Repainting a concrete windowsill - Zinsser paint not sticking.

Hi all, I've got a question about the best paint to use for a concrete windowsill. I've recently repainted two concrete sills that are adjacent to each other with the Zinsser All coat exterior water based satin which I thought was supposed to stick to everything...

One sill is perfect, the other though has already peeled once, and despite my efforts cleaning all the loose paint, sanding it back etc., before repainting, the paint has once again started to lift/peel.

What can I do to prevent this? Should I use a solvent based paint? Primer? A different paint (if so, what?), wait until it is warm and dry?

I'm slightly at a loss as it's just the one windowsill which is affected.

Grateful for any advice / thoughts

Comments

  • maisie_cat
    maisie_cat Posts: 2,055
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    When you say recently, do you mean in the winter? I have used that paint many times but it has a working temperature & humidity range like most paint.
  • Emmia
    Emmia Posts: 2,953
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    edited 22 January at 9:32AM
    When you say recently, do you mean in the winter? I have used that paint many times but it has a working temperature & humidity range like most paint.
    It was in the winter, but both windowsills were painted at the same time - at temperatures which the label said were fine to paint in, and on dry days.

    The paint on only one sill has failed, twice after very careful preparation which is why I'm a bit mystified.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    edited 22 January at 11:19AM
    Emmia said:
    Hi all, I've got a question about the best paint to use for a concrete windowsill. I've recently repainted two concrete sills that are adjacent to each other with the Zinsser All coat exterior water based satin which I thought was supposed to stick to everything...

    One sill is perfect, the other though has already peeled once, and despite my efforts cleaning all the loose paint, sanding it back etc., before repainting, the paint has once again started to lift/peel.

    What can I do to prevent this? Should I use a solvent based paint? Primer? A different paint (if so, what?), wait until it is warm and dry?

    I'm slightly at a loss as it's just the one windowsill which is affected.

    Grateful for any advice / thoughts

    That's strange, Emmia.
    You say you have 'repainted' these cills? What was on them before, and what preparation did you carry out?
    Zinsser 'AllCoat' is pretty impressive stuff, but it still needs some proper prep to work fully.
    It does sound as tho' there is 'something' on that existing cill that's rejecting the Zinsser - and would do so to anything you apply. If it was bare concrete, for example, could anyone have applied silicone water-repellent or anything like that to it at some point?
    I tend to become a bit fixated on various building products at times, and my most recent go-to is SBR which is a water-based primer/sealer/waterproofer. I did some North-facing concrete cills last summer which were peeling in many places, but had some paint patches still secure. After scraping off all the loose, I wire-brushed it all, and feathered any remaining paint edges. I then gave the bare concrete sections a good coat of SBR, and over-brushed it thinly on it all. Tobesuretobesure, I then added a glug of SBR to the first coat of charcoal masonry paint that I applied, and then a couple of neat masonry coats on top of that.
    If Zinsser AllCoat is peeling, I can only surmise there's summat amiss with the surface below. Unless it was weather/temp-related as asked above, and perhaps that cill is on a colder face, out of the sun, anything like that - a couple of degrees made the difference?


  • Emmia
    Emmia Posts: 2,953
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    Emmia said:
    Hi all, I've got a question about the best paint to use for a concrete windowsill. I've recently repainted two concrete sills that are adjacent to each other with the Zinsser All coat exterior water based satin which I thought was supposed to stick to everything...

    One sill is perfect, the other though has already peeled once, and despite my efforts cleaning all the loose paint, sanding it back etc., before repainting, the paint has once again started to lift/peel.

    What can I do to prevent this? Should I use a solvent based paint? Primer? A different paint (if so, what?), wait until it is warm and dry?

    I'm slightly at a loss as it's just the one windowsill which is affected.

    Grateful for any advice / thoughts

    That's strange, Emmia.
    You say you have 'repainted' these cills? What was on them before, and what preparation did you carry out?
    Zinsser 'AllCoat' is pretty impressive stuff, but it still needs some proper prep to work fully.
    It does sound as tho' there is 'something' on that existing cill that's rejecting the Zinsser - and would do so to anything you apply. If it was bare concrete, for example, could anyone have applied silicone water-repellent or anything like that to it at some point?
    I tend to become a bit fixated on various building products at times, and my most recent go-to is SBR which is a water-based primer/sealer/waterproofer. I did some North-facing concrete cills last summer which were peeling in many places, but had some paint patches still secure. After scraping off all the loose, I wire-brushed it all, and feathered any remaining paint edges. I then gave the bare concrete sections a good coat of SBR, and over-brushed it thinly on it all. Tobesuretobesure, I then added a glug of SBR to the first coat of charcoal masonry paint that I applied, and then a couple of neat masonry coats on top of that.
    If Zinsser AllCoat is peeling, I can only surmise there's summat amiss with the surface below. Unless it was weather/temp-related as asked above, and perhaps that cill is on a colder face, out of the sun, anything like that - a couple of degrees made the difference?


    I removed all the loose paint, sanded to get it as smooth as possible, thoroughly brushed off any dust etc. 

    The unpeeling cill is in more of a shadow, if anything, but it might also be more protected - I'll have a look at the SBR, but might wait for the weather to warm up before re attempting painting.

    The cills have been painted before, but what with is unknown, as it was before we bought the place.

    I have considered trying a tester pot of Sandtex masonry paint instead to see if that will adhere better.

    Thank you
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    It's a mystery indeed.
    Tbh, I would (and do) just use masonry paint (yes, Sandtex!) for my cills. 
    Yes, I'd wait until more favourable weather too :smile:
  • ChilliBob
    ChilliBob Posts: 2,041
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    For an sbr you could use Zinzzer peel stop - it's suitable for outside and works well. Means you'd stick to products from the same 'system' so to speak.

    Zinzzer are very good with advice if you email them too, I have done a couple of times. 
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