Building Pathology Specific L2 & L3

Question 1

What are common profiled roof defects?

Answer 1

Cut edge corrosion, fixings, condensation, expansion and contraction.

Question 2

What causes cut edge corrosion?

Answer 2

Occurs due to the cut side of sheets, on the laps, are exposed to the elements and oxidises.

Question 3

How do you treat cut edge corrosion?

Answer 3

Sand blast the corrosion from the cut edge joint, removing any peeling paint and feathering up the sheet. Provide a anti corrosion primer, provide a flexible fibre-reinforced membrane, provide top coat of paint.

Question 4

How did you identify it was carbonation?

Answer 4

I noticed it was in specific areas within the construction to the concrete columns where leaks had occurred previously. This suggested that moisture over a period may assist in the carbonation of the area in specific areas, rather then additives through both sulphate attack and chloride attack, as it would be expected this occurring in more locations through additives. I carried out Phenophalein tests to ensure, and involved a concrete specialist to further confirm with lab tests.

Question 5

How were you able to review costing for the schedule of condition?

Answer 5

BCIS

Question 6

What causes salt efflorescence?

Answer 6

From hygroscopic salts through the mortar and water during the construction.

Question 7

Why did the structure cause salt efflorescence on the internal face?

Answer 7

From hygroscopic salts through the mortar and water during the construction. This was not allowed to escape as the weep holes had been sealed within the structure and water travelling along the cavity tray into the property.

Question 8

How did you provide defect rectification for the internal water ingress?

Answer 8

This was a contract management contract, as part of this we had no influence with the previous designs related to this and only brought in as QS on the project and separate scope of services in snagging final outcome. Due to the defect, I suggested a bulkhead to be installed so the water may escape.

Question 9

How long does salt efflorescence usually occur for from construction?

Answer 9

Approximately 36 months.

Question 10

What are the different roofing waterproof membranes for a flat roof?

Answer 10

• EPDM (Rubber): excellent properties, expensive.
• Bitumen (asphalt): cheap, provide hot and cold, requires coating on top to protect.
• Liquid Applied:
• GRP roofing:
• Single Ply membrane:
• Green roof:

Question 11

What are flat roof defects?

Answer 11

Dependent on the roof itself, but in the case of bituminous felt roof:

• Crazing
• Ponding
• Blistering
• Poor workmanship

Question 12

Why did you not choose to overlay the flat roof?

Answer 12

Currently, the property had no insulation within the roof. I decided to make it a warm roof due to this with tapered insulation and removing the existing covering due to the amount of water within the blisters.

Question 13

You mentioned you were to replace the mortar, what did you specify?

Answer 13

I specified a 1:3 ratio with cement and sand.
Walls are typically 1:5 ratio.
Lime Mortar to allow breathability 1:3 or 1:5.

Question 14

How did you identify the leaks within a building?

Answer 14

Electronic Leak Detection carried out by a specialist.

Question 15

What is spalling?

Answer 15

Spalling is a term used to describe areas of concrete which have cracked and delaminated from the substrate.

Question 16

What is concrete made up off?

Answer 16

Cement (typically Portland Calcium silicates), water, aggregates (stones, rock, sand) and admixtures where required.

Question 17

What are the disadvantages and advantages of having a concrete frame on a property?

Answer 17

Advantages - Quiet, cheap, fire resistance, compressive strength,
Disadvantages - Formwork of casting expensive, less distance then steel for frames, bad for the environment.

Question 18

What are the other concrete defects that the frame could have been subject too?

Answer 18

Carbonation - CO2 with calcium hydroxide to make Calcium Carbonate which reacts with passive layer of reinforcement.
High Alumni Cement - Not Portland cement, but calcium aluminates and causes more frequent chemical attacks and loss of strength.
Sulphate Attack - Present Sulphate Ions in gypsum, admixtures (ash), or environment mixing with hydrated calcium silicate or hydroxide.
Chloride Attack - Chloride Ions in admixtures 1950-78 or environment salts. Attacks reinforcement with hydrochloric acid.
Alkali Silica Reaction - Silica reacts with hydroxide to form a gel that swells with water.

Question 19

How do you diagnose and repair Carbonation?

Answer 19

Cracking, spalling & rust. Phenophalein (pheno-fal-een) tests for under pH over 9.

PATCH REPAIR

• Remove loose concrete and sand blast corrosion steel.
• Prime reinforcement with alkali solution
• Concrete patch repair or sprayed concrete.

ELECTROCHEMICAL TECHNIQUE (cathodic protection,
Chloride Mitigation, Re-alkalisation)
- Cathodic attached to concrete permanently has sacrificial anodes. Although expensive.
- Chloride Mitigation

Question 20

How do you diagnose and repair High Alumni Cement?

Answer 20

Provides a loss of strength and collapse.

Question 21

How do you diagnose and repair Sulphate Attack?

Answer 21

Efflorescence, cracking & spalling.

I would carry out repairs in accordance with BS EN1504

Question 22

How do you diagnose and repair Chloride Attack?

Answer 22

Pitting of steel, spalling and rust leaks through cracks.

Question 23

How do you diagnose and repair Alkali Silica Reaction?

Answer 23

Random cracks, more frequent to areas of high moisture.

Dry out as best remedy. If further works required, need breathable membrane and metal mesh.

Question 24

How did you repair the wall following concrete repairs?

Answer 24

Provided battens to the wall with insulation between then vapour control barrier and plasterboard above.