New Lime Pointing Cracking

[Mike_England]

Hi all, hoping for some guidance on lime pointing… I’m in a early Victorian terrace and just had the chimney stacks repointed, it’s grade 2 listed so lime mortar was required

After a couple of days I’m seeing hairline cracks mostly at the perpendicular joints, pretty much every other brick.

Should I be concerned ? The contractor states that any cracking under 2mm is considered normal so nothing for them to address

But should I be concerned?

The contractor has used natural hydraulic lime NHL3.5, building sand and I believe Portland cement in the mix. Not sure on ratios

Attach a photo

Thanks for the help
Mike

 

[aockenden]

Probably won’t make any big difference to anything. Just keep an eye on the cracks as you go through a few freeze/thaw cycles this winter and make sure they’re not expanding or any of the mortar fillets are starting to get loose or fall out.

Some free advice: In the future I think you should get really clear with yourself about what materials you want to use for various jobs and why. If I paid somebody to lime point my chimney and then found out they’d cut their lime with Portland cement I’d be looking for a full refund.

 

[Cherryburn]

You're also not supposed to tool off lime mortar like this, it should be cut flush with the bricks, left to start to go off and then hit with the bristles of a brush until some of the stones in the mix show through. This opens up the "pores" of the surface and really allows it to breathe.

 

[a twig]

Very late in the year to be doing external lime work even in NHL - was it covered with hessian afterwards?

And agree with others - if using NHL then no justification for cement in the mix whatsoever and should have been flush pointed.

Sorry to be bearers of bad tidings

 

[Cherryburn]

Just saw that this is just the chimney which is a bit of a saving grace. It's not ideal, but if there's anywhere it makes sense to have a bit of a stronger mortar it is on the chimney, which is more exposed than the rest of the walls. Tradies tend to go a bit belt and braces on it because it's not a job you want to be called back to. So I wouldn't worry too much about it for now, just don't let them work on the rest of your house.

 

[Stevers]

Having some sharp sand in the mix would have helped with the shrinkage, and bashing it in and off with a brush would also have helped with that too.

 

[Mike_England]

Very late in the year to be doing external lime work even in NHL - was it covered with hessian afterwards?

And agree with others - if using NHL then no justification for cement in the mix whatsoever and should have been flush pointed.

Sorry to be bearers of bad tidings

No apologies needed appreciate the thoughts . They actually started the job in late summer and it’s being dragging on, finished on Monday this week, I was replacing the roof also. It wasn’t covered at any point

 

[Mike_England]

Probably won’t make any big difference to anything. Just keep an eye on the cracks as you go through a few freeze/thaw cycles this winter and make sure they’re not expanding or any of the mortar fillets are starting to get loose or fall out.

Some free advice: In the future I think you should get really clear with yourself about what materials you want to use for various jobs and why. If I paid somebody to lime point my chimney and then found out they’d cut their lime with Portland cement I’d be looking for a full refund.

Thanks for the practical advice, that’s kind of what I’m looking for at this point… what to do next, I haven’t actually paid for half the job but to ask them to re cut it out and redo the whole thing feels like a fairly nuclear option if it’s not a huge risk, though it is frustrating to have a half baked job done

And yes I take your point about being more informed, I hired a company who specialise in this type of work so was hoping not to have to tell them how to go about their trade, but I feel like it may be necessary in the future

 

[Mike_England]

Just saw that this is just the chimney which is a bit of a saving grace. It's not ideal, but if there's anywhere it makes sense to have a bit of a stronger mortar it is on the chimney, which is more exposed than the rest of the walls. Tradies tend to go a bit belt and braces on it because it's not a job you want to be called back to. So I wouldn't worry too much about it for now, just don't let them work on the rest of your house.

Haha thanks, that’s very helpful, yeah they were not in the best condition either

 

[stuart45]

Adding cement to NHL 3.5 had probably made it too strong, which is one reason for the cracks. Drying out too quickly can be another. It's best to keep it misted for a while in dry weather. It shouldn't be a problem on a chimney stack though. Weather cut and struck pointing was used years ago when lime mortar was being used. Back when lime mortar was the only mortar, a sharper type of sand was normally in the mix rather than the softer, rounded grains of the modern building sand. A sharper sand has less shrinkage, but with cement mortar is really difficult to work with, so for modern mortar the softer building sand is used.

 

[aockenden]

And yes I take your point about being more informed, I hired a company who specialise in this type of work so was hoping not to have to tell them how to go about their trade, but I feel like it may be necessary in the future

Yeah if it were me I would just pay these dudes out for whatever work they’ve done so far, then pause and do more reading / research about materials and techniques for old buildings. Once you’ve got your own mind sorted then you can restart works, either doing it yourself or by hiring people who you can then ask very directed and informed questions to before allowing work to progress. Unless you’ve gotten uncommonly lucky and found the one in a million contractors who is really solid in old building theory and practice, your options are to 1: trust the tradies (yes even those who say they specialize in old houses), 2: get the job done right.


I always recommend people read “Lime and Clay Based Plasters, Renders and Paints - A Step-by-Step Guide” from cover to cover before doing any work (themselves or hired). It’ll generally get your head on straight and set your foundational understanding.

 

[Lacan07]

NHL 3.5 alone would have probably been sufficient for a chimney stack so no need for the cement. The finishing isn't great though, as others have already said it needs to be flush, no ledges, and whacked with a churn brush to bring out the aggregate.

It is a bit late to be pointing but its NHL and its been unusually warm so far this autumn so no worries there. I wouldn't worry too much about the cracks.

Its difficult dealing with trades and even the so called heritage contractors. I passed one yesterday in Chertsey, Surrey, they were repointing a house, incredibly neat mortar beds. 'Traditional' emblazoned on the van but obviously no sign they'd been slaking their own lime on site.

 

[stuart45]

One of the problems when you use specialist pointers is that a lot of them aren't time served bricklayers. In general, the best bricklayers don't want to spend all their working life repointing walls.
Although a flush finish, or very slightly recessed one is the most popular type used for lime, other styles can be used with lime mortar when required. Weather struck and cut as done in the stack dates back to the 19th century.
The flush joint is normally used because it's easy, more breathable, and also suits older, misshapen and battered bricks. It can still look a bit rough with really big joints, a contrasting colour and the mortar specks all other the brickwork when the churn brush was used too early.
Weather struck and cut is more difficult to do, and tends to drop out sooner, especially if not done properly.

 

[aockenden]

One of the problems when you use specialist pointers is that a lot of them aren't time served bricklayers. In general, the best bricklayers don't want to spend all their working life repointing walls.
Although a flush finish, or very slightly recessed one is the most popular type used for lime, other styles can be used with lime mortar when required. Weather struck and cut as done in the stack dates back to the 19th century.
The flush joint is normally used because it's easy, more breathable, and also suits older, misshapen and battered bricks. It can still look a bit rough with really big joints, a contrasting colour and the mortar specks all other the brickwork when the churn brush was used too early.
Weather struck and cut is more difficult to do, and tends to drop out sooner, especially if not done properly.

Flush pointing also reduces the amount of rainwater that soaks into the wall. Non-flush pointing creates little ledges all over the wall which catch, hold and soak droplets of water running down the face of the masonry.

 

[Cubist]

These 'Pointing Guns' - whatever the proper name is escapes me - the pros are using today look rather good in some respects but sadly it seems the time and effort advantage they give to the tradesmen concerned is then thrown away by an absence of of any effort to 'finish the job' properly.

I suppose that's only to be expected with the constant de-skilling of so many roles in life but I do miss the 'personal touch' not seen in many such modern examples of workmanship. (Ah well....Put another one on my Grump list)

 

[stuart45]

Flush pointing also reduces the amount of rainwater that soaks into the wall. Non-flush pointing creates little ledges all over the wall which catch, hold and soak droplets of water running down the face of the masonry.

It depends on the type of bricks used. Softer, more absorbent bricks will benefit from a flush joint with exposed aggregate, as the idea is that the wall absorbs the water evenly over the wall, and it evaporates well before it reaches inside. Known as the overcoat effect.
With a hard, less absorbent engineering brick a weather struck, or weather struck and cut joint performs better, as the idea is for the joint to be more watertight. Using a metal tool brings laitance to the surface to form a more waterproof seal. British Rail normally used a weather struck joint with their engineering bricks. Known as the raincoat effect.
Hundreds of years ago, a struck joint was common, which is the opposite to weather struck, or sometimes double struck which has a pointed finish.
There's around 20 different types of pointing, although most are rare, and they need to be picked for the job.

 

[stuart45]

These 'Pointing Guns' - whatever the proper name is escapes me - the pros are using today look rather good in some respects but sadly it seems the time and effort advantage they give to the tradesmen concerned is then thrown away by an absence of of any effort to 'finish the job' properly.

I suppose that's only to be expected with the constant de-skilling of so many roles in life but I do miss the 'personal touch' not seen in many such modern examples of workmanship. (Ah well....Put another one on my Grump list)

The problem with a pointing gun is that you're making the mix to suit the gun rather than the wall. Remember, a lot of pro pointers are not time served tradesmen.

 

[Cubist]

time served tradesmen.

Is it just me or do others think that many of these so called tradespeople need to be serving more time - at HMGs pleasure maybe?

 

[stuart45]

Is it just me or do others think that many of these so called tradespeople need to be serving more time - at HMGs pleasure maybe?

When you think about the amount of money involved I'd say that a lot of them do deserve prosecuting. I suppose in legal terms, there is a fine line between someone who thinks he's doing a good job but isn't and someone who's just out to rip people off.