How much cure time does an oil based polyurethane floor finish need before I cover it with rosin paper and start hanging doors and running interior trim? I’m talking about Varethane on 1200 sq. feet of new white oak in a climate controlled house.
We just now (Thursday) put down the last coat and would like to stat hanging doors on Monday. Any and all advice is welcome.
Thanks,
Huplescat
Replies
a week from this monday I take it...
full week cure time...
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I like a week, but often settle for three days...
It is a variable answer too, because this is dependent on temp and humidity.
When the air is extremely humid, the moisture is filling the spaces between air molecules, so there is less space available to uptake the VOCs that are escaping as the carrier evaporates.
When the temp is cool, there is less energy available to cure the chemical and evaporate the carrier.
So the worst time of year for this is early spring in an unheated house.
Best time is late suimmer/early fall when all is warm and not too humid.
Best of all is a conditioned house with controled temp and humidity.
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LOL
So, uh, whats in that space between the "air molecules"?
Edit: I see..moisture is.
never mind.
Edited 8/2/2007 6:40 pm ET by Sphere
Space - seriously! You learnt that flyboy! The air over the wing has more space between molecules than the air under the wings. the lower pressure lifts the aircraft.Higher temperature is from greater energy. The greater eneergy increases the activity of the individual molecules so they move around more, bouncing off each other and pushing/shoving and creating more space between them. A fluid has less space than a gas and the solid version of the same material has even less spacce between molecules.But even the nice solid gold in your teeth has spaces between its molecules.
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I know, I just took a chortle to the "space" between air and Non -air molecules..cuz, Space is more of everything, than anything at that level of scrutiny.
Huplescat,
Too bad you didn't shellac it,, you could be hanging doors that afternoon.
I know you wanted the softer finish that poly gets so that when it get's scuffed over time you have to completely strip it in order to get a nice finish..
plus you wanted to pay more for your finish and not have as durable or deep looking shine..
Sorry In case you didnb't notice I like shellac ;-)
Thanks all.... I’m a trim guy, forced by cruel economic contingencies to try and do pretty much everything. I can do seven stage crown with egg and dart wall base in an octagonal room, but I don’t know squat about finishing floors.
Huplescat
You know more than squat now though. It is dangerous to come in here with a question, you can't get out without learning!
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The main thing that you will have to avoid is marking the new floor finish with "sharp" objects that concentrate weight like ladder feet, etc. Our painters came in 7 days after we completed refinishing the floors, and the painter's ladders made little "puddle" looking marks in the floor finish (through the canvas) where the ladder feet pushed the still soft poly finish around with weight and movement.
I later learned that poly takes about a month to harden sufficiently to completely avoid this. I think that if we had put heavy cardboard or 1/4 inch hardboard under the ladders, we would have avoided the problem.
Mike D
Sometimes that is from going too fast with the actual finishing. Other than evaporation of carrier, Poly cures hard from contact with oxygen and or moisture in the air. It is a chemical reaction. If you isolate it from the air, it slows down the curing process a great deal.So what can happen is that the first coat goes on and seals the wood. it kicks pretty quick, being exposed from both directions.Then the second coat goes on and it is only exposed to air in one direction, so it cures much more slowly. It is far to common to see it harden off on top only, while still soft under when this second coat gets covered by the third coat which totally isolates the second from oxygen, other than what pecolates through to it from underneathe in the wood. So the third coat cures off in three days, the first coat is already pretty well cured, but the second caot is still taking another week to a month to cure, sometimes never getting as hard as it could if it were given several days to harden off before doing the third coatWe test that second coat with thumbnail before doing the third coat.
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I seem to recall that poly directions usually say "recoat within x hours" "If more than XX hours, sand lightly before recoating"
Is that not true? If true, seems like a real pain to wait a week for the second coat to cure.
What's your expeience?
Thanks..
I ALWAYS sand between coats. I don't know any way to get a baby bottom smooth finish otherwise.but the reason for that advice from the manufacturers is this -
If you are re-coating within a day or less, the first coat is still not fully cured, so you get a very good adhesion, or chemical bond as the new coat re-activates the previous coat. Bonding is their point, not final hardness.When you wait for full or nearly full cure before applying the next coat, you are adding it onto a harder, slicker surface, and with less chemical bonding, so it is important to increase the mechanical bond by giving 'tooth' to it with the sanding etching microscopic teeth into the surface.Pretend that YOU are the new coat of finish.
Will you stick to the floor better if it has just been (a)lightly sanded or (b)heavily waxed?That is the reason for sanding between coats - plus there will always be craters, dust, and other tits of stuff settled into coats that need to be sanded off before the next goes on. Fail to do that and it will keep getting worse with each coat. So I sand, then vacuum, then tack, then the next coat.
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We only did two coats because the second coat took so long to fully cure. It was "new" in that it was picked up from Lowes the day prior to putting it down, and all instructions were followed to the letter.
Perhaps the chemistry for that batch was slightly off, but it sure didn't cure to full hardness for a month.
Mike D
What brand? Something not right when only two coats take that long.
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Thank you very much... Mike D and Piffin for your comments 2 or 3 posts back. You gave me just what I was looking for.
Anyway, the finish looked great this morning. So now my mule-headed partner can see the cross-board gouges and chatter marks that he left with the drum sander, that I was trying to show him all along. He said there were "dimples" in the floor, and started pointing here and there. I didn’t know wether to laugh or cry.
To make a long story short, he’s back there now, on his own, re-doing the floor for free. I hope he gets it right but I’m not overly optimistic.
We went to Home Despot and rented a rectangular oscillating floor buffer with red pads and 36 thru 100 grit paper. I told him to get the 4 head random orbital instead, but he was already pretty close to the brink and there was only just so much I could do with him. His wife just got back from a week on Hilton Head with her family, and now she’s giving him a hard time because she wants to be rich again.
Thanks again, also to Frenchy...
I was going to say Varathane, but I went to the paint shed and found that the stain that we used was Minwax, so, since I usually try to stay within one manufacturer's brand on a given task, the finish was very likely Minwax as well. No way to tell for sure, since the finish cans were all left open to dry and then to the land fill.It looks great now - lots of nice comments whenever we have people over, so we're happy, but it did take longer than expected to completely harden.
By the way, someone posted a note about the need to keep the floor dust moped, and I second that, strongly. Before we even redid the floors, I went to a janitorial supply place and bought a big hardwood floor dust mop and the spray to use with it. After a year, the floor still looks new with only a quick twice a week run over all the floors.Mike DAh, the little gray cells finally kick in. The poly was indeed Minwax. The reason that I have a full gallon of the stain still in the shed was because, on this floor, the Minwax stain turned the test piece pink. SHMBO said "Ich!", so I substituted a Behr stain that gave us the color we wanted.Now that could have been the cause of the slow cure time, since the different chemistries may have been incompatible.
Edited 8/4/2007 5:33 pm ET by Mike_D
Very likely. I think Minwax uses sterates thaat are not always compatible with other brands
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I had that problem once with a can of McClosky's. The first coat took over a week to dry. Bad batch.George Patterson
Rather than a single period of time I'll throw out that it's better to view it as a continuum. In a day you can probably get by with walking on it jingerly with stocking feet, but touch it with anything hard and you've got a scratch. In a month it's about as hard as it's going to get and in between the extremes is where most work gets done.
Personally, I'm easy on a floor so don't mind doing simple stuff after 24-48 hours and will even run base with the assistance of a clean new dropcloth runner for cushion.
It's much better to finish on thursday and have any construction start the next monday at earliest. Still, if other subs are involved they need to take off shoes and pad ladder feet. One builder fines their subs $100 every time they catch someone with street shoes in the house and it's a great way to keep everyone in line.
More than any other time, dust mop the floor at least once a day or more often if dust is building up or dirt gets on the floor. Any foreign material will scratch the floor under a persons body weight, especially if under a ladder leg.
Good flooring
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