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Zinsser primers - do I also need undercoat?

Discussion in 'Decorating and Painting' started by allthebuttons, 15 Aug 2018.

  1. allthebuttons

    allthebuttons

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    Zinsser’s primers (BIN, 123 and Cover Stain) all say in their technical docs that they can be painted over with any water-based or solvent-based topcoat.

    But they never actually use the word “undercoat”; they only describe themselves as primers.

    I’ve already primed a new wooden door with Cover Stain. Do I need a separate undercoat or can I move straight on to the (water based satinwood) top coat?

    Thanks
     
  2. Bilabong007

    Bilabong007

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    Hi,

    I'm by no means an expert, but figure you may want to crack on with this. My experience with bin and 123 is to proceed to topcoat and I have had very good results with oil based satinwood on top of both.

    One could assume it's the same for cover stain and water based satinwood in the absence of another users reply

    Maybe test a bit?

    Graeme
     
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  3. Nige F

    Nige F

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    I would concur (y)
     
  4. Gerrydelasel

    Gerrydelasel

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    The purpose of an undercoat is to get a an even coat of colour, since this affects the uniformity of of the top coat. Often a coat of Zinsser looks 'streaky', white in places, kinda wood-coloured (or whatever is underneath) in others. In that case you need undercoat to get everything the same colour, or those streaks may show through in the top coat. But it depends. Red paint tends to be the most translucent and needs a nice uniform undercoat, whereas black probably wouldn't. Similarly if you use Zinsser on a white object like a PVC window then you probably won't need undercoat since it still looks completely white with a coat of Zinsser. So it depends on what you're doing.
     
  5. allthebuttons

    allthebuttons

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    I’m painting wooden doors, and my plan is two coats of water-based white satin on top of the Cover Stain.
     
  6. Gerrydelasel

    Gerrydelasel

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    Then I think you'll need undercoat. It's cheap enough so why risk it.
     
  7. opps

    opps

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    Satinwood and eggshell don't technically need undercoat but as Gerrydelasel says, you may need to use an undercoat to obliterate the previous colour.

    Personally, I have never found a waterbased finish that I like (and thus my advice might be slightly prejudiced). I normally use oil based undercoats when I am forced to use WB finishes, purely and simply because WB paints have awful opacity. The major caveat being that you need to let the OB UC cure for longer, otherwise fisheyes may form in the WB finish.

    I have also encountered fisheyes when painting (WB) over BIN. One big advantage of BIN is that it fully cures in about 3 days. Waterbased paints typically take over a week and oilbased about a month.

    Unfortunately, BIN is a pig to work with if you care about the quality of finish. Additionally it is very hard to sand out brush marks. I tend to use it as a "problem" solving product.
     
  8. allthebuttons

    allthebuttons

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    Thanks for the advice!

    Can you recommend a good undercoat to use under white satin water-based paint?

    All the undercoats I can find are combined primer-undercoats, and I’ve already done the primer!
     
  9. opps

    opps

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    Primer/undercoats are waterbased. They can be used as a primer or an undercoat. Apply one coat to bare wood and you have primed it and undercoated it in one hit. If the wood had been previously painted (or in your case, primed), apply one coat and you have undercoated it.

    Personally I would use Dulux trade oil based undercoat, but that is just my preference.

    If you want to stay with waterbased just apply more coats of any old primer/undercoat until you are satisfied that you can see the wood grain grinning through any more. The Dulux trade primer/undercoat isn't too bad at obliterating but it is difficult to sand back any brush marks. Water based paints tend to clog sandpaper.
     
  10. allthebuttons

    allthebuttons

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    Could I just do a second coat of the Cover Stain since I’ve already got it? In places where I’ve gone over twice it seems to hide pretty well, and it sands easily.
     
  11. opps

    opps

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  12. allthebuttons

    allthebuttons

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    Thanks very much opps. I think I’ll just use 2 coats of cover stain this time so I can finish the tin. Next time I’ll buy a combined primer/undercoat.
     
  13. opps

    opps

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    Given the cost of coverstain, I wouldn't buy it to use as a bog standard primer and undercoat, but as you say, you already have it, so sure use it.
     
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