Raking out old mortar / repointing

[EH11]

After some advice regarding an area of brickwork that I am looking to re-point around my house. Not a big area, around a front porch.

I used a diamond blade on an angle grinder to clean out the old mortar. Any areas that the blade couldn't access such as corners, i've used a chisel to clean out to approx 20mm depth. The grinder does a good job at removing the mortar, albeit a messy job. On close inspection, on the underside of some of the brick there remains a thin layer of old but stable mortar - 1 or 2mm. There's plenty of room to pack in new mortar when it comes to re-pointing but my question is, do I need to chisel out the 1-2mm of mortar that remains on the underside of some of the brick?

I want to do it right but equally, don't want to spend a load of time manually chiseling if it's not necessary.

Last question is around new mortar. I have Blue Circle mastercrete cement. Understand it is decent for repointing as it is a portland / limestone mix. I was going to mix 1 part cement to 4 parts builders sand. Does that sound reasonable?

Cheers.

 

[Gerrydelasel]

I have Blue Circle mastercrete cement.

You mean the existing mortar in the wall is cement, or you have a bag of Blue Circle lying around? (Reason I ask is because people often make the mistake of using cement on a lime wall)

 

[EH11]

I have a bag of blue circle cement that i was going to use to repoint.
How can I tell if its a lime wall? Its an early 1950's build, red brick (not painted).

 

[Gerrydelasel]

I have a bag of blue circle cement that i was going to use to repoint.
How can I tell if its a lime wall? Its an early 1950's build, red brick (not painted).

Probably cement in the 1950s. Cement looks grey and smoothish, lime is more yellow and course grained. Never use cement on a lime wall, it will spall your bricks and then fall out!
I don't know how ruthless you have to be when raking out. I presume the stuff that remains stuck to the bricks can stay there.

 

[^woody^]

Grind it better or chip the remnants off with a sharp bolster chisel as there is risk of failure if left.

Don't mix any greater than 4:1, and it's the tooling of the joint that gives it the weather protection not so much the mix strength.

Dampen the joints first before repointing but dont soak them - nor the brick faces