Building Pathology - OFS Flashcards
What is clinker? How did you establish it was clinker?
- A fused material produced at high temperatures – a waste material from coal-fired glass furnaces
- Produced by heating limestone and clay to liquefaction around 1,400-1,500 degrees
- Composition of the slab typical for age of building
- Could have sent the clinker to a lab for testing, however I considered the time and cost implications and advised the client this was not necessary
What are the defects associated with clinker?
Damp conditions produce sulphuric acid from coal in clinker which corrodes steel joists, leads to loss of section
It is a deleterious material
What is a deleterious material?
- Materials that are:
o Harmful to health
o Harmful to safety
o Harmful to the environment
o Not suitable for their intended purposes
o Pose a risk where they have been used
What are some examples of deleterious materials associated with the building age / type?
- Asbestos
- Lead paintwork/lead pipework
- Filler joists
What are the remedies to filler joist construction?
- Localised breaking out and coating with resin repair systems
- Replacement of the joists where serious section loss has occurred.
- Regular inspection and keeping the joists dry
What were the sources of internal water ingress?
- Leaking rainwater goods
- Cracked / crazed asphalt roof coverings
- Cracking to parapet walls
- Poor flashing termination of dormer windows
Why was a structural engineer was required?
To confirm my advice in respect of roof replacement and parapet wall rebuilding
How did you propose to rebuild the parapet walls?
- Protect internal rooms an ensure no water ingress – top hat scaffold
- Remove soldier course down to top layer of brickwork
- Remove creasing tiles and mortar
- Carefully take down brick courses to an acceptable level – i.e. a safe level that is structurally sound
- Install new brickwork to match similar – key in with matching mortar – NHL 3.5
- All soldier course brickwork to be mechanically fixed and installed using NHL 5 mortar
What defects did you identify? How?
- Undertook opening up works using a jackhammer
o Revealed double-skin brickwork with the steel joist embedded – no joist hangers or waterproofing present - Identified severely corroded steel with delamination
- Observed severe cracking above the steel on the asphalt roof covering, and through the parapet soldier course
- Identified slipped, missing and cracked ridge and roof tiles
- Cracking and blisters across each of the asphalt roof coverings
- Observed all defects via safe access from scaffold platforms
Can you describe delamination of steel joists? How did you establish this?
- Delamination – separation of layers of the steel joist due to corrosion
- Delaminated section was embedded into inner brick skin – I judged this to be very risky in respect of being structurally sound
- Internally, acro props had been installed behind plasterboard – opening up works revealed this
- Structural engineer confirmed my diagnosis
Why was a timber frame used over steel or traditional construction?
- Quick construction time
- Manufactured off site, quality control etc. no on site cutting or storage
- Lower embodied energy
How did you select the joists and centres for Roof 1?
- C24 is strongest and for external uses
- Centres – checked the NHBC guidelines which advises:
o Minimum centres of 450mm for 15mm deck
o Minimum centres 600mm for 18mm deck - Selected 400mm centres due to potential future loading of roof
- Checked all proposals / measurements with structural engineer before proceeding
What is the difference between C16 and C24?
- Used to grade softwood, under BS EN 338
- C24 can take a higher point load and has fewer, and smaller knots in the timber
- Timbers are evaluated after being kiln dried to 20% moisture content.
How were the joists supported?
- Installed timber wall plate bedded into mortar on top of the inner skin using galvanised holding-down straps using M10 steel bolts
- Joists installed onto joist hangers, fixed onto the wall plate using M10 steel bolts
How did the contractor carry out the joist & deck installation?
- Joists as above
- 70mm timber firings
- Deck fixed onto joists using screw fixing of 53mm allowing embedding into joist of 35mm
- Minimum fastener edge distance 8mm
- Minimum bearing distance 18mm
- Panels fastened to joists at 300mm centres
