Why will my mortar not set?

Discussion in 'Builders' Talk' started by stinkydog, Mar 8, 2013.

  1. stinkydog

    stinkydog New Member

    I've just been building a couple of retaining walls in the garden. The mortar I've used is a 4:1 ratio mix that I know works well.

    However, even after 48 hours, the mortar has not gone properly hard and is still very soft and crumbly. The cement has been stored in plastic bags, on a pallet in my garage since I bought it 5 months ago. It has a "use by" date of December 2012.....but doesn't appear to have "gone off" - it's still dry and powdery/ no lumps. Having said that - I've used cement well after date in the past and not experienced this .... it's a new one on me and a complete mystery!

    Anybody got any ideas why my mortar won't go hard?
  2. Has the frost got it, or heavy rain.
    Id give it a couple more weeks, cover the work, its not really drying weather.
    The mix sounds okay.
  3. surfermick

    surfermick New Member

    yes, agreed, maybe frost, maybe damp miserable conditions. looks like you may need to build 4 coarses every two weeks
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Did you put any additives in the mix? Maybe that is where your problem lies.

    Too much, too little, out of date, settled???

    Fairy liquid don't quite do the job

    Mr. HandyAndy - Really
  5. Little Biff

    Little Biff New Member

    Hi SD,
            There are several reasons why mortar does not go off quick enough,Sometimes the plastersiser containes a retartder and it takes three days,especially if everything is damp and wet. If the frost gets to it then the joints will swell out slightly and go powdery,Just stick a nail in the joint and see how far in the frost penetrated,if its only about 20mm,then you can rake it out and repoint it.Too much fairey liquid will kill the cement and rewetting and reworking the mortar when it starts to dry out will kill it.Sand is another big problem,some sands are quite dead and take ages to harden but they do.Some sands require more cement than others,sharp washed sand requires a lot less than soft dead sand.obviously.You are best off to cover up all your work before you head home in the evening.
  6. gadget man

    gadget man Well-Known Member

    Did you use clean water??..........dirty water will prevent it 'going off'
  7. stinkydog

    stinkydog New Member

    Thanks, all good answers so far.... thanks to lLittle Biff - got some stuff I can do a bit of "googling" on !!

    In answer to the other members - I haven't used any additives 'cos they didn't appear necessary, I get a good workable mix without them. I used the same sand and cement to re point the garage in Oct/Nov last year and that "went off" in less than 24 hours (as it should) and was rock hard in 3 days.

    As I say, it's a complete mystery. It's almost as if it returns to the original dry mix state as it dries out without actually "curing". I can't lay bricks with it 'cos any disturbance completely destroys the new courses and I have to start again.
    It's a real b*gger 'cos I've 8 bags of the stuff on a pallet that I'm loathe to feed to a skip :(
  8. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Were the bricks stored inside? They may be too dry, and sucking the water out of the mix too quickly.

    Mr. HandyAndy - Really
  9. surfermick

    surfermick New Member

    i would say that i wouldnt keep cement for that length of time, it can loose its usefulness after time. it depends how long it had sat on the shelf in the builders yard when you purchaced it. it could have been around a while when you purchased it and by now has had its day. try mixing a little mortar up and keep it in the garage, see if it goes off, thus finding out if the problem is weather conditions.
  10. stinkydog

    stinkydog New Member

    Thanks for all your input. A lot of the answers I'd been kicking around anyway - but it's always good to get a 2nd and 3rd opinion eh?
    I tried mixing a small batch in an old bucket and left it in the porch to test the "weather theory". It's taken nearly 4 days to go off, but still has no real integrity or strength.
    Going to take this as a lesson learned....in 20 years experience I've never known portland cement go bad to such a serious degree, so I'll buy what I know I can use in one build in future.
    On the plus side, I can use it for flagging.....and I get some free paper sacks into the bargain !
  11. Could It even be that over time the sand has degenerated by absorbing impurities from the rain? Someone else mentioned that not using clean water could be a problem.

    My brick layer refused to use a bulk bag that had sitting around uncovered for a year or so saying that it would have "gone" by now. He wouldn't even use it for the blockwork behind the outer face brickwork.

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