Mortar (was: Sealing bricks on a chimney stack?)

[paulb33]

Still poking around the roof and chimneys….

One contractor suggested that the Edwardian engineering bricks of the stacks will be somewhat porous. He proposed a waterproofing sealant be applied to limit water penetration into the flue and roof. In fact, I'm wondering if the bricks have been sealed previously given the darkening evident in patches.

Only one of the ten fireplaces are in use, but most remain viable. I'll be installing a cowl on each pot to reduce water penetration but maintain ventilation.

Is sealing brickwork really a good thing? :?:

Paul

 

[Feltwell]

I wouldn't. I presume he means sloshing on some silicone waterproofer. Any kind of waterproofing treatment tends to trap moisture in rather than keep it out.

That stack looks to me like it might benefit from repointing (not in cement but I'd use a strong lime mix for a stack) - but it's clearly been patch-pointed before and it's not in bad nick, I've seen far worse - the pots might need re-flaunching (which you can do in cement), difficult to say without a closer look, and put some pepper-pot caps on those pots. You've got one or two bricks where the faces are starting to go that you could cut out and replace if you wish, but you could equally leave them, it will be a long long time before they *have* to be replaced.

 

[paulb33]

I wouldn't. I presume he means sloshing on some silicone waterproofer. Any kind of waterproofing treatment tends to trap moisture in rather than keep it out.

That stack looks to me like it might benefit from repointing (not in cement but I'd use a strong lime mix for a stack) - but it's clearly been patch-pointed before and it's not in bad nick, I've seen far worse - the pots might need re-flaunching (which you can do in cement), difficult to say without a closer look, and put some pepper-pot caps on those pots. You've got one or two bricks where the faces are starting to go that you could cut out and replace if you wish, but you could equally leave them, it will be a long long time before they *have* to be replaced.

Thanks, Feltwell. That's what I assumed. Yes: the bricky I employ to rebuild the lost stack will be raking out & repointing the others. We've got minor water ingress on this stack and I'll be reflashing it. At the same time, I want to make sure every other likely point of water entry is dealt with by whatever means. Good advise on the haunching.

Recognise this is a 'new' chimney compared to most 'period' houses folks are dealing with on this board…. I often look at the projects on here to raise spirits around my own lesser challenge.

 

[Feltwell]

Recognise this is a 'new' chimney compared to most 'period' houses folks are dealing with on this board…. I often look at the projects on here to raise spirits around my own lesser challenge.

There are a few other "new builds" on here - there are so many Victorian houses in the UK that there are inevitably some on this forum (my place is only a youthful 115 years old), and we've had some very nice Edwardian Arts & Crafts places posted up, some gothic revival (my favourite!) and very occasionally a 1930's house. So yours is at the newer end of the scale but not the newest!

 

[paulb33]

That stack looks to me like it might benefit from repointing (not in cement but I'd use a strong lime mix for a stack)

On the subject of mortar, this is the original pointing at ground level. Is this a standard lime mortar? Or…?

 

[MatthewC]

On the subject of mortar, this is the original pointing at ground level. Is this a standard lime mortar? Or…?

It's hard to tell from a photo but it's very dark grey and so if I was to place a bet I'd say it is cement-based.

Find a loose bit and try the acid test.

 

[Feltwell]

How soft is it if you try to rake it out? Does it crumble or come out in hard pieces?

Lime mortar can be dark - I had to take a dangerously leaning garden wall down and rebuild it, the mortar used throughout was definitely lime and was very soft and crumbly, but it was almost black with white lumps of lime in it - my guess is that it had been mixed with coal dust or coal ash, which would have been plentiful round here at the time, it was a coal mining area.

I'd love to recreate it for when I repoint the house. The house has been patch pointed over the years in various shades of cement, but there is an arch in the brickwork on the front gable end that is picked out in pure white pointing - obviously original - and the pointing around it is dark.

If you manage to work out how to get dark coloured pure lime pointing then please do post up on here how, I'd love to know. First step I'd suggest would be to speak to one of the well known lime specialists like Mike Wye or Ty Mawr.

 

[paulb33]

It's hard to tell from a photo but it's very dark grey and so if I was to place a bet I'd say it is cement-based.

Find a loose bit and try the acid test.

Mortar shot with a different camera lens below… Its set very hard but crumbly once it finally does move with a sharp blade.

The mortar joints are fairly wide - 7 to 10mm.

The architect was known for his experimental use of cement. It has flecks of pale mineral in it but also dark stuff. I'm guessing the black is coal, Feltwell. This is Penarth, near Cardiff……

Now, we have a LOT of coal dust in our coal shed. The bottom layer must be 113 years old. I wonder if its worth mixing this with a modern cement render?

Sorry for my profound ignorance: what's the acid test?

 

[paulb33]

If you manage to work out how to get dark coloured pure lime pointing then please do post up on here how, I'd love to know. First step I'd suggest would be to speak to one of the well known lime specialists like Mike Wye or Ty Mawr.

The brickies I've spoken to all suggested dyed sand and cement mortar…..

 

[plasticpigeon]

The shot you have put up shows a brick with the corner broken off and mortar on the broken bit which would suggest to me that the particular mortar in that shot isn't the original. What is the mortar like deeper into the joint??

I used a cement dye to dye the lime grout I used when laying quarry tiles. It went grey when it dried. That mortar is very black. Didn't Stuart45 on this forum say something about how to make mortar black. He seems to always give very helpful advice, he just doesn't come on the forum very often.

 

[LadyArowana]

Sorry for my profound ignorance: what's the acid test?

If you put a chunk of lime mortar in an acidic solution it should fizzz, cement won't. Apparently ordinary vinegar will do as the acid. I suppose strictly speaking I should remind you to wear all manner of personal protective equipment, but since most people can douse their fish and chips quite happily without injury I won't bother :lol:

 

[paulb33]

The shot you have put up shows a brick with the corner broken off and mortar on the broken bit which would suggest to me that the particular mortar in that shot isn't the original. What is the mortar like deeper into the joint??

I used a cement dye to dye the lime grout I used when laying quarry tiles. It went grey when it dried. That mortar is very black. Didn't Stuart45 on this forum say something about how to make mortar black. He seems to always give very helpful advice, he just doesn't come on the forum very often.

The house elevations have many bricks like that. I assume there were irregularities in the bricks at time of building.

The mortar varies considerably in colour around the house. I assume due to weathering and the mix used at the particular time of building. From a pale sand colour to uniform dark grey. Most of it is similar to the photographs I've posted though: dense grey with pale tan and black flecks.

 

[paulb33]

Apparently ordinary vinegar will do as the acid. I suppose strictly speaking I should remind you to wear all manner of personal protective equipment, but since most people can douse their fish and chips quite happily without injury I won't bother :lol:

I'll give this a go (I'm assuming this is what you use on your chips, your Ladyness…?) :wink:

 

[paulb33]

It fizzes! Not a lot. But, small bubbles do rise. And, a lump blew apart in the vinegar. The fizzing can be heard quite distinctly when the cup is close to the ear.

So, it likely contains lime and coal dust. Any thoughts on the tan coloured flecks?

Paul

 

[LadyArowana]

Apparently ordinary vinegar will do as the acid. I suppose strictly speaking I should remind you to wear all manner of personal protective equipment, but since most people can douse their fish and chips quite happily without injury I won't bother :lol:

I'll give this a go (I'm assuming this is what you use on your chips, your Ladyness…?) :wink:

I'm more of a tomato ketchup sort of person really, although for a special treat there are some places I know that do "truffle fries" which are sinfully good. Good luck with the testing and subsequent mortar alchemy.

 

[stuart45]

Probably Black Ash mortar, common in S.Wales back then. Tends to rots wall ties in cavity walls.
I wouldn't advise using coal dust in the mortar. Better to use a dark sand with some pigment.
If you have to use a sealer, siloxane is said to be breathable, although I don't really recommend any sealers on brickwork.