Building Pathology

Question 1

What are the typical defects on Victorian Properties you have come across?

Answer 1

I have worked on multiple Victorian school properties (1837-1901), particularly in London. I have come across defects that include: - Leaning chimney stacks - Missing lead flashing or split/distressed leadwork on stepped flashing or aprons - Delaminated masonry - Cracked masonry and brickwork - Missing pointing - Dropped brick arches - Eroded stonework - Rotten timber cills and frames to windows - Corroded embedded steelwork - Corroded and defective cast iron rainwater goods - Internal damp

Question 2

and what repairs have you recommended on Victorian Properties?

Answer 2

I have recommended repairs that include the replacement on lead flashings and use of patination oil, replacement brickwork, pointing repairs, replacement of stonework, linseed oil putty repairs, timber repairs to windows and decorations.

Question 3

And what type of splicing joint could you specify?

Answer 3

Half lap, biscuit joint, Dovetail, tongue and groove

Question 4

Name some advantages of using timber splice resin repairs?

Answer 4

Aesthetically pleasing finish No ugly bolts or steel plates visible Little disturbance to existing building fabric Reduction in overall cost of repair & restoration Complimentary with traditional carpentry methods and skills

Question 5

What are the typical roof defects you have come across?

Answer 5

I have experienced on pitched roofs, the likes of slipped slates and clay tiles, missing point on ridge tiles, chimney stack missing brickwork and leaning. Also on metal profiled roofing, I have reported back to my client cut edge corrosion, rusted fasteners and fixings to the roof.

On flat roofs I have experience, ponding, blocked gutters, inappropriate abutment details, poor joints, use of fragile roof lights, crazing and blistering of the surface, missing flashings.

Question 6

What is meant by the term Deleterious?

Answer 6

Deleterious materials are materials that can be harmful to people and also to buildings. The term can also be applied to materials which unexpectedly fail

Question 7

Can you name some deleterious materials?

Answer 7

• Woodwool slabs
• Lead
• Asbestos
• Urea Formaldehyde
• High Alumina Cement
• Mundic Block

Question 8

Where are woodwool slabs found?

Answer 8

Woodwool slabs on roof decks, found on the soffits.

Question 9

Why are woodwool slabs deleterious?

Answer 9

They were used in shuttering and formwork for casting concrete. The woodwool due to its structure can cause honeycombing to the concrete, which reduces the cover of the concrete on the reinforcement. This makes the concrete weaker, reduces fire resistance and makes it more susceptible to corrosion to the reinforcement.

Question 10

When was asbestos illegal to use in the UK?

Answer 10

Asbestos was banned in 1999. Chrysotile was banned in 1999 and amosite and crocidolite was banned in 1985.

Question 11

Do you know what type of asbestos was the last used form of asbestos in construction?

Answer 11

Chrysotile (white) – 1999.

Question 12

In what circumstances are WWCB slabs classed as fragile?

Answer 12

When used as formwork for concrete as it can result in reduced fire resistance, reduced cover which results in risk of reinforcement corrosion and in extreme cases reduced strength. WWCB is most dangerous when wet and exposed to wet conditions as it loses its rigidity.

Question 13

How did you determine the thickness of the WWCB slabs?

Answer 13

WWCB are available in thicknesses ranging from 15 to 100 mm and vary in the following thicknesses. Taking a a core sample after and R&D survey is carried out is the most accurate way of determining the thickness.

Question 14

How did you advise the client on the risks posed by the WWCB slabs?

Answer 14

Once I established the moisture content of the material and its overall condition and the impact it had had on the concrete, I advised my client to monitor the condition of the concrete and plan to replace the woodwool with a new suspended ceiling to improve the thermal efficiency of the sports hall and improves acoustics of the room.

Question 15

When the structural engineer inspected the existing slabs, what were they looking for?

Answer 15

Signs of damage on the concrete, i.e cracking, spalling. Was there any honeycombing on the slab, was there adequate cover on the reinforcement?

Question 16

You mention repointing in Lime Mortar, what mix did you use?

Answer 16

On one occasion on a Victorian Property, I used a Natural Hydraulic Lime 3.5 with a 1:4 mix on pointing. This is a moderate lime. I had to provide the conservation officer with a few samples to pick from and the contractor had to build a sample wall using the chosen brickwork.

Question 17

What is the difference between Natural Hydraulic Lime and Non Hydraulic Lime?

Answer 17

NHL is produced by heating limestone. Hydraulic lime is as bagged powder and non-hydraulic lime is a putty. Builders find it easier to work with as it is almost like working with cement. Non-hydraulic lime has a slower setting speed.

Question 18

What are the dates for each of the different period properties?

Answer 18

• Georgian – 1714 – 1837
• Victorian – 1837 – 1901
• Edwardian – 1901 – 1910

Question 19

When were DPCs introduced?

Answer 19

1870’s

Question 20

When was the Victorian period?

Answer 20

1837 -1901

Question 21

What are the different gradings for Listed Buildings and what do they mean?

Answer 21

There are three different gradings, Grade I – Exceptional Interest, Grade II* - Sites of particular importance and Grade II – Special Interest. Properties are listed because of their special historical and/or architectural interest.

Question 22

What era were Victorian buildings built? How about Georgian or Edwardian?

Answer 22

Victorian era is 1837 – 1901 and Georgian is 1714 – 1837. Edward follows the Victorian period for a short period between 1901-1910. Edwardian and Victorian were very similar in style.

Question 23

You mention concrete repairs and specifically carbonation in your Summary of experience, please could you give me other examples of concrete defects:

Answer 23

1. Sulphate attack
2. Alkali silica reaction,
3. Chloride attack.
4. Carbonation.

Question 24

What is carbonation?

Answer 24

This is when the alkalinity of the concrete is reduced from carbon dioxide in the atmosphere and removes the passive layer protecting the reinforcement within the concrete. This causes the steelwork to corrode and expand.

Question 25

What can cause carbonation?

Answer 25

Carbonation can be caused by lack of coverage above the reinforcement. It can also be brought on by local factors such as the local environment or the use of the property.

Question 26

Tell me more about alkali silica reaction and chloride attack

Answer 26

Alkali silica reaction is when the alkalinity within the cement reacts with the silica when exposed to water and this creates a gel like substance and expands causing cracking.

Chloride attack corrodes the steel reducing the strength of the structure as the steel reinforcement expands. The chlorides can be present within the mix from additives, sea dredged aggregates, or from using sea water as a mix. The chloride is present externally from salts from sea breezes, or road salts that splash on to a surface.

Question 27

How could you treat Chloride attack?

Answer 27

You could avoid chloride attack in construction by coating the rebar in epoxy. Alternatively, you could increase the coverage of concrete on the rebar. To limit the damage caused by chloride attack, the exposed rebar can be treated and recovered or cathodic protection can be installed.

Note: BRE Digest 444 provides advice on the corrosion of steel in concrete. The Eurocode provides advice on concrete cover for reinforcement to prevent such attacks, however, the Structural Engineer will provide these details.

Question 28

Name some types of Concrete Inspection?

Answer 28

Visual inspection (VISUAL)

Schmidt Rebound Hammer Test – Surface hardness test, rebound of an elastic mass. (PHYSICAL)

Carbonation Depth Measurement – Phenolphthalein Solution (CHEMICAL)

Permeability Test – Tests the ease in which the liquid penetrates concrete. (PERMEABILITY/WATER)

Electromagnetic – checks coverage over the reinforcement bar. (ELECTRICAL)

Question 29

What is the CBR?

Answer 29

California Bearing Ratio - test used to evaluate the subgrade strength of roads and pavements.

Question 30

What indicated to you that the concrete was being affected by Carbonation? What further investigations did you complete or recommend?

Answer 30

The concrete was spalling in vertical bands on the concrete ring beam. Rust stained concrete on the external face of the concrete. I recommended for the concrete to be tested using Sandberg. They applied the phenolphthalein solution which determined that carbonation was present as it was clear. I produced a specification using an epoxy primer on the steelwork, anti-carbonation concrete repair mortar and anti-carbonation paint to the externals.

Question 31

What are the types of water ingress in a property?

Answer 31

• Penetrating damp
• Rising damp
• Condensation

Question 32

What are the mechanism for water entry into a property?

Answer 32

• Kinetic
• Capillarity
• Gravity
• Pressure Differentials
• Surface Tension

Question 33

How would you inspect damp in a building?

Answer 33

Before attending site, I would ensure I have all the appropriate tools with me. I would ensure that I have a calibrated damp meter, tools for opening easily accessible areas. I would ensure that I have check the asbestos management survey for the property (if required). I would review the client brief on the project and existing information. Ask the site premises manager/building user for further detail on the issue to establish when and where the issue is occurring. Review internally, checking internal conditions. Try and establish the type of damp, is it penetrating, is it rising or is it condensation. Check the extent of the issue. Try and establish the source of the issue. If I cannot determine the source of the issue on the day, review externally. If still cannot pinpoint issue, suggest further investigations.

Question 34

How would you advise on remedial work for damp?

Answer 34

It depends on the type of damp as they all require different remedial works. If it is rising damp, then it may require alterations externally to reduce ground levels. Has a DPM been installed? If it was penetrating damp, why is the water getting in, what is contributing to the water ingress, are the gutters blocked, is there flashing or slates missing. Is there a joint on a pipe which is loose. If it is condensation, then I would be looking down the route of, is there cold bridging, is there enough ventilation in the property or is the lifestyle conditions of the building use contributing the internal damp issues.

Question 35

How would the remedial work for damp in normal building differ for listed building?

Answer 35

There is less opening up you can do legally without consent. Also, the buildings are built in completely different ways, in terms of how they differ with water ingress. Listed buildings may have solid brick walls which have been pointed in lime, allowing the water to absorb and then evaporate back out of the wall over time. The cavity wall construction is used in modern buildings to provide the gap between two skins to prevent water ingress and cavity trays direct water out toward the external leaf.

Question 36

What inspection techniques would you use for identifying damp?

Answer 36

Visual inspections, smell also helps to identify if there is damp. Also using different types of equipment.

Question 37

What equipment could you use to obtain a more accurate analysis of damp?

Answer 37

Using damp meters or carbide meters to detect moisture and analyse the content in masonry and/or timber.

Question 38

Do you carry a Carbide meter with you on a survey?

Answer 38

No, this is not a tool I carry. It tends to be used by a damp specialist who carries out these surveys on a regular basis. It also requires disruptive work, which tends to be excluded on our surveys.

Question 39

What other equipment could you use to inspect damp (other than a carbide meter)?

Answer 39

A Protimeter or Gravimetric testing.

Question 40

What are the limitations to using a protimeter?

Answer 40

Protimeters are designed to measure timber and measure the moisture within timber and can measure the molecular structure of timber. Limitations are caused by the requirement for the device to be calibrated. The devices measure electrical conductance and therefore metals and salts can distort the readings.

Question 41

What did you advise the client in the project that suffered from damp?

Answer 41

I advised my client to rectify the areas where there was water ingress. In this case there was lead in the roof valley that had split and this needed replacing. Then I proposed the works to replace the plasterboard and redecorate.

Question 42

What are the causes of rising damp?

Answer 42

• Existing damp proof no longer works.
• No damp proof ever laid.
• Ground outside the external wall is higher than damp proof course
• Internal plastering bridges the damp proof course.
• Build up of rubble inside a cavity wall bridges the damp proof course.
• Previous penetrating damp issue has left residual damp at the base of a wall.
• Poor circulation causes condensation at the base of a wall.
• Leaking water pipes at the base of the wall.

Question 43

What are the remedies of rising damp?

Answer 43

In many cases, there may be a drainage issue in your area that will mean the ground water level rises above the barriers. A surveyor would be able to assess the source of the problem and advise you on the best course of action, which could include adjusting the space below the floorboards so water can evaporate, improving local drainage or ensuring the ground slopes away from your home so water won’t collect near walls.

• A) Excavation of the soil
• B) Inject silicone DPC
• C) Asphalt tanking to 1.2m high to prevent water penetration

Question 44

What are the three main types of basement waterproofing?

Answer 44

A) External tanking

B) Dense monolithic concrete

C) Cavity drain

Question 45

You mention repointing, what mix did you use?

Answer 45

On one occasion at Gainsborough Primary School, we used a Natural Hydraulic Lime 3.5 with a 1:4 mix on pointing. This is a moderate lime. I had to provide the conservation officer with a few samples to pick from and the contractor had to build a sample wall using the chosen brickwork.

Question 46

What is the difference between Natural Hydraulic Lime and Non Hydraulic Lime?

Answer 46

NHL is produced by heating limestone. Hydraulic lime is as bagged powder and non-hydraulic lime is a putty. Builders find it easier to work with as it is almost like working with cement. Non-hydraulic lime has a slow setting speed.

Question 47

What are the dates for each of the different period properties?

Answer 47

Georgian – 1714 – 1837

Victorian – 1837 – 1901

Edwardian – 1901 – 1910

Question 48

When were DPCs introduced?

Answer 48

1870’s

Question 49

When was the Victorian period?

Answer 49

1837 -1901

Question 50

What are the different gradings for Listed Buildings and what do they mean?

Answer 50

There are three different gradings, Grade I – Exceptional Interest, Grade II* - Sites of particular importance and Grade II – Special Interest

Question 51

What types of leak detection tests are there? How do they work?

Answer 51

• Electronic leak detection whereby a weak electrical field is created on the dampened surface and any current that ‘earths’ into the building changes the nature of the field locally. This should pinpoint the penetration or just as importantly show when water penetration is not caused by a roof leak.
• Also, Firstly, a thermographic examination could be carried out to identify areas of leaks.
• Other forms of leak detection are flood test using a bung or a dye test which uses more of a trial and error approach

Question 52

Name the types of rot?

Answer 52

Wet Rot and Dry Rot.

Question 53

What are the differences with wet rot and dry rot?

Answer 53

The physical characteristics and the moisture content of the timbers.

1. Wet rot is 40-60% moisture content, cracked along the grain, dark brown.
2. Whereas dry rot is 20-40% moisture content, cuboidal cracking and fruiting bodies with white mycelium.

Question 54

What moisture content does wet rot require in wood to grow? What about dry rot?

Answer 54

Wet Rot - 40-60%

Dry Rot - 20-40%

Question 55

For the window repairs at Daubeney Primary School how did you identify it was wet rot and not dry rot?

Answer 55

I identified it to be wet rot because of its location, being externally and exposed to weather. It had high moisture content, was dark brown, soft and spongy.

Question 56

How would you remedy dry rot?

Answer 56

Identify the source of moisture and improve ventilation in the space. Identify how far the dry rot has spread and whether there is any other timber decay. Cut back timbers from last sign of infection by 500mm. Replaced with pre-treated timbers and if any masonry has been affected use a fungicidal fluid.

Question 57

Whereabouts in a building would you be likely to find dry rot?

Answer 57

In hidden places below finished surfaces in voids and in attics. Where humidity and moisture levels were increased.

Question 58

For the school in Merstham how did you identify where the leak was on the roof? What did you specify?

Answer 58

The sloped roof was showing damp at the base of the pitch roof. There was a valley at the base of both pitches, and it was evident that the valley was the weak point. From visual inspection, there were splits in the lead where the lead did not have any expansion joints. The lead would be replaced.

Question 59

What is the difference between the appearance of wet rot and dry rot?

Answer 59

Wet rot is dark brown almost black and olive knobbly texture. Red spore dust for dry rot, white mycelium, mushroom like fruiting bodies.

Question 60

What was the cause of the dry rot in your example?

Answer 60

Usually found in unheated, dark rooms, particularly where the moisture and humidity are high for instance trapped behind linings or building fabric. Tends to be found in hidden areas, i.e., below suspended timber floors or in roof voids where leaks can be present, and ventilation is at a minimum.

Question 61

What the remedial work for dry rot you found?

Answer 61

Exposing the leak, rectifying the roof leaks and encouraging ventilation.

Question 62

Other than removal, is there any other action you could take for remedying dry rot?

Answer 62

Where the dry rot has infected the timber the best course of action is removal. You need to sterilise the surrounding masonry and replace with pre-treated timbers. Guidance states timbers need to be cut back 500mm from last known area of infection.

Question 63

How is wood pre-treated?

Answer 63

It is treated with chemical preservatives which are then forced deep into the timber through pressurisation cylinders.

Question 64

What remedial measures did you recommend for the instance of dry rot you identified?

Answer 64

Rectifying the damp issue and removing plywood trapping moisture. The dry rot was dormant, however I recommended removing the plywood back 500mm from last sign of infection, remove plaster back 1m from last sign of infection. Use a fungicidal treatment on all masonry affected. Install pre-treated timber in its place and improve ventilation in the area as well as rectify damp issue.

Question 65

If you noticed cracks on the building, can you explain what the likely causes are and how would you assess this?

Answer 65

Cracking may show how a building is moving. Assess the size of the cracks, the cracks may indicate that an element of the external envelope of the building is rotating, could be corroded steel elements, washed out drains etc, local factors contributing to the issue such as trees?

Question 66

Is there any guidance you could use to assess the impact from Local Factors such as trees? Also what guidance is available for cracking.

Answer 66

NHBC Chapter 4.2 - Building near trees. NHBC offer guidance and it reviews the height of trees and the distance they are away from the building. In cohesive soils, the felling of trees can have a major effect on the water table, which can take many years to stabilize. Existing buildings on the site may be affected and new buildings may require deeper or piled foundations. Chapter 4.2.

BRE Digest 251 - Assessing cracks in houses - Scale is 0 - 5 (Hairline crack 0.1mm up to 25mm structural damage). Provides guidance on the remedial measures to take with regards to the size of the cracks.

BRE Digest 361 - Why do buildings Crack

Question 67

What else does the NHBC provide guidance on?

Answer 67

Roofing – both pitched and flat and provides guidance on the materials used, thicknesses. For instance, the guidance states that plywood should be 15mm thick for 450mm centres and should be square edged with 2-3mm gaps between boards. The gap provides room for expansion.

Question 68

How do buildings crack?

Answer 68

• Thermal expansion
• Differential movement between materials
• Frost damage
• Steelwork corrosion.

All construction materials have the capacity to expand or contract to a greater or lesser degree as temperature varies. The combined effect of changes in temperature and moisture content within a building depend on a number of factors: The stiffness of the materials, Potential for the material to “creep” i.e., continue to move over time under constant stress, Degree of restraint (i.e., is the material free to move, is it “built-in” at the ends?). The resultant combined effect may result in: Oversailing of DPC, Buckling (bulging of walls), Fracture of the masonry units (tension or shear).

Question 69

What is subsidence?

Answer 69

Downwards movement of soil. The ground beneath a building sinks, pulling the property’s foundations down with it. It usually occurs when the ground loses moisture and shrinks, which can be caused by prolonged dry spells

Question 70

What is settlement?

Answer 70

Settlement is the downward movement of the ground caused by a load consolidating the soil below it or causing displacement of the soil.

Question 71

What is heave?

Answer 71

Heave is the upward movement of the soil beneath a property expanding and pushing the ground upwards, which can cause structural damage to a building.

Question 72

How would you design movement Joints?

Answer 72

I understand the purpose of movement joints, if I were needing to design movement joints, I would seek a Structural Engineers advice.

Question 73

How can you tell with the appearance of cracking whether a building may be suffering from subsidence or heave?

Answer 73

Cracks are likely to be visible on the inside and outside. Crinkling wall paper, cracks around openings, cracks through the DPC. The shape of the cracks and whether they taper. Wider at the top or bottom

Question 74

What document would you refer to for cracking to buildings?

Answer 74

BRE Digest 251 - it defines the repair methods and course of action based on size of crack.

• 0 - Hairline cracks less than 0.1mm.
• 1 - Fine cracks of up to 1mm.
• 2 - Crack widths up to 5mm.
• 3 - Crack widths of 5 to 15mm (or several of e.g., 3mm).
• 4 - Extensive damage, cracks 15 to 25mm.
• 5 - Structural damage, cracks greater than 25mm.