Building Pathology Flashcards
What is damp?
A building or building element is considered damp when moisture becomes visible through staining, discolouration, sulphate attack, mould growth, frost damage or persistent visible surface moisture.
How can you test for damp?
Using a protimeter can help establish the presence of damp in buildings.
Moisture meters or a speedy carbite meter can be used to determine the moisture content of walls, and the level of damp.
What is a protimeter/ moisture meter
Protimeter’s work by measuring the electrical resistance between two applied electrons.
Protimeters are generally used to measure the moisture content of wood and when used on other materials the readings can be misleading, however this approach does give a sense of moisture content.
Describe the three causes of rising damp and the remedies?
Rising damp is caused either by a lack of a damp proof course, a defective damp proof course or external features bridging the damp proof course.
The remedy therefore involves removing the external feature causing bridging, the injection of water repellent chemicals into the brickwork or, the fitting of a new physical damp proof membrane.
Where a damp proof course is not suitable, lime plaster and wash can be used to minimise the damage caused to the internal finishes.
What is cut edge corrosion?
Cut edge corrosion is a common issue that affects the metal roofing and siding on commercial buildings.
It occurs when the cut edge of a metal sheet is exposed to the weathering and begins to corrode over time predominantly around the sheet laps and sheet end areas. As corrosion develops the coating delaminates and peels back from the sheet edge.
This is a manufacturer defect as a result of on-site mechanical cutting of roof sheets.
How is cut edge corrosion repaired and what is the process in doing this?
This is repaired by using cut edge corrosion treatment. The process includes:
- Preparing the surface by removing roof sections of pre-applied coatings and remove surface corrosion leaving by wire brush or hand grinding the sheet edge ready to receive the corrosion treatment.
- Then the application of a sealant which forms a fillet to the lap joint followed by the basecoat.
3.This is then over-coated with the final topcoat, in a colour to compliment the existing roof sheets.
What are the causes of wet rot and how is it identified?
Causes:
- Wet rot begins to propagate and spread in areas of a high moisture content, usually around 50-60%.
- It is usually found in areas surrounding a potential water leak, or building fabric failure such as around window cills and roof voids.
Appearance / Characteristics:
- It is identified by wood surface appearing flaky and spongy in texture.
- The colour of the wood becomes darkened.
- Mycelium can feature and can be white, brown, amber, green or black in colour with strands that are flexible when dry.
- The fruiting bodies can be a number of different colours and can occur both inside and outside.
How is wet rot treated / remediated?
- The first step to remedy wet rot is to find and eliminate the source of dampness to prevent the timbers becoming damp.
- All infected and damaged timber should be removed, as these may be structurally impaired due to decaying action of the wet rot and the remaining timber treated with a suitable preservative.
- If wet rot is in a confined space, such as a cupboard or loft space, ventilation should be introduced to prevent condensation occurring.
What are the causes of dry rot and how is it identified?
Cause:
Dry rot can occur where the moisture content is as little as 20%
- (SPORE) to begin to germinate a spore (orange/brown dust) needs to come into contact with timber and moisture.
- (HYPHAE) the spore then produces fine white strands called hyphae that allows the dry rot fungus to grow by feeding on the timber.
- (MYCELIUM) the resulting hyphae mass forms mycelium which has the ability to grow over various materials, allowing an outbreak across timbers timbers within an entire building.
- (FRUITING BODY) to continue development of the fungus, mushroom like fruiting bodies develop to distribute spores which are carried by air currents to infect other susceptible timbers, thus restarting the process.
Identification:
- Wood splits into large cuboidal cracks.
- Wood is light in weight and crumbles to touch.
- Effected wood is a dull brown colour and will feature orange/brown dust which are the spores.
- Visible mycelium which which is often a greyish colour when wet or yellow when dry.
How do you remedy dry rot?
- Establish the full extent if the breakout by exposing exposed timber areas.
- Cut out all affected timbers within approximately 300-450mm beyond the last affected area.
- Treating surrounding timbers with a chemical biocide, ensuring all strands and spores are removed.
- Removing all plaster finishes within contact, or close proximity to affected timbers need to be removed with walls treated with biocide.
- Remove the source of moisture (which in this case was introducing cross ventilation), and ensure all timbers are fully dried.
What is the difference between wet rot and dry rot?
- 20 % moisture content for Dry Rot to germinate vs 50% moisture content for Wet Rot to germinate.
- Myscelium is generally visible in dry rot and is a yellow or greyish colour vs Myselium being less commonly visible for Wet Rot.
- Dry rot can be identified by the presence of orange-brown spore dust vs wet rot does not feature this.
BUILDING PATHOLOGY: At Longman Road, how did you identify the source of moisture to the basement to be ground water and why was the installation of a waterproofing system proposed?
- I carried out a process of elimination in ruling out rising damp as the level of water was at a height closer to 2m compared to the typical height of rising damp which is
considered to be around 1m. - I also inspected the condition of the rain water goods and drainage outlets to the surrounding area and there was no evidence of defect.
- Furthermore, the basement wall were saturated to the full perimeter to the approximate height of the external grounds. This suggested water was percolating through the walls from the ground.
- Waterproofing was advised because of the client’s brief included providing a lettable space and this could not be provided without a waterproofing system which would achieve a Grade 3 performance in accordance with BS 8102.
BUILDING PATHOLOGY: What would you have considered when specifying a waterproofing system?
I would need to identify the minimum level of water ingress required as prescribed under BS8102:
GRADE 1a Seepage and damp areas from internal and external sources are tolerable.
GRADE 1b No seepage. Damp areas from internal and external sources are tolerable.
GRADE 2 No seepage is acceptable. Damp areas as a result of internal air moisture/ condensation are tolerable.
GRADE 3 No water ingress or damp areas is acceptable.
- In order to provide a lettable space I would need to consider a system that would achieve Grade 3 to BS8102.
- The system types which are applicable to be retrofitted to an existing basement are Type A Barrier Systems and Type C Drained Membrane Systems as Type B systems allow for water proofing installed as part of the structural fabric of a basement.
BUILDING PATHOLOGY: What are the different types Waterproofing systems as described within BS 8102 and can you explain the differences between them?
The different systems are Type A (Barrier Systems), Type B (Integral Protection) and Type C (Drained Protection).
TYPE A - BARRIER SYSTEM
- These systems consist of a continuous barrier formed of either bonded sheet membrane or liquid applied membranes formed of bituminous material, sodium bentonite matting or a liquid applied system (such as bitumen and cementitious products).
- These systems can either be installed to the external leaf of the building or the internal leaf.
- In this system any weakness in the design can result in failure as water pressure as water pressure from the ground water with track through the weakest point.
TYPE B - Integral Protection
- These systems are designed from the construction of a building or basement with the basement structure itself acting as a moisture resistant shell.
- These basements are typically formed of reinforced concrete so any defect to the concrete can allow water into the basement. With this in mind close attention is made to joint sections.
TYPE C - Drained Cavity
- This system allows water to enter the external walls and/ or floor as far as the cavity drainage membrane.
- Water is collected via the cavity drainage membrane into a controlled drainage system which may include a sump tank and sump pump to divert water away from the basement.
- As this system allows water to permeate through the walls and does not try to hold water back there is no pressure applied to the system unlike TYPE A and B. However, any blockages or other defect to the drainage system may cause issue.
BUILDING PATHOLOGY: At the Savoy Park Hotel, you recognised that timbers were visibly damp and that accessible timbers were of a moisture content of 20%. Is wet rot or dry rot is more likely? how would this be identified? and how would you recommend this is treated?
At 20% dry rot is more likely, from this moisture content dry rot can begin to germinate if spores are in the air. Timber is not susceptible to develop wet rot until the moisture content of 50%.
I would identify dry rot if
- The timbers splits into cuboidal cracks and is visibly lighter in tone and appears dry.
- The timber would crumble under touch.
- Mycelium - greyish if wet, yellowish if dry.
- Spores - orange/ brown dust.
Remedy dry rot by:
- Establish the full extent if the breakout by exposing exposed timber areas.
- Cut out all affected timbers within approximately 300-450mm beyond the last affected area.
- Treating surrounding timbers with a chemical biocide, ensuring all strands and spores are removed.
- Removing all plaster finishes within contact, or close proximity to affected timbers need to be removed with walls treated with biocide.
- Remove the source of moisture (which in this case was introducing cross ventilation), and ensure all timbers are fully dried.
