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What pointing mix to use ?

Discussion in 'Building' started by trevorbayliss, 4 Jun 2019.

  1. trevorbayliss

    trevorbayliss

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    I am repointing a 1950's ex council house which i rent out. The pointing is totally shot and i have some cavity tie expansion as well.

    So i am taking out some bricks and fixing the bad ties, plus adding a few new ones as well.

    I am also fitting some helical bar above 3 windows where there has been some movement from past new D/G being fitted.

    Just started this week and have been doing a bit of ripping the mortar out today with my grinder.

    I was planning on doing a sand and cement mix, but wondered if i should go for lime and sand instead. Would there be any point in this ? I think the pointing is sand and cement, but apparently these houses were built using ash as part of the mortar. So i think this has contributed to the tie failure.

    The brick is a hard engineering one, so if i do it in sand and cement would a ratio of 3:1 be ok?
     
  2. trevorbayliss

    trevorbayliss

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    Just read an article and it says even if you have cement mortars it is a good idea to add lime to the new pointing. So a mix of 4:1:1 is a good one.

    What do people think of this mix using lime and cement in the sand ?
     
  3. John D v2.0

    John D v2.0

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    4:1:1 sounds very strong, I was under the impression mortar for above dpc should be quite weak. The lime will really help the workability.
    I repointed our unbelivably soft 1920s bricks (small area under ground floor bay) with 5:1 lime and sharp sand I think as that seemed to match the original, and it was nice to work with due to the lime. But I don't think you'd use sharp sand with cement. I spent a while researching online and youtube and then just guessed in the end! Hope that helps a bit!
     
  4. trevorbayliss

    trevorbayliss

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    Some articles say 3:1:1/4, so even stronger with only a little lime.

    It is confusing. My own house is lime and i am going to redo some old cement pointing done in the past, but use the sharp sand and lime.

    But on this house i thought i had to use cement, because it was built that way originally. I am wondering if more lime and less cement is a good way to go. Say a 4:1:1/2, with the half being the cement.

    Any comments appreciated. Rob singer on Utube has some good videos, but he uses lime mostly.
     
  5. John D v2.0

    John D v2.0

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    well I'm not an expert in anyway but from my research I found some things out last time
    in cement mortar the lime is not for making it go hard, it's for workability. but it still takes up space between the sand so the mix needs reducing.
    If you really have engineering bricks you don't have to worry about the mix being strong from the bricks point of view but I think it can affect shrinkage.
    Also regarding the lime, I did tell a lie, actually the original was slaked lime basically the bog standard stuff, and I used NHL 3.5 in the repointing. That does harden even in wet conditions, wheras the original mortar in the house is like paste in any of the damp walls.
     
  6. trevorbayliss

    trevorbayliss

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    They are not modern engineering, but are a hard brick. They have a smallish frog.

    I have used nhl 3.5 before so would probably use that.

    I am certainly going to use the lime to help with movement, but its just getting the best mix of cement with it.

    I have seen Rob Songers video on mortar mixes now and his favourite mix is 9 sand, 2 lime and 1 cement. So i will be making up smaller batches so it looks like a 4 1/2 sand / 1 lime / 1/2 cement. That sounds good to me.
     
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  7. StephenStephen

    StephenStephen

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    I'm not an expert, but I would (and have in the recent past) just use NHL 3.5 and sand - simpler and it'll not be stronger or harder than the brick. I'm not quite sure why you'd want to put cement into it.
    There has been some research which suggests that adding a little bit of cement to a lime putty mortar can make it fail ( https://www.buildingconservation.com/articles/cement/cement.htm ) which suggests just using hydraulic lime and sand
     
  8. trevorbayliss

    trevorbayliss

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    Just makes life so much harder all this stuff. So many different variables. I want to use the lime which sets quickly. So using less cement is more risky it seems. Oh what to do.
     
  9. StephenStephen

    StephenStephen

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    I think you might have misread the article - my reading of it was that the accepted wisdom was that a little bit of cement did no harm, but then the research showed that even small proportions of cement were problematic with lime putty, and that if you wanted the advantages of cement in your putty - just use hydraulic lime instead.

    I'm slightly confused by what you mean about lime setting quickly - do you mean you want quick setting lime, or that you want to use lime but it sets too quickly?
     
  10. trevorbayliss

    trevorbayliss

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    Im not using the lime putty.

    I would use the NHL 3.5 hydrated stuff.

    This is normally mixed with cement quite a bit.

    Your confused by the article and so am i. It is just annoying when you read stuff like this.

    I am sure it was saying less cement is worse because you get less binding with the cement. So use more cement and all ok, but i am confused still and so i will not follow articles like this because they are not very clear.
     
  11. StephenStephen

    StephenStephen

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    Ah yes - I see what you mean about the particular implications in the article of a smaller proportion of cement - thank you.

    Setting such rarefied academic research to one side...
    The problem with adding more cement is that the mortar is harder, which is problematic when you're pointing.
    I'm confused as to why you'd want to add cement at all - doesn't it just complicate things? I would have thought that 3.5 hydraulic would be hard enough?

    You might have your hydraulic and your hydrated mixed up - they're quite different, and I don't think there is such a thing as NHL 3.5 hydrated (and I've not heard of hydraulic lime being used as a cement additive)
     
  12. trevorbayliss

    trevorbayliss

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    All I know is the NHL limes set ok. So yes you use them on own with sand. All good in lime built walls but what do I do with my sand cement wall?

    I thought adding the NHL would give me a more flexible mix but I also get some cement benefit. No one seems to have solid answers on this.

    There was a product called lime bond which was cement and lime already mixed up. I have seen some guys using this before.
     
  13. noseall

    noseall

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    3 or 4:1 (sand:cement) will be fine. No need for fannying about with lime at all. Make sure that after the joints are raked that the masonry is jetted or hosed and is always damp when applying the pointing. This may mean several wettings in the summer.
     
  14. stuart45

    stuart45

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    As above, soaking the wall is key, not just slinging a few brushes of water from a bucket on to it. Use the jet to clean it out, and then the shower or mister to really soak the wall, and then let the surface dry a bit.
    I'm repointing a barn with NHL3.5 at the moment, but you don't add cement to the mix. Just let it mix for 20 minutes and fatten up for 20.
    Then cover like this and keep damp for a week.
    DSC00024.JPG DSC00014.JPG DSC00025.JPG
     
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  15. trevorbayliss

    trevorbayliss

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    I am def soaking the wall and will use a mist spray when i come to pointing so that bit is covered.

    I have nearly ripped out the pointing on the back of the house today. Here are some pics. The rear is by far the worst as i think it gets the full sun all day and gets the rain as well.

    The pointing is almost sand. I am going into it fully with my small grinder. So minimum i am in is 25mm, maybe 30mm in many bits.

    2 bricks to the right of the top right bedroom window just pulled out after i had chased around that area. I have cleaned them out fully and just left in place for now. I also have some blown ties and they have pushed the bricks out a touch in one or two places. So i am going to fit some cavity ties in the odd place.

    I am leaning to a 6:1:1 mix to include some lime to hopefully give me more flexibility.
     

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