openings.

An overloaded prop attachment relies solely on the lateral strength of the masonry and is why the Brick Brace should be used when possible especially within weak or lime mortars.

The Brick Brace Safety tool and correct procedures address all the main causes of minor and major collapse during masonry alterations.

Please view our masonry weight awareness chart for further guidance.

——

Part Five

In layman terms of British law, the user of any temporary support equipment should;

A, plan a task in advance due to every task being totally different.

B, have the ability to choose and correctly use a variety of temporary support equipment most suitable for the task.

C, have a clear understanding of masonry loads and know not to overload the equipment.

D, Adapt to technical progress, replace the dangerous by the non dangerous or the less dangerous. Respect legal responsibilities and respect the welfare of others.

To allow the next generation of builder to work safely, every structural engineer and tradesman must ensure the temporary support equipment they specify or use provides sufficient fitting work space without dangerously overloading itself.

Back in 2013 the H.S.E website stated that the main cause of collapse during masonry alterations is  from overloading equipment due to the lack of awareness of the equipment capacity and underestimating the weight of the load.

 Through our own research, the cause of collapse during alterations is also due to the following;

1,Making assumptions of correct use due to not understanding the misleading Strongboy instructions or verbally misinformed of how to use the equipment safely.

2, Unknowingly decreasing the safe working load when removing equipment away from the wall to gain further fitting work space.

3, Recommended and permitted by structural engineers when the device is not most suitable for the task and when not offering the correct fitting access.

4, Inadequate guidance provided by retailers.

5, The user making assumptions of correct use as no warnings or guidance are provided at the point of sale.

6, No correct procedures of supporting 4″, 9″, 13″ and the different sized cavity walls and a lack of guidance from H.S.E.

7, Using Strongboy’s on larger openings when the props and needles method is far safer and offers the correct fitting access with fewer impeding Acrow props.

8, Compromising safety to save time and to reduce costs by using inferior S.W.L equipment and propping dangerously from only one side to avoid internal wall damage upon finished 1st floor rooms.

9, Taking unnecessary risks due to the lack of correct planning and preparation.

10, Insufficient testing and research of the Strongboy of which has never been tested upon the different sized Acrow props.

11, Rushing  a task through not pricing correctly.

12, Not seeking expert temporary support advice when in doubt.

13, Misleading instructions, no drawings and no Acrow prop guidance provided.

14, the H.S.E allowing misleading instructions for over twenty five years and allowing a product to be sold without any warnings or guidance.

15, The market monopoly of a product with a brand name that implies strength but reduces the safe working load of an Acrow prop by at least 90%  and is overloaded with the same amount of ease as the manufacturer’s say it is to use.

16, A product that is designed to be misused and increases the risk of overloading due to the long bendable tongue that exceeds the maximum 215mm eccentricity without warning.

17, The Strongboy and similar product manufacturer’s making false claims and devaluing the correct method of props and needles.

18, Misleading old and new instructions of correct use.

19, The lack of awareness that every task is totally different and also not knowing a variety of temporary support equipment is required to tackle every different task safely and correctly.

20, Not knowing that eccentrically propping is dangerous and not using the fully tested Brick Brace safety tool to maximise the unknown variable safe working load of all existing propping methods to reduce the risk of minor and major collapse when eccentrically propping.

The New Flawed Strongboy Instructions

Taken from the Strongboy Ltd website

(updated Nov’ 2015)

Prior to using any Strongboy masonry support, you should identify that this is a suitable method to carry out the intended works.

You must correctly identify all loading that the Strongboys will have to support. The total load may simply be the masonry above the opening, but it will also include loads from a floor and/or a roof that is supported by the wall. Floor loading may need to include any heavy furniture in an upstairs room, a full bath, people walking on the supported floor, etc. Roof loading includes supported timbers/steelwork, roof tiles, loft mounted water tanks and the like.

It is recommended that only one single opening in any one length of wall be created at any given time.

You should check that the wall masonry and any floor/roof timbers are in good condition prior to any work being carried out as remedial work may be needed prior to the opening being altered or created.

Strongboy Masonry support is not recommended to be used to provide temporary support to unstable structures.

You should obtain competent structural engineering advice if there is any doubt about the condition of the structure or the nature of the loading, or if any unusual loads are suspected.

!!!CAUTION!!! STRONGBOYS ARE HEAVY AND MAY HAVE SOME SHARP EDGES. ALWAYS WEAR PROTECTIVE GLOVES AND APPROPRIATE PROTECTIVE CLOTHING / FOOTWEAR WHEN HANDLING !

Instructions for use:

Mark the wall in the correct position where the Strongboy is to be inserted

Scrape or grind out the mortar, or remove a brick prior to insertion of the Strongboy in the identified position. Always ensure the underside of the brick to be supported is clean and will sit flat on the blade of the Strongboy.

The Strongboy is designed for use with standard telescopic screw props with a 6” x 6” (150 x 150mm) head. Strongboys should not be used on struts as these have a much smaller head. The prop should only be placed on firm, flat, compacted ground that is capable of supporting the load. A sole board should be placed under each prop – eg 18” x 9” x 1½” (450 x 225 x 36mm)

Hold prop vertically upright with one hand close to where the intended usage is.

With your other hand holding the supporting web, tilt leading edge of Strongboy blade up approximately 30 degrees.

Lower the leading edge of the Strongboy blade until the web bracket is located against the vertical tube of the plate and the blade of the Strongboy is horizontal.

To check the Strongboy is correctly engaged, pull the front edge of the blade down. The Strongboy should not move.

The Strongboy may now be manoeuvred into the correct position for use.

Insert the blade into the mortar space or brick hole until the blade is at least at the same depth as the rear of the brick on the leaf of the wall which is intended to be supported. Where possible the Strongboy should be inserted until the tip of the web is nearly touching the wall.

Ensuring the prop remains completely vertical and in plumb, tighten the collar of the prop until the Strongboy and prop are fully engaged with the wall and do not move. Do not over tighten as that may cause the blade to bend. Hand tight is generally sufficient. Over tightening may damage the brickwork and the prop and Strongboy and may cause the blade to slide out of the brickwork.

Maximum load bearing capacity of 340 Kgs per unit (750lb )

Maximum safe working height 3 metres from firm base .

The distance between props should be calculated from the assessment of the loading, but in any case, it should not exceed 3ft or 900mm.

Always have the loadings checked and use the correct number of Strongboys for the job. If in doubt, you should obtain competent structural engineering advice.

If the width of the intended opening is greater than 4m we recommend that the props be horizontally laced and diagonal braced together using scaffolding poles and proprietary couplings .

The Strongboy can be use on single or double skin walls where each leaf is up to 4 ½” (112mm) thick. If double skin, the maximum cavity is 2” (50mm). Ensure the blade of the Strongboy is fully supporting the second skin.

Check that the prop is not working loose on a regular basis – eg continuously while the opening is being made, otherwise daily. Arrange the work so that the Strongboys and props are not knocked or displaced. If this could happen then lacing and bracing using scaffold poles and fittings can help prevent accidental movement (standard fittings onto the prop inner tube and 68.3mm fittings onto the outer tube).

Our Further Research

The maximum 340kg safe working load of the traditional Strongboy is calculated from the maximum eccentricity of 215mm which is the maximum measurement from the centre line of the Acrow prop to the centre line of the cavity wall. Where the eccentricity is more than 215mm the task becomes dangerous as the safe working load is reduced to an unknown quantity.

 

 Within the new instructions there is no mention of the maximum measurement of eccentricity of 215mm. Strangely, all measurements are taken from the end of the oversized tongue, “If” this was a correct way to measure eccentric loads it is actually safer to support a 100mm cavity wall (which is not permitted) than a 50mm cavity wall which is permitted as the measurement from the centre of the Acrow prop is actually a minimum of 25mm less eccentric than a 50mm cavity wall which has an increased eccentricity of 280mm from the centre line of the wall to the centre line of the Acrow prop.

To change the instructions to suit the design of an existing product after twenty five years with no explanation or any further research or testing can not be lawful when it dangerously increases the eccentricity and reduces the S.W.L to an unknown quantity and endorses further misuse of which causes a higher risk of collapse.

Thank you for reading

KEEP IT SAFE, BRICK BRACE.