Sulphate attack

SULPHATE ATTACK

WHERE DOES SULPHATE ATTACK OCCUR?

SULPHATE ATTACK OCCURS MOST COMMONLY IN……..

• MORTAR CONCRETE (FOUNDATIONS & FLOORS)

• RISING WALLS

• FLUE LINERS & CHIMNEYS

SULPHATE ATTACK IN MORTAR

THIS OCCURS WHEN…

• THE SOLUBLE SULPHATE SALTS WITHIN SOME CLAY BRICKS REACT WITH A CONSTITUENT (TRICALCIUM ALUMINATE) OF THE PORTLAND CEMENT WITHIN MORTAR

SULPHATE ATTACK IN MORTAR CONTINUED.

• THE RESULT OF THIS REACTION IS THE FORMATION OF CALCIUM SULFOALUMINATE, A CRYSTAL WHICH EXPANDS DURING ITS FORMATION - CAUSING CRACKING WITHIN THE MORTAR JOINT

WHEN DOES IT OCCUR IN MORTAR?

• ONLY OCCURS ON BRICKWORK WHICH HAS BEEN EXPOSED TO SATURATION.

• THESE INCLUDE AREAS SUCH AS RISING WALLS, PARAPETS, BRICK CAPPINGS, CHIMNEY STACKS OR WHEN BRICKWORK HAS BEEN EXPOSED TO AN

EXCEPTIONAL AMOUNT OF RAINFALL

SIGNS & EFFECTS SIGNS OF SULPHATE

ATTACK IN MORTAR?

• MORTAR JOINTS TURNING A LIGHTER COLOUR AND BEGINNING TO CRACK IN THEIR CENTRE

• INSIDE OF THE MORTAR JOINT CRUMBLING

• EXPANSION OF THE JOINT LEADING TO SPALLING OF THE BRICK FACE OR DISTORTION OF THE WALL

Prevention

• PREVENT BRICKWORK BECOMING SATURATED WHERE POSSIBLE USE FROST RESISTANT BRICKS THAT CONTAIN SMALL AMOUNTS OF SALT

• USE SULPHATE-RESISTING CEMENT – WHICH CONTAINS LIMITED AMOUNTS OF TRI-CALCIUM ALUMINATE. (STRONG MORTAR MIXES (1:4) CAN ALSO HELP PREVENT ITS OCCURRENCE)

• ALTHOUGH A CEMENT RICH MORTAR CONTAINS MORE OF THE CONSTITUENTS THAT REACT WITH THE SULFATES, DENSER MORTARS RESIST WATER PENETRATION & ARE MORE ABLE TO RESIST DISRUPTION

SULPHATE ATTACK IN CONCRETE

• CONCRETE IN CONTACT WITH SOIL THAT CONSISTS OF HIGH LEVELS OF SULPHATE CAN SUFFER ATTACK.

• MEASURES OF SULPHATE LEVELS IN SOILS ARE OFTEN TAKEN AND TESTED TO CHECK WHETHER SPECIAL CEMENTS NEED TO BE INCORPORATED INTO A CONCRETE MIX TO PREVENT SUCH ATTACK

SULPHATE RESISTING CEMENT

• CONCRETE LAID IN SOILS CONTAINING SULPHATE SHOULD NOT CONTAIN ORDINARY PORTLAND CEMENT. INSTEAD IT SHOULD CONTAIN SULPHATE RESISTING CEMENT

SULPHATE ATTACK IN CONCRETE

SULPHATE ATTACK IN RISING WALLS

• BECAUSE RISING WALLS ARE EXPOSED TO SOIL SULPHATES AND SATURATION THEY ARE PARTICULARLY VULNERABLE TO SULPHATE ATTACK.

• BOTH THE BLOCK AND THE MORTAR NEED TO BE

RESISTANT TO SULPHATE ATTACK

EXTERNAL ATTACK

• AS SULPHATES IN BRICKS CAN DISSOLVE IN RAINWATER, THEY CAN MIGRATE INTO THE MORTAR JOINTS CAUSING EXPANSION DUE TO THEIR REACTION WITH TRICALCIUM ALUMINATE IN THE CEMENT

SULPHATE ATTACK IN FLUE LINERS & CHIMNEYS

• DUE TO THE EXPOSED NATURE OF A CHIMNEY STACK IT MAY BE VULNERABLE TO SULPHATE ATTACK.

• SULPHATE ATTACK CAN OCCUR EXTERNALLY AND/OR INTERNALLY ON A CHIMNEY

• A COMMON EFFECT SULPHATE ATTACK HAS ON CHIMNEYS IS TO CAUSE IT TO LEAN SIGNIFICANTLY

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INTERNAL ATTACK

• A RESULT OF WATER VAPOURS BEING PRESENT IN GASES TRAVELLING UP THE FLUE WHICH OFTEN CONTAIN SULPHER DIOXIDES

• WHEN THE GASES MEET A COLD POINT IN THE FLUE - CONDENSATION OCCURS (WHICH CONTAINS SULPHER DIOXIDE)

• THEN MIGRATES INTO THE MORTAR JOINTS BETWEEN THE FLUELINERS FORMING CALCIUM SULFOALUMINATE AND SUBSEQUENTLY, SULPHER ATTACK.

REPAIR

• SULPHATE ATTACK IS VIRTUALLY IMPOSSIBLE TO STOP. RE-BUILDING

IS USUALLY THE ONLY OPTION!!

• However…….

SULPHATE ATTACK? SALT EROSION? WALL TIE FAILURE? WHICH ONE??

Sulphate Attack? Wall Tie Failure?

How do we know it isn’t all three causes?

Salt Erosion?

As trained ISSE surveyors….

• THE PROPERTY IS EVALUATED BY MEANS OF A COMPREHENSIVE INSPECTION CHECK LIST WHICH TAKES INTO ACCOUNT:

• THE PRESENCE OF MOISTURE IN INTERNAL WALLS

• THE TYPE OF SOIL IS EXAMINED FOR LIKELIHOOD OF SULPHATES AND THE GEOLOGICAL MAP IS USED TO FLAG AREAS OF HIGH SULPHATE CONTENT

• IN STRUCTURAL MATTERS SUCH AS WALL TIES A TIE CAN BE LOCATED WITH A METAL DETECTOR AND THE END CHECKED FOR CORROSION – AGE OF STRUCTURE IS ALSO IMPORTANT

• IN THE CASE OF WALL TIES BUILDINGS OVER 50 YEARS OLD ARE AT RISK THUS THE INSTALLATION OF NEW TIES WOULD BE RECOMMENDED TO RESTORE STABILITY WHERE TIES HAVE CORRODED

• A SAMPLE OF MASONRY CAN ALSO BE TESTED FOR PRESENCE OF SULPHATE