A street in Radlett will have to close again because there is concrete in the sewer.
Watling Street was closed on Thursday so Thames Water could deal with the blocked sewer near Radlett Station.
During the work they found the sewer has been completely blocked by concrete causing sewerage to back up and a full replacement of the sewer will be required where the concrete is causing the obstruction.
The road will be closed between from A411 Elstree Crossroads North to the A414 North Orbital Road.
The excavation required to undertake these works will be approximately four metres down and fall within the centre of the road.
It is now anticipated that works will need to continue under the closure until at least Tuesday.
A full CCTV survey was carried out on Friday which should help find out what needs doing and if further works are required up or down the sewer line.
Terry Douris, cabinet member for highways, said: "We are extremely frustrated that this situation has arisen due to what appears to be someone’s irresponsible actions and residents affected by this disruption have our sympathy. Due to the nature of these works council taxpayers will not be footing the bill.
"All parties are working as hard as they can to minimise the disruption in the area. It is frustrating that the closure needs to be in place longer but due to the nature of the blockage it is essential that all of the problems are investigated and resolved while contractors are on site."
Thames Water operations manager Mark Grimshaw said: "Normally blockages are caused by fat, oil and grease building up in the sewer but unfortunately in this case it’s concrete, so we can’t just jet it through.
"It’s in there and it’s set to the pipe, so unfortunately it means we need to remove the pipe and replace it with a new one. This is very frustrating and not the first time damage has been caused by private contractors pouring concrete into our sewers.
"Our main priority is to fix the problem and restore normal service as soon as possible, and then reclaim the costs from whoever is responsible."
Thames Water has been dealing with a blocked sewer near Radlett Station under an emergency response permit since February 19, using temporary two-way traffic signals during peak times.