Repointing 1930s solid wall property

[danlightbulb]

Hi all.

I need to repoint my house. It's a mid 1930s solid brick semi detached.

The pointing is a mess. Some sections have been redone in the past with cement slapped over the existing pointing without raking out. Other sections haven't been done and the mortar is very weak. Other sections have been repointed with proper raking out but again with cement.

I intend to do the whole house over time. It will take me a while.

I did a section myself last Autumn. I did a lot of research on what mix to use but found so much conflicting advice. I ended up using cement and building sand in a 1:5 ratio, with a bucket handle finish.

I don't like how it's come out. The bucket handle finish doesn't suit the house at all in my opinion. And the colour has come out a very dull grey.

So I'm back to trying to figure out what to use. I either want to do flush or weather struck finish this time.

Regarding the mix. I don't really know if the original mortar would have been lime or not. Underneath the poor repointing it certainly looks more of a brighter colour but that could have just been the sand they used.

I don't want it too bright/white. It won't suit the house. Needs to be a buff sort of colour I think, maybe a medium yellow. I think a rougher finish with aggregate on show will suit the house as well.

So...I'm thinking lime or cement plus lime. Maybe a mix of both builders and sharp sands. I intend to buy a selection of bagged products and mix up some small batches to test how it comes out.

Anyone got any advice? I will post some photos of my brickwork and current state of pointing tomorrow as well.

Thanks.

 

[aockenden]

I'd skip the cement either way. If you really feel the need to have a quicker hydraulic set or a harder final strength then go for an NHL 3.5. Adjust your sand choice and do test patches to narrow down the final color you are going for. Brushing the pointing back with a churn-brush will expose aggregate and is a typical method for producing a flush finish. It needs to be done at the right time during the curing / drying process, otherwise it'll smear lime stains all over the face of the masonry.

 

[danlightbulb]

I'd skip the cement either way. If you really feel the need to have a quicker hydraulic set or a harder final strength then go for an NHL 3.5. Adjust your sand choice and do test patches to narrow down the final color you are going for. Brushing the pointing back with a churn-brush will expose aggregate and is a typical method for producing a flush finish. It needs to be done at the right time during the curing / drying process, otherwise it'll smear lime stains all over the face of the masonry.

Thanks for the reply.

As I said, there is much differing advice online about what to use. On another forum, I asked detailed questions on a few occasions but got barely any replies. A couple of folks said lime, a couple said use hydrated lime additive plus cement, and a few said just use cement it won't make any difference. No-one advised what finish to use so I just bought a half round pointing iron but it doesn't look right. I posted pictures of what I'd done and it was heavily criticised for being crap.

I now understand that hydrated lime is not a suitable product and is just a substitute for plastisicer so I can discount that. However I cant see anywhere that sells NHL lime locally (Birmingham, UK) - the DIY stores don't sell it. It looks like its even harder to get non-hydraulic lime. Also noticed lime is much more expensive than cement, but I don't think that's a huge issue as I won't need that much of it (probably a few bags will do the whole house I imagine).

It seems that NHL3.5 is the 'default' lime that people use. Whether that is right is questionable as again the advice seems to be highly variable.

On the sand - again I have the same issue of availability. All the local places sell building sand and sharp sand, but there isn't really anywhere where I can select different colours of basic sand.

My house is common bricks on heavy clay soil. I'll get some photos in a bit, hopefully that will help select the right product.

 

[aockenden]

I now understand that hydrated lime is not a suitable product and is just a substitute for plastisicer so I can discount that. However I cant see anywhere that sells NHL lime locally (Birmingham, UK) - the DIY stores don't sell it. It looks like its even harder to get non-hydraulic lime.

Sry but this is rubbish. Hydrated lime is a non-hydraulic lime product which (assuming it's fresh), sets / carbonates as properly as any other lime. The myth that it's only suitable as a "plasticizer" (god only knows what that's supposed to mean) is unfortunately pushed by block-head mainstream builders who know absolutely nothing about lime and also for some reason is repeated on the text / instructions on the bags themselves. I've used non-hydraulic, hydrated powdered lime successfully for years now.

Also I 100% guarantee that builders-merchants in Birmingham sell both powdered Naturally Hydraulic Lime (ask them for "NHL") and powdered Non-Hydraulic Lime (ask them for "hydrated lime" or "builders lime").

 

[danlightbulb]

Sry but this is rubbish. Hydrated lime is a non-hydraulic lime product which (assuming it's fresh), sets / carbonates as properly as any other lime. The myth that it's only suitable as a "plasticizer" (god only knows what that's supposed to mean) is unfortunately pushed by block-head mainstream builders who know absolutely nothing about lime and also for some reason is repeated on the bags themselves. I've used non-hydraulic, hydrated powdered lime successfully for years now.

Also I 100% guarantee that builders-merchants in Birmingham sell both powdered Naturally Hydraulic Lime (ask them for "NHL") and powdered Non-Hydraulic Lime (ask them for "hydrated lime" or "builders lime").

Thanks. Its very difficult for a DIYer like me when other sites have completely conflicting advice. Here is a link which appears to be quite genuine and knowledgeable but which says the opposite to you - not to use powdered hydrated lime:

Myth #1: Hydrated Lime Mortar | Conserv®

Lime mortar is commonly confused with the use of hydrated lime in modern cement mortars. Lime mortars are 100% natural and traditional, they don't contain any cement or hydrated lime.

www.lime-mortars.co.uk

I quote:
"Hydrated Lime is readily available at the local builder's merchant and can be used to increase the workability of cement mortar. It is used more widely in schools, colleges and training centres where it is mixed with sand (no cement) to make a mortar that does not set and is reused again and again - ideal for teaching brickwork."

So according to this, one wouldn't use hydrated lime as it won't set. I can understand why someone with a very old building might want a softer product but I don't think that applies to my house - its still just a normal brick house albeit 1930s. I don't think I need something really soft?

Regarding availability - I can easily get hydrated lime from B&Q but I can't see anywhere (at least online) that sells NHL lime. I'll phone round a few places.

 

[stuart45]

I remember using hydrated lime at Tech. It does set, but the brickwork is knocked down quite soon after it's been built. Also, the mix isn't very strong, as it's partially carbonated, and they only stick a bit of fresh lime in now and then. From a technical point it's slated lime, the same chemical compound as pure lime putty.
One of the reasons that plasterers prefer mature lime putty is that they claim that as soon as hydrated lime is bagged up it's starting to carbonate.
Also they say that there will be some spots of calcium oxide in there.

 

[aockenden]

Thanks. Its very difficult for a DIYer like me when other sites have completely conflicting advice. Here is a link which appears to be quite genuine and knowledgeable but which says the opposite to you - not to use powdered hydrated lime:

Myth #1: Hydrated Lime Mortar | Conserv®

Lime mortar is commonly confused with the use of hydrated lime in modern cement mortars. Lime mortars are 100% natural and traditional, they don't contain any cement or hydrated lime.

www.lime-mortars.co.uk

I quote:
"Hydrated Lime is readily available at the local builder's merchant and can be used to increase the workability of cement mortar. It is used more widely in schools, colleges and training centres where it is mixed with sand (no cement) to make a mortar that does not set and is reused again and again - ideal for teaching brickwork."

So according to this, one wouldn't use hydrated lime as it won't set. I can understand why someone with a very old building might want a softer product but I don't think that applies to my house - its still just a normal brick house albeit 1930s. I don't think I need something really soft?

Regarding availability - I can easily get hydrated lime from B&Q but I can't see anywhere (at least online) that sells NHL lime. I'll phone round a few places.

It's rubbish. It sets, aka carbonates, slowly under cold humid conditions. But it absolutely DOES set when put on the wall and left to do it's thing. I have rock-hard plaster all over my home made from hydrated, non-hydraulic lime.

WHEN your house was built matters less than WHAT your house was built with (which MAY be correlated to the date at which it was built). If your bricks are soft, then you want a soft mortar. If your bricks are hard, you can get away with a harder product without risking damage to the bricks. NHL 3.5 should be the absolute maximum needed. Zero reason needed for cement to point your bricks with.

 

[danlightbulb]

WHEN your house was built matters less than WHAT your house was built with (which MAY be correlated to the date at which it was built). If your bricks are soft, then you want a soft mortar. If your bricks are hard, you can get away with a harder product without risking damage to the bricks. NHL 3.5 should be the absolute maximum needed. Zero reason needed for cement to point your bricks with.

Ok so its mid 1930s solid wall construction, Birmingham UK, on heavy clay soil.

Front elevation is a patterned decorative imperial size brick (see photos below).

Rear and side is a plain common brick, again imperial sizing, with some colour banding within it.

I don't think these bricks are particularly soft. Maybe not as hard as modern bricks. The brickwork isn't particularly even, some perps are wide others narrow. The mortar horizontal joints are quite wide, over half an inch sometimes three-quarters.


Here is a photo of the front elevation:

And rear elevation. You can see where the lower half of the wall (around the back door) was previously painted white. I removed this horrible latex paint last year but its left a white tint to the brick that's different from the more yellowy top half.

Close up of front elevation brickwork. You can see the 'slathering' of cement mortar over the existing pointing which is only a few mm thick - they've made a right mess of it. Im hoping some brick acid will dissolve the slop and I can make it look ok.

Here is a close up of what I think is the original mortar underneath the cement that's been put over the top. Its a nice yellow colour which I like.

Here is the corner of the property where the brickwork transitions from the patterned facing bricks on the front to the plain common bricks at the side of the house. Again I think this is the original mortar here - it is very weak by the way, just touching it makes it fall away like sand.

Here is the work I did at the rear (it was done in an emergency as the brickwork/mortar was heavily deteriorated with large voids and I was worried about its structural integrity). I used 5:1 building sand:cement for this and finished with a half round tool. As I said in my opening post, I don't like how its come out so I intend to redo it - but at least its now structurally ok even though it looks poor. Its bought me some time to research and do it properly. This was the part of the wall that was covered by paint as seen in the wider angle rear elevation image above.

 

[danlightbulb]

Any more opinions now that you've seen the pictures please?

Still think NHL3.5 is my best option?

Any idea how I might get rid of that white tinted brickwork where Ive removed the paint?

 

[jamest]

I've seen a lot of similar bricks near where I am (I'm not far from Redditch) and they are quite hard, especially the commons, so you'd probably be fine with NHL 3.5, though the original mix may have been a bit weaker. I would do what aockenden recommends - I've found a churn brush beaten finish to be very pleasing. It's a bit of a pain, but if you time it right you don't get lime smears and you avoid the nasty finish that's in your third photo.

 

[danlightbulb]

What sand mix should I use to go with the lime? Builders, sharp, mix of both?

I saw a youtube video yesterday from someone who seems to be very knowledgeable saying that NHL doesn't have much free lime (he prefers mixing hot lime from quicklime, but I don't think I want that kind of hassle). However he briefly suggests adding lime hydrate to NHL in 1:1 ratio. Any thoughts on this?

 

[a twig]

That works as a halfway house between the two, if going ahead with that then I’d use 1 NHL : 1 Hydrated Lime : 2 sharp sand : 4 builders sand

Otherwise just 1 NHL : 1 sharp sand : 2 builders sand

 

[danlightbulb]

Ok cool.

And do you think a flush finish with some brushing after it's starting to go off will be the right finish for the style of my house?

Now I need to get some lime and sand to do a test batch and see what colours I can get. I don't want it too light, a buff/sandy/yellowy cream is what I'm looking for.

 

[a twig]

Yep, brushing back would look closest to your photo of the original if that’s what you’re after

 

[danlightbulb]

Yep, brushing back would look closest to your photo of the original if that’s what you’re after

The original is deteriorated so I don't really know what it would have looked like when newly built.

 

[stuart45]

The original was probably either bucket handle or weatherstruck. Once it weather's back it looks like a slightly recessed flush joint.

 

[danlightbulb]

Hi all. I'm still really confused about the type of line and mix to use. I've been watching more videos and reading more stuff about the topic, and with every video there is more confusion.

1. I'm seeing evidence that NHL is variable in quality/strength and a poor NHL will be hardly better than cement.

2. I'm seeing a lot of videos using a hot mix quicklime on site. This probably would have been how they did it originally BUT that approach only sets via carbonation and so I'm worried it won't have any strength and I'll need to keep it wrapped it Hessian for ages.

3. Still very confused about hydrated lime. Its the most easily available lime (I can only directly buy hydrated lime or NHL3.5 locally, not quicklime or putty or NHL2 which all have to be ordered online), but I'm confused whether I can use hydrated lime alone (or if it's practical to given the setting time) or it has to be mixed with NHL.



I only want to do the job once and I want to do it right. What would be perfect and what would be 'good enough'?

My main considerations are sourcing the materials, ease of mixing, ease of pointing with it as a DIYer, how long it takes to set and whether it needs protecting/keeping damp and it's eventual weatherproofness.

If this was your house what would you use?

 

[jamest]

You're overthinking it!
You've got reasonably hard bricks, no evidence of spalling or damp penetration. You could probably get away with using a cement mortar and suffer no ill effects. However, there is a small risk and there are other reasons for avoiding cement.

You can make lime putty from hydrated lime by adding water and keeping it in a sealed container like this:

However, mixing and using a lime putty mortar in your situation is a big faff for not a lot of gain. There's the making of the putty, the mixing of the mortar and the pointing itself - with putty mortars you need to damp things down well and keep it damp by spraying the completed joints with a mister for several days as it sets slowly. It's often recommended that you mix in a pozzolan for external work, especially with harder bricks.

Using a pre-mixed NHL mortar would be much easier, it sets quicker and being harder than putty based mortar will last longer. If you had soft bricks that would be undesirable, but in your situation it won't be an issue. IF you can get NHL3.5 locally and you're happy to mix your own mortar, then that would probably be the cheapest option and would be highly unlikely to cause any issues at all. That's what I'd do if I were looking to save a few bob.

If you're feeling a bit flush, then a premixed NHL2 mortar would be the overall best option in my opinion.

 

[stuart45]

I would say you're overthinking the job as well. As jamest said, although the brickwork is 90 years old, the methods of production in the kilns are similar to modern bricks. The back of the house looks like LBC commons.
The 30's was a period when a lot of builders were gauging cement into the lime mortar, so there's a fair chance you've got cement in the mix.
The rule of thumb for repointing, is to use virtually the same mix as the original, but just a touch weaker.
The main reason that cement mortar has got a bad reputation for repointing is that for quite a number of years tradesmen were using a really strong mix of either 3/1, 2/1, or even 1/1. I've still got some trade text books that recommend those mixes. It's taken a long time for the damage caused by these mixes to really show itself.
A mix of 6/1/1 is similar to NHL3.5, and a 1/2/9 is like NHL2.
Are you sure it's a solid wall? Stretcher bond usually suggests it's a cavity wall, although not always.