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Mortar mix

Discussion in 'Roofing and Guttering' started by diver, 2 Feb 2007.

This topic originated from the How to page called Replacing ridge or hip tiles.

  1. diver

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    Can anyone advise, I have been given conflicting advice sas to what sand to use with cement to fix the ridge tiles. Some say building sand, as for bricklaying others say sharp sand, does it matter? what gives the best grip? Thanks
     
  2. Roofer

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    Mortar made with sharp sand does dry harder and weathers better but it is almost impossible to work with because as soon as you try to trowel it up the water comes to the surface and it all gets a bit messy.

    Virtually all roof cement work is done with building sand and it is acceptable; a good compromise is to combine them both with a 3:1 mix (mostly building sand)
     
  3. marksson

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    Sharp sand mix:
    If you let the sharp sand/cement mix run in the mixer for 30 mins with only very little water added initially it eventually starts behaving much as soft sand (building sand), add water towards the end and then only a very small amount at a time until consistency acceptable.
    I have found this out in areas such as S.Wales where very little pit sand/soft sand is used (it's all dredged).
     
  4. diver

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    Thanks Guy's, will give it a go.
     
  5. Zeberdee

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    Try adding some PVA glue and some rapid hardener!
     
  6. corrie

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    Mmm...don`t use fairy liquid in cement IMO. Sharp sand is always recomended for roofing work........but not 100% concrete sand. The spec just means sharper than building sand ie. 3 building and 1 concrete.

    The mixup comes when people see sharp sand in a bag which is actually concrete sand. That sand mixed with cement on it`s own is far too rough for bedding and pointing. The original washed plaster sand is about right but is hard to get unless you get a minimum 3 ton or so from a quarry.

    Alex
     
  7. ^woody^

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    I see more ridge tiles from properties less than 30 years old with soft eroded mortar, than I do with pre-1950's properties.
    And all of these recent ones have soft mortar which it seems is 'modern' soft building sand only.

    You really need a sand which is flexible to cope with some roof flexing (building sand), but with less loam to give weather resistance (sharp sand).

    So you need to mix the two. Either 3:2:1 or 2:1:1 building:sharp:cement

    If you try and compensate by doing a strong building sand only mix, then it just cracks in no time. And as mentioned, sharp only will mostly end up in the gutter after falling off the trowel

    I have seen quite a few verges with what looks like concrete sand in the mix, and this seemed to have excellent weather resistance, but must have been a pain to lay.

    And remember to compact and iron the joints well, to give it weather.
    resistance.

    And don't use fairy or any other additive. It softens the mix and reduces the longetivity of the mortar in this location. OK for walls, but not roofs

    I've seen lots of ridges rebed with poorly finished joints. They look OK from the ground or scaffold, but the poor roofers are not happy when I clamber up the roof to check and tell them to re-do the whole lot if not done correctly. :evil:

    Its even worse for them when I find the ridges have been repointed and not relaid :evil: :evil:
     
  8. craig melvin

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    I am also interested in knowing the best way to re-point ridge tiles.

    It nice to have the advice from people who are far more experienced.

    Unfortunately I have only 6 years experience and I am learning all the time - basically self taught.

    I seem to be doing more and more repointing all the time.

    I will start and add some sharp sand to my mix in future. I have be using an additive to speed up the setting time becuase Im always looking over my shoulder for rain!

    Craig
     
  9. corrie

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    Lets face it Craig ..........repointing old ridges is never going to be a first class A1 job. It is a compromise. You can`t always get the key you would like as some of the original is hard and wont come out. At the same time you know that if you start taking the ridges off it is going to be major and therefore a bigger bill...........but this is a superior job.

    I wire brush any moss and loose pointing off first. Yes rain is the enemy. I went into builders merchants and ordered some tins of the different febtones. I then asked the guy if he had any of the white Febtone for roofs that The Pikeys use :LOL:

    Alex
     
  10. vinty

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    I use rapid set cement and plastering sand which is courser than building sand, the rapid set cement is stronger than ordinary cement but it costs twice as much, i use it if i 'm doing a small job like replacing one or two ridges it dries in about 20minutes which means if it rains it won't wash out you can buy it in BandQ.
     
  11. corrie

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    Yeah that`s a sound method Vinty. I do doubt that rapid set is ultimately stronger though. Most things that cure slowly cure harder eventually That is why rapid sets are sometimes frowned upon if used structurally. I may be wrong but i do believe also that OPC is harder than Mastercrete. We used to use Fondhu Cement which was fast set. High Alumina it was called. It attacked the steel in concrete causing many failures ultimately.
    I do put Glycol in mortar/concrete in bad weather as long as loadbearing etc aint involved.. Safe Climbing ;)

    Alex
     
  12. vinty

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    According to the manufacturers, it's quick set high strength, or so it says on the bag, as it only has to support the weight of a ridge tile i don't see relative strength as an issue the main reason i use it ,is when there is a chance of rain.
     
  13. occoris

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    I have always used sharp sand for ridge tiles, mix 3 to 1 with cement in the mixer dry for 10 minutes, add correct ammount of mortar plasticiser not fairy liquid, then very slowly , allowing up to 30 minutes add the correct ammount of water (with stain powder diluted in if needed)
    If you over water it will turn to slops very quickly, the difference can be as little as half a cup full !
    Patience is everything.
    It should sit on the trowel vertically with no slump.
    The correct mix will allow ridge tiles at angles of up to 60 degrees to be placed.
    Always use a rubber hammer for tapping.
    Always use a building sand morter with plasticiser for pointing lines, finish with a wet brush after 4 hours.
     
  14. SASroofer

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    I use a 2 soft, 1 plastering and 1 cement mix, with pva and frost proofer mixed into the water.
     
  15. Regencyroofingipswich

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    My favorite recipe is....

    10 shovels Soft washed/ plastering sand

    1 Bag of dust

    1 mug/cup of febmix.

    Dont let it turn over for more than a couple of minutes, i hate that "fluffy" muck that inexperienced labourers knock up.
     

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