Which kind of lime mortar to use?

[jimodoherty]

Hello all,

Looking for a bit of expert advice with an external wall I'm debating repointing in my flat as I'm getting a fair bit of rain water in around the windows. I've not attempted it before so apologies if the questions seem a bit novice-y. My building was built in 1903, so I believe I should be using lime mortar rather than cement.

Should I be using hydraulic/non-hydraulic lime mortar? Its bloody confusing! From reading around I suspect NHL 3.5 but I'd rather be sure. My flat is on the top floor, located in Clapham, London so isn't subject to huge amounts of water. I've no idea what type of bricks they are but they seem like pretty standard small red ones!

Also, as I'm top floor and don't really have anywhere to mix, would the easiest option to buy a bag of ready made lime mortar? If so, would it be available from standard builders merchants?

Any help greatly appreciated!

Cheers
Jim

 

[Joe Malone]

Depends on exposure really, if the building is highly exposed to severe weather conditions then I wouldn't even consider using a non-hydraulic lime. Non-hydraulic doesn't contain pozzolans and therefore doesn't have a chemical set. It dries in the presence of carbon dioxide and can take an awful long time to set which can be a problem foe really exposed buildings. More often that not, hydraulic lime is chosen for external applications as it has a chemical set.

 

[jimodoherty]

Cheers for the reply Joe. The wall I'm doing is the front of the building facing a road so I guess its pretty exposed to the elements. I read it may take up to a few months for the non-hydraulic to properly set.

At least I know what to get now, I found a bag of it in Travis Perkins. Do you know if the hydraulic stuff needs to be soaked in water for a while before using or it or should it be ready to go as soon as I mix it (I'll be doing it by hand)

Thanks
Jim

 

[pinenot]

Non hydraulic lime mortars require air to set, hydraulic sets under water. These are indicative statement/rules, not by any means hard and fast as it depends on the brick, location, relative humidity etc.

Your building date puts it right on the cusp of changeover to cement mortar, in fact it wasn't unusual about hat time to have some Portland cement mixed in with lime mortar mix

To be on the safe side probably best you go to go these guys http://www.lime-mortars.co.uk/ who are fairly good at providing answers,
or give these guys a call, The Scottish Lime trust, Charlestown Workshops 2 Rocks Rd, Charlestown KY11 3EN
01383 872722, they are educators in the old skills of lime mortars etc...pinenot

 

[Joe Malone]

To be on the safe side probably best you go to go these guys http://www.lime-mortars.co.uk/ who are fairly good at providing answers,

Unlike yourself Pinenot.

Now I really do know that you make it up as you go along. 'Hydraulic lime sets under water'? Did the word hydraulic help you make the link to water? Pinenot, you need to bow out from handing out advice, too late to do it gracefully or to save face but you need to bow out nonetheless. There's an excellent site where you could lurk in the background for three or four years reading up on all the technicalities of the building trade after which point you might consider occasionally contributing what you have learned. It's called diynot.com.

 

[Joe Malone]

Cheers for the reply Joe. The wall I'm doing is the front of the building facing a road so I guess its pretty exposed to the elements. I read it may take up to a few months for the non-hydraulic to properly set.

At least I know what to get now, I found a bag of it in Travis Perkins. Do you know if the hydraulic stuff needs to be soaked in water for a while before using or it or should it be ready to go as soon as I mix it (I'll be doing it by hand)

Thanks
Jim

It has a chemical set Jim so you don't want to be waiting too long after its mixed.