[Help needed] How to clean and repair this brick retaining wall

[thetyreman]

Cement/lime mixes with more lime than cement are deprecated these days because apparently they micro-crack. 2:1:9 or 2:2:9 or 1:1:6 are said to be much better. I've just used 2:1:9 for for a very minorly retaining wall to try to match my house's lime pointing but needed to lay in Nov/Dec temps. It works, they all work, only time will tell how well.

yes but is that a like for like replacement? even if your house isn't listed you should use what they used in the 1930s if it was built in the 1930s, time will indeed tell, I have not really seen much evidence of a 1:2:9 mix cracking or failing especially if it was hot mixed, in my opinon a 2:1:9 is too strong, too much cement in there.

 

[thetyreman]

this is taken from nigel copsey's hot mixed lime and traditional mortars book.

 

[thetyreman]

I'd do some tests, try some 1:2:9 and 1:1:6 cement lime mixes, you can also use white cement to make it look more white than grey.

 

[Jake]

yes but is that a like for like replacement? even if your house isn't listed you should use what they used in the 1930s if it was built in the 1930s, time will indeed tell, I have not really seen much evidence of a 1:2:9 mix cracking or failing especially if it was hot mixed, in my opinon a 2:1:9 is too strong, too much cement in there.

That wall wasn't like for like, modern stocks so much harder bricks. The house is 1890s and was repointed in hydraulic lime and sharp sand (no cement). The 2:1:9 work with the modern stocks was with white sand and white cement to get a similar enough look on front garden stuff. Turned out well looks wise, too early to say otherwise. Some pillars in reclaimed stocks were done in 1:1:6 for a less hard mix to match the bricks. That has effloresced a lot more but it'll be fine.

Apart from the newer pointing mortar the house itself is mostly held up by dust between the bricks these days.

 

[earnest]

Cement/lime mixes with more lime than cement are deprecated these days because apparently they micro-crack. 2:1:9 or 2:2:9 or 1:1:6 are said to be much better. I've just used 2:1:9 for for a very minorly retaining wall to try to match my house's lime pointing but needed to lay in Nov/Dec temps. It works, they all work, only time will tell how well.

I think this will be fine anyway with whatever mix as it's just some pointing (although the coping is going to get a hard time of it, as the bricks are saying). However a mix with lime in it will come up much lighter than the existing pointing, so that would look a mess unless he repoints the whole wall (despite that not looking necessary for the most part).

Whatever he does with mortar, those bricks are not up to the role of being copings so a long term fix would replace those, a decent brickie will be able to match the existing mortar well enough to patch point it where that is needed.

Should I not repoint it now and wait for colder months in winter?

I would love to DIY as much as possible to learn and save costs but obviously having no skills and knowledge about this field is a huge factor.

Would a partial pointing be that obvious (eye soar)?

Also after reading yours and @thetyreman comments, I am still not sure which mix ratios to use also any chance anyone can recommend actual products please? Or any would do?

 

[thetyreman]

The 2:1:9 work with the modern stocks was with white sand and white cement to get a similar enough look on front garden stuff. Turned out well looks wise, too early to say otherwise. Some pillars in reclaimed stocks were done in 1:1:6 for a less hard mix to match the bricks. That has effloresced a lot more but it'll be fine.

Apart from the newer pointing mortar the house itself is mostly held up by dust between the bricks these days.

I've never heard of 2:1:9 mix before, who recommends these kinds of mixes? and why would you have double the cement or triple vs a 1:2:9 mix, I don't get it, surely it's better to have more not less free lime content?

 

[Jake]

Sorry to OP, we ended up going off on tangents and complicating things with details. But yes, patch pointing can stand out if it isn't reasonably close in colour.

Looking at the photos again the 'layer cake' looks like movement but its not clear how or why from the photo.

I'd just get a brickie or three to come and look at it.

 

[Jake]

I've never heard of 2:1:9 mix before, who recommends these kinds of mixes? and why would you have double the cement or triple vs a 1:2:9 mix, I don't get it, surely it's better to have more not less free lime content?

More lime is fine in a lime only mix but research apparently shows not so in cement lime mixes. https://www.buildingconservation.com/articles/cement/cement.htm

That talks about 1:1:6 (good) and 1:2:9 (bad). I can't recall where 2:1:9 came from, but it was recommended for the same reasons as 6:1:1 but for a below DPC mix. I dug in pretty deep so it may be underlying English Heritage/Smeaton Project study.

 

[thetyreman]

More lime is fine in a lime only mix but research apparently shows not so in cement lime mixes. https://www.buildingconservation.com/articles/cement/cement.htm

That talks about 1:1:6 (good) and 1:2:9 (bad). I can't recall where 2:1:9 came from, but it was recommended for the same reasons as 6:1:1 but for a below DPC mix. I dug in pretty deep so it may be underlying English Heritage/Smeaton Project study.

it's from 1995! almost 30 years out of date, copsey's book was published in 2019, he argues in it that a cement lime mix with the right proportions like a 1:2:9 actually has more free lime content in it than any NHL and can show you the exact amount of free lime content in it, in a 1:2:9 mix it has 66% free lime in it, a 1:1:6 is 50%. an NHL 2.0 has only 35% free lime content in it...

 

[earnest]

Sorry to OP, we ended up going off on tangents and complicating things with details. But yes, patch pointing can stand out if it isn't reasonably close in colour.

Looking at the photos again the 'layer cake' looks like movement but its not clear how or why from the photo.

I'd just get a brickie or three to come and look at it.

I wouldn't want to waste their time just to provide some feedback knowing I will not take their services. Like I said, I would like to learn it myself, save a bit of money and to improve the overall look of the wall. The wall is also very long and there's similar damage in the garden and the driveway, so it will be very expensive

 

[Jake]

Interesting, I'll have to buy a copy. How scientific is his approach though? Lots of guff in conservation (I may have fallen for some of it). But Smeaton used an academic scientific approach, so does he say their results were not replicable or does he just go on his tangent?

 

[Jake]

Right, well I think mortar mixes aren't your main problem.

More work but better lasting and looking would be to replace the whole brick on edge top course with a more impervious brick (and use the still existing bricks you remove to replace cracked bricks in the main face of the wall).

Otherwise find as close to a match flettons as you can to the existing bricks, and patch repair, accepting that some of the old and new coping bricks will continue to blow over time and that there will be a bit of variation in the bricks where they have been replaced.

The layer cake bit needs to be relaid by the look of it, but it seems also to be the top course?

If you are just patching it up then just try some sample mortar mixes in different proportions until you get close enough to the same colour when its dry. Personally I wouldn't add lime if you take that approach because the existing looks like just sand/cement and lime will make it significantly lighter.

 

[earnest]

it's from 1995! almost 30 years out of date, copsey's book was published in 2019, he argues in it that a cement lime mix with the right proportions like a 1:2:9 actually has more free lime content in it than any NHL and can show you the exact amount of free lime content in it, in a 1:2:9 mix it has 66% free lime in it, a 1:1:6 is 50%. an NHL 2.0 has only 35% free lime content in it...

yeah... not confusing at all which mix to use

 

[Jake]

I would ignore all of mine and Tyreman's lime debate (sorry for the thread diversion). That's all a conservation approach for old buildings and materials, not appropriately directed at your modern fletton retaining wall.

 

[earnest]

@Jake not at all, it was a very informative and interesting, much appreciated.

Out of curiosity, what is your background @Jake and @thetyreman, very interesting discussions from both of you

I am pleasantly surprised with the quality of content, level of help and contributions here from so many UKW members

 

[thetyreman]

Interesting, I'll have to buy a copy. How scientific is his approach though? Lots of guff in conservation (I may have fallen for some of it). But Smeaton used an academic scientific approach, so does he say their results were not replicable or does he just go on his tangent?

I'd say it's a very good book and well worth the cost if you are serious about lime and how to make lime mortars, but it also covers limewashing, cement lime mortars, NHLs (why to not use them), there's a lot of detail in there, sometimes he does go off on a tangent but it's an excellent read, plenty of science as well to back up what he's saying, his website is a very good resource as well https://www.hotmixedmortars.com/documents.html

 

[thetyreman]

I would ignore all of mine and Tyreman's lime debate (sorry for the thread diversion). That's all a conservation approach for old buildings and materials, not appropriately directed at your modern fletton retaining wall.

well yes, but you can still use hot lime mortar or cement lime hybrid mixes today, it's not just for conservation.