New Plaster Efflorescence

Discussion in 'Plastering and Rendering' started by CortinaV8, 30 Apr 2010.

  1. CortinaV8

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    Recently had a single skin wall built to replace an existing single skin externall wall that was spalling badly, only small, probably about 2 meters wide with a door in it.

    Engineering commons were used for the wall, the internal wall was rendered with sand/cement, about a 3/4 days later the finish coat was applied.

    I've left it to dry for about two weeks and I am starting to get some efflorescence appering on the plaster, it seems worse around the angle beads to be honest.

    Any ideas or suggestions? I ideally want to paint the wall soon, but not if it's going to cause the paint problems.
     
  2. Micilin

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    Don't panic yet, it may still be drying out or have condensation in the room.

    A few questions -

    Is it dry apart from the salts - any dark patches?

    Are the patches high up on the wall?

    Are they higher than 1m up the angle beads?

    Does the floor have a damp proof membrane?

    Is the render / beading touching the floor?

    Was there any damp proofer used in the render?

    If so was it used with lime/ plasticicer or anything else?

    Any signs outside of water ingress?

    After rain or if you put a hose on outside can you see damp/dark patches?

    Is there good airflow in the room?
     
  3. CortinaV8

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    Thanks for the reply, I shall answer all your questions.

    Is it dry apart from the salts - any dark patches? - Yes, the wall is dry.

    Are the patches high up on the wall? - Nope

    Are they higher than 1m up the angle beads? - Yeah, floor to ceiling pretty much.

    Does the floor have a damp proof membrane? - No, however the new brickwork is built on a dpc

    Is the render / beading touching the floor? - Nope, stops about 2 inches short of the floor

    Was there any damp proofer used in the render? - Yes, as directed on the container.

    If so was it used with lime/ plasticicer or anything else? - A small quantity of lime was added into the mix, although a small amount given the size of the mix.

    Any signs outside of water ingress? - Nope, the wall seems dry, the brickwork is new and the pointing is good.

    After rain or if you put a hose on outside can you see damp/dark patches? - nope, still looks dry even in the heavy rain.

    Is there good airflow in the room? - the wall has a catflap in it, the house is fairly old and I don't go in for sealing off every single draught, so yeah I think it's got reasonable airflow, we certainly never get any condensation issues in the house anyway.

    [b[/b]
     
  4. Micilin

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    If no water getting in , or condensation then -

    It sounds like it is still drawing salts , so I'd be inclined to wash them off and let them reappear to see how bad they get - there is not a lot you can do at the moment, and I would not paint it just yet, or panic as I'm sure you will get more suggestions here. T

    he salts are either from

    A - the render itself , or

    B being drawn through the render from the bricks and mortar.

    Two more questions -

    was the sand washed salt free? If you don't know, and have any left soak it in container for a couple of days, take the sand out and let the water evaporate - the salt will be left (you can also taste the water -but unless you are a connoisseur.... :D ) - source A above

    Lime should not be used with waterproofer (it sets as a lattice in the render, so doing the opposite of sealing something up) - it should say this on the container - what brand was it ? The waterproofer is supposed to stop salts being drawn through - source B


    As and aside -

    No material is really truly dry, and there is always a certain amount of moisture in the atmosphere - and the salts in the materials can draw moisture in, and with it more salts. A waterproofer should mention that it protects against hygroscopic salts. Sometimes breathable lime renders are used to allow moisture to dissipate, but if you use a sand and cement waterproof render, it has to be done to spec to work.
     
  5. roughcaster

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    Are the beads full float coat corner beads? (not thin coat beads),, and how were they actually fitted to the corner,, ie, dabs of render/nailed, dabs of plaster/multi finish?
     
  6. Micilin

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    Good point - on a single skin finish dabs etc could be drawing it in, or holding it there.

    Nails too which will be in to the mortar
     
  7. CortinaV8

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    They were a kind of wide mesh type bead, galv clout nails held them in place.
     
  8. roughcaster

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    That's the type of bead i mean. They are more often than not, put on with dabs of plaster or render, with the odd nail, just to hold it in shape. Are you sure the plasterer didn't use "plaster dabs" as well as the galv' nails?

    If you put cement render over plaster, ie (the dabs holding the beads), then any efflorecence in the brickwork "might" draw into the plaster, and could show up on the render,,,, you can put plaster over cement dabs, but "not" cement render over plaster dabs ,,,, just a thought. Apart from that, i think Micilin's covered the rest,,, anyone else??
     
  9. Micilin

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    On the beading line,

    Assuming there is some damp getting thru the brickwork -

    for damp proofing to be done properly, you would not use any bead in contact with the brickwork. This is because yo are breaking the seal of the render, and giving the damp something to track along.

    ie the metal wing of the bead is touching the bricks, making the surrounding damproofing redundant.Nails do the same.

    I would always float up the render to a batten and return it and then use a skimming bead - either dabbed slightly into the soft render (preferred), or stuck on after the render sets - perhaps using a small cable tidy nail to pin it if needs be - on the edge so not breaking the seal.

    Don't panic just yet, nothing to be gained by rushing into anything - it may be a case of just letting the salts pull out and when they stop , then painting.

    Are the beads on reveals, where they may be close to outside of bricks?
     

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