Problems with 3rd Coat of Poly - Woodworking Talk - Woodworkers Forum

 
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post #1 of 6 Old 05-30-2013, 03:06 PM Thread Starter
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Unhappy Problems with 3rd Coat of Poly

Hey all - I'm having a issue with the 3rd coat of poly I put on last night and had a few questions. I figured I'd give a full background thus far so you know all the details. Questions and picture are at the bottom.

I have a large piece of butcher block I'm staining/finishing for use as a desk for my wife and I. This is my first time staining/finishing.

Prep
I prepared the block by sanding it with 120 and then 220 for a smooth finish. I then used the Minwax Pre-Stain Wood Conditioner, waiting 15 minutes and moved onto the stain.

Stain
I used one coat of Minwax Wood Finish (Red Chestnut), wiped off and let that dry for 24 hours.

Finish
I put on the first coat of Minwax Fast-Drying Polyurethane (satin) and let it dry for 12 hours, then lightly sanded with 220, and proceeded with the second coat of poly. I made sure to do light coats and followed my brush stroke the distance of the block. I let that dry for 12 hours as well and it looked fantastic. I figured I'd do a third coat for added durability (which I'm now regretting), so I followed the same steps as above.

When I came out this morning it did not look like the second coat. It's still quite tacky and I'm noticing "dry spots" and brush strokes.

Link to picture:
https://www.dropbox.com/s/52jxuc8sl5...4.37%20HDR.jpg

Q. Could this simply be that it's not fully dried? I live in AZ so I figured 8-12 hours would be fine, but maybe not for the final coat?

Q. Is there typically steps you take after the final coat of poly (rubbing with steel wool, mineral oil, etc.) or is it usually finished after the last coat of poly dries?

Q. Would any of the above help with the dry spots / brush strokes I'm seeing for the third coat of poly?

Q. If no to the above, what are the best next steps to take?

Thanks in advance, I really appreciate it!
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post #2 of 6 Old 05-30-2013, 05:36 PM
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I can't open your link with my bad internet. Everything I'm saying is from your description.

You shouldn't have had any more problems with the third coat than the second. I'm wondering if you thoroughly stirred the finish prior to using it. Sometimes the finish sits on the store shelf so long you need to stir it and let it sit for a hour or two and stir it again. The stuff separates with the solvents on top and solids go to the bottom and sometimes it takes a bit of work to get it suspended again. It sounds like since the brush strokes were more pronounced in the last coat the finish was thicker on the last coat suggesting you used most of the solvents out of it with the first two coats.

Another possibility is if you wiped the sanding dust off with a cloth that had a foreign substance on it and the foreign substance is having an adverse reaction with the finish.

For now you need to get it dry before you can proceed. If you would put a fan on it, the ventilation should help the drying process.

Since you are working with satin, I wouldn't attempt to rub it out. Anything you do will make it glossier and usually in spots. I believe I would let it dry good and wet sand it with 400 grit paper and water taking most of the last coat off and put a fourth coat on. To be on the safe side I believe I would use a fresh can of fast dry poly. You might have the paint store put it on their shaker before you bring it home.

I wouldn't recommend using mineral oil on any polyurethane finish. Leave it for cutting boards.
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post #3 of 6 Old 05-30-2013, 06:09 PM
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This type of problem makes seeing the photo necessary to venture a guess. To me it looks like the top was sanded too roughly in that area. You may have drawn off the finish too much, where you didn't get enough coverage to match the surrounding area.







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post #4 of 6 Old 05-30-2013, 11:48 PM
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Another cause would be - you tried to smooth by brush already slightly dried poly thus you see the marks. Sometimes it happens when the temperature was hot and poly was drying too fast.
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post #5 of 6 Old 05-31-2013, 12:58 AM
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I work with poly almost exclusively. A little lacquer here n there for the special projects

What type of poly are you using? (Edit) Never-mind on this. I use the exact same poly and buy it by the gallons. Water-Based Poly by MinWax.

What are you using to apply it (type of brush)?

Your workpiece is very large, so I can only imagine that it would be next to impossible to brush on poly in Arizona with something that long. Just a thought, but you may want to thin it a bit (depends on what you are using) to help slow down the dry time. I am in Houston and it is VERY humid! So it takes longer to dry when I brush on and and if I backstroke a 48" bench, I will leave a brush mark.

(Edit) I would recommend thinning with a bit of water. Test it on some samples first. But if you are brushing it, you need to slow it down. I know that product well, and you can not load enough on ANY brush to make a clean stroke for that distance. This is why imo you would want to thin it just a tad.

I spray all of my poly now with an HVLP (1.4mm tip) and get great results. I do not have to worry about brush strokes or how fast it sets/flashes. (Edit) After seeing what you use, I would recommend spraying it. It turns out so much better and you can apply coats much faster. No matter what Do Not Forget To STIR this stuff! It settles as fast as it dries.

No matter what you use, you are going to need to sand off the last layer or two to get the brush marks out. In my past, 320 grit (lightly) does the trick. Then wipe with a damp cloth to get all the dust out.

Let us know what you are using and we can go from there.


.

You can always check out the cool stuff Angel and I are working by going to our Etsy.com shop HERE... Let us know what you think

Last edited by Ryn0nTX; 05-31-2013 at 01:07 AM. Reason: re-read post... Duh!!!
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post #6 of 6 Old 05-31-2013, 08:51 AM
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The picture loaded for me this morning. I'm wondering about this white spot. Is it in the finish or just caused by the photo? If the spot is in the finish thats a bad sign and I would stop working on the finish. It looks like an adhesion problem.

Cabinetman is correct that the wood wasn't sanded thorough enough to begin with. It can be fixed but I wouldn't put any more satin poly on the table until that spot was leveled. It may take two or three coats of gloss poly on that spot before it could be topcoated with the satin. The flattening agent clouds the finish and it's best to use the clear gloss to fill with and use the satin for the last coat.
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