Repointing Chimney Stack - Thin joints

[tododo]

Hi all

We have a leak in the attic around the chimney stack thats been there probably for a while now in reality

Anyway we have scaffolding in place around the chimney and while we are up there we may aswell do the repointing of the chimney stack as it has plants all over it and the crown has a big crack in it too - this crack may be the source of the problem I dont know so we will be checking the lead etc too

Anyway question is what sort of additive do you need in the motar mix for the joints and crown - just a waterproofer or is there anything else - 4:1 mix Ok or stronger???

Also some of the brickwork joints are very thin - is there any special motar mix or silicone type available for these thin joints

Hopefully we will find the source of the leak otherwise its proabably a new roof
Thanks

 

[stuart45]

How thin are the joints? For really thin ones a finer sand such as silver sand is required. It's no use using a sand that's been through a 4mm sieve for 2mm joints. For the flaunching around the pots a coarser sharp sand is better.

 

[tododo]

Not sure as we havnt been up there in a while and I cant remember - some were very thin though

Heres a screen grab of wehn I sent drone up to have a look not too bad - some look a touch thin

 

[stuart45]

The bed joints are quite tight. With some bricks that were regular sizes and shapes, but dense, heavy bricks such as Accringtons the bricklayers used tighter joints with a finer sand. The reason was that with a normal sized bed joint it was difficult to go up more than a couple of courses without them starting to sink, whereas with a tight joint they don't move so much.
Having small joints also means the weather does not get at them as easily. It does make them more difficult to repoint, and you need a tool thin enough to push the new in properly.

 

[cdbe]

Looks very similar to mine, which I did a few weeks ago. I actually raked it out with a multitool (there wasn't much solid to offer any resistance and it was a lot safer than a grinder when working off a cat ladder). I managed with normal building sand and used a finger trowel side on to really push the mortar into the joints - it's surprising how you think you've filled it and then it pushes back.