Lime mix for a re-pointing gun?

[Feltwell]

Had my first go with lime mortar yesterday, went fine except that the re-pointing gun I was planning to use didn't like the mix - it just jammed up.

The mix I made was 1 part lime putty (made up from hydrate a couple of days earlier) with 3 parts sharp sand.

The instructions with the gun, aimed at cement users, said not to use sharp sand, but what else would you use? It didn't say! I thought soft sand was for plastering, not pointing, or is there another type suitable for pointing of which I am not aware?

Task is to re-point brickwork around some windows, including filling in between the brickwork and the frame (1/2 - 3/4" gap)

 

[Ian Bond]

http://www.eastherts.gov.uk/index.jsp?articleid=2575

Is this any use?

You might recognise characteristics of your particular brickwork in the document, and hopefully it will help you to decide how to proceed.

Not gauged or rubbed brickwork by any chance?

 

[Ian Bond]

Oh, nearly forgot.

I use well graded sharp sand for making coarse stuff, for the base coats of plaster, and fine silver sand for the fine stuff finish coats.

 

[Nemesis]

We had similar problems with one of those guns and lime mortar.

 

[borischarlton]

The Lime centre in winchester sell a ready made mix specially for motar guns.
Rob

 

[jason.p]

I've tried these mortar guns and had the same problem. It seems that as you compress the mixture it gets thicker until there's a plug of dry mix which blocks the nozzle. I personally can't see the point (no pun intended!) of them, and I'm not sure they do the job as well as a pointing iron, especially with narrow joints. It's nice to be able to really push the mortar in hard, and the only way to do this with the gun is to slightly overfill the joint (with the risk of getting lime on the stone surface), then letting it go off for a bit then compressing it with a pointing tool.
I know I'm probably a bit of a Luddite, but there's no place for for one of these contraptions in my tool kit :!:

 

[chuckey]

The "special" mortar as sold by the Lime Centre Nr. Winchester contains a lubricant to allow the the mortar to flow down the gun tube, as demonstarted by Dave and Bob. It is available in many colours to match existing mortar. The downside is that it costed £17 for 5 Kg in 2001.
I can't afford this so I tried the S******* gun and it blocks. One day I will fiddle about with suitable lubricants and market my own brand!!
Frank

 

[jason.p]

I'm probably being pedantic, but I wonder if any of these lubricants would affect the integrity (esp breathability, moisture transfer etc.) of what is otherwise a simple but highly effective material.
It just seems like fixing something which ain't broke. By all means use a gun if you really want to, but not if it compromises the job :roll:

 

[borischarlton]

yes you are. The aditive is an animal by product, kind of fat, the name of which escapes me, that is added to lime as it is slacked (sp) its also I belive a traditional additive in lime wash.
Quite agree about the price though
Rob

 

[Nemesis]

Tallow?

http://www.rose-of-jericho.demon.co.uk/products/rj3_03.htm


Yes it does reduce the 'breathability' in that case.

Tallow limewash

Tallow is a type of animal fat. It is incorporated during the slaking process as the heat which is produced melts the fat enabling it to be evenly dispersed throughout the product. It can be used on the interior and exterior of buildings, but it is more popular for exterior use as it is slightly less porous than other forms of limewash and can prevent excessive water penetration. It also tends to brush off on clothes, making it less popular for interior use than some other types of limewash, such as casein.

Other oils and waxes can be incorporated as an alternative to tallow. Linseed oil is a popular alternative as it provides durability, some flexibility and better adhesion to some substrates.

http://www.buildingconservation.com/articles/lwdistempers/lwdistempers.htm


Usually added to limewash, but not to normal lime putty for pointing.

 

[inwood]

I have to say that I've not had a problem using pointing guns (Durgun) and lime putty/sharp sand. I have tried it using hydraulic and sharp sand which behaved in exactly the way you say but the lime putty mix worked perfectly. Maybe the mix was too wet or dry.