Newly plastered ceiling sagging

qtlc

Hi. Any plasterers out there? We got our bedroom in our bungalow replastered on the 14th May. We started decorating on the 29th and have had some problems with the ceiling. We've painted the walls and ceiling with B & Q new plaster paint which is supposed to prepare the surfaces for painting. When painting it to the ceiling the plaster seemed to come off on the roller in places. We got our plasterer back and he repaired the 3 places where it was bad. This was last Saturday. Today we carefully painted the areas he repaired with a brush and noticed this evening that it's starting to sag in patches. Some look like very small air bubbles, some are much more noticeable bigger patches that sound hollow when pressed. He said when he came to fix it on Saturday that the PVA didn't adhere properly and that sometimes it just happens. The walls are fine, no problems at all and this is the 2nd room that he has done for us, the first had no problems. Can anyone help or suggest anything? Has anyone come across it before? I've been searching online but everything I've found mentions old plaster sagging, nothing about new.

foxwales

Plaster retains moisture for quite some time; therefore needs a good amount of time to try out. Applying new plaster paint to newly plastered ceilings has probably added to the weight of the plaster; including it's current water content resulting in the sagging.

Give the plaster a week or two to dry out thoroughly; if you see little bubbles or uneven surfaces; it maybe easier to sand these down using a fine sand paper and then applying a smooth over coat; such as polycell smooth over or use a light filler to achieve a nice smooth surface.

Once dry you are then ready to paint.

madeane

Definately sounds like problems with adhesion, what was on the surface of the ceiling before he plastered?

qtlc

A painted ceiling with cracks. Didn't seem to be anything out of the ordinary. Wondered if it was 2 weeks wasn't long enough before preparing the plaster but in the previous room we did we only waited 1 week (what he suggested). That was in October and we didn't have windows open for 2 weeks like in this room.

rdpro

sounds like the old ceiling must've been pretty dirty - I'd bet even a pva bonding coat wouldn't adhere to a greasy/tarry/dusty ceiling.

misgrace

Did you thin the paint down before you coated the ceiling?

qtlc

misgrace wrote: »

Did you thin the paint down before you coated the ceiling?

Yes quite a lot. It was "new plaster" paint from B & Q but was incredibly thick.

woodbutcher_2

It has "boxed" which basically means it has not stuck to the ceiling and is coming off.The only way forward IMO is to pull all the loose stuff off and redo it.I had one happen at my last place.Took a scraper to it and ended up scraping most of it off and reskimming.

misgrace

qtlc wrote: »

Yes quite a lot. It was "new plaster" paint from B & Q but was incredibly thick.

Hmmmm very strange, therefore it must be in the plaster finish like Woodbutcher said.

I can offer you a suggestion which worked for me along similar lines, admittidly it wasnt on new plaster, but was on a previously painted ceiling which I sanded down, then applied as a first coat a thinned emulsion in mat.

It was taken the paint the off as I was rolling, so what I did was, when it dried, sanded back the bits that had lifted, applied a light film of filler, sanded the filler down very gently.
I then got some oil based undercoat, thinned with white spirit, and brushed the UC on the filled/lifted bits, infact, I undercoated the whole ceiling, as there was other little bits that was coming away, so I thought I may as well do the whole ceiling.
I waited till the next day, and started again with a thinned first coat of emulsion, when dry, did my 2nd coat, still very slighty thinned, but it did the trick.

The UC is a flat finish, so the emulsion will take to it no problem, I undercoat loads of ceilings specially Nicotene ones,and never had any problems.
Just make sure if you do this, you must thin down your first coat of emulsion, it doesnt matter if the first coat is too thin, its best to be safe than sorry.:D

john_kent

When I did the bathroom , i was told to leave it 4 to 6 weeks before preping and painting. Does sound liek a bonding problem though