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White residue on bric

Whole house needs to be repointing so I tried in an inconspicuous area to practice. This white residue appeared and won't come off with a wet sponge.

  • I'm using Spec Mix tuckpointing mortar type O. Higher lime content than other mortar.
  • I have Chicago common brick, it's soft and quite chipped around the edges. Can't really get a clean joint, so I used a wet sponge to smooth the edges, but I think it kind of made a slurry on the face of the brick?

I'm assuming diluted muriatic acid wash will take it off? How do I prevent it to begin with if possible?

APP
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    Avoiding this grout haze- especially with brick which is very porous is difficult. Skilled masons will set the brick and then not touch it until the mortar is dry enough that it can be scraped off (called tooling) without smearing it all over the surrounding brick. Using a drier mortar mix will make it easier to place without getting on the brick. Honestly, when re-pointing mortar this is more difficult than when actually setting the brick. – Kyle Oct 02 '22 at 16:32
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    Just for posterity, when diluting, add acid to water. Not the other way around. And definitely don’t do what a guy did at the swimming pool where I worked, which was to add a bucket of acid to the vat of chlorine. – Aloysius Defenestrate Oct 02 '22 at 23:29
  • If that's typical of the mortar in the wall, I'm wondering why you think it needs repointing? (pro builder and repointing specialist). – handyman Oct 04 '22 at 20:19

3 Answers3

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Your mortar is probably too wet and you're trying to point flush. It sounds [& looks] more like you're using a grouting technique, where you can just wipe excess off afterwards, rather than pointing. You can't do that with pointing, they are different disciplines. "Damp wiping" makes a mess, because you don't have a smooth surface like tiles that you can just wipe clean.
Flush pointing is hard to do, recessed [like the original] is relatively easy.

You have old & uneven brick, so avoid any technique that requires a surface clean afterwards.

If you use much firmer mortar & a pointing trowel to inset it like the original, excess would fall to the floor/mortar board, not stick on the brick face.

enter image description here

If you get a round-end tool, look at hollow-key, which is possibly the simplest, least messy way for a DIY-er.
https://www.diydata.com/techniques/brickwork/pointing/pointing.php

Tetsujin
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  • Thanks that's very helpful. I'm going to try a firmer mix next time. Should I discard the excess mortar that I tool off, or can I reincorporate it into my mix (assuming it falls back onto my hawk)? – APP Oct 02 '22 at 18:00
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    You can keep recycling it right the way through the job, assuming you don't take all day with each mix. It should remain workable for a good time, hours not minutes. Cement 'cures' rather than dries so wetness in & of itself isn't the primary factor in its workability. – Tetsujin Oct 02 '22 at 18:24
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Diluted muriatic acid and a brush will clean off the mortar haze for sure. It is not very fun to use and handle. You need to use the right gloves and eye protection and even a respirator.

I have had good results cleaning haze on ceramic tile with white vinegar. It is a much more mild acid than Muriatic. You might need to brush it a bit more than the stronger acid but it is much easier to work with.

Kyle
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    Vinegar worked quite well! Still some haze remaining, but I have more pointing to do, so I'll wait until I'm done to finish that. – APP Oct 02 '22 at 20:44
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Preventing the smearing means not using a sponge at all. To start with you need a fairly dry mix, way drier that used for laying bricks for example. It should be firm and not sloppy.

Damp down the raked out joints and leave to soak a little, the brick face should look damp but not running with moisture. Press the mix back into the joint and slightly over fill the joint. Don't mess about with it too much, i.e. push it in and move along.

Once it's firmed up a little (i.e. you can still press in a finger nail) you can play around with the joint finish. Some folks use a churn brush at this stage, kinda beating the surface to expose grit in the sand and compact the mortar. A simple cutting off the excess leaves a flush, old fashioned look.

Leave it a couple more hours and then tidy it up with a soft natural bristled brush, working across the joints. By now the mortar is dry enough not to mark the bricks.

I'm struggling a little recognise the joint finish you have there, it almost looks like a slightly eroded twice struck, or birds beak joint. Is this the original pointing?

handyman
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  • Thanks. I'm not sure what the original joint was. It's pretty weathered and deteriorated. The previous owner did not take good care of the house. I think I'm going to attempt a flush joint because that's what I mostly see on repointed work in my neighborhood. All the houses around here have common brick on the sides and back of the house. So many bricks have imperfections on the edges, a flush joint seems to just cover them up better. Anything more ornate seems like it would be quite difficult to do properly. – APP Oct 06 '22 at 10:08