Patchy coverage on repaired plaster wall

[di9]

What am I doing wrong? I've read a few posts on patchy paint, but I'm not sure what the exact cause is for me.

I'm trying to paint this kitchen wall white. So far, I've:

. Applied 2 coats of watered down paint (to the consistency of milk) to the entire wall which I understood from Googling served to prime the surface. (The patches were so obvious, I applied the second coat.)
. Applied 3 or 4 quite thick coats of undiluted paint to each patchy area with a brush - that ended up covering about 60% of the wall.
. Applied 1 coat of undiluted paint to the entire wall with a roller.

But still the patches are visible, although much less so than to begin with:

The plaster isn't new, and the wall looked a bit like this other one before I started painting:

The property is in Spain, and these are the paints I've used, with both seeming to cover just as badly:

I don't remember ever needing so many coats. Is it just poor quality paint? Should I have primed with something else? How can I fix this?

 

[sparkwright]

The diluted paint, every time, was preparation as far as I am concern.

Nearly every job needs a minimum of two undiluted coats, if not three.

That said, I've no idea what that Spanish paint is like.

Maybe you could try a few more coats on a small area first, to see if you're wasting time.

If not, you need a thicker paint, or - and hopefully not - some sort of stain block, that covers things.

 

[di9]

The diluted paint, every time, was preparation as far as I am concern.

Nearly every job needs a minimum of two undiluted coats, if not three.

That said, I've no idea what that Spanish paint is like.

Maybe you could try a few more coats on a small area first, to see if you're wasting time.

If not, you need a thicker paint, or - and hopefully not - some sort of stain block, that covers things.

The patchy areas have had 4 or 5 undiluted coats, which is why I'm scratching my head. Good to know diluted paint is a way to prep though. Thank you.

I'm beginning to think both paints I tried are just really bad quality, but confirmation from someone would be very helpful.

 

[sparkwright]

The patchy areas have had 4 or 5 undiluted coats, which is why I'm scratching my head. Good to know diluted paint is a way to prep though. Thank you.

I'm beginning to think both paints I tried are just really bad quality, but confirmation from someone would be very helpful.

Sorry, I mis-read some of your post, and got muddled up with diluted and un-diluted. My brain can't cope like it used to.

 

[securespark]

My brain can't cope like it used to.

You have my genuine sympathy.

 

[securespark]

That BASIC Matt white paint looks cheap. The best way is to check the price.

I always use 2 coats of Dulux Trade watered down on naked plaster, then a couple of coats of undil paint.

Leroy Merlin sells Dulux, but I don't think they sell the trade version.

 

[di9]

Sorry, I mis-read some of your post, and got muddled up with diluted and un-diluted. My brain can't cope like it used to.

That BASIC Matt white paint looks cheap. The best way is to check the price.

I always use 2 coats of Dulux Trade watered down on naked plaster, then a couple of coats of undil paint.

Leroy Merlin sells Dulux, but I don't think they sell the trade version.

Thanks both of you for your replies.

I think both paints are probably not up to scratch - I didn't buy them so I can't be sure.

It's looking like I'm finally one more coat away from getting a uniform finish, so that's about 6 coats. But on the second wall I pictured, which joins to the first wall and was in the same sort of condition, 2 or 3 coats seem to have done the job. So I have no idea what caused the problem on the first wall.

It's academic now, but if anyone knows the reason, I'd love to know!

 

[opps]

There is a lot of really, really bad advice on the internet about thinning paint. I do not understand why those people think that they know more about the paint formulation than the manufacturer. Emulsion cures through a process called coalescence. As the water evaporates off, the molecules bond down together. It the substrate is very porous (eg new plaster), water gets sucked in to the substrate rather than evaporating off- hence watering down the emulsion- it takes into account the water sucked into the plaster and then allows sufficient water to evaporate into the room.

A porous surface has a high level of "suction" (ie. it sucks in the water from the paint). A correctly thinned paint should deal with that. A paint that has been over thinned will do little for the level of suction.

My advice would be to read the manufacturer's advice and not someone on youtube/etc. If they say dilute by 10%, trust them. They made the paint.

I suspect that your problems were down to stoopid internet advice...

Sorry, I am not intentionally being confrontational, but as a decorator, I have turned up to jobs where the customer did the milk type coat, as I apply the second full fat coat, the roller pulls off the previous coat. I then have to sand the whole walls back to bare plaster and start again.

And seriously... don't get me started on advice from youtube plasterers to use PVA on new plaster...

 

[di9]

There is a lot of really, really bad advice on the internet about thinning paint. I do not understand why those people think that they know more about the paint formulation than the manufacturer. Emulsion cures through a process called coalescence. As the water evaporates off, the molecules bond down together. It the substrate is very porous (eg new plaster), water gets sucked in to the substrate rather than evaporating off- hence watering down the emulsion- it takes into account the water sucked into the plaster and then allows sufficient water to evaporate into the room.

A porous surface has a high level of "suction" (ie. it sucks in the water from the paint). A correctly thinned paint should deal with that. A paint that has been over thinned will do little for the level of suction.

My advice would be to read the manufacturer's advice and not someone on youtube/etc. If they say dilute by 10%, trust them. They made the paint.

I suspect that your problems were down to stoopid internet advice...

Sorry, I am not intentionally being confrontational, but as a decorator, I have turned up to jobs where the customer did the milk type coat, as I apply the second full fat coat, the roller pulls off the previous coat. I then have to sand the whole walls back to bare plaster and start again.

And seriously... don't get me started on advice from youtube plasterers to use PVA on new plaster...

You don't sound confrontational at all, and I appreciate very much you taking the time to offer an explanation, without which I would have been none the wiser. So thank you.

The internet is often a good source of info, but sometimes, as in this case, it probably wasn't. When that fails, I turn to the forums.

Your explanation makes sense. And I would have loved to have followed the manufacturers instructions, but in this case there weren't any for either paint. Not even a mention of basic things like drying time. So my mistakes were probably diluting too much when I primed, and using any old paint that was supplied to me. I wasted a lot of hours (actually days) there, but now I know. Thanks again.