OK...not had time to post much recently so here goes a little taster.
Galletting. Poking about in the gable and removing cement pointing reveals some holes that are too deep for back pointing. So how do we fix this ? What's the traditional approach ? Any one who says foam goes to the back of the class.
The technique is called galletting where you embed small stones (ideally of similar material to the stone in the wall) using hairy lime mortar. If you lay on lime mortar too thickly then it will crack. The stones in the galletting help prevent that happening (according to my stonemason).
First up is preparation of the orifice. The aim is to clean it out especially any loose bits ...which can be washed out with the hose.
Those areas that can be back-pointed need their sides cleaning up square. What you don't want to see in the hole are tapered slopes of old mortar as the new stuff will start to break away as it has no strength at the thinner parts of the taper. Bit tricky to see in the photos as they are two-dimensional.
From this
to this
When all your preparation is done, wash the wall down with the hose pipe and leave it to dry a little while you mix up mix up the 3:1 hairy lime mortar.
I use 1.5 units of this sand
1.5 units of this coarser stuff
and 1 unit of NHL 5 lime (I use 5 to give a stronger mix than using NHL 3.5). I hand mix it dry in a wheel barrow (wearing thick rubber gloves) and then start to mix it in a bucket with one of those larger paint stirrer thingies that you stick in a drill. When it's thoroughly mixed, I add the 'hairy' part...either goat or horse hair.
It comes in a bag like this
and you have to painstakingly tease it out by hand gradually adding it to the mix. Ideally not on a windy day!
The best way to mix it in is to use a trowel and chop it in because if you try the paint stirrer it acts like a carding machine and wraps the hairy bits round itself pulling them out of the mixture...a rather pointless exercise. My stonemason uses scissors but I think that defeats the object. You need long fibres...not wee ones.
Leave to one side to ferkle away to itself.
Get the tools of the trade ready. Apply some HLM and stick in the stones. That's all there is to it.
If you're back-pointing then make sue you leave a depth of about 30mm for the top pointing coat. No hard and fast rules.
Once the back-pointing has gone off...an hour or so but, again, not critical..apply the final top coat of pointing
But we're not yet done as it's wrong to leave a smooth finish and so we wait an hour or so until it's started to go off and then get out the 'special' brush
and you use it to stipple (quite hard) the top surface until you've bashed the HLM in a bit more, as a by-product cleaned off any whiskery flakey bits round the edges and exposed the rougher stone in the mix.
and you can just make out some of the hair.
I find it quite meditative to do. Some areas are trickier than others and some like this one lend themselves to a very simply job using a wide palette knife
A few odd pictures
Bit of back-pointing
So, to recap, looking at the end to end process for one area.....
We started with this cement blocking up everything
and started to break it away with the hammer drill (if it was a Listed Building than the chances are the Conservation Officer would have insisted it was all done by hand !)
to reveal what was possibly old galletting (but the surrounding lime mortar has not survived the cement treatment)
to reveal great lumps of brick
and finally a great hole
Once cleaned out, we do a bit of galletting
But it's a deep hole so we're in no rush and can let the first layer go off overnight. Then finish of the galletting/back-pointing
Leave this to go off and add the top coat of pointing
Let it harden for a couple of hours and apply the 'magic' brush....ta da !!
If opportunity doesn't knock, build a door.