Repointing Brick Wall.

[BearTricks]

I'm back for my 6 monthly clueless DIY post.

I need to repoint parts of the brick wall around our bay window. We thought we'd got rid of our damp by clearing a blocked drain but I think we just got lucky with the weather and its back with a vengeance after it pissed it down the past couple of weeks.

The pointing is crumbling in parts. Am I better off chiselling/grinding 1/2" out the whole lot, or should I just identify the bits that definitely need doing? If I do the whole area around where the damp is I'll be looking at a 3 foot by 15 to 20 foot area, at a guess, with some fiddly bits behind the down spout.

On top of that, some of the damp seems to be worst right under the window frame, almost like it's running down the wall. Is pointing the joint at the underside of the window frame best or would an exterior window frame sealer be better? Similarly, indoors there's a gap of a couple of mm under the window frame due to the house settling over the years. What's best to fill that?

Finally am I better using a bagged mortar mix or mixing up my own sand and cement (I think 4/1 is what I've seen recommended).

As for technique I've actually pointed before with no complaints on another job so fairly confident with that but I was just given the tools and shown what to do. As it's my own job I'd rather do it all right from start to finish and understand what I'm doing and why for future reference.

 

[HappyHacker]

I would not try to patch it but rake out the whole lot. Otherwise it will always look patched as it is very difficult to match the existing pointing/cement/sand colour, weathering and possibly profile with new.

Hammering it out is cheap but time consuming and can end up with damage to the bricks, using a raking blade in an angle grinder is quicker but can lead to even more damage to the bricks if you are not careful. Start on an area that is not too obvious.

The other questions I will leave to others.

 

[sunnybob]

Bay window roof's and gutters are a major cause of damp underneath the window. Start at the top and work down, or the wet will keep getting into what youve just repaired.

 

[MikeG.]

........Finally am I better using a bagged mortar mix or mixing up my own sand and cement (I think 4/1 is what I've seen recommended)...........

No!!! Absolutely not 4:1. That's one of the best ways of wrecking a wall*. Your pointing should be the same strength as the rest of the mortar, and that won't be stronger than 6:1. However, there is a BIG other issue.....

...........is it a cement mortar at all? Or is it lime? How old is the house? If it dates back to the early 20th century or before it could well be lime. What colour is it? Is the sand coarse and granular, of mixed particle sizes? Finally, if you can rake some out and put it in vinegar, what happens? If it is lime, then I think you are better off employing a brickie who has worked with it.

A photo of your wall would help no end. For a start, there must be a source of damp, a reason why the pointing has failed. There are all sorts of things to consider there, with leaking gutters, blocked drains, over-flows and so on being the obvious starting points, but hard surfaces adjacent to the wall, raised ground levels (the ground should be 6 inches below the floor level, minimum), inappropriate modern DPCs. My view is that failed pointing is more likely to be a symptom of damp than a cause.........but again, it is impossible to generalise.



* Seriously. That can lead to frost damage ("spalling") and the loss of the face of the bricks.

 

[BearTricks]

Seems to be sandy. Doesn't do anything if I stick it in vinegar. It's grey on top but if I scratch some away it's a sandy colour.

I actually just went out to remove some mortar to do this and the mortar right under the window, exactly where the damp is worst, is crumbly and soaked. Similarly it looks like the downspout has been moved at some point. The mortar where the holes were screwed in to the wall has failed so they're partially exposed and there's some damp on the other side of this.

I'm convinced that the flat roof over the bay window overflowing is to blame. The pipe that drains it in to the main downspout was completely blocked for a while and since its out of view we had no idea it was running down the walls pretty much exactly where the damp is.

The house is Victorian but if I had to guess I'd say the brickwork around the window has been redone at some point. None of the area is obvious as it is obscured by some hedging so I think I have some space to get in to the swing of things. The area affected worst is a bit of a pain to get to which is why the damp was allowed to sneak in.

So if I'm right...

- 6:1 mortar mix (or buy pre-mixed)
- chisel/grind out the damaged pointing
- I've heard tales of using watered down PVA to help the new mortar bond and/or a couple of drops of washing up liquid in the mix for consistency but both sound like cowboy builder tricks to me at least.
- peanut butter consistency on the back of a trowel roughly the thickness of the space being filled & feed it in in slivers with a pointing tool. Use tool to smooth it out.

Hopefully the worst of this rain will be gone by Monday when I plan to do it. We're only forecast light rain, but is there any harm in me covering it with a plastic sheet overnight to direct any heavy rain away from the fresh mortar?

I'm fairly confident I can do a good job with this and I've got a friend-of-a-friend brickie on standby at last resort.

 

[MikeG.]

Seems to be sandy. Doesn't do anything if I stick it in vinegar. It's grey on top but if I scratch some away it's a sandy colour.

So it sounds as though it has been re-pointed in cement mortar over the original lime mortar. You really aren't helping by not posting a photo.

I'm convinced that the flat roof over the bay window overflowing is to blame. The pipe that drains it in to the main downspout was completely blocked for a while and since its out of view we had no idea it was running down the walls pretty much exactly where the damp is.

Don't even think about re-pointing until you have sorted out the damp. Ideally, you'll leave it weeks or months and allow the bricks to dry first.

So if I'm right...

- 6:1 mortar mix (or buy pre-mixed)

It really isn't as simple as this. You have to try to match the finished colour of the rest of the mortar. That means buying the right colour sand, the right colour cement, and adding lime or not. You DEFINITELY don't buy pre-mixed.

- chisel/grind out the damaged pointing

Don't grind it. You'll end up with an over-wide joint, and damaged bricks. Removing the existing without damaging the bricks is really important, and not easy.

I've heard tales of using watered down PVA to help the new mortar bond and/or a couple of drops of washing up liquid in the mix for consistency but both sound like cowboy builder tricks to me at least.

Mortar requires a plasticiser. Use a proprietary one, because washing up liquid is high in salt and can lead to effervescence.

peanut butter consistency on the back of a trowel roughly the thickness of the space being filled & feed it in in slivers with a pointing tool. Use tool to smooth it out.

No, feed it in with a pointing trowel. Then the finish depends on how the rest of the pointing is finished. You leave it a few hours and then use the appropriate tool. Again, if you could post photos, I can tell you what tool to use and how.

Hopefully the worst of this rain will be gone by Monday when I plan to do it. We're only forecast light rain, but is there any harm in me covering it with a plastic sheet overnight to direct any heavy rain away from the fresh mortar?

Don't do the job with rain around. At all. Full stop. And you are jumping the gun. Get the wall dry first, and point in August/ September.

 

[MikeG.]

Seems to be sandy. Doesn't do anything if I stick it in vinegar. It's grey on top but if I scratch some away it's a sandy colour..........

Which did you put in the vinegar: the grey, or the sandy coloured stuff?

 

[BearTricks]

Both. Neither did anything.

 

[sammy.se]

Photo Photo Photo pleeeease
Then it's much easier to help

 

[Artiglio]

Any cable entries ? Tv, sattelite, phone etc, if so do they have a “drip loop” for want of better description. If the damp penetration is as extensive as your description suggests , penetration via the pointing for me would be pretty unlikely unless combined with additional poor detailing somewhere, ( flashings, gutters, window/door frame/brick joint etc.)
Working with lime is pretty straight forward if a bit time consuming, depending on how its finished.
Mike Wye are a good source of premixed lime mortars but gets expensive if you can’t fill a full pallet. You tube videos for pointing with lime .
A mix i’ve found more akin to modern mortar is 4:1:1 sand/cement/hydrated lime, more easliy found locally.

 

[Inspector]

You mentioned that there is some hedging in front of the problem area. It may also contribute to the dampness issues by not letting the wall dry.

Pete

 

[johnfarris]

So many things it could, you really need to post a picture