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Thread: Polyurethane dry/cure time

  1. #1
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    Polyurethane dry/cure time

    I already searched on this forums and have not find an straight answer or consensus.

    I'm using Minwax products, Oil Based Polyurethane, and I'd like to know:
    - How much time does it take to dry in order to give a slight wet sand to remove dust and bubbles?

    - How much time does it take to fully cure in order to rub it out buffed and polished?

    Thanks in advance,

  2. #2
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    Oil based finishes dry/cure in two steps. First the thinners evaporate and the finish becomes tack free. Then oxygen begins to combine with the varnish and curing begins. It's the curing that makes the finish hard, durable and develops full adhesion. This curing process can take 3-4 weeks depending on environmental conditions and how thick a film was applied. As long as it is emitting and odor, it's still curing.

    You can lightly sand with a 24 - 48 hour drying time. "Rubbing out" should not be attempted until the full cure time has elapsed. But keep in mind that urethane is added to finishes to make them more resistant to scratching. Sanding, or rubbing out, is scratching. Poly varnishes will never be any more glossy that they are right off the brush.
    Howie.........

  3. #3
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    You haven't said where you are located so its hard to give an answer. It does depend on humidity and air temperature. As Howard said 24+ hours should be good this time of year for most of the US. In my experience, the first coat will dry faster than the following coats.

  4. #4
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    Thank you both for your responses.

    Here's an average of 77° to 95° on the months without "R", with rarely more than 20%-40% humidity. Things get dry pretty quick.

    I'm aware of how polyurethane reacts in term of the final finish and that you can't get it very glossy. I need it satin anyway

    Well... about the curing time... heck that's too much... I guess that's why we should not use "polyoneverythane" as I read somewhere.

    This is for a closet, and I can't think either of having to wait a month to deliver the project or installing it and going back to the client site, then removing doors and drawers to rub it out.

    I'm just an amateur and don't have a spray gun..... yet... so I have to stick with brushing finishes and the polyurethane had worked fine for the few jobs I've done.

    What else could I use that cures faster?
    I'd like to use Lacquer, but I almost can't find anything about good non-spraying techniques... what else?

  5. #5
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    The non-poly varnishes are a little easier to apply and often give decent results right of the brush or wipe on rag. They still take about the same time to cure though. Look at Behlen's rockhard or Waterlox original.

    Shellac can be brushed or padded on.

    Target coatings had a brush-able finish but I can't recall what it is at the moment.

    Joe
    For best results, try not to do anything stupid.

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    "So this is how liberty dies...with thunderous applause." - Padmé Amidala "Star Wars III: The Revenge of the Sith"

  6. #6
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    >>>>> This is for a closet,

    Let me make a couple of points. First, the issues are not with polyurethane, the drying and off-gassing issues are with any oil based finish.

    Second, you should never use an oil based finish on anything like a closet that will contain cloth or clothing or any foodstuffs that may by in unsealed containers. The off-gassing goes on forever but at a very slowly reducing rate. An enclosed space will allow the gas and resulting odor to be concentrated and the odor will affect the above items almost forever. My recommendation is to use shellac or a waterborne acrylic clear finish. These do not off-gas once dry.
    Howie.........

  7. #7
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    Oops..... and that gas expeling problem is also present in say, Lacquer?

    Where I live, everybody uses lacquer for closets.... and kitchens, too, though, in kitchen the tops are always melamine.

    About Shellac, I've always know shellac as a glossy finish, after it cures and being rubbed it shines like the sun.
    I was asked to give a solemn satin finish for this one.
    Can I get shellac to be non-shiny?

  8. #8
    I get a satin finish with shellac by hitting it with 0000 steel wool or a synthetic pad equivalent. Once I knock the shine off of it I will give it a couple coats of paste wax to warm up the look. YMMV.
    “If liberty means anything at all, it means the right to tell people what they do not want to hear.” -- George Orwell


  9. #9
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    You can also add Shellac Flat to the shellac and make it anything from semi-gloss to dead flat.
    Scott

    Finishing is an 'Art & a Science'. Actually, it is a process. You must understand the properties and tendencies of the finish you are using. You must know the proper steps and techniques, then you must execute them properly.

  10. #10
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    >>>> and that gas expeling problem is also present in say, Lacquer?

    No, the long term off-gassing is only a characteristic of oil based finishes. Lacquer is fine.
    Howie.........

  11. #11
    +1 for an waterborne acrylic topcoat. Shellac is certainly easy to do, quick to dry, and can be rubbed down to a warm satin. In fact, even unrubbed, it's not as glossy as the Minwax PolyU will be. However, it'll get dinged and scratched easily. If any shelves are going to be used for belts or shoes, it might be problematic.

    Minwax Polycrylic might be a good choice for you.

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