Building Pathology 2 Flashcards
Coanwood: What did you recommend following your inspection?
Invasive inspection, if it was tree root damage as expected:
- Cut all existing roots and installation of a root barrier and root barrier.
or
2..Cut down all trees including their root systems, if appropriate as due diligence must be taken prior to this application to determine if the removal of such trees will have any effect on the ground which in turn may cause damage to the property.
Rectification:
Replace the floor in full or patch.
Bonus:
Obtain all council records to verify the pruning frequency and programme of such works with thought to obtain all attendance records. Regular maintenance may have prevented such damage occurring through controlling tree growth.
Coanwood: You say you considered Sulphate Attack, what do you mean?
What is it:
Sulphates found within the soils, hardcore or building materials which under wet conditions react with the cementitious concrete, resulting in cracking, expansion and an upwards lifting motion within the slab itself which may lift the walls in turn causing cracking elsewhere around the building.
Why not:
- Isolated and localised damage to concrete floor.
- No salt deposits as you would expect.
- Elm tree roots directing towards the property and damaged area.
- DPM’s also were widely introduced in 1960s and this was a late 1970s home.
Coanwood: You considered Heave, what do you mean?
What is it:
I considered…
- seasonal heave which is expansion of the ground during seasonal periods (i.e. winter).
- excess water in the ground by removed or over pruned trees or defective drains.
Why not:
- Expect to see more external damage to walls etc.
- Client advised the council don’t prune frequently (this would increase soil volume if they did)
- No removed trees or visible surrounding drains.
- Visible tree roots externally indicated invasive roots.
Coanwood: Why did you think Elm trees were the primary factor?
- Several Elm trees identified externally which are able to cause damage to buildings at 15m or less.
Some conflicting information..
Hollis states 19m or less
BRE Good Repair 2 states: 15m or less
- Specifically I identified 1nr large elm tree which was 3.7m away from the property and was a considerable height (may have been mature).
- The tree roots were also visible which were directing towards the property.
Coanwood: Did you consider any other damage to the building?
I inspected the remaining of the property though could not establish other damage, though this may have been masked behind finishes.
Further severe damage may have occurred to the building if the issue is left unresolved, this may include:
- Foundations
- Floors
- Walls etc
Coanwood: How would you treat sulphate attack if it was that?
- Soil, hardcore and concrete samples may be taken to measure the sulphate content and help identify root cause of the sulphate attack. Will determine likely hood of further activity, if low patch, if high repair in full.
Repair
- Remove the concrete floor slab in full or part.
- Remove existing hardcore
- Prepare sub-base and lay clean graded limestone or low sulphate hardcore.
- Install new DPM to separate concrete from ground.
- New slab laid (B Regs will require thermal insulation installed)
Sulphate resisting cements may be used if required within the concrete to prevent attack. However, a suitable damp-proof membrane installed between
the hardcore and the concrete slab dramatically reduces the risk of sulphate attack.
Coanwood: How would you rectify the issue if it was heave?
Establish the reason why the ground had become saturated and swollen.
Instructed a Geo-technical engineer to determine the soil, water table and any other issues which may have caused the swelling of the soil.
Remedial strategies:
1. Put the ground back into a state of equilibrium.
- Let heave take its course and then underpin/stabilise the ground and rectify any damage to building.
- Soil replacement with dense material such as concrete.
4, Seek advice from SE regarding the installation of cellular structures to mitigate heave.
Coanwood: Did you consider Alkali Silica Reaction?
Reaction between the alkali in cement and silica in aggregates under damp conditions.
Why not:
Different characteristics:
- ASR would expect to see crazing like cracks in a jelly like substance.
- Expect to see throughout concrete floor not in an isolated location.
Coanwood: What’s the repair for Alkali Silica Reaction?
There is no known repair.
Cut out and start again with Low Alkali cement and less aggressive reacting aggregates to lower the risk of occurrence.
Coanwood: Did you consider HAC?
Yes I considered HAC though further consultation with the occupiers identified the property was built in the late 1970’s and after 1976 when HAC was banned.
Unlikely as HAC is usually found in pre-cast beams or lintels, though lab analysis would determine this.
HAC usually weakens and is prone to chemical attack.
Coanwood: What category were the cracks and where did you source this information?
BRE 251.
Cat 3 - Cat 4.
