hairline cracks and hollow plaster.

macgooner · May 13, 2015

Hi lads.
I plastered a house last year and it turned out fine but i was back there recently and there are alot of hairline cracks and the plaster is hollow to touch it. The problem is the blockwork in the house was very pour ,not that it was not straight but the mortor in the joints was very weak and had very little cement, there has also been cracking on the inside were the walls are mortored. Most of the cracking seems to be under sills and lentens there was also a machine around there working and was wondering would the vibration cause movement, have any of ye experienced a similar problem would appreciate the help.

raytheplasterer · May 13, 2015

was it munocushe?

macgooner · May 13, 2015

Nope ordinary sand and cement with lime finish mixed 4-1 wall was scudded and scratched.

raytheplasterer · May 13, 2015

probably rendered over bone dry blocks.

johniosaif · May 13, 2015

Ghost writer alert

raytheplasterer · May 13, 2015

always scud for piece of mind.

macgooner · May 13, 2015

No always would wet down walls before plastering and no frost got at it either. Just wonderung why it took this long to come through if it failed to key in properly it would happen in the first week.

johniosaif · May 13, 2015

raytheplasterer said:
always scud for piece of mind.

Thanks ray , hugs out too you

BigK · May 13, 2015

If the cracks are from the edge of lintels & under windows its settlement, not a lot you can do about that, although for last six months or so I've started putting the alkali mesh in scratch coat at those delicate areas and its decreased cracks ten fold.
If it's coming away, (hollow) stronger top coat than scratch coat? Or scratch too thin to go with a deeper top coat, which in effect makes it stronger....
They are all possibles along with too much suction which you've already discounted.

Fatarm · May 13, 2015

When was the dodgy, poor blockwork joint house built?...and what machine used ??? Coffee machine?..or a big digger machine? Or a lawnmower???? :aburrido:

macgooner · May 13, 2015

About two years ago house was built. It was 12 tonne machine around the house couple of months ago.

radford · May 14, 2015

You've lost me! What's going on? Plastered a sand castle then a big machine came then he went back to look at the render and saw cracks and it sounded hollow ... Am I missing something?

Arti · May 14, 2015

raytheplasterer said:
was it munocushe?

what flavour monstermunch are you using

thebearbeef · May 14, 2015

@johniosaif scud?? Is that a term for splashing a wall down?? Not heard this saying before in my years... Only relating to doing a poo [emoji85]

Arti · May 14, 2015

its an SBR/S&C slurry

User___removed · May 14, 2015

If the block joints were soft and you mixed your gear 4/1 then there's your problem.
Cracking will happen at stress points.using mesh under cills/above windows should prevent this.your mix should of been weaker.

macgooner · May 14, 2015

bobby said:
If the block joints were soft and you mixed your gear 4/1 then there's your problem.
Cracking will happen at stress points.using mesh under cills/above windows should prevent this.your mix should of been weaker.

Cheers what mix would you recommend

User___removed · May 15, 2015

If the block joints we're soft perhaps a product like rendaid/microgetobtis would of been better to use over the substrate before a scratch coat mix of 5/1/1 with mesh,then topped off with a 6/1/1.

raytheplasterer · May 15, 2015

if a crack in the block causes a crack in the render should the crack be at right angles following the block?

hairline cracks and hollow plaster.

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