Repointing... Very crumbly mortar... how deep to scrape out?

[MattB83]

We're looking at a DIY pointing attempt. It's a 1950's red brick council house which I'm told has a cavity wall.

There has been some repointing done relatively recently however on close inspection it looks like it's a very thin layer of new cement, eg 3mm on top of the old crumbling mortar, and the new stuff comes off with a gentle poke.

In terms of scraping out the old stuff, it seems like it's very soft quite far in, I'm sure that more than 25mm will come out quite easily. In this situation do I still stick with not taking more than an inch out?

Secondly I've been reading about different types/mixes of mortar depending on cavity/non-cavity, what do I need to use if it has a cavity? Does this change for the parts without a cavity (outhouses)?

Any thoughts much appreciated.

 

[Bonni]

Yes, 25mm (one inch). As long as you get 25mm deep, leave the rest. Make sure you pack the mortar in with a pointing iron.

Solid house walls must have lime mortar, NEVER cement. Solid walls breathe out through the mortar, cement traps the damp it.

With half brick outhouses, I would just use sand:cement mortar. Only reason why, if you were to convert the outhouse to a room, you would build a stud wall away off the outer leaf leaving a cavity between the two.

I use the Irwin 8mm mortar rake that goes on an angle grinder that has a dust extractor attachment. Make sure you get an angle grinder where you press the switch in as opposed to the type you slide with your thumb. Thumb fatigue explains why.

https://www.mytoolshed.co.uk/irwin-mortar-rake-starter-kit-8mm?utm_source=bingshopping

You can also buy a bog standard 8mm mortar rake and I have a much thinner one, looks about 3mm to 4mm that I keep in a spare angle grinder for thinner joints.

https://www.screwfix.com/p/mortar-r...50&gclid=CK-TsoyP8-QCFdmMhQodUgQGnQ&gclsrc=ds