Q. Could a suspected chemical attack on copper hot water pipes be due to lime in cement? Could you suggest which codes of practice cover the repair of copper pipes?

A. Copper water tube is largely corrosion resistant. It is very infrequent that waters or special conditions are encountered which can cause corrosion. Such corrosion problems as do occur usually stem from the following:

  1. Aggressive, hard well waters causing pitting
  2. Soft, acidic waters that do not allow a protective film to form inside the copper tube
  3. System design or installation which results in excessive water flow velocity or turbulence
  4. Unacceptable workmanship
  5. Excessive or aggressive flux
  6. Aggressive soil conditions.

Aggressive pitting waters can be identified by chemical analysis and treated to bring their composition within acceptable limits.

Pitting can also be caused or intensified by faulty workmanship, which leaves excessive amounts of residual aggressive flux inside the tube after installation. If the joints have been overheated during installation and the excess residual flux has polymerised, the pitting problem can worsen. Erosion can also be aggravated by faulty workmanship. For example, burrs left at cut tube ends can upset smooth water flow, causing localised turbulence and high flow velocities.

An improper horizontal slope can also create a situation where corrosive solutions could lie in the tube and attack it. If hydrogen sulphide gas in large volume is allowed to vent back into the house drainage system, it can, for instance, attack the tube.

I do not recall any specific codes of practice but there are several relevant BSI standards on this area.

Q. How do I determine which contract should be used for a) specific projects and b) for a refurbishment project subject to late design change for a private client?

A. There is no definitive answer to the first question as selection of appropriate strategy is a very complex subject area. Usually, the client/architect would consider a clear list of the client's objectives, identify risks involved for undertaking the project, decide and finalise the payment mechanism (i.e. price based or cost based contract), prepare cost and time estimates, evaluate all possibilities and then finalise a contract strategy. The client/architect would also ascertain the level of risk to be owned by the client and what is to be passed to the contractor. There are CIOB, CIRIA, and other publications and books on this subject, for instance, CIOB's Code of Practice for Project Management for Construction and Development and CIRIA's Planning to Build? A Practical Introduction to the Construction Process.

To answer the second part of your question I would suggest that in a situation where there is the likelihood of late design changes and a large volume of variations and additional works; my personal advice would be to go for a cost-based payment mechanism (cost reimbursement or target cost). In this way, the client owns most of the risks and generally the contractor gets paid for the belated design and other changes, amicably and timely. New forms of contract such as NEC Engineering and Construction Contract are more suitable for such type of work.

Q. What interpretation should I put on Clause 4.2.3 of the IFC 98 regarding payment of interim certificates?

A. My understanding is that the final date of payment of each interim certificate is 14 days from the date of issue [Clause 4.2(a)]. This means that 14 days commences with the issue date of the certificate (please note that it is not the date of its receipt by the Employer), and that the payment should reach the contractor by the final date for payment.

Clause 4.2.3 sets out the requirement for giving notice with regard to interim certificates (it is required under the Housing Grants and Regeneration Act 1996), and under Clause 4.2.3(b) Employer may give notice (no later than 5 days) of how much he intends to pay. If the Employer does not give notice, under Clause 4.2.3(c) the Employer must pay amount notified/certified in full.

In case the notified/certified amount is not paid by the final date, interest accrues until amount paid in full [Clause 4.2(a)], contractor may give notice of suspension and after 7 days, suspend work until amount paid in full [Clause 4.4]