Blebs

Blebs
 
To get rid of blebs let the gear pull and near the end put your trowel flat on the wall and rub round in a circle over the blebs it gets them out then give it a cross job done
 
The Apprentice said:
Finish will bleb if the background is to wet, no suction or applied thickly
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Do you know, or can you find out from BG, what is actually happening, technically-speaking, that causes blebs?

Is it a problem with chemistry? By all means correct me if I'm wrong, but your above answer seems to point to moisture lingering too much in the skim, but that wouldn't explain why it invariably tends to happen when skimming over bonding. It seems the bonding itself is affecting the skim in some way.

Do bonding plaster additives like perlite or vermiculite make the surface of the dried bonding plaster have different suction in the tiny localised areas where the perlite or vermiculite particles are closest to the surface?

I tried to glean some insight with a few web searches, but about the only thing even slightly relevant didn't answer my question (well, not that my limited intellect could see), and it's 40 yrs old:

nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote755.pdf

I'm not asking to be a nerd. I'm asking for a more thorough understanding, as blebs are bloody annoying, and it'd be nice to have a definitive answer from BG.


Cheers.
 
MakeItSmooth said:
Do you know, or can you find out from BG, what is actually happening, technically-speaking, that causes blebs?

Is it a problem with chemistry? By all means correct me if I'm wrong, but your above answer seems to point to moisture lingering too much in the skim, but that wouldn't explain why it invariably tends to happen when skimming over bonding. It seems the bonding itself is affecting the skim in some way.

Do bonding plaster additives like perlite or vermiculite make the surface of the dried bonding plaster have different suction in the tiny localised areas where the perlite or vermiculite particles are closest to the surface?

I tried to glean some insight with a few web searches, but about the only thing even slightly relevant didn't answer my question (well, not that my limited intellect could see), and it's 40 yrs old:

nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote755.pdf

I'm not asking to be a nerd. I'm asking for a more thorough understanding, as blebs are bloody annoying, and it'd be nice to have a definitive answer from BG.


Cheers.
Click to expand...
I just thought it was not a background too wet thing but that the water gets pulled away too fast or in a way the air can’t escape with it and it gets trapped
 
MakeItSmooth said:
Do you know, or can you find out from BG, what is actually happening, technically-speaking, that causes blebs?

Is it a problem with chemistry? By all means correct me if I'm wrong, but your above answer seems to point to moisture lingering too much in the skim, but that wouldn't explain why it invariably tends to happen when skimming over bonding. It seems the bonding itself is affecting the skim in some way.

Do bonding plaster additives like perlite or vermiculite make the surface of the dried bonding plaster have different suction in the tiny localised areas where the perlite or vermiculite particles are closest to the surface?

I tried to glean some insight with a few web searches, but about the only thing even slightly relevant didn't answer my question (well, not that my limited intellect could see), and it's 40 yrs old:

nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote755.pdf

I'm not asking to be a nerd. I'm asking for a more thorough understanding, as blebs are bloody annoying, and it'd be nice to have a definitive answer from BG.


Cheers.
Click to expand...
I’m not 100% sure that they have the data in a technical format but I will ask.
With regards to your question on blebs on your bonding, how long are you leaving it before you skim it? Blebs tend to appear when the substrate is still wet, which it is when it’s set, or when applied to thick which leads to excessive moisture on the substrate. The vermiculite in Bonding would not be effected by the application of a finishing coat once it has set.
I will ask the scientists but be warned, I might not be able to spell some of the words they use, never mind understand them.
 
Monkey Boy said:
I just thought it was not a background too wet thing but that the water gets pulled away too fast or in a way the air can’t escape with it and it gets trapped
Click to expand...
If the plaster dries out to fast, high suction or heat, you get crazing and the plaster will be soft. The water is drawn from the material before it sets and stops the crystal growth in the Gypsum.
 
Which is it perlite or vermiculite? Vermiculite holds water and doesn't give it up easily. Often used to insulate chimneys with liners - not a good choice, holds water and eventually soaks thru' brickwork.

Maybe in bonding it holds water then releases and/or blebs the skim? Definitely won't dry out in the same way as the gypsum.
 
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