pimples, thought i was done with those in my teens!!

[trowelmonkey1]

boy oh boy, i have a good day and then..well a day to balance it out.

doing a bathroom, walls are made up of many materials, blockwork, friable render, skim, artex on top of that, and vinyl paint on top of that, oh and some tile adhesive!!

i've cut away all blown stuff, and covered the lot with WBA (good for friable backgrounds and not sure how PVA likes that kinda suction?), i then coated the walls with a tight coat of bonding and scratched it up, so far so good one thinks.

came to skim this afternoon and it goes of like a rocket and i get bubbles all over the place, why so chaps?

from time to time i get pimples/bubbles but never really know why, seems to happen without reason most of the time and gets on my ti*s not knowing why it happens.

 

[noseall]

Charlie bonding (now known as thistle bonding) provides a reasonably tight, dense medium for skimming. It MUST hydrate before skimming particularly if the substrate (backing) is low suction.

It does not have to be bone dry, but it does need to shed the initial water content and be in a position to absorb moisture as opposed to be shedding it.

Scratch it with a nail poked into the poly-float and let the stuff go hard, but not 'pale pink' dry.

Ive suffered with blisters too.

 

[marshman]

Is your memory going noseall ( Charlie bonding ) or maybe that's local one, how about Carlite bonding,

trowelmonkey1, did you seal your wall up the day before as it sounds like you had very high suction,
I've no idea why they happen they just pop up where you least expect them.

 

[noseall]

My nick name for carlite is charlie.

p.s. it is a LACK of suction that causes blisters.

 

[Micilin]

IMHO it can be either - a high suction background, like bonding left a day or so and very dry, leads to the finish drying as soon as it hits the bonding - it forms a skin over any small holes, rather than going into them, giving blisters.



If you catch it right, be it a hard trowel, buit not too soon, you'll get rid of them. Failing that, , when it's gone off -even next day in the morning, cut them polish with the trowel, not ideal, but there you go.

 

[trowelmonkey1]

hello boys!

thanks for the replies, nice to know i'm not the only one scratching my head over pimples!

quick summary:

composite background, applied lashings of Wickes (knauf) bonding agent the day before.

applied tight bonding coat this morning, about 3-5mm this morning and devil scratched.

went hard and dark brown by the time i got to it this afternoon, skimmed first wall, LOADS of bubbles, went to second wall with a wetter mix and SOAKED the wall with about 3-4 litres of water as it seemed to keep drinking it, many fewer bubbles.

have been removing most bubbles by hard troweling and the last few i'll remove tomorrow but would LOVE too know why this happens.

THANKS again fellas

 

[joe-90]

The main reason you get them is that you are trapping the air in the little cavities with your multifinish. When you press the trowel on you compress the air and when your trowel passes and the pressure is released the air pressure decompresses and comes up as a bubble. If you hold your trowel at a steep angle and put very little skim on you can drive out the air as your trowel passes over. Then just skim as normal.

 

[trowelmonkey1]

hi joe! thanks for the contribution!

was back at the job today trying to finish off, had 2 more walls to do, 1 was artex only underneath and the other the same composition as the 2 trouble walls.

i went at the bigger of the 2 first which had only artex underneath it, wet it down until the water ran off the bonding coat i'd put on the day before (i know not ideal but i ran out of time the previous day) then skimmed as normal, had far fewer bubbles so was thinking the suction (too much) on the other walls was what got me.

so then went at the last wall which was the same as the trouble walls except this time i wet down again until water ran off bonding and slapped as thick a coat of multi-finish as i could get on, was perfect!! had too much time on it actually and not a single bubble, so not sure how i fixed the problem now, was kinda thinking that applying it so much thicker than i had been was the fix but your suggestion says the contrary.

CONFUSED!

 

[noseall]

CONFUSED!

Blistering, i.e. the blisters that do not compress when run over with a trowel are appearing because of almost zero suction and a substrate that is still hydrating.

A high suction background will receive even the most aerated mix. It may snap crackle and pop whilst the skim is being applied but any bubbles appearing can be flattened.

 

[trowelmonkey1]

thanks noseall...but seems like i had both going on on the same wall!

had pimples that would compress with troweling, had to try and hard trowel them off towards the end, also had some snap, crackle and pop when i was putting the skim on!

STILL CONFUSED!

like i said, completley covered the substrate with WBA but i'm really not convinced by it's ability to control suction.

when i did the 3rd wall, a day later after applying bonding, wet it down thouroghly and applied skim thick as i could get away with and without much pressure, ended up with loads of time to work with it and not a single bubble.