UKC

Hi ukc,

Our house was built in about 1885. The walls are two layers with a gap between which is mostly filled with rubble. It's taller than all the other houses around us except for the two to either side and is about a mile from the sea. As a result the back wall (facing west towards the sea) gets a lot of slightly salty wind and a lot of weathering.

The wall still has all the original bricks and lime mortar, but in many areas it needed repointing and some of the bricks were badly spalled. So we have just had some people round to replace the spalled bricks and repoint. I would guess he has repointed around 1/5 - 1/4 of the wall in total.

He told me he would be using lime mortar and seemed like an honest guy who knew what he was talking about, so I just let him get on with it. However after completing the work he mentioned that the mortar also contains cement. The mix he has used is as follows: 1 part hydrated lime, 1 part cement, 2 parts grit/sharp sand, 2 parts building sand.

Uneducated internet research would suggest one needs to use a lime mix without any cement in a house of this age. I know that using normal cement mortar can cause damp problems and brick damage due to a lack of breathability and flexibility in the mortar. But the guy seemed to honestly think what he had used was the right mix.

How big a problem is this, if at all? Do I need to find someone to undo his work and start again or would that be an over reaction? Is there some way I can monitor it carefully to see if there is an adverse effect over time?

Really appreciate any expert advice.

Thanks

Si

Not sure on specific query, but in true ukc style.... 

Spray or paint your exterior walls with something like this

https://www.google.com/search?q=thompson%27s+water+seal&oq=thompsons+wa...

DWR for your building. 

No expert but I can't imagine that being a problem. I had a section of my house wall rebuilt after a subsidence issue. They used a lime mortar to lay the bricks (like the rest of the house) then pointed the very outside of the joint with a normal cement mix. Also the whole house was repointed with cement circa 1990 and I've had no damp issues. My house is a bit younger than yours but not by much.

My house is a little older than yours, but of the same construction. When I bought it it was covered with modern cement render, which many people will say is a no-no for that type of construction. I believe that there is an injected damp proof course. The only damp-related problems that I have experienced in 8 or 9 years are from condensation from cooking. I certainly wouldn't advise panicking - as you suggest, monitor for problems.

My house has a couple of hundred years on yours and he's talking cr*p. Lime mortar does not have cement in. It uses lime putty and sand (and hair in some cases). This is the company I've used. You can ring and they are very helpful.

https://www.traditionallime.co.uk/architects-guides/traditional-mortar

It might be the case that 1 part cement isn't enough to cause problems, it could be worth a google to find out about that?

There's sometimes fudges which work and don't cause any harm, but this suggests that it shouldn't be used. I guess your decision comes down to the mixture of convenience and cost and concern which applies to you, it might turn out to be fine.

https://www.spab.org.uk/advice/inappropriate-cement-pointing

I used to work for a building firm which worked mostly with lime mortars on old limestone buildings. Having said that, I was mostly the resident chippy so take the below with a pinch of salt...

Adding a bit of cement into lime mortars is fairly common practice, and is generally done to plasticise the mortar (make it easier to work with). It's not period correct, and its use would probably be strictly prohibited on a National Trust stately home for example, but I've never heard of any instances where a small amount has caused problems.

I think the main thing with the mix your builder was using is that the overall ratio of cement to lime/aggregate is pretty low, so the mortar will probably have breathability and hardness properties  closer to lime mortar.

Cement mortar is problematic with old buildings because it is so much less porous, but also because it can be much harder than the stone/brick. The mortar should be a sacrificial seam which will absorb any movement and break before the stone, as the wall expand and contract. In your case, because the ratio of cement to aggregate is so low, I wouldn't have thought it would be a problem - Much of the damage done by unsympathetic post-war re-pointers was with mixes around 1:3 cement to sand. It's also probably not as serious a problem with brick as with stone, as bricks are generally harder anyway.

As for monitoring over time - Lime mortar takes years (sometimes decades!) to fully go off, so it might be difficult to find anything out in the short term. One thing you could look for is the colour of the mortar - if it's very grey then it may contain too much cement. Lime mortars should usually be a slightly lighter shade of the colour of the aggregate used.

My red brick terrace was built 1890 and originally lime mortar. It looks like it has repointed ad hoc over the years with various mixes, and in small areas with pure cement. Any damp issues I have are where the mortar has fallen out. I had a couple of builders come round and quote for a full repoint and asked about lime/cement as there are a few people online adamant that cement should not be in the mix. They all use 1:3 or 1:4 sand cement, and it looks like all the houses on my road / area have cement in the mix. From reading online I understand that as long as the mortar mix is softer than the brick it will allow for the flex and breathability, and take the brunt of the weather, rather than the brick. So Sounds like red brick will be fine with a weak cement mix. And it’s older soft sandstone buildings that want a lime mortar.

I spoke to a mate who’s a structural engineer, with no knowledge in this particular area but seemed to agree with those principles  

Anyway after much panic I’m now confident enough , so I’m halfway through doing the repoint myself with 1:4 sand cement mix

Ie don’t worry about it

Thanks everyone, appreciate the input.

Ralph, you've put my mind at least partly to rest with your knowledge of the different mixes, thanks. In terms of monitoring, what I was wondering was whether there was anything I could look out for that might indicate a significant problem (leading me to get the pointing redone at that point) before that problem actually resulted in large areas of damaged bricks or a significant damp problem. It's difficult though because the bricks are all old, weathered and not of consistent colour or finish.

DON@T DO THIS !!!!  You will likely f*ck-up the building for ever.  It needs to be breathable.

Thanks Mark. I'm less confident about my bricks. I'm not sure what they are like in Sheffield , but there are many houses round here that were built from what I would call consistent high-quality-appearance red brick about 1900-1910, and there were many similar ones in Derby too, including where we used to live (built 1906). Comparing to those, the bricks in this house seem to be earlier era and I think might be quite a lot softer. (It could have been closer to 1880 and use older tech. It certainly has no damp proof course eg engineering bricks near the bottom.) Your post is still reassuring though, cheers.

This was the sort of thing I had found before starting the thread. If I'd been asked to make a decision beforehand, I'd have definitely paid extra for 100% lime, but the job having been done differently, it's too late for that and starting the whole thing again with a new builder would seem a big step. So I was trying to get more perspectives, as it's really difficult to know what website advice to take really seriously and what is idealistic. I think this thread has helped a lot, thanks.

I am a structural engineer but not  a specialist in this area but...

He probably shouldn't have done it if the rest of mortar is pure lime.

Lime mortar has various potential benefits.  It is "softer" than most cement mortars so is less likely to crack than cement based mortars if the building moves a bit, which old buildings will tend to.  Small cracks in mortar aren't a big issue except for aesthetics.  However, if very hard cement mortar is used this may be stronger than the units (bricks/stones) which then may crack rather than the mortar which isn't good.   The mortar your builder has used sounds relatively weak - probably "M4" so you should be alright here.

Lime mortar is also more breathable than cement with is beneficial with old buildings normally.  If you are lucky you won't have a problem.  If you are unlucky the new mortar will prevent moisture travelling through it, potentially forcing it inside (damp), or into the units where it can freeze and lead to faces coming spalling off. See figure 7

https://www.cheltenham.gov.uk/download/downloads/id/810/pointing_with_lime_...

The whole area is a bit of a rabbit hole with enthusiasts taking fairly extreme positions to the point of insisting on "hot lime", which is even softer.

The Thompsons is breathable. 

A true hydraulic lime mortar will take months to go off, particularly in the current weather. You could have other problems with it washing out and weathering before it gets a proper set.

Hydrated line (ie with water added and some initial set) with cement in a weak mix seems a low risk, reasonable compromise for workability and immediate weather tolerance. If he’s achieved a decent colour and texture match, you’ve probably done well compared to a lot of work out there.

I'm not sure to be honest. If the mix were too strong then signs of damage would probably appear only very gradually. Personally I might check the wall periodically over the next few years for any damaged bricks, but wouldn't worry about it too much. With the accelerated weathering from the sea air, it might even be the case that the wall needs repointing before any damage from the cement could manifest itself (although that's pure speculation from someone with no experience of building anything by the sea).

the breathability of lime is useful in old buildings when they already had damp problems, as the moisture can leave.  nowadays nearly all old builds have been retro fitted with air bricks, vents, ground lowered, weather proof windows etc etc. all of which will remove the actual cause of damp.  there therefore shouldnt be any moisture that needs to escape, so using cement shouldnt be a problem.

The only issue I see, is you mention your cavity is filled with rubble.... why?  That could cause damp no matter what you use.  hopefully your workman cleared it out when they replaced the bricks?

If it makes you feel any better, my house is very similar sounding, in basically the same location and mines been repointed (badly) with cement.  No issues here.

Because that's how they used to build them, mine is limestone built in the 1880's, no cavity just 3 foot thick walls filled with rubble.

I repointed mine (with advice from a builder friend) with normal mortal as has the rest of the terrace, never had a damp problem (apart from below the windows due to degraded porous Sandstone cills) in 20 years

Our house was built immediately after ww2 using brick/cavity/brick..  It was built using lime mortar.  We got the 3 walls repointed and most of the spalted bricks replaced.  Normal modern cement mortar was used throughout.  That was ten years ago and we've had no problems since.  We live within a few hundred yards of the North Sea facing North.

I'm a drystone waller and I often use the same mixture as your builder used to point up your old brickwork, when carrying out  sympathetic repairs of old mortared walls.  It sets quick enough (unlike pure lime mortar), and does the job well enough.

When we lived in the SW of Eire, in an area facing the SW gales from the Atlantic it was normal practice for all builders to use a strong cement mixture to plaster over old buildings of thick stone to render them totally dry of moisture ingress.   Despite my scepticism this worked well.

No, he only replaced a few bricks and there is loads of rubble so it wouldn't have been sensible to ask him to remove it, as the other guy that's how they were built back then unless the house was single skin.

The house is definitely not damp proof - it was built before damp proof courses became mandatory and doesn't have one, neither does it have any air bricks or places they could be placed. The rooms are a mixture of suspended and solid floors.

There are also lots of old fireplaces, 4 of which are open - so lots of ways for damp to get in and out elsewhere in the house.

There were some high damp readings near this wall when we moved in, but not high enough to cause major concern and no indication of any decay.

Anyway, overall this thread has been very encouraging, thanks everyone. I will just keep a close eye on it over time.

Yes, but the op said two layers of brick, not solid filled stone walls.  They're a whole different kettle of fish.  Brick with lime, there shouldn't be any rubbish in the cavity (other than the inevitable overspill).

edit- should have read your reply.  That's not how they built with brick. rubble fill walls and brick cavity are two different things. The rubble shouldn't be there. It will be from lazy brickies who couldn't be bothered to clear up and from years of mortar sluffing off into the void, worse with each re-point.

It sounds like it would be worth installing air bricks under the suspended floors where you can and emptying the cavity (if damp becomes a problem). Open fires wont make the house damp, increased airflow should dry the house out (I have 5 too! and a mix of suspended and solid.... are you sure you don't live next door?)

How does one re-point inside a cavity wall???

Agreed. No air circulation under suspended floors with no DPC = rotten floors. Even with airbricks they'll rot. I speak from personal experience having had to replace two of the floors in my house.

There are good comments from others about keeping mortar strength lower and porosity higher than the masonry units. The only other thing to check is that the mortar joints are flush or slightly recessed and that they are not making those god awful raised joints that are often seen inappropriately applied to old buildings (although usully to stone walls, not brick)