Scrub down and repaint?

[RobMit]

I have an area around one corner of my house where the paint (over render) has flaked badly (see attached photos below). The render does not seem to have blown - it sounds solid when I rap it with my knuckles. Do you think it might be sufficient to just scrape/brush off the loose paint and repaint, or is more extensive work likely to be required (ie redo the rendering)? The underlying surface doesn't seem chalky to me, but even so, would Sandtex stabilising solution or similar help?

Any advice would be greatly appreciated.

TIA,

Rob

 

[Mr diy a lot.]

Was probably rubbish paint combined with time and weather. Just scrape back get some high quality masonary paint, slap it on and the job is a good un.

 

[JohnD]

Scrape it off.

You'll need a mist coat.

On render I prefer two, well-thinned.

 

[RobMit]

Thanks for your answers. After I first posted, I checked the render more thoroughly, and discovered that there was an area where the render had blown, contrary to what I had thought. That has been removed (cut back to firmly attached render) and replaced. I've scraped off all the loose paint, so that now the remaining paint seems quite firmly attached. However, it is in lots of separate patches; would it be necessary to scrape it all off, back to the sand/cement render, to avoid the existing paint giving an uneven surface once I repaint it, or would the new paint tend to level it off?

And JohnD, just to make absolutely sure that I've understood you correctly: you're recommending applying two successive mist coats (diluted 50/50 ?), before the unthinned top coat (just one, or two of those as well?)

Edited to add: I'm also thinking of using Zinsser Peel Stop (which I've seen recommended elsewhere) before repainting.

 

[JohnD]

Yes, I think you'll find the first mist soaks in so fast that it disappears. You'll know when you have killed the suction, when it no longer pulls the moisture out of your brush it is ready for a topcoat.

 

[opps]

And JohnD, just to make absolutely sure that I've understood you correctly: you're recommending applying two successive mist coats (diluted 50/50 ?), before the unthinned top coat (just one, or two of those as well?)

Please don't do a 50/50 mix.

In all of the years that I have been decorating, I have cannot recall any manufacturer recommending thinning paint by 50%.

Water based paints through a process called coalescence. As the water evaporates off the molecules shrink down and bond. If the substrate is too porous, the water is sucked in to the substrate and the process is disrupted.

If you thin the paint too much, the same process is bound to fail.

One adequately thinned coat should be sufficient. You should not need two.

Not an issue at this time of year, but the curing will potentially fail if the temperature drops below 5 degrees C because of the formation of ice crystals.

 

[RobMit]

Ok, thanks. 50/50 was just a guess on my part, and I'm not sure whether JohnD noticed that part when he replied. I haven't yet done it, but I've seen another reply of yours (ie opps) where you quote Dulux's Weathershield advice to dilute up to 1 part water to 5 parts paint, which I assume would also apply for the Sandtex that I'll be using.

 

[opps]

Ok, thanks. 50/50 was just a guess on my part, and I'm not sure whether JohnD noticed that part when he replied. I haven't yet done it, but I've seen another reply of yours (ie opps) where you quote Dulux's Weathershield advice to dilute up to 1 part water to 5 parts paint, which I assume would also apply for the Sandtex that I'll be using.

From image number 2, I can see a crack in the render. Have you managed to deal with that?

The build up of paint looks pretty minimal, that is to say, it hasn't been painted many times. If you have access to a decent pressure washer, you could use that to remove the loose paint. If the paint is only a couple of coats thick, it is unlikely that when you apply the new paint, the old stuff will generate too much of a step.

A common reason for paint blowing on render is water ingress, via cracks etc.

 

[RobMit]

Yes, that crack (on the RH top corner of image 2) was eliminated when the render was replaced in that area.

Many thanks for your advice.

 

[opps]

Yes, that crack (on the RH top corner of image 2) was eliminated when the render was replaced in that area.

Many thanks for your advice.

Best of luck.

BTW, having spoken to Dulux Trade tech support before, they have told me that most of their waterbased paints can be diluted by up to 20%.

The 1 part to 5 is probably the easiest for them to explain on the tin. In reality, that means 16.6% water Vs paint. I tend to aim for 10% water, the thinner the paint, the more it splatters.