Lime mortar mix

jc808 · 23 Nov 2010

Finding a straight answer on this is maddening - perhaps you can help

I have bought several bags of powder-form (ie not putty in tubs) hydrated lime for repointing several walls (Already raked out c1 inch) in my 1899 built house.

What is the mix of mortar I need to make to do the repointing? Can I just mix the lime and sand (what type? shapr sand i presume) together or do i need water (I presume the lime is already slaked)

Sorry if i sound confused

any help appreciated

PrenticeBoyofDerry · 23 Nov 2010

Go
1:1:5
cement:lime:soft/building sand.

marshman · 23 Nov 2010

I think 1.1.5 is to hard for the old bricks.
My house is 1870's and I used plastering sand mixed at 10. 3 lime & 1 cement for the laying and pointing of all my brickwork above the
engineering bricks.

The-brickie · 23 Nov 2010

Why dont you buy some ready mixed? save waste if your not a fast pointer, its dependable and will not contain any portland cement, which will mean its better for your building.

Just search 'Lime Mortar' and if in doubt phone and ask for the best ready mix for you application.

^woody^ · 23 Nov 2010

You don't want to use any cement if the walls are lime mortar - the pointing will crack and fall out.

Too much sand will give a course mortar and you wont be able to give it the required smooth weathering face to protect it

Conservation work normally requires a sharp sand with bigger grit particles - similar to screed sand rather than the finer sharp sand. However this can be difficult to work with. Soft/building sand is an easier option

I'd say a 1:3 or 1:4 mix to get a nice smooth, lasting joint. More sand = weaker, and more voids, and so less durable. Too much lime and it gets washed out

lostinfens · 23 Nov 2010

I'd go with Woody on this, it's not a lime mortar with cement.
A proper lime mortar will harden sufficiently & "breath" better than a cement mix. Personally, I'd use lime putty, its far better, but I have used bagged lime slaked to a putty then mixed, it's not pukka but it does the job.
Don't get locked into the idea of using cement to harden the mix, it will harden enough. You could use a pozzolan as an extra strenghtener, such as ash, cinder or ground brick. This way also tones down the brightness of the finished product, which can be a little too white otherwise. Also as Woody mentioned, a good quality sharpish sand or a soft/sharp mix.
I recently repointed part of a gable & used old lime mortar from some demolished brickwork, ground up to dull down the mix a little. It worked a treat.

stuart45 · 24 Nov 2010

I would consider using a hydraulic lime. I have found it to be better for external work. Recent analysis of old mortars has found them to be more like 1.5/1 or 2/1 rather than the generally accepted 3/1 mix. The lime was not as pure as modern limes either. This table will give an idea of the mix required.

jc808 · 24 Nov 2010

Thankyou guys

FYI all these walls are internal
Regards

lostinfens · 24 Nov 2010

Where can I find this recent analysis Stuart?

stuart45 · 24 Nov 2010

I was told this on a historic house repair job, but I found this on the net.
http://www.buildingconservation.com/articles/mythmix/mythmix.htm

theoldun · 24 Nov 2010

lostinfens said:
Where can I find this recent analysis Stuart?

You will find this on

Pointing with NHL - St Astier
Click Restoration & Conservation
Click Bedding and pointing for stone and brick masonry using Lime Mortar.

You will have to do a lot of other reading on this web site to make up your own mind as this chart applies to NHL pre mixed dry bagged EcoMortar. Will say no more on this item.

jc808
With U.K hydrated lime you never know how long it has been sitting in the shed or how pure it is, so it is always a gamble to pool and banker it to try to make a putty. Also a lot of work.
Would suggest you throw your Hydrated lime away and use Moderately Hydraulic Lime NHL 3.5 in tubs. Works out expensive and not the way we would do it, but if you do not understand lime, this will be the most foolproof.
Do not understand why you are bothering with lime as you have said that you have used a cement lime mix to build the wall?
oldun

jc808 · 26 Nov 2010

lol i was going to use hydraulic lime - bought hydrated lime instead

i never said i was going to use a cement mix on the walls - was just a bit concerned about whacking cement into soft brick walls

andyb30 · 26 Nov 2010

nhl 3.5,costs about £12 per 25kg bag
mix 3 to 1 with soft building sand.

you could even use nhl 2 because its internal.

imo hydrated lime is only any use for whitening up a cement based mortar.

lostinfens · 26 Nov 2010

As I said before, you can produce a lime putty with it (hydrate),--of sorts, used it in muck & for cornice work.
I also used it neat!! as an external render finish, just to see it was still sound years later when I knocked it down.

:

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Lime mortar mix

Similar threads