Which type of mortar for pointing stone?

[nitch]

Hello,

I live in a terraced house in Bristol and it has brickwork like this:

Untitled

• nitch
• 3 Sep 2012
• 1

The pointing is crumbling in quite a few places so we've decided to re-point the front. I've started raking out the old mortar but I was just wondering if I can use the ready mix multi-purpose mortar you can buy from B&Q or does it need to be a hydrating lime mortar mix?

Many thanks

 

[jeds]

That looks like it might be tuck pointed. What is the light coloured band in the middle of the joint?

Stonework like that should really be bag jointed with a soft lime mortar. Bag joint just means the joint was rubbed back with a hessian bag when the mortar was firm. All that cut pointing and what you have there isn't original. Do you have to do the whole lot or just patches? If it is tuck pointed you'll have a job replicating it.

 

[nitch]

Thanks for your reply. We're not bothered with replicating it, we'd rather the mortar not to protrude so the water doesn't sit on it and cause problems with the frost.

I'd like to do this myself if possible...so do I need to find a lime mortar mix for this? Will normal mortar cause problems?

Thanks again

 

[jeds]

Cement mortar can cause damage to the stonework over time and will increase the chances of dampness building up in the wall. Stone walls need to breath and they mostly do that through the joints. Cement doesn't breath at all so the walls will breath a lot easier through a lime based joint. The joint is also really a sacrificial escape route for moisture. The escaping moisture will cause the lime joint to deteriorate over time but that's not a problem because it can always be replaced. The alternative is that the moisture bypases the joint through the edges of the stone. The result of this is that the stone deteriorates instead - which is obviously a lot more difficult to replace. If you look at old stone walls there are loads of examples of damaged stonework due to cement pointing.

My advice is use a lime based mortar. Work the mortar into the joint and leave it slightly proud. Let it go off fairly firm and then rub it back with something slightly rough. The old boys used to use an old hessian bag.

 

[stuart45]

A lot of those houses in Bristol have ribbon pointing which does tend to hold the water.
Using a churn brush is another way to finish the joints, as it opens the pores in the mortar, especially if a sharp sand is used.

 

[nitch]

Thanks for the tips. I was going to use this:

Tarmac Multi-purpose mortar

But this stuff sounds like it might be breathable:

Lafarge Mortar Mix

Or should I go fully hydrated lime?

CASTLE NATURAL HYDRAULIC LIME

 

[stuart45]

Thanks for the tips. I was going to use this:

[
Or should I go fully hydrated lime?

CASTLE NATURAL HYDRAULIC LIME

Yes, use the 3.5 NHL.

 

[cotswoldbuilders]

Either as Stuart said, or get ready mixed lime, in tubs from Trad-Lime.

 

[geraldthehamster]

Thanks for the tips. I was going to use this:

Tarmac Multi-purpose mortar

But this stuff sounds like it might be breathable:

Lafarge Mortar Mix

Or should I go fully hydrated lime?

CASTLE NATURAL HYDRAULIC LIME

That's odd - I thought hydrated lime and hydraulic lime were two different things...

Cheers
Richard

 

[ConcreteDrBill]

You need Natural Hydraulic Lime (NHL) not Hydrated Lime (yes the are different)

The Lafarge mortar contains cement as well as 'hydrated'lime, its good for general purpose pointing but not for weaker bricks or stone