Building Pathology L3 Bridgeway / Preston School

Question 1

Explain the advice you gave about the cause of structural cracking.

Answer 1

Based on the initial inspection, the cracks appeared to be caused by thermal expansion on the SW side of the building or heave.

Question 2

How did you determine the cracking was likely to have been caused by thermal cracking?

Answer 2

1. Vertical cracks of consistent width
2. Cracks only 2 - 3mm wide (Cat 2 / BRE 251)
3. Cracks only on SW wall / N wall no visible cracks

Question 3

What other possible cause of the cracking did you consider?

Answer 3

Heave due to clay soil and proximity of surface drains

Question 4

Explain the advice you offered in terms of the building posing no significant risk.

Answer 4

1. Cracks only cat 2 (BRE 251) and consistent width - does not suggest subsidence
2. It is rare for damage to progress beyond Category 2 (BRE 251)
3. Cracks did not appear recent (recent cracks in brickwork have a clean appearance, whereas older cracks show signs of dirt accumulation).
4. I recommended monitoring with a telltale to determine if damage/cracks were progressive, warranting further investigation.

Question 5

How long did you advise monitoring the building for, and explain why you consider this was necessary?

Answer 5

Minimum 12 months to allow for the influence of seasonal changes, which may result in heave or shrinkage.

Question 6

Explain what remedial works you will advise once the period of monitoring has elapsed.

Answer 6

Fill cracks with mortar to ensure building weather tight

Question 7

What advice did you give regarding the cost of the works?

Answer 7

Based on the damage or cracks not being progressive and remaining between1 - 5mm, the cost to fill the cracks would be approximately £500

Question 8

What advice did you offer in respect of the cracks to the concrete mullions?

Answer 8

1. Cause probably Carbonisation, subject to tests to confirm (A spray of 0.2% solution of phenolphthalein is use as pH indicator. Magenta or dark pink indicates concrete is in good health. Light pink or no change of colour indicates carbonation).
2. Repair is possible but not viable compared to replacement.
3. Repair would involve the rebar being descaled and cleaned ready for an anti-corrosion coat to be applied before repair mortar and then an anti-carbonation coating applied.

Question 9

What remedial works did you advise?

Answer 9

Replace the mullion with either a precast concrete or stone mulion.

Question 10

Explain your advice about treating the cut-edge corrosion to the school ‘s modular buildings.

Answer 10

The works should e completed by a specialist contractor who can offer an insurance backed guarantee.

Question 11

Please ensure you can produce a quick sketch to illustrate the construction arrangements of the first example above, to show the relative position of the walls, floor and the roof and the location of the cracks etc.

Question 12

How would you test the concrete for carbonation

Answer 12

PHENOLPHTHALEIN. To find the carbonation depth, cut a part of concrete, spray it with 0.2% solution of phenolphthalein. The carbonated part will have no color and the not-carbonated part will be magenta in color.