Building Pathology 3 Flashcards
Littleburn Farm: How did you establish the rot was dry rot and not wet rot?
Deep cuboidal cracking
Hard and dry to touch
Fruiting body found (darker rust/brown) suggested old/aged and not active.
It didn’t have the characteristics of wet rot:
Generally longitudinal cracking,
Cuboidal cracking can occur too but not as deep.
Moisture content: 45-60%
Hyphae is brown\black and is thin thread-like strands
Mycelium doesn’t occur.
Immediate source of moisture required.
Knobbly or honeycomb fruiting body (if found)
I checked the surrounding areas and the rot hadn’t spread or appeared active.
Littleburn Farm: How did you know what to recommend?
I followed BRE Good Repair Guide 12.
Littleburn Farm: Why did you only recommend the removal of the decayed timbers, what did you do with the other timbers?
The decayed timbers felt weak and structurally defective requiring replacement.
I didn’t recommend treating the other timbers within the roof void as the they weren’t subject to rot and were below 20% therefore not requiring any treatment.
Littleburn Farm: Why did you advise to replace the rotten timbers on a like for like basis?
The timbers were performing adequately in this location due to not structural movement identified which suggested these were not undersized.
If the structure was to be modified to include these I would consult with a SE and Building Control.
It wasn’t suitable to replace the timber with concrete or steel given its location/use.
Littleburn Farm: What were the characteristics of the timbers within the roof void?
2nr rotten timbers
(Located far end/corner of the void which were near the porous stonework and double laid thermal insulation which was causing the humid and moist conditions):
- Deep cuboidal cracking
- Hard and dry when touched
- Fruiting body to 1nr rafters suggested the rot had reached final stage at some point (potentially died in winter and may have been due to be resurrected in summer). Fruiting bodies darker suggested old fruiting body.
- Approx. 13% moisture content (20-40% needed to be active)
Satisfactory timbers:
- Moisture content below 20%
- No evidence of hyphae, mycelium or fruiting bodies.
Littleburn Farm: How did you establish the dry rot hadn’t spread to other parts of the building.
- The other immediate timbers in the roof void had no signs of Hyphae, Mycelium or Fruiting Bodies.
- Where the masonry wall was exposed in the void - no evidence of rot was noted.
- The ornate timber panelling which was extensively clad to the walls had no signs of this either.
Unlikely that the rot has spread elsewhere - though because I am aware how problematic dry rot is I did recommend to expose some of the panelling to determine the masonry walls, though this would need to be subject to Listed Building Consent.
Littleburn Farm: what did you conclude?
The dry rot was not active and had died. Perhaps previously died in the winter when temperatures and humidity/moisture in the roof void would have been lower.
When I inspected (June) the rot may have been on its way to being resurrected if it could find damp timbers and enough to feed on.
The porous stonework walls together with the thermal insulation and lack of ventilation was causing the dry rot in the localised area of the roof void at the far corner.
Teesside Industrial Estate: What is corrosion? And how does it occur?
Corrosion is a chemical reaction between the environment and a ferrous metal. Direct oxidation of the metal occurs which leads to the formation of Hydrated Iron Oxide which gives the known red layer of rust.
The rust offer some protection but when it flakes off, the metal is exposed more resulting in further corrosion. The oxidation also results in the volumetric expansion of the metal. (wrought iron is capable of expanding 7x)
Direct oxidation:
- Electrochemical reaction that occurs when the metal is in the presence of either:
1. Water
2. Oxygen
3. Electrolyte (Electrically conducting solution, can be iron)
Teesside Industrial Estate: What is wrong with the manufacturing process?
The sheets are usually coated and then cut exposing the unfinished metal/sheet.
Teesside Industrial Estate: How will frequent roof cleaning prolong the life span of the repair?
Soiling will allow water to site on the roof covering which will enhance oxidation of the ferrous metal. Thus resulting in corrosion.
Teesside Industrial Estate: What are the provisions of the guarantee?
Usually requires cleaning and recorded inspections
Teesside Industrial Estate: What are the consequences of not rectifying the corrosion?
Water ingress, failure, unsafe.
Teesside Industrial Estate: Why do you rub down and prepare before re-coating?
So the new coating will adhere to the substrate and provide a suitable bond.
