Having some building work - lime mortar or not?

[danlightbulb]

Thanks for the reply.

They wouldn't have had pre manufactured hydrated lime powder in the 30s, so they likely would have slaked their own lime.

So if you actually want to match the existing mortar mix, is it hydraulic lime or hydrated lime you want to use? Would they have had hydraulic lime in the 30s? If not, then all the advice recommending nhl3.5 is wrong?

Also you briefly touch on sand in your post. The mortar in my house does appear to based on sharp sand, from what I can tell. Now I used building sand to repoint as obviously that is the sand you use with a standard cement mortar. If you use full on lime with no cement, you're meant to use sharp sand with it, not building sand. If you try using sharp sand it is more difficult to work with though is that correct? So which sand is recommended?

 

[stuart45]

Hydraulic lime was around in the 30's. It was either made by adding a pozzolan to lime putty, or the Lias lump lime (hot lime) that was delivered on site produced a hydraulic lime.
With lime mortar, a sharp sand can be used because unlike cement mortar it's still a workable mix.

 

[danlightbulb]

Hydraulic lime was around in the 30's. It was either made by adding a pozzolan to lime putty, or the Lias lump lime (hot lime) that was delivered on site produced a hydraulic lime.
With lime mortar, a sharp sand can be used because unlike cement mortar it's still a workable mix.

So you mentioned earlier that the difference between hydraulic and hydrated lime is in how they set. Once set, is there no difference in properties between the two types, so once set, it doesn't matter which you use?

Given the OP's house (and mine) was likely to use lime (maybe also with cement, we don't know), then why would you recommend 1 lime, 1 cement, 6 sand in your reply above? Why not recommend what they would have done in the past which is probably more like 1 lime to 2 or 3 sand, and possibly a bit of cement (maybe half part?)?

Also you said yourself that hydrated lime doesn't set with water, so why recommend that over hydraulic lime?

And are you recommending the OP use building sand, or sharp, or a mix of both?


Im trying to understand the thought process that goes into selecting the mix here, and to ensure there is clarity on exactly what materials are used.

In my case, Ive already started with cement only mortar, because that's the advice I received in my thread. I was actually keen to use lime as well, and if the consensus had been to use it, I would have done. Im left quite frustrated that I now have started in cement only because I wanted to do a proper job of it. So what's the consequences to me of this choice, and should I change my choice now for the rest of the house, which might eventually mean redoing the 12m2 Ive already pointed?

 

[stuart45]

There is a difference between the finished article. A pure air lime, such as lime putty, or hydrated lime when fully cured will be more flexible and breathable than a hydraulic lime. The disadvantages of pure lime are that one: it takes much longer to harden up and needs damping down and protecting for longer, and 2: when building with it because it cures only by absorbing carbon dioxide, the outer part of the joint hardens up first and tends to cut off a lot of the air getting to the inner part. As the wall gets dryer in time the lime doesn't absorb it as well, so a lot of the mortar might not cure so well. The speed of the process also means that the build speed is much slower. For internal plastering however a pure, well matured lime putty is preferred.
For building back then stone or grey chalk lias was normally used, which is slightly hydraulic. Blue lias was much more hydraulic.
The reason I suggested a 6/1/1 mix was more of a compromise, as it seemed like the builder was set on only using a cement mortar. He sounds like he's possibly unaware of the correct methods for mixing up and aftercare for a lime mortar, so as he's actually building, rather than just pointing a 6/1/1 might be a safer, more reliable option.
In your case I think I'd stick with the mix your using now. The bricks look like Flettons, so they will be OK, with a 5/1 mix.
Just a point about pointing styles. There are around 20 different types, so people don't always have to use the half round(bucket handle)type. It's the most popular one to use on new work, being quick, easy, watertight and looks OK provided the brickwork has regular, even and straight joints. However, with more rustic brickwork, and irregular joints a flush joint finished with a churn brush, or coco brush can look better. The metal half round tool tends to highlight brickwork that's not too accurate. The churn brush also exposed the aggregate, which puts a softer colour to the jonts.
This is some brickwork I did about 4 weeks ago, using a 6/1/1 blocking up a door at home. My wife wanted a rustic looking brick and joints, as it's an old cottage. It's a flush joint.

 

[danlightbulb]

On pointing style, my uneven brick joints did make it hard work to use the brick jointer (the half round style). But it's come out ok. I need to get some more sizes of brick jointers for the various joint widths that are all over my house.

Some of the perps were so narrow I widened them with an angle grinder. Others were nearly an inch in width.

 

[stuart45]

Brick

Brick trowels of a professional standard can be purchased from Speedcrete, United Kingdom who supply a range of masonry tools. W.Rose, Kokoro and Marshalltown are all available.

www.speedcrete.co.uk

I get of lot of my jointing tools and trowels from here. They are really good quality, especially the Rose ones. They might be a bit pricey for DIY, although they give a better finish.

There is a method of pointing rough brickwork known as Tuck pointing, Although it's hard for a DIYer, the method can be adapted for a bucket handle finish. You fill in with a coloured mortar to match the brickwork, and then cut out 10mm grooves when it's hardened up enough. Next day point it up with normal mortar.