chimney flaunching over cement

[kreyszig]

I've recently had one of 3 chimneys re-flaunched while some lead was replaced. I repointed the same chimney in lime myself, while I was up there I realised the new flaunching was just laid on (in cement) over the top of the old cement. I'm now looking at the other two and thinking I can do as good a job myself.

Questions:
a) is a lime mortar the best choice for this task
b) can I put a lime mortar over the top of the existing cement? I presume in an ideal world all the old cement would come off first, but I dont want to risk damaging the pots if possible.

 

[plasticpigeon]

I'm not surprised you are questioning whether you can do better yourself. It is the curse of the engineer to want everything to be perfect. I think cement is the best material for flaunching as it gets the brunt of the weather and something strong and impermeable is best, just like coping stones on the top of a wall. I wouldn't think going over the top of old flaunching to be a good idea, so I think your builders have let you down there, but if it doesn't leak it is probably sufficient if not neat of optimal.

 

[kreyszig]

Thanks for the quick response! I had thought along those lines.. perhaps breathable isn't what I want on the top surface of the chimney!

 

[a twig]

Just did new pots on my place - went as follows:

1 ) Remove old knackered muck with help of a bolster, pitcher, punch and hammer.
2 ) Remove old pot
3 ) Brush down and clean away all gunk/moss/algae.
4 ) Decide to use up remains of pre-mixed NHL 3.5 lime mortar from Ty Mawr.
5 ) Replace pot and whack in big old bed of muck

Time passes...

6 ) Go back up to check mortar has gone off and to fit cowlings - realise one of the pots wobbles
7 ) Remove new knackered muck with help of a bolster, pitcher, punch and hammer.
8 ) Remove pot
9 ) Not having any more lime mortar - mix up new mortar - 1 Cement: 1 Sharp Sand: 4 Builders Sand
10 ) Replace pot and whack in a big old bed of muck

11 ) On final pot, realise that expensive new cowl doesn't agree with non-original pot, and scaffold is coming down in 40 minutes.
12 ) Carefully modify pot with hammer - cowl now fits pot - happy days.
13 ) Go down the pub, become mortified when friend tells you that pot you "modified" would have been worth £500 to a reclamation yard who would have sold it on for £700.
14 ) Console yourself that scaffold to do it all again a week later would have cost you a similar amount, so you would have been no better off (maybe).

15 ) Once scaffold has gone, remember you didn't check the pots, so precariously balance on a long ladder a few days later in gaps between rain showers - all solid...

16 ) Congratulating yourself on a job well done, then suddenly remember that when you took one of the old pots off you saw that the liner looked pretty shot, and note to self to start saving for a replacement liner for next year.

So yes, cement based I would say for such a job.

 

[kreyszig]

Phew! That could have been me - thanks

Even got my lime and aggregate from Ty Mawr too!
(Their Blaenavon dark aggregate is a great match to our dark mortar. Only problem is my messy pointing has left tell all stains on the bricks when it rains.. hopefully that will weather out a bit)
That must have been one hell of a pot!