Repointing front of house

Nobbie1967

Just been installing new windows upstairs at the front and although it has clearly been repointed at some stage, it looks like they just applied some mortar to the front rather than raking out properly. Some of the bricks were also loose below the wooden sills where the old windows had warped and pushed the sill out an inch.

You can just see where I’ve scraped the old mortar away with my fingernail after the top bit fell off. I think the house is about 1920’s and don’t know what the original mortar material was, but it’s not got much strength now.

Just after any tips for repointing. I’ve got a tool for the angle grinder that can take out the old mortar to a depth of 40mm which will be dusty, but not very hard.

As the old mortar is so dusty, is it worth priming the old mortar with some diluted SBR or similar?

Is 40mm about right for depth?

What mix to use for the mortar? I’ve heard if it’s too strong it make cause the bricks to break at the edges, 6:1 sand to cement?

Any ideas on pointing profile? I was going to use a standard pointing tool which gives a slight recessed curve, but I’m aware there are other styles. The house is in south Manchester, so not exposed.

Anything else to consider?

stuart45

40mm is a bit too deep. Rough guide is double the joint size, so 2x10mm gives 20-25mm. Mix you need depends on the original mix. Damp the brickwork down with a  mister on the hose. The pointing style you pick depends on what on like the look of. There's about 20 to choose from.

casper_gutman

Please, please, ensure you have a really good dust mask. We had our house repointed earlier in the year, and the guys who raked out the mortar looked like they were ready for chemical warfare with filtered full face masks. 

Raking out to 20mm will already produce way more dust than you imagine so no need to double it by going to 40mm deep. The dust on ours was confined under the sheeted scaffold they used and covered the ground up to about 1m out from the house to a depth of 10-20 mm. Anything you can do to reduce the dust, do it - this is a seriously messy job you're undertaking. 

stuart45

Are you going to re-point the whole wall, or just patch point?

Nobbie1967

stuart45 said:

Are you going to re-point the whole wall, or just patch point?

Whole wall over the next year, but just doing the section above the bay window in the next couple of weeks while I have scaffold up.

stuart45

Once you've started.pointing make sure you keep to the same mix, with the same sand and make of cement/lime. The old mix looks like black ash mortar.
1920 was the period when lime mortar was still being  used, but cement was starting to be gauged into the mix to help with the set.
The main choice for pointing style would probably be either half round as you said, weather struck and cut,  or flush. 
A flush joint is often a good choice for older brickwork if the joints are a bit large and irregular. This sometimes gets worse after the joints have been hacked out.
If you go for a half round joint I'd fill a bed joint and then see if it's ready to joint up. If you let the beds get too hard they can be difficult to do. Do a few bed joints, then do the perps, and then run the jointer over the beds again. Use a soft coco brush over the joints.
Worth getting some good quality jointers, not cheap ones from B&Q.
Speedcrete have a good selection.

danrv

I've been using a cheap 10mm wide Amtech tuck pointer plus a Ragni jointing tool from Homebase with good results.
I'm gradually working my way up the sidewall of my property. Doing it in one go is out but I have good access via the flat garage roof.

For raking out I just use a suitably sized hand tool rather than an angle grinder which is way too messy albeit quicker.
Not quite 20mm deep but the mortar is in good with a bucket handle profile.
My brickwork is textured which isn't easy to keep the mortar off.

With helpful advice from Stuart45 and others, I've managed to do almost half the wall. 
Dampening down and keeping the mortar from drying out too quickly is important.
It's a problem if the sun is on the wall plus
I don't have any Hessian sheet to keep it damp so I lightly spray with a hose periodically after repointing.

I use a 5/1/1 mix of builders sand, cement and hydrated lime plus a little plasticiser.
I tested a small bit of original mortar for lime by mixing it with white vinegar. It fizzed which apparently indicates lime content.

FreeBear

Nobbie1967 said:

Just after any tips for repointing. I’ve got a tool for the angle grinder that can take out the old mortar to a depth of 40mm which will be dusty, but not very hard.

As the old mortar is so dusty, is it worth priming the old mortar with some diluted SBR or similar?

Is 40mm about right for depth?

What mix to use for the mortar? I’ve heard if it’s too strong it make cause the bricks to break at the edges, 6:1 sand to cement?

Please, do not use a mortar rake or an extra wide disc with an angle grinder - One slip and you'll make a mess of the bricks (and you will slip on countless occasions). If you must use an angle grinder, use a thin diamond disc just to cut through the skin of any cement. The old lime mortar behind can then be raked out with a screwdriver or old wood chisel to a depth of around 20mm. Or get a plugging chisel to tackle any hard mortar.

Mix up some lime putty & sand (three parts sand to one part lime), and wet the walls down. if you are careful about the choice of sand, you should be able to get a close colour match with the original. Don't use SBR or any other bonding agent, it isn't needed. Any unused lime mortar can be left in a sealed bucket with a little bit of water on top. Store it in a frost free location, and when you come to use it again, just pour off the water and give it a good mix.

Oh, and don't waste your money on one of those mortar guns - Whilst they are OK for injecting grouts, for most mortar mixes, they just squeeze the water out and leave you with a solid plug of mortar.

stuart45

Getting the colour right can make a lot of difference to the appearance. Limebase do one similar to a black ash mortar.

https://www.limebase.co.uk/product/gm110-coarse

Nobbie1967

stuart45 said:

Once you've started.pointing make sure you keep to the same mix, with the same sand and make of cement/lime. The old mix looks like black ash mortar.
1920 was the period when lime mortar was still being  used, but cement was starting to be gauged into the mix to help with the set.
The main choice for pointing style would probably be either half round as you said, weather struck and cut,  or flush. 
A flush joint is often a good choice for older brickwork if the joints are a bit large and irregular. This sometimes gets worse after the joints have been hacked out.
If you go for a half round joint I'd fill a bed joint and then see if it's ready to joint up. If you let the beds get too hard they can be difficult to do. Do a few bed joints, then do the perps, and then run the jointer over the beds again. Use a soft coco brush over the joints.
Worth getting some good quality jointers, not cheap ones from B&Q.
Speedcrete have a good selection.

Thanks, this is really useful info and gives me some good pointers to google. Looks like a lime mortar may be the way to go.

stuart45

Lime mortar is good, but take the advice of your local lime merchant. I would consider using a fuel ash pozzolan to help with the set. Plastic sheets protect it from the rain, hessian from the sun or frost. Lime mortars need a bit more care for a while.