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cracks in plaster - why?

cracks in plaster - why?

RE: cracks in plaster - why?

Without meaning to be flippant - Cracks in plaster are due to movement of the wall surfaces behind, or shrinkage of the joint compound.

Walls do not move with such regularity as to explain why such cracking would be commonplace.

Without knowing a great deal more details, I don't believe anyone here can tell you why this is happening. I would hazard a guess that the contractors in your area are not using ready-mix plaster, and are trying to get away with cheap over-watered mix.

Please provide:

- Typically between panels, or also at inside corners.
- Does the cracking also appear at wall to ceiling interface?
- Is paper joint tape always used, or does this also occur where the more modern fibrous plastic tape is used?

RE: cracks in plaster - why?

These are drying shrinkage cracks. Based on the crack pattern and size of the cracks, the plaster was not properly mixed, applied and cured. I would question the contractor's ability to do this properly considering what you have shown.

RE: cracks in plaster - why?

I've seen cracks like these in long walls which were due to movement. They are rare, but just the crack shape cannot tell you the cause.

If this is typical, as Ron and I have already said (and you listed as a possibility), it is poor mix.

Tips for getting this right: Follow the manufacturer's directions.

RE: cracks in plaster - why?

(OP)
thank you guys

yes it must be OVER WATERED MIX as Celin was saying. I just wanted to be sure and get a 2nd opinion before I confront the contractor.

What would you do now? Try to fix it somehow or take down and redo?

Should you astually water the wall prior plastering by hot weather?


lolobau

RE: cracks in plaster - why?

Ron is correct. Plaster is line concrete... the more water the more shrinkage.

Either that or when he did the job, he was plastered.

Mike McCann, PE, SE (WA)


RE: cracks in plaster - why?

Line concrete... Is that like Architectural concrete?

Have we been drinking on a Sunday again? More details, I want to know if this line concrete has been cracking at the curves and corners too. *sarcastic smile*

RE: cracks in plaster - why?

Like...like concrete... sheesh!

Mike McCann, PE, SE (WA)


RE: cracks in plaster - why?

I like concrete too, but not necessarily enough to dedicate a post entirely to the subject. ;0)

RE: cracks in plaster - why?

Just one more point. I suspect it is shrinkage caused by too much water in the mix, but I would not give the subcontractor any tips regarding mixing or proportioning plaster because he may claim to have followed your instructions religiously and still have cracks afterward. That would put the onus square on your shoulders.

BA

RE: cracks in plaster - why?

Nice point BA! Still comes down to telling the contractor to follow the manufacturer's written instructions.

RE: cracks in plaster - why?

Agreed, CELinO.

BA

RE: cracks in plaster - why?

(OP)
thank you guys for the valuable comments

as we can see the contractor was not expirianced. Are there any rule of thumbs for the correct plaster mix? Any tricks?

One other thing, I saw sometimes contractors watering the wall prior plastering. So that the dry wall doesn´t suck imidietly the moisture of the plaster. The same methode I saw also by watering wall bricks prior using them for construction.

would you recommend this?

RE: cracks in plaster - why?

It is common and accepted to 'wet down' walls prior to plastering using a similar technique called 'saturated, surface dried' that is used on horizontal flat work. Alternatively, a scrub coat of wetted plaster slurry works very well as both a bond layer and avoiding unwetted walls from sucking moisture from the plaster.

FYI - Excessive pre-wetting of bricks/blocks can be problematic if the bricks or blocks are too porous - it causes the bricks/blocks to absorb excessive water, making them heavier and more difficult to lay using normal mortar.

RE: cracks in plaster - why?

(OP)
@Ingenuity: Thanks for the confirmation so actually you woudl always recommend it? What will happen to the plaster is you apply int on a very extrem dry wall? how will it result in the quality or cracks when it looses the water to fast?

lolobau

RE: cracks in plaster - why?

Follow ASTM C926....as good as anything else out there and better than most

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