Paint applying unevenly / separating out when using a roller on an interior wall

[Basildon_Bond]

Hi There

Just wondered if anyone has experienced this. I've started applying a standard matt emulsion paint (B&Q Valspar matt mixed to colour in the shop) to an interior wall using a short-pile roller. The wall was washed previously with sugar soap and then dried. For the first few seconds, the roller applies the paint in a nice consistent layer as expected, but then the 3rd 4th roller actions seem to pull the paint back off the wall - and leaves an uneven patchy layer with the older paint showing underneath. I've used valspar paints and these screwfix roller sleeves before on other rooms without any problems ? Do I persevere and hope the second coat will stick properly, or is there something fundamentally wrong with the paint and/or the wall surface ? I've attached pictures but the colours aren't well reproduced (sage green on an older yellow paint)

TIA

B

 

[Basildon_Bond]

Just a thought - I didn't wash off the sugar soap solution but let it dry on the surface. Could this be the cause ? If so - what's the best remedy? I've painted the majority of the wall surfaces (albeit badly) so it's not just a case of washing it off.

Thanks

 

[opps]

I am a decorator.

I am inclined to think that you have a "suction" problem, but I am only guessing.

When bare plaster walls are painted with a dilute coat of "regular" emulsion, the extra water in the paint allows the paint to soak into the very porous plaster. Ideally, if the water levels are correct, some water is sucked into the plaster, and then the rest evaporates off.

Water based paints cure via coalescence. The water evaporates away from the surface and the molecules bond down.

If the base coat was too thin or too thick, when you roll extra coats, the roller/paint will soften the base coat, and potentially pull the non-adhered paint off. Rollers will expel air and grab paint off the wall if that paint is not properly adhered.

If it was paint over new paint over new plaster, it might be the case that the previous coat was one of those "contract" paints- they are designed to deal with potentially wet plaster. They are (potentially) a mare.

They do not reduce the level of suction and increasingly, I find myself working in properties where they were used by people that sold themselves as being a decorator.

Those praints are cheap, and yes, on new plaster, they cover well... but....

 

[RrogerD]

What was the previous coat? What it a vinyl or a gloss finish perhaps?

 

[Basildon_Bond]

Thanks both. Not exactly sure what the previous paint was; it was done by a decorator several years ago - but I know that it was matt finish paint - same as the paint I'm trying to apply now.

 

[Paulintheprocess]

Sugar soap definitely needs rinsing off, it leaves a residue that can stop new paint bonding properly, and what you’re describing looks a lot like poor adhesion rather than a bad roller or bad batch of paint.

If the wall wasn’t rinsed and you’ve already painted most of it, the usual fix is to wash a small test patch, let it dry properly and try another coat to see if it behaves differently. If the cleaned patch takes paint normally, you’ve found the culprit.

If it still pulls off, you might be dealing with an old contract matt or a very porous base coat, in which case a primer or a mist coat of regular emulsion can help stabilise it before you repaint.

 

[Basildon_Bond]

Thanks PaulTP, QuantumF.... Have sanded down the walls to smooth the rough texture and have washed them down. Waiting for them to dry before I do a test paint.

 

[sparkwright]

How did it go?

 

[Basildon_Bond]

How did it go?

So I washed any trace of the sugar soap off the walls and sanded down when it had dried- because the gloopy paint had left the surface pretty uneven. The roller and brush applied paint much better after that. The only puzzle is that - even in a couple of obscure places eg underneath the radiator - where I know I hadn’t applied any sugar soap- I still got a similar problem when brushing on the first coat. I checked what the old paint was and it was also matt valspar - so nothing unusual. Anyway - the main thing is that the second coat applied everywhere as normal and it now looks ok