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Building Pathology > Building Pathology L3 > Flashcards

Building Pathology L3 Flashcards

1
Q

Flat Roof, OL - How was the penetrating damp identified?

A

Water staining to ceiling, ceiling removal, staining on timber joists.

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2
Q

Flat Roof, OL - What was the build-up of the existing roof?

A

Timber joists with firings, PIR insulation, RBM (reinforced bitumen membrane) waterproof membrane.

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3
Q

Flat Roof, OL - What is the correct build up for a RBM warm deck roof?

A

Timber joists with firings, Deck - marine ply 18mm / 24mm, vapour control layer laid on deck, PIR insulation (can be tapered if firings are not present), two layer RBM membrane.

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4
Q

Flat Roof, OL - Why was the roof installed to a poor quality?

A

No timber roof deck, stained timber joists from penetrating damp, covering was showing signs of poor adhesion.

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5
Q

Flat Roof, OL - How should the roof be constructed?

A

Timber joists, Firings on top of joists for fall, Deck – timber (marine ply / OSB), Vapour control layer, Insulation, Roofing system e.g. 2 layer RBM

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6
Q

Flat Roof, OL - What are the risks of just using PIR insulation as the deck?

A

Does not provide the structural stability required to take loadings of the covering or working on the roof. Decks are commonly timber ply or OSB – differing in thicknesses.

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7
Q

Flat Roof, OL - What was the recommended specification of the roof replacement?

A

Minimum fall of 1:80 – design to 1:40 using timber firings, 18mm marine ply deck, Vapour control layer, PIR insulation to meet 0.18 u value, two layer reinforced bitumen membrane, raising of parapet wall with installation of flashings to increased height, Min 20 year insurance backed warranty.

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8
Q

Flat Roof, OL - What is the minimum upstand you would have required on the flat roof?

A

150mm – BS 6229

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9
Q

Flat Roof, OL - Why was a performance specification produced and not a prescriptive specification?

A

As the project was already on site I wanted the contractor to used their knowladge and supply chain links to provide a soloution that was innovative and provided VFM. I required a 20 year garantee and therefore the contractor could engage a supplychain link to provide a covering that could be installed in a timely manner.

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10
Q

Flat Roof, OL - What standards and regulations were referred to in the performance specification?

A

Part A - Structure, Part B - Fire Safety, Part C - Resistance to moisture, Part H - Drainage, Part K - Protection from falling, Part L - Fuel & Power, BS 6229 flat roofs with continuously supported flexible waterproof coverings.

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11
Q

Flat Roof, OL - What roofing product was installed following contractor proposal?

A

Siltec two layer RBM system. Insulation was 140mm PIR. Timber firrings to create fall.

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12
Q

Car park, Parkside - What is carbonation and how does it occur?

A

Calcium hydroxide in the concrete reacts with carbon dioxide in the air and creates calcium carbonate and water. Starts on the outer surface and slowly moved towards the centre. Reinforcement is protected by the alkalinity of the concrete, which is then neutralised by the carbonation allowing corrosion to occur (oxygen & moisture).

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13
Q

Car park, Parkside - How could you test to clarify that it is carbonation occurring?

A

Sample of concrete is removed, a solution is applied called phenolphthalein to test alkalinity, pink reaction means no carbonation clear means carbonisation.

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14
Q

Car park, Parkside - Why does spalling and cracking of the concrete mean carbonation is occurring?

A

Corrosion of the reinforcement occurs it expands causing cracking and spalling of the concrete.

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15
Q

Car park, Parkside - What is causing the corrosion of the steel reinforcement?

A

The carbonation reaction that occurred reduced the alkalinity of the concrete which protects the reinforcement. With moisture and oxygen present the reinforcement will then start to corrode.

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16
Q

Car park, Parkside - Why did you instruct a structural engineer to assess the car park deck prior to specifying remediation?

A

Undertake the test to identify if carbonation was occurring, clarify the structural stability of the concrete column,

17
Q

Undertake the test to identify if carbonation was occurring, clarify the structural stability of the concrete column,

A

hammer test, hack off loose concrete, expose the reinforcement, remove corrosion form reinforcement using wire brush or grit blast, apply alkali primer and epoxy encapsulation to the reinforcement, patch repair the concrete using cementitious material and sane, add protective coating if desired.

18
Q

Car park, Parkside - Where can you find additional information on carbonisation?

A

BRE 405 - Guidance on carbonisation. BRE 444, part 3 - Guidance on repair methodology.

19
Q

Car park, Parkside - How would you avoid the carbonation of concrete?

A

Ensure there is sufficient concrete cover over reinforcements, allow adequate curing period, use an ad-mixture to modify the pore structure to reduce permeability, use concrete coatings to slow down the process.

20
Q

Car park, Parkside - What is corrosion and how does it occur?

A

Chemical reaction between surrounding environment and the metal causing the metal to deteriorate i.e. rust and expand in size.

21
Q

Car park, Parkside - What is a steel filler joist?

A

A filler joist is a early from of slab construction where a steel is embedded within a concrete slab commonly about 1m apart.

22
Q

Car park, Parkside - How did the SE determine that the structure was still structurally sound?

A

The SE was instructed to undertake an assessment of the extents of the reinforcement corrosion to assess whether replacement or repair was required.

23
Q

Car park, Parkside - What does a corrosion inhibitor do?

A

Neutralises the corrosive agents.

24
Q

Car park, Parkside - What product did you received using for the repair of the carbonisation?

A

Sika repair including rebar inhibitor & primer, & repair cementitious mortar.

25
Q

Car park, Parkside - What type of concrete would you use for the patch repairs? And why?

A

Either a cementitious repair mortar or a resin mortar. It enhances the strength and integrity.

26
Q

Car park, Parkside - How would you prevent carbonisation from re-occurring?

A

I would recommend using a concrete protective coating, such as those offered by Sika depending on the application. They protect from water saturation, are flexible and allow the concrete to breath.

27
Q

Flat Roof, OL - How did you confirm the loading requirement to the roof was suitable?

A

Within the performance specification I included requirement of the structure, including meeting the requirements of BS 199-1 Eurocode 1 - Actions on structures: Densities, self-weight, imposed loads for buildings. This defined minimum loading requirements.

28
Q

Flat Roof, OL - How did you establish that the timber joists were not defective following moisture saturation?

A

Visual inspection, confirmed no evidence or rot was present. To the touch the timber was still solid and did not crumble. I promoted heating and ventilation to assist in the drying process prior to the installation of the new covering.

29
Q

Flat Roof, OL - How did you determine that the joists were correctly sized and at the correct centres?

A

On this project I requested that the project engineer reviewed their suitability. However I would want to review the TRADA span tables to clarify permissible clear spans for the required loading. Timber joists are never more then 600mm centres.

30
Q

Flat Roof, OL - What other information did you include within your performance specification?

A

Compliance including BS 6229 for flat roof coverings, warranty requirements, drainage falls, thermal performance, requirements of the RBM warm deck system including provision of BBA cert , 150mm up stand requirement.

31
Q

Car park, Parkside - Are you aware of any other remedies of steel reinforcement corrosion?

A

Cathodic protection.

32
Q

Car park, Parkside - Car park has a high risk of salts, what other options are available for long term remediation?

A

Carbonation coatings such as Sika Gaurd. Applying a waterproof coating to exposed concrete decks to protect the concrete from carbonation.

33
Q

Car Park, Parkside - Provide system name for protection of concrete?

A

SIKA Gaurd - water repellent coating.

34
Q
A

Building Pathology (3 decks)

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