Help! Some cracks in multi-finish??

Discussion in 'Home Cinema Building DIY' started by srfeo, Jan 25, 2008.

  1. srfeo

    srfeo
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    Hi,

    Yesterday I filled in the chases that I made in the wall with multi-finish plaster. In general it went OK, but in some of them I have some small cracks that appeared after it started to dry? I have more cracks where I tried to fill in plaster that had come loose.

    My process was to paint in 1:5 PVA:water a few days ago and let dry. Then before plastering I painted in 1:3 PVA:water and let it go tacky before filling the channels and repairing plaster.

    I'm not really sure what went wrong. Did I use the wrong product? Any ideas? Do I just need to put another thin coat on top to smooth/fill the cracks? Thanks!

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  2. albriscoe

    albriscoe
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    Hi Mate

    now I`m no plasterer but I`ve just had a bloody great big house done, my plasterer has said that you might have had the mix to dry or it has dried out too fast ie. using an heater on it or something

    eitherway way he went on to say that if it is solid to the wall you can simply repair the cracks with fine fill or decoraters caulking and rub down

    hope that helps mate

    Allan
     
  3. srfeo

    srfeo
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    Thanks, I've been reading and I think that it was the wrong product and dried too quickly.

    Rookie move, I'll just either pull it out if it doesn't harden properly and try again or try to finish it off with poli-fill and sand (there is nothing in the room so dust doesn't matter).
     
  4. Staypuff

    Staypuff
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    Be carefull will polyfill m8 , id use decorators caulk which has much more elasticity so wont recrack when the plaster work continues to dry and shrink. To boot its usually cheaper, i use caulk on all cracks smaller that 1.5/2.0 mm. Polyfiller is ok above this but usually have to re do with caulk after a few months once poly shrinks too.
     
  5. srfeo

    srfeo
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    Was reading elsewhere that I should have used bonding or hardwall to fill and then multi-finish on top to skim.

    I'm now considering taking it out and using the right material or letting it dry and putting a top layer of easi-fill and sanding.

    Strange thing is that the front channels have no cracks, only the channels for the rear speakers. Maybe because the channels were shallower or it dried slower being an outside wall...
     
  6. Staypuff

    Staypuff
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    The deeper the fill the larger the shrinkage in general. I would be tempted to redo the whole thing using a bonding agent between the wall and plaster making the fill shallower. Wicks stock many bonding plaster/fillers.
     
  7. lowmans100

    lowmans100
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    Sounds like you have the multi finish too thick. As you said hardwall or bonding should have been used to render the wall then use finish for the last few millimetres.
     
  8. gypsybuilder

    gypsybuilder
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    Them there's plastic shrinkage cracks caused by the upper (exposed) surface drying at a faster rate than the lower. They probably go right through the plaster but may be filled if the remaining plaster is sound.
    When it's fully dry tap it -if it sounds hollow its fooked. If its a big job to replace and you think it's ok, fill it with a flexible filler. If it is not totally sound rip it out and start again.
    The external walls probably didn't crack because they will be a lower temperature / lower absorbtion than the internal uns. If you do it again try not to overheat the room until it cures a bit. Could have been worse it could habe been 300 cubic metre concrete pad in June...

    Yeeha.
     
  9. scott R

    scott R
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    as mentioned multi finish is no good for filling i would personaly rake it all out and use some bonding/hardwall also when making good small areas your better off using filler/joint compound to skim it as you can take it down tighter to lose the joint. I wouldnt use caulking either unless its just in corners
     
  10. Groover

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    If you decide to dig the exisiting plaster out and then refill with bonding, it can be a good idea to add a good handful of normal cement powder to the bonding mix. This makes for a stronger and harder fill and will dry out in no time. You could plaster on top of it in a matter of hours.
     

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