another question about lime

I have a question about lime
I have an old inglenook fireplace that was rendered I have removed all the render
And I now wish to know the best way to clean the bricks off?
And the old pointing is lime do I need to re-point with lime or can it be done with ordinary cement?
If lime how do I mix it with sand/sharp sand etc?
The old pointing is very crumbly and I will be having an open fire what would be the best thing to do with it.
It’s a DIY job so keep it simple please.
Thanks

Hi

Im structural engineer (well, new graduate) however just come out of my last year on writing a 10,000 word dissertation and carrying out laboratory tests on traditional lime mortar mixtures.

Yes, you will need to repoint using lime. Cement based mixtures are much stronger, therefore mixing the two as composite can cause bricks to crack.

If you wish, you could produce your own mixture using sharp/grit sand aggregate (straight off the shelf from TP), Castle cement Natural Hydraulic Lime binder and water. UNDER NO CIRCUMSTANCES DO NOT USE BUILDERS SAND. Lime mortar relies on the grit to achive a sound bond, this is not possible using builders sand.

If you do mix your own, add 2/3 water first then half the sand, then half the lime then the rest of the sand and lime. Add more of the water sparingly, as there is a short transition between a good workable mix and a sloppy mixture.

Its always good practice to dampen bricks down daliy for the first 5 days or so and avoid working in cold and falling temperatures

Alternatively you can buy ready mixed bags of lime mortar containng the sand aggregate and lime binder (just add water). that way you are more likely to achive a consistancy between mixtures, an essential when carrying out decorative pointing.

Not sure on best way to clean the bricks. You obvisly cant blast them with water inside the house. i guess a bit of patience with a wire brush will do the trick??

Hi Rick

Well done on getting your degree and good luck with progressing to taking - and passing! - the AM/CM exam at some point (which one will you be doing?).

Nive to see that your dissertation covers a more traditional building material. Would be interested in having a flick through, if a) you're happy for me to do so and b) it's in pdf format?

Thanks for the reply
So how much lime to sharp sand ?
Thanks

Hi Rick,

I too would be interested in a read of the dissertation. where did you study? I'm a structural Engineer and have an interest in traditional/ historical building methods. and have done more than my fair share of pointing.

one of the best ways to remove the old lime mortar is to use diluted brick acid. put it on with a stiff brush but you'll obviously have to be careful.

I wouldn't use a pure sharp sand mix to point with as this will give a really jagged looking finish i'd use half builders half sharp this'll give a nice smooth finish with a nice size aggregate in it. mix it one part hydraulic lime to 4 parts sand.

Am I missing something here regarding lime mortar? I was & am still under the impression that true lime mortar is made with lime putty/sand with a possible pozzolanic. It's what I've always used & believe in as the one true lime mix. Anything else is a modern compromise surely?