29-08-2012, 03:22 PM
Hi Lawrence,
Wow - fantastic pictures! My "renovations", if you can call them that, are much more modest in ambition - all I want is to get the house back to the state it was in before all the recent bodges that took place. At the moment I'm sorting out the plumbing - it's amazing how previous plumbers sent pipes all over the place rather than taking direct routes - presumably because they couldn't be bothered to lift more than a couple of floorboards. I keep meaning to start a new thread about all of this - one day...
Col, I must admit that I use lime in my mortar - I use 1:1:3 lime, cement, building sand. From what I've read, if you plan to add lime, it's best to use these proportions - apparently adding more lime makes it too weak, and if anything, you'd be better going for "pure" lime mortar. Because I live in an old house that was originally constructed using lime mortar, I feel that this is what I ought to be using, but I haven't got around to trying it yet.
My understanding is that one should use sharp-sand with lime mortar, rather than builders sand, which is finer...
I also understand that one should make a lime putty before mixing with the sand. I believe that this involves pouring hydrated lime (the standard stuff you can buy from builders merchants) into a bucket and mixing water into it. Providing you make sure there is always a layer of water covering the putty, the stuff stays good for ages - the chemical reaction is with the carbon dioxide in the air, and it does take a while to go off - certainly a lot longer than cement.
There are a few houses around here that have been re-pointed in hard cement, and all the bricks have spalled as a result, leaving perfect rows of cement mortar protruding from the wall. Certainly, I'd be wary of using 3:1 sand/cement on this building. But for new bricks, it's a bit questionable - I build a small garden wall about 5 years back, and spent ages getting a perfect result - but sadly the frost has got the mortar (which was 1:1:3 lime, cement, sand). I'll need to re-point soon, and I'm wondering if I should use 3:1 sand/cement?
Another factor is that our house has had quite a lot of movement over the years, and the lime mortar has been very tolerant of this - there are no broken bricks, for example. Cement mortar would just crack, whereas lime is self-healing to a large extent (as it forms lots of microscopic cracks that expose the mix to carbon dioxide, which is able to set).
As to what you should use Col, I think it really depends on how tough the bricks or stones are. Aim to use something that is softer - remember, mortar is sacrificial. I'm not sure that the lime would mark the stones if it was washed out by the rain, and in terms of setting time, you're talking about a couple of days (I guess), so you should be OK if you can trust the weather forecast. The worst part about re-pointing is raking out all the old stuff - most people don't do enough of that - I think you need at least an inch. Cement-based mortars are clearly much hard to clean out, whereas lime can almost be washed out with a hose...
Cement-based mortars are less breathable too, so if the wall is solid, it's worth considering lime instead.
But as I said, I haven't yet tried this myself, so the above is just based on what I've read (which is a lot!) rather than practical experience.
All the best,
Mark
Wow - fantastic pictures! My "renovations", if you can call them that, are much more modest in ambition - all I want is to get the house back to the state it was in before all the recent bodges that took place. At the moment I'm sorting out the plumbing - it's amazing how previous plumbers sent pipes all over the place rather than taking direct routes - presumably because they couldn't be bothered to lift more than a couple of floorboards. I keep meaning to start a new thread about all of this - one day...
Col, I must admit that I use lime in my mortar - I use 1:1:3 lime, cement, building sand. From what I've read, if you plan to add lime, it's best to use these proportions - apparently adding more lime makes it too weak, and if anything, you'd be better going for "pure" lime mortar. Because I live in an old house that was originally constructed using lime mortar, I feel that this is what I ought to be using, but I haven't got around to trying it yet.
My understanding is that one should use sharp-sand with lime mortar, rather than builders sand, which is finer...
I also understand that one should make a lime putty before mixing with the sand. I believe that this involves pouring hydrated lime (the standard stuff you can buy from builders merchants) into a bucket and mixing water into it. Providing you make sure there is always a layer of water covering the putty, the stuff stays good for ages - the chemical reaction is with the carbon dioxide in the air, and it does take a while to go off - certainly a lot longer than cement.
There are a few houses around here that have been re-pointed in hard cement, and all the bricks have spalled as a result, leaving perfect rows of cement mortar protruding from the wall. Certainly, I'd be wary of using 3:1 sand/cement on this building. But for new bricks, it's a bit questionable - I build a small garden wall about 5 years back, and spent ages getting a perfect result - but sadly the frost has got the mortar (which was 1:1:3 lime, cement, sand). I'll need to re-point soon, and I'm wondering if I should use 3:1 sand/cement?
Another factor is that our house has had quite a lot of movement over the years, and the lime mortar has been very tolerant of this - there are no broken bricks, for example. Cement mortar would just crack, whereas lime is self-healing to a large extent (as it forms lots of microscopic cracks that expose the mix to carbon dioxide, which is able to set).
As to what you should use Col, I think it really depends on how tough the bricks or stones are. Aim to use something that is softer - remember, mortar is sacrificial. I'm not sure that the lime would mark the stones if it was washed out by the rain, and in terms of setting time, you're talking about a couple of days (I guess), so you should be OK if you can trust the weather forecast. The worst part about re-pointing is raking out all the old stuff - most people don't do enough of that - I think you need at least an inch. Cement-based mortars are clearly much hard to clean out, whereas lime can almost be washed out with a hose...
Cement-based mortars are less breathable too, so if the wall is solid, it's worth considering lime instead.
But as I said, I haven't yet tried this myself, so the above is just based on what I've read (which is a lot!) rather than practical experience.
All the best,
Mark
