Repointing sand mix?

tony3619

Hey, 
Can anyone take a guess as to the mix of this mortar? I'm aiming for a similar mix to repoint a wall?. 

neilmcl

If you're just doing that small repair pictured then I'd just get a small tub of the ready mixed stuff. Generally though a 4:1 mix is the way to go for repointing.

stuart45

Are you looking to match the colour?

FreeBear

neilmcl said: Generally though a 4:1 mix is the way to go for repointing.

Personally, I'd go for a weaker mix of 6:1 or a 3:1 using HNL3.5 lime instead of cement.

Regardless of the binder used (lime or cement), the colour of the sand will make a big difference to the colour of the finished mortar.

stuart45

A rough rule of thumb for repointing is to copy the original mix, just a touch weaker. 
NHBC mortar mixes Untitled | DIYnot Forums
What comes out of the mixer on site is often a lot different to what it's supposed to be.

tony3619

It's the colour im trying to match, the ready mix stuff is nowhere near the colour

stuart45

You can either use black sand which about double the price, or use black dye. I've found that being a bit darker than the original blends in better than lighter. Dyed mortar will fade in time. 
You take take a sample of the original and soak it. This gives you some idea of what the new wet mix should look like.
Drying off the new mix as a sample with a heat gun gives you an idea what the new mix will look like when dry.
If you need a sample of the original sand, stick a piece of the mortar in brick acid.

tony3619

Do you think this mixture definitely has black dye or black sand in it? I was going to get building sand, mastercrete cement and black dye but if I mix a small sample using a 4:1 ratio I don't know how to up the dye amount in a bigger amount?

stuart45

It's trial and error. 

danrv

stuart45 said:

It's trial and error. 

Yes. Took me a while to work out what mix to use for my repointing job. With lots of help here I settled on 5.1.1 sand/cement/hydrated lime.
Not sure what the mortar in the pic is made up of. Looks dark grey.
Helps to use a small measuring container for small amounts of mortar. 

clive0510

I wouldn't do it if there's a risk of frost. if you do you will be scraping it all out and doing it again. also if there's rain forecast, the rain will wash all the cement out and make a mess all down the brickwork. as for the mix probably 4-1. shouldn't worry about the colour, just let it whether in.