Lime Mortars

[Anonymous]

Hi all

I have a 17th Century farmhouse built with Northamptonshire Ironstone/Sandstone. Some monkey repointed the back of the house with a standard portland cement mix, which I am now removing, and am now at the stage of working out the mix for the new pointing.

I have had different advice, some people say 3/1 lime putty/sand and others say 4/8/2 Sharp/grit/lime.

I also have to fully rebuild a garden wall thats about 50 meters long, so would appreciate any advice on the mix for the wall....

I need to get this sorted as I need to get on with the inside before my wife reads me the riot act for doing too much outside and not enough decorating.

ATB

Rob

 

[Anonymous]

>3/1 lime putty/sand

No, it's the other way round, 3:1 sand:lime putty
The other recipe hasn't got enough lime.

For the garden wall I'd make putty out of bagged hydrated lime from the nearest builders' merchant as it's cheaper than traditional lime putty. Enpty the bag into a plastic dustbin of water. It'll be good enough for a garden wall.

 

[Anonymous]

Opps, too much red wine already.......

Hydrated lime in a dustbin? How long should I leave it, and I presume I drain off the water?

Thanks for the reply

Rob

 

[Anonymous]

You can use it straight away but it gets better with age. When you out it in the water stir it thouroughly to let all trapped air escape. The longer you leave it the more it settles into the texture of traditional lime putty. Just pour off the water and scoop it out. You may not need any extra water unless your sand is very dry. It takes longer to mix than sand and cement, but persevere. Suddenly you will find it all goes to a workable texture.

 

[Anonymous]

Robert - you will find that many lime suppliers also offer mortar analysis. So, if you really want to be purist you could go down this route. Just phone around and find out costs.
Even then you may have problems finding exactly the right constituents because the place was built rather a long time ago. Also the original builders may not have used the best mix anyway!
Personally I have always used a standard 1/3
lime putty/sand mix and never encountered any problems.
Again personally- I have shunned the use of bag lime because apparently it's quality depends very much on it's freshness. However, a guy I know used it to render the outside of a cob cottage more than 20 yrs ago and the job is fine! Mind you very very few people used lime in those days and it was a bit of an experiment - since then he has used lime putty. Not sure what the economics are but at least you know where you are with a well made and matured putty. The choice is yours.
Good luck Mike.

 

[Anonymous]

Mike

Thanks, I will probably use bagged lime for the wall, and then purchase some lime putty for the pointing on the house. I did think about getting the mortar analysed, but there isn't much of it left after the chap who pointed the house up with OPC cut back some way in.

Has anyone used House of Jericho (sp)?

Thanks

Rob

 

[Anonymous]

Biff

Thanks for your help, I can leave it for about 2 weeks as I have other stuff to do, like sorting 7 bags of random course stone........

I have heard of buffing the mortar when it is placed in the wall, otherwise the lime comes to the surface and it just looks white, any advice on buffing?

Sorry about the 20 questions, just want to get it right and not make a pigs ear, as the house deserves better

All the best

Rob

 

[Anonymous]

Rose of Jericho? Good people.

Don't forget it's getting rather late for lime if you live in an area affected by frosts.



http://www.rose-of-jericho.demon.co.uk

 

[Anonymous]

Evelyn

I am in Northants, I know its late in the year, but hopefully it won't be too cold by the time I start. I will check the weather forecast, and maybe put some hessian sacking over the wall to keep it a bit warmer.

If it does get too cold, then I will just have to do the work inside the house

Best Regards

Rob

 

[Anonymous]

You need to rig up some hessian to cover it anyhow - it helps stop the surface drying too quickly and cracking.

With regard to rubbing back - leave the pointing for a day to start to harden, then you can do one of several things' Assuming you have a proper thin pointing trowel, there's the Marianne and SPAB way - simply scrape the surface lightly with the blunt bit of the trowel, to remove the surface lime, and expose the aggregate. It works a treat.

Some rub with a stiff brush, oters use hessian scrunched up.

 

[Anonymous]

What a great source of useful information.

Thanks very much for all your help.

Rob

 

[Anonymous]

The weather forecast isn't much use because you want to keep the lime mortar frost free for weeks rather than days, hence Evelyn's warning. If we have a winter as mild as last you'll be allright. But we might not.
The colour of the pointing depends partly on the sand. If you have sand that is a dark reddish yellow colour with lots of iron oxide you may not end up with bright white pointing, but it does take a lot of colour to alter the finished result. You can add some pigment. Yellow ochre powder is available from art suppliers. Soot probably works but I've not tried it. It's all a bit hit and miss so if you are concerned to get it right you'll have to make little samples and let them dry. And then the colours may change over the years so it might not be worth the bother.
When the mortar surface is a bit dry, say after an hour, you can brush the pointing with a stiff brush. This exposes the surface of the sand grains and results in a less white colour. You can get the same effect even more effectively by spraying the finished wall with a hose with a very fine spray. It's tricky though. You need just enough water to wash the surface of the sand grains without washing out the lime that holds them in place. And then you have to brush the bricks to remove the white streaks of lime that have dribbled down.

 

[Anonymous]

Biff

Hmmm, washing down the walls doesn't seem like a good option knowing my luck. As you say, it will probably wash it out.

I will have a play in the garage with different sands and see how they look.

It may be better to stop working outside and just concentrate on the inside, will take a view on it over the weekend.....

ATB

Rob

 

[Anonymous]

I'm in Northants too, I do have a small area of repair to make, and I'm hoping to do it in the next 2 weeks, but I'll leave it covered for weeks afterwards. It's not ideal, and if you have a lot to do, I'd wait until spring when you can have a good run at it. Meanwhile experiement with sands.

You need at least 1 of the 3 parts of sand to be course grained, quite biggish bits and very sharp. This gives a lovely finish.

We all have our pet ways of finishing, but mine is slightly different to the above so I'll let you have yet more decisions to make!

I have some pieces of wood about 1/2" thick, pencil length and with a good angle cut on one end. Depending on the weather (and I keep wetting the mortar I've put in for a few days with a fine spray and then covering it back over to let it dry properly), you need to test for a 'green hard' finish, ie one that you can't dent with the end of your finger, but you can dent with a finger nail, then rub it over with the angled wood to remove all the nibby bits round the edges and to get a good even surface, then I get a churn brush and bash it all with a flicking motion. This knocks off the surface lime and exposes the agregate beautifully. The finished surface tends to look more like it's always been there.

As I say, we all have our ways, but having seen the cowboy who's just done the cottage over the road (see previous post) I know which I'd rather have. The main thing is to avoid rubbing the lime into the stone surface, hence the flick/bash motion rather than a side to side rub. I suspect mine is the most labour intensive way, but then that's just me.

Sue