Sir, The photograph of sewer laying entitled 'Backing Plastic' in Construction News (January 16) reinforces the objections to the use of plastic pipes long held by the manufacturers of rigid pipes.
Plastics pipes are extremely susceptible to the effects of incorrect installation. There are at least five examples of bad practice in this one photograph.
First, an inadequate granular surround has been used. Large items from the fill have been allowed to fall into contact with the outer skin of the pipe and are likely to cause damage under compaction. Mechanical compaction is used at too shallow a depth. Assuming the photographer is standing at a manhole base, a length of sewer projects too far beyond the base concrete without the use of a rocker pipe.
Finally, the open end of the pipeline has evidence of concrete in the invert.
As PVCu pipes are expected to lose 80 per cent of their initial strength over a predicted lifespan of 50 years, the need for correct installation is vital, or their life will be even shorter.
Is it any wonder these products remain effectively banned by a number of major water companies who require the security of the reliable clay or concrete options?
Les Richardson Consultant Clay Pipe Development Association