A new build Hotel in Edinburgh had suffered a catastrophic leak to the sewage tank in the basement. The tank had failed due to high pressure from the water table (ground water). Attempted emergency repairs had resulted in around 2m² of the 20mm thick polyethylene tank wall being cut out.

It was assumed that the tank could be simply repaired by patching this area with GRP. The tank was, however, manufactured from polyethylene a material that is incompatible with polyester. It was then assumed that repairs could be affected by a PE specialist plastics company repairing the huge hole using polyethylene welding techniques. No company could be found that would undertake this repair far less offer a guarantee.

GRP Aberdeen Ltd were engaged by the main contactor to see if a repair could be achieved using GRP. The client had a deadline of 12 days before the hotel was due for handover. GRP Aberdeen Ltd surveyed the tank and produced a method statement for repair which was accepted by the client.

Graphic of tank repair.
Bonding of GRP during repair.
Layup of tank.
Gel coating out tank.
Successful tank repair.

The repair involved coring out a 400mm diameter by 500mm deep sump so that the ground water could by continually drained using a submersible pump. The pump was installed and the tank was dried out. GRP Aberdeen Ltd then proceeded to create an intermediate surface which was bonded to the PE and would equally bond to the new GRP.The material used and the bond achieved to the PE and the GRP was entirely successful and GRP Aberdeen Ltd confined space GRP specialists proceeded to create a 20mm GRP tank within the existing tank.

Work was carried out in a safe and efficient manner and all safety controls and equipment were in place throughout the job along with the continual draining of the ground water. It is interesting to note that the ground water was actually crystal clear and look like pure spring water. Once the entire tank had been laid up to 20mm thick a 100mm x 100mm GRP internal, peripheral ring beam was laminated in place. The entire internal surface was thereafter gelled out yellow.

The last operation carried out by the GRP specialists was to remove the sub–pump and close out the sump. The sump was closed using a 20 thick GRP plate which was successfully laminated (accelerated) in position before the water reached the top of the sump.

Lessons Learnt

Survey, design and clear definition of methodology and communication allowed the GRP specialists in the team to carry out an effective repair in record time

Safety controls and equipment are paramount to the efficient and confident completion of tank works

A clean work place is a safer workplace

Clear communication with client and other sub-contractors is paramount at all times

GRP is an effective and stronger alternative to PE

Costs for repair using GRP Aberdeen Ltd were minor compared to replacing the entire tank – and that was without addressing ground water issues. Estimated for replacement, £250,000.00 – Repairs in situ by GRP Aberdeen Ltd were 80% less than that estimate.

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