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I went to Ace hardware store to buy Varathane water base polyurethane. Store clerk told me that the polyurethane has to be thoroughly mixed before applying put them in the paint mix shaker. I came home and read the label and it says not to shake the can because it forms bubbles. How long do I have to wait until the bubbles goes away? Or do I have to return the product and get another one?

Thanks in advance

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If you bought any level of reduced-sheen varnish — satin, semi-gloss, semi-matt, matt — it has a matting ingredient (a very fine powder of some sort) which needs to be very thoroughly mixed into the liquid component to give consistent results. So if you bought one of these the clerk did the right thing, knowing that the matting agent could have settled to a dense layer at the bottom of the can since manufacture, and would be quite difficult to thoroughly redistribute by stirring alone (especially stirring by hand with a paint stick).

If you bought a full gloss finish however the clerk did not do the right thing, since simple stirring may be all that's required to mix the contents adequately for use. Some gloss finishes don't require any stirring.

Either way it's no biggie, since you can just wait for the bubbles to disperse prior to use — depending on how long it's been since you bought much of, possibly all of, the bubbles may already have risen to the surface and popped.

How long do I have to wait until the bubbles goes away?

Look in the can for bubbles. This'll take as long as it takes (but shouldn't take days if that's your worry).

Once you see no bubbles you're probably fine, but this is a fast-drying finish so it's quick to test and be sure. Brush a little onto a scrap (or the underside/backside of what you're working on), wait for it dry and examine it closely looking for very tiny pinprick bubbles which are the smallest and take the longest to go away.

Do note however that all finishes are prone to a little bubble formation during application. One way to combat this is to always ensure that the brush is dampened before dipping it in the finish; you'd use water in this case. With oil-based products you use mineral spirits or any equivalent.

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  • Nice little essay on bubbling - thanks.
    – Ast Pace
    Feb 2, 2023 at 23:28
  • @AstPace, ta very much!
    – Graphus
    Feb 3, 2023 at 7:53

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