Wall tie failure - Revision history

Editor at 17:37, 5 July 2021

2021-07-05T17:37:26Z

← Older revision		Revision as of 17:37, 5 July 2021
Line 79:		Line 79:
	* Defects in stonework.		* Defects in stonework.
	* Efflorescence.		* Efflorescence.
		+	* Galvanising.
	* Interstitial condensation.		* Interstitial condensation.
	* Pattern staining and soiling in stonework.		* Pattern staining and soiling in stonework.

Designing Buildings at 09:37, 14 September 2020

2020-09-14T09:37:18Z

← Older revision		Revision as of 09:37, 14 September 2020
Line 89:		Line 89:
	* Weep hole.		* Weep hole.

−	[[Category:~~Regulations~~]] [[Category:~~DCN_Regulation~~]] [[Category:Construction_techniques]] [[Category:Design]]	+	[[Category:DCN_Guidance]] [[Category:DCN_Product_Knowledge]] [[Category:Regulations]] [[Category:Construction_techniques]] [[Category:Design]]

Designing Buildings at 08:33, 4 March 2019

2019-03-04T08:33:49Z

← Older revision		Revision as of 08:33, 4 March 2019
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	But, because wall ties are situated within the wall’s cavity and cannot be seen externally, it’s important to know what signs to look out for that could indicate wall tie failure. Identifying and fixing problems with wall ties as early as possible can prevent serious damage to a property’s structure and keep repair costs down.Owners of properties with cavity walls should look out for signs of wall tie failure to avoid serious structural damage occurring.		But, because wall ties are situated within the wall’s cavity and cannot be seen externally, it’s important to know what signs to look out for that could indicate wall tie failure. Identifying and fixing problems with wall ties as early as possible can prevent serious damage to a property’s structure and keep repair costs down.Owners of properties with cavity walls should look out for signs of wall tie failure to avoid serious structural damage occurring.
−
−

	{\|		{\|
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	Corrosion refers to a partial or complete wearing away or a dissolving or softening of a substance by a chemical or electrochemical interaction between the metal and its environment. Rusting is a type of corrosion and it is caused by the interaction of water and iron or steel in the presence of oxygen. Rust is a hydrated iron oxide, which although solid in form, is weak and brittle.		Corrosion refers to a partial or complete wearing away or a dissolving or softening of a substance by a chemical or electrochemical interaction between the metal and its environment. Rusting is a type of corrosion and it is caused by the interaction of water and iron or steel in the presence of oxygen. Rust is a hydrated iron oxide, which although solid in form, is weak and brittle.

−	Galvanising is a means of protecting iron or steel by coating it with zinc. The zinc protects the steel electrochemically. Of the two metals zinc is the more chemically inactive and it will slowly corrode in ~~the~~ preference to the steel. The thicker the original coating of zinc, the longer it will last. The zinc protection reduces in thickness but it does not undergo a chemical change. Eventually the zinc coating will disappear.	+	Galvanising is a means of protecting iron or steel by coating it with zinc. The zinc protects the steel electrochemically. Of the two metals zinc is the more chemically inactive and it will slowly corrode in preference to the steel. The thicker the original coating of zinc, the longer it will last. The zinc protection reduces in thickness but it does not undergo a chemical change. Eventually the zinc coating will disappear.

−	Properties built between 1935 and 1981 are most at risk of wall tie failure for a couple of reasons. Firstly, most houses built before 1935 had solid walls, and secondly, during the early years of cavity walls the wall ties were not made durable enough and frequently suffered from premature corrosion. It was in 1981 that the British ~~Standard~~ recognised the problem with wall ties and the zinc coating on the wire tie was tripled in thickness.	+	Properties built between 1935 and 1981 are most at risk of wall tie failure for a couple of reasons. Firstly, most houses built before 1935 had solid walls, and secondly, during the early years of cavity walls the wall ties were not made durable enough and frequently suffered from premature corrosion. It was in 1981 that the British Standards Institute recognised the problem with wall ties and the zinc coating on the wire tie was tripled in thickness.

	The process of rusting can accelerate due to:		The process of rusting can accelerate due to:
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	The portion of the tie in the outer leaf will usually be the most severely affected because of exposure to rain penetration. However, condensation may also produce enough moisture to allow rust failure to occur.		The portion of the tie in the outer leaf will usually be the most severely affected because of exposure to rain penetration. However, condensation may also produce enough moisture to allow rust failure to occur.

−	= British Standards and ~~Premature Failure~~ =	+	= British Standards and premature failure =

	In the UK during 1945, a British Standard (BS) was introduced which set out, amongst other things, a minimum thickness for the galvanising layer. The standard identified the two basic shapes of tie – vertical twist and butterfly. The standard specified that the galvanising should be twice as thick on the vertical twist as it was on the butterfly ties. Unfortunately this minimum thickness was reduced in 1968, because it was thought that the standard was excessive.		In the UK during 1945, a British Standard (BS) was introduced which set out, amongst other things, a minimum thickness for the galvanising layer. The standard identified the two basic shapes of tie – vertical twist and butterfly. The standard specified that the galvanising should be twice as thick on the vertical twist as it was on the butterfly ties. Unfortunately this minimum thickness was reduced in 1968, because it was thought that the standard was excessive.
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	In 1981 the standard was increased and specified the same thickness for both types. The reason for this was the increasing evidence regarding performance in use and the realisation of the scale of the problem. The problem of rusting was thought at one time to be localised as it was believed that it occurred mainly in areas where a catalyst, for example black ash mortar, increased the likelihood of breakdown. It was later appreciated that the problem was more widespread and the causes more complex.		In 1981 the standard was increased and specified the same thickness for both types. The reason for this was the increasing evidence regarding performance in use and the realisation of the scale of the problem. The problem of rusting was thought at one time to be localised as it was believed that it occurred mainly in areas where a catalyst, for example black ash mortar, increased the likelihood of breakdown. It was later appreciated that the problem was more widespread and the causes more complex.

−	The Building Research Establishment has suggested that all steel or iron wall ties inserted prior to 1981 are at risk of (premature) failure (premature relates to the notional 60 years life of a building.) Because cavity walls tended to be first introduced in areas with high rain penetration, including salts, there can be a potent combination of age and aggressive environments.	+	The Building Research Establishment (BRE) has suggested that all steel or iron wall ties inserted prior to 1981 are at risk of (premature) failure (premature relates to the notional 60 years life of a building.) Because cavity walls tended to be first introduced in areas with high rain penetration, including salts, there can be a potent combination of age and aggressive environments.

−	= Stainless ~~Steel Ties~~ =	+	= Stainless steel ties =

	Stainless steel walls ties are available. Stainless steel is a ferrous alloy which contains at least 10% chromium. Since chromium is more reactive than iron, a ‘self healing’ impermeable layer of chromium oxide forms naturally on the surface of the steel. Chromium oxide is durable in a wide range of exposures and prevents the formation of rust. Where there is exposure to chlorides, for example in marine conditions, care must be taken in selecting the appropriate grade.		Stainless steel walls ties are available. Stainless steel is a ferrous alloy which contains at least 10% chromium. Since chromium is more reactive than iron, a ‘self healing’ impermeable layer of chromium oxide forms naturally on the surface of the steel. Chromium oxide is durable in a wide range of exposures and prevents the formation of rust. Where there is exposure to chlorides, for example in marine conditions, care must be taken in selecting the appropriate grade.

−	= Detection and ~~Investigation~~ =	+	= Detection and investigation =
−		+
−	Wall tie failure can often be identified by the horizontal cracking that results from the expansion caused by the rusting process. Unlike sulfate attack the cracks will coincide with the position of the ties (and will obviously only occur in cavity walls). However, because butterfly ties will usually not cause cracking it may be necessary to carry out investigations where the problem is suspected or anticipated.	+

	The main signs of wall tie failure are:		The main signs of wall tie failure are:

−	Horizontal cracks in the walls – ~~The commonest symptom of wall~~ tie failure is the ~~appearance of cracks in~~ the ~~wall~~. ~~These~~ cracks ~~are usually horizontal and appear at~~ the ~~point~~ of the ~~internal wall tie~~. ~~The~~ cracking is ~~usually caused by wall ties expanding due to rusting~~.	+	* Horizontal cracks in the walls – Wall tie failure can often be identified by the horizontal cracking that results from the expansion caused by the rusting process. Unlike sulfate attack the cracks will coincide with the position of the ties (and will obviously only occur in cavity walls). However, because butterfly ties will usually not cause cracking it may be necessary to carry out investigations where the problem is suspected or anticipated.
−		+	* Bulging walls – Rusty and expanding wall ties can also cause brickwork to bulge outwards.
−	Bulging walls – Rusty and expanding wall ties can also cause brickwork to bulge outwards.	+	* Collapsing walls – In extreme cases, if the problem is left to worsen, wall tie failure could eventually cause entire walls to collapse.
−		+
−	Collapsing walls – In extreme cases, if the problem is left to worsen, wall tie failure could eventually cause entire walls to collapse.	+

	Ideally, strip ties should be identified before the cracking occurs. This might involve a visual inspection of the suspect ties, either by using an optical probe or by removing bricks. It should be kept in mind however, that a tie can be in good condition in the cavity but poor in the outer leaf and therefore exposure of the end embedded in the outer leaf is a sensible step.		Ideally, strip ties should be identified before the cracking occurs. This might involve a visual inspection of the suspect ties, either by using an optical probe or by removing bricks. It should be kept in mind however, that a tie can be in good condition in the cavity but poor in the outer leaf and therefore exposure of the end embedded in the outer leaf is a sensible step.
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	[[File:Wall-tie-repairs.jpg\|link=File:Wall-tie-repairs.jpg]]		[[File:Wall-tie-repairs.jpg\|link=File:Wall-tie-repairs.jpg]]

−	Disguising wall tie replacement is difficult, particularly where houses are rendered. Painting will help, but it is very difficult to ~~often~~ match the texture of the original render. In plain brickwork, extensive repointing is usually necessary.	+	Disguising wall tie replacement is difficult, particularly where houses are rendered. Painting will help, but it is very difficult to match the texture of the original render. In plain brickwork, extensive repointing is usually necessary.

	= What should you do? =		= What should you do? =
Line 95:		Line 89:
	* Weep hole.		* Weep hole.

−	[[Category:Regulations]] [[Category:Construction_techniques]] [[Category:Design]]	+	[[Category:Regulations]] [[Category:DCN_Regulation]] [[Category:Construction_techniques]] [[Category:Design]]

Designing Buildings at 08:26, 4 March 2019

2019-03-04T08:26:53Z

← Older revision		Revision as of 08:26, 4 March 2019
Line 1:		Line 1:
	= Introduction =		= Introduction =

−	Failure of wall ties has become a significant problem in recent years. The main cause of failures is rusting of metal ties, although there can be other causes, such as failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties.	+	Failure of wall ties has become a significant problem in recent years. The main cause of failures is the rusting of metal ties, although there can be other causes, such as failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties.

−	Wall ties are used to hold the internal and external walls that make up a cavity wall together as a single unit. Over the years wall ties have been made from a variety of materials, the most common being metal that has been coated in zinc or bitumen, with stainless steel becoming more common ~~over~~ recent years.	+	Wall ties are used to hold the internal and external walls that make up a cavity wall together as a single unit. Over the years wall ties have been made from a variety of materials, the most common being metal that has been coated in zinc or bitumen, with stainless steel becoming more common in recent years.

−	Wall ties play an essential part in a property’s structural stability. ~~Because~~ wall ties ~~are situated within your wall’s~~ cavity ~~and cannot be seen externally, it’s important to know what signs to look out for that could indicate~~ wall ~~tie failure~~. ~~Identifying and fixing problems with your wall ties as early as possible~~ can ~~prevent serious damage to your property’s structure and keep the repair costs down.~~	+	Wall ties play an essential part in a property’s structural stability. The obvious danger with rusting wall ties is the possible collapse of the outer leaf of the cavity wall. Other consequences can include:

−	The obvious danger with rusting wall ties is the possible collapse of the outer leaf of the cavity wall. Owners of properties with cavity walls should look out for signs of wall tie failure to avoid serious structural damage occurring. Other consequences include:	+	* Rust will have a significantly greater volume than the original metal. This expansion of the tie may cause cracking and distortion of the structure, particularly where strip ties have been used. The rust-induced expansion in strip ties can lead to secondary damage, such as a redistribution of loads, buckling and bulging of wall, and damage to the roof as the external leaf increases in height.
−		+
−	* ~~The rust~~ will have a significantly greater volume than the original metal. This expansion of the tie may cause cracking and distortion of the structure, particularly where strip ties have been used. The rust-induced expansion in strip ties can lead to secondary damage, such as a redistribution of loads, buckling and bulging of wall, and damage to the roof as the external leaf increases in height.	+
	* The less bulky wall ties will not generally produce enough expansion to induce cracking unless the joint is abnormally thin or the mortar is very dense. Unfortunately, wire ties produced in the UK before 1981 had less rust protection than strip ties and therefore are likely to have a shorter life expectancy; a particular problem because failure can occur without the outwardly visible warning signs produced by cracking.		* The less bulky wall ties will not generally produce enough expansion to induce cracking unless the joint is abnormally thin or the mortar is very dense. Unfortunately, wire ties produced in the UK before 1981 had less rust protection than strip ties and therefore are likely to have a shorter life expectancy; a particular problem because failure can occur without the outwardly visible warning signs produced by cracking.
	* Cracking will also reduce the weather resistance of the wall, which in turn accelerates the rusting process.		* Cracking will also reduce the weather resistance of the wall, which in turn accelerates the rusting process.

−	~~[[File:Rusted-~~wall-tie.~~jpg\|link=File:Rusted-~~wall-tie.~~jpg]]~~	+	But, because wall ties are situated within the wall’s cavity and cannot be seen externally, it’s important to know what signs to look out for that could indicate wall tie failure. Identifying and fixing problems with wall ties as early as possible can prevent serious damage to a property’s structure and keep repair costs down.Owners of properties with cavity walls should look out for signs of wall tie failure to avoid serious structural damage occurring.
		+
		+

−	A wall tie from a house built in the 1920's - When placed, both sides of the wall tie would have been symmetrical in size and shape to each other. The right hand side of the tie was in the outer leaf, and has been heavily corroded since then.	+	{\|
		+	\| [[File:Rusted-wall-tie.jpg\|link=File:Rusted-wall-tie.jpg]]
		+	\|-
		+	\| A wall tie from a house built in the 1920's - When placed, both sides of the wall tie would have been symmetrical in size and shape to each other. The right hand side of the tie was in the outer leaf, and has been heavily corroded since then.
		+	\|}

−	= Corrosion and ~~Rusting~~ =	+	= Corrosion and rusting =

	Corrosion refers to a partial or complete wearing away or a dissolving or softening of a substance by a chemical or electrochemical interaction between the metal and its environment. Rusting is a type of corrosion and it is caused by the interaction of water and iron or steel in the presence of oxygen. Rust is a hydrated iron oxide, which although solid in form, is weak and brittle.		Corrosion refers to a partial or complete wearing away or a dissolving or softening of a substance by a chemical or electrochemical interaction between the metal and its environment. Rusting is a type of corrosion and it is caused by the interaction of water and iron or steel in the presence of oxygen. Rust is a hydrated iron oxide, which although solid in form, is weak and brittle.

Designing Buildings at 08:22, 4 March 2019

2019-03-04T08:22:21Z

← Older revision		Revision as of 08:22, 4 March 2019
Line 1:		Line 1:
−	~~--[[User:AtlantisDamp\|AtlantisDamp]] 14:41, 01 Mar 2019 (BST)Main article: [[Defects_in_Brickwork\|Defects in Brickwork]]~~
−
	= Introduction =		= Introduction =

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	If you suspect that there may be a problem with your property’s wall ties, it’s important to seek advice from an expert as soon as possible to prevent the building becoming structurally unsafe.		If you suspect that there may be a problem with your property’s wall ties, it’s important to seek advice from an expert as soon as possible to prevent the building becoming structurally unsafe.

−	~~= Find out more =~~	+	--[[User:AtlantisDamp\|AtlantisDamp]] 14:41, 01 Mar 2019 (BST)

−	=== Related articles on Designing Buildings Wiki ===	+	= Related articles on Designing Buildings Wiki =

	* Brick.		* Brick.

AtlantisDamp at 14:41, 1 March 2019

2019-03-01T14:41:56Z

← Older revision		Revision as of 14:41, 1 March 2019
Line 1:		Line 1:
−	Main article: [[Defects_in_Brickwork\|Defects in Brickwork]]	+	--[[User:AtlantisDamp\|AtlantisDamp]] 14:41, 01 Mar 2019 (BST)Main article: [[Defects_in_Brickwork\|Defects in Brickwork]]

	= Introduction =		= Introduction =
Line 5:		Line 5:
	Failure of wall ties has become a significant problem in recent years. The main cause of failures is rusting of metal ties, although there can be other causes, such as failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties.		Failure of wall ties has become a significant problem in recent years. The main cause of failures is rusting of metal ties, although there can be other causes, such as failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties.

−	The obvious danger with rusting wall ties is the possible collapse of the outer leaf of the cavity wall. Other consequences include:	+	Wall ties are used to hold the internal and external walls that make up a cavity wall together as a single unit. Over the years wall ties have been made from a variety of materials, the most common being metal that has been coated in zinc or bitumen, with stainless steel becoming more common over recent years.
		+
		+	Wall ties play an essential part in a property’s structural stability. Because wall ties are situated within your wall’s cavity and cannot be seen externally, it’s important to know what signs to look out for that could indicate wall tie failure. Identifying and fixing problems with your wall ties as early as possible can prevent serious damage to your property’s structure and keep the repair costs down.
		+
		+	The obvious danger with rusting wall ties is the possible collapse of the outer leaf of the cavity wall. Owners of properties with cavity walls should look out for signs of wall tie failure to avoid serious structural damage occurring. Other consequences include:

	* The rust will have a significantly greater volume than the original metal. This expansion of the tie may cause cracking and distortion of the structure, particularly where strip ties have been used. The rust-induced expansion in strip ties can lead to secondary damage, such as a redistribution of loads, buckling and bulging of wall, and damage to the roof as the external leaf increases in height.		* The rust will have a significantly greater volume than the original metal. This expansion of the tie may cause cracking and distortion of the structure, particularly where strip ties have been used. The rust-induced expansion in strip ties can lead to secondary damage, such as a redistribution of loads, buckling and bulging of wall, and damage to the roof as the external leaf increases in height.
Line 20:		Line 24:

	Galvanising is a means of protecting iron or steel by coating it with zinc. The zinc protects the steel electrochemically. Of the two metals zinc is the more chemically inactive and it will slowly corrode in the preference to the steel. The thicker the original coating of zinc, the longer it will last. The zinc protection reduces in thickness but it does not undergo a chemical change. Eventually the zinc coating will disappear.		Galvanising is a means of protecting iron or steel by coating it with zinc. The zinc protects the steel electrochemically. Of the two metals zinc is the more chemically inactive and it will slowly corrode in the preference to the steel. The thicker the original coating of zinc, the longer it will last. The zinc protection reduces in thickness but it does not undergo a chemical change. Eventually the zinc coating will disappear.
		+
		+	Properties built between 1935 and 1981 are most at risk of wall tie failure for a couple of reasons. Firstly, most houses built before 1935 had solid walls, and secondly, during the early years of cavity walls the wall ties were not made durable enough and frequently suffered from premature corrosion. It was in 1981 that the British Standard recognised the problem with wall ties and the zinc coating on the wire tie was tripled in thickness.

	The process of rusting can accelerate due to:		The process of rusting can accelerate due to:
Line 45:		Line 51:

	Wall tie failure can often be identified by the horizontal cracking that results from the expansion caused by the rusting process. Unlike sulfate attack the cracks will coincide with the position of the ties (and will obviously only occur in cavity walls). However, because butterfly ties will usually not cause cracking it may be necessary to carry out investigations where the problem is suspected or anticipated.		Wall tie failure can often be identified by the horizontal cracking that results from the expansion caused by the rusting process. Unlike sulfate attack the cracks will coincide with the position of the ties (and will obviously only occur in cavity walls). However, because butterfly ties will usually not cause cracking it may be necessary to carry out investigations where the problem is suspected or anticipated.
		+
		+	The main signs of wall tie failure are:
		+
		+	Horizontal cracks in the walls – The commonest symptom of wall tie failure is the appearance of cracks in the wall. These cracks are usually horizontal and appear at the point of the internal wall tie. The cracking is usually caused by wall ties expanding due to rusting.
		+
		+	Bulging walls – Rusty and expanding wall ties can also cause brickwork to bulge outwards.
		+
		+	Collapsing walls – In extreme cases, if the problem is left to worsen, wall tie failure could eventually cause entire walls to collapse.

	Ideally, strip ties should be identified before the cracking occurs. This might involve a visual inspection of the suspect ties, either by using an optical probe or by removing bricks. It should be kept in mind however, that a tie can be in good condition in the cavity but poor in the outer leaf and therefore exposure of the end embedded in the outer leaf is a sensible step.		Ideally, strip ties should be identified before the cracking occurs. This might involve a visual inspection of the suspect ties, either by using an optical probe or by removing bricks. It should be kept in mind however, that a tie can be in good condition in the cavity but poor in the outer leaf and therefore exposure of the end embedded in the outer leaf is a sensible step.
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	Disguising wall tie replacement is difficult, particularly where houses are rendered. Painting will help, but it is very difficult to often match the texture of the original render. In plain brickwork, extensive repointing is usually necessary.		Disguising wall tie replacement is difficult, particularly where houses are rendered. Painting will help, but it is very difficult to often match the texture of the original render. In plain brickwork, extensive repointing is usually necessary.
		+
		+	= What should you do? =
		+
		+	If you suspect that there may be a problem with your property’s wall ties, it’s important to seek advice from an expert as soon as possible to prevent the building becoming structurally unsafe.

	= Find out more =		= Find out more =

Designing Buildings at 07:57, 16 June 2018

2018-06-16T07:57:53Z

← Older revision		Revision as of 07:57, 16 June 2018
Line 59:		Line 59:

	* Brick.		* Brick.
		+	* Building damp-free cavity walls.
	* Cavity wall.		* Cavity wall.
	* Damp		* Damp

Editor at 14:25, 8 May 2018

2018-05-08T14:25:55Z

← Older revision		Revision as of 14:25, 8 May 2018
Line 68:		Line 68:
	* Penetrating damp.		* Penetrating damp.
	* Preventing wall collapse.		* Preventing wall collapse.
		+	* Repointing.
	* Rising damp.		* Rising damp.
	* Spalling.		* Spalling.

Editor at 12:08, 17 August 2016

2016-08-17T12:08:08Z

← Older revision		Revision as of 12:08, 17 August 2016
Line 67:		Line 67:
	* Pattern staining and soiling in stonework.		* Pattern staining and soiling in stonework.
	* Penetrating damp.		* Penetrating damp.
		+	* Preventing wall collapse.
	* Rising damp.		* Rising damp.
	* Spalling.		* Spalling.

Editor at 16:08, 14 January 2016

2016-01-14T16:08:46Z

← Older revision		Revision as of 16:08, 14 January 2016
Line 63:		Line 63:
	* Defects in brickwork.		* Defects in brickwork.
	* Defects in stonework.		* Defects in stonework.
		+	* Efflorescence.
	* Interstitial condensation.		* Interstitial condensation.
	* Pattern staining and soiling in stonework.		* Pattern staining and soiling in stonework.