Chimney stack repair or take down

[Geetar500]

Having a new roof done and they have found the bricks/mortar on at least one of the sides has basically turned to powder. That right hand corner you can see in the photo is also loose.

The other side of the stack *seems* solid but render has blown in patches all the way around.

The second shot is from inside the loft, the mortar is very crumbly at least down to where I have shoved the screwdriver all the way in (with very little resistance).

The tricky thing is that it is a shared chimney with our neighbour and after being up on the roof with him he thinks it is repairable in situ with some cement blocks and mortar and that will be fine as it doesn't need to take a lot of weight. However the roofers are saying it would basically need to be taken down until they get to solid all the way around and then rebuilt.

I want to just take it down below the roof as neither of us are using it or plan to use it in the future, so it seems by far preferable to just be done with it and never have any more issues.

In terms of an in situ-repair, I am no expert but tend to agree with the roofers, seems like it would be impossible to get a solid repair without removing a substantial amount of material which seems to me rather dodgy and would risk collapse. I need to check with them but I'm 99% sure they wouldn't do this anyway. I am sceptical you would even find a reputable tradesman who would undertake such a job?

What do we think? Can a safe and long-lasting repair be done by mortaring some blocks in and then re-rendering?

 

[Loofah]

If they're a decent outfit then the roofers would refuse to complete the job unless the knackered stuff is properly fixed. I don't think bodging it is an option.
Try to convince your neighbours to have it removed

 

[Alastairreid]

Take it down then it ceases to be a liability, unused stacks act like sponges and require regular maintenance.
Hopefully your neighbour will see sense.