Polyurethane issues - Woodworking Talk - Woodworkers Forum
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post #1 of 8 Old 09-04-2019, 07:17 PM Thread Starter
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Polyurethane issues

I'm renting a house from a couple I know, and am redoing the floors in the house. First room turned out amazingly well. Second room is getting there. While I've sanded them down, and applied the first coat of polyurethane and let it dry for 24 hours, I started in on the second coat. The first can of polyurethane, I will add, was from when I did the first room in the house and it did sit for about a month or so, not sure if this will be the issue or not.. anyways. Halfway through the second coat I ran out of polyurethane in my gallon and opened a new can that I purchased this morning. Now that its drying, I'm getting two different finishes. Can you help me to explain how I can fix this issue? If I add a 3rd coat to the duller part, will that help? Or should I just continue with my 3rd coat over the entire floor?*
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post #2 of 8 Old 09-05-2019, 01:41 AM
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It's just like paint. It is always possible to have slight variations in the sheen, especially when using a satin finish. If the 2 cans are not from the same batch number, you would do well to mix them together before applying if you want it all to be exactly the same. For future reference, I know it's too late now. For the present, your best bet is probably to coat the entire floor with what you've got now. If you won't have enough and you will need more, I would suggest mixing it together in a 5 gallon bucket to get an even sheen throughout.
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post #3 of 8 Old 09-05-2019, 05:46 AM
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Some polyurethane finishes come in different sheens: gloss, semi-gloss, satin, flat, etc. They start out glossy, but add flattening agent to the finish to achieve the desired effect.

Sometimes the flattening agent can settle to the bottom, so you end up with a glossy finish on top, and a flatter than expected finish on the bottom. The trick is to mix the polyurethane very thoroughly before you use it, to make sure the flattening agent is well-blended throughout. Be patient and stir very slowly, to avoid introducing bubbles.

As mm_wood pointed out, the sheen can vary between batches. If it is too glossy, then you may be able to fix it by applying it to the rest of the floor to even the coat, go back and gently sand with a fine grit (say 220 or 320), and then reapplying another coat of flatter finish on top of it to even it out. If it is too flat, then applying another coat of glossier might help, but the flatter finish is still underneath. Yeah, sanding it off sucks.

You are spending a lot of time and effort, so take extra time to test on scrapwood, and then in an unobtrusive corner first.
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post #4 of 8 Old 09-05-2019, 08:18 AM Thread Starter
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@mmwood_1 @Tool Agnostic thank you both for replying. Will take both of your advices and do what I can!
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post #5 of 8 Old 09-09-2019, 05:03 PM
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Quote:
Originally Posted by Ktbug123 View Post
I'm renting a house from a couple I know, and am redoing the floors in the house. First room turned out amazingly well. Second room is getting there. While I've sanded them down, and applied the first coat of polyurethane and let it dry for 24 hours, I started in on the second coat. The first can of polyurethane, I will add, was from when I did the first room in the house and it did sit for about a month or so, not sure if this will be the issue or not.. anyways. Halfway through the second coat I ran out of polyurethane in my gallon and opened a new can that I purchased this morning. Now that its drying, I'm getting two different finishes. Can you help me to explain how I can fix this issue? If I add a 3rd coat to the duller part, will that help? Or should I just continue with my 3rd coat over the entire floor?*
Assume the same brand? Urethanes do have different Sheen's, at worst, you'll do two full costs with a common sheen product. You may also call the manufacturer of place you bought from and ask them? Tom k

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post #6 of 8 Old 09-09-2019, 05:43 PM
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KT - this is a little late for your issue now, but, when finishing
or painting large surfaces where two or more cans of finish will
be used, "boxing" is strongly encouraged for a satisfactory finish.

"Boxing" is the term used to ensure color and texture consistency
in a paint or finish. This is when you combine all the material you'll be using
into one large container, mix it well and return it back to the original containers.
This is especially important when painting large surfaces such as floors
or multiple walls in a large room.
paint and finishes have the amount of square feet it will cover per gallon
on the label. try to estimate the square footage for your project and add
a little more in case you do run out.
if a "non-gloss" type of finish is used, it has solids in the liquid to give the
finish that sheen when dry. when it sits for weeks, months or years in the can,
all the solids sink to the bottom and must be THOROUGHLY mixed back into
the liquid to achieve the finish it was designed for.

.

.
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post #7 of 8 Old 09-10-2019, 12:49 AM Thread Starter
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@John Smith_inFL

And @ the above comment reply as well, I dont see a name to be able to tag the person.

John- I wasnt made aware of boxing until after this issue, and my first can of poly was gone. I will definitely keep it in mind for future projects and do just that!!

@ the untaggable reply- My polyurethane I used was minwax, semi-gloss quick dry, both cans were exactly the same except as noted, purchased at different times and one sat for a while.

However, I did go ahead and apply a 3rd coat over top of the entire floor covering the dull and shiny differences (halfway thru the floors) and after it dried it dried evenly and you cant even tell there was an issue!! Such a HUGE relief as I was not looking forward to having to do anything like strip or sand them all back down!

The project is waiting on the 4th coat and these old oak floors will be marvelous!!

Thank you both very much for taking the time to respond.
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post #8 of 8 Old 09-10-2019, 12:51 AM Thread Starter
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Adding that I did go ahead with a 3rd coat over the entire floor and it evened out! You cant tell there was a difference and these old oak floors look marvelous!
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