Final finishing/sanding of polycrylic - Woodworking Talk - Woodworkers Forum
 
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post #1 of 11 Old 10-20-2009, 01:22 PM Thread Starter
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Final finishing/sanding of polycrylic

I have a coffee table top that has given me years of grief. It's some sort of pine with at least one knot that has seeped in the past. This past week or so I stripped it completely, stained it and have finally finished it with polycrylic from minwax. I'm pretty satisfied but probably should have given it a coat or 2 less than I did. I think the last coat or 2 left me with unnecessary brush marks.

So, I've been researching when and how to do a final sanding/rubbing to get the imperfections out, but keep a near glass-like finish.

My plan as of right now (without any further info) would be to sand with 1200 only, and then wax it with maybe johnsons furniture wax, OR start with 400 and work up to 1200 or 1500, then wax. I'm no expert and only rarely work on wood projects, but for some reason this one is driving me insane and I'm trying to get it as perfect as I can.

Oh and I almost forgot....tonight at about 11:30 pm it will have been 24 hours since the last coat. How long should I wait before the final sanding? I've seen from 24 hours to 4 weeks!! I definitely want the finish to be hard enough before I start the sanding. For the record, it has 5 or 6 coats. Thanks for any help!
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post #2 of 11 Old 10-20-2009, 01:48 PM
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Start with 400 and use a rubber sanding block or a cork block. Wait a few days before sanding and you should be fine. I like to go from 400 to 800, 1000, 1500, then use automotive rubbing compound and either a buffer or a soft cotton cloth and a LOT of elbow grease.
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post #3 of 11 Old 10-20-2009, 02:27 PM
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Start with 400 and use a rubber sanding block or a cork block. Wait a few days before sanding and you should be fine. I like to go from 400 to 800, 1000, 1500, then use automotive rubbing compound and either a buffer or a soft cotton cloth and a LOT of elbow grease.

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You might give it a week or so to cure. Every application delays the previous coat from curing completely. You'll be able to tell if the sanding gets gummy.

This would be a good schedule, but to use wet-or-dry silicon carbide sandpaper and water. Using a polishing compound on the last sanded coat will bring out the glassy finish, but I wouldn't use a power buffer. It creates a lot of heat, and the buffing pad can load up with compound and burn the finish. I would do it by hand.

Waterbased polyurethane finishes much better when sprayed.






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post #4 of 11 Old 10-20-2009, 02:54 PM Thread Starter
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Wow, Thanks for the quick replies :) Yeah I'll give it about a week before trying any sanding, as I've run into the issue with the finish gumming up before (it was polyurethane).

I had thought of using the spray, but don't really have an appropriate place to spray paint. I figured I'd end up having to sand anyway when all was said and done, so no big deal there. I was really pleased with the low odor of the polycrylic...there was a time that I stained, then finished a dresser and bookcase in a small bedroom and had a headache all weekend from the polyurethane fumes!!

I have a palm sander, and forgot to ask about hand vs power so I'm glad you mentioned the rubber block. I don't even have anything I could buff it out with so yeah, I'll be using good old elbow grease for that too :) Thanks again for the info!
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post #5 of 11 Old 11-01-2009, 12:39 PM Thread Starter
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Hey guys...

I finally finished this up last night, but I have a couple questions.

I finished with 1500, and polished it after that, but there seems to be a slight bluish/white cast to the finish. It didn't get back to the actual glass-like look that it had before I sanded it down.

What would happen if I used sc johnson pastewax on it now? I have a feeling that it might get a temporary shine to it, but not keep it. Any thoughts on this?

Finally, it seems that it marks very easily in the state that it's in. Should I let it sit for another week or so before using it? Will the polycrylic get harder over time? It just seems soft, and since this is a coffee table top I'm worried about it getting messed up easily.
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post #6 of 11 Old 11-01-2009, 01:39 PM
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A thick coat of polycrylic is not a tough finish at all. You need to polish it more to get the haze off the finish. Bye the way, what products (polish and pad type) did you use to polish it?
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post #7 of 11 Old 11-01-2009, 05:05 PM Thread Starter
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A thick coat of polycrylic is not a tough finish at all. You need to polish it more to get the haze off the finish. Bye the way, what products (polish and pad type) did you use to polish it?
Hi,
Thanks for the reply. I used 3m wet/dry sandpaper, then 3m rubbing compound for cars. I only used a rag to polish, no kind of special pad or anything.
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post #8 of 11 Old 11-01-2009, 05:44 PM
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Originally Posted by gba88 View Post
......I finished with 1500, and polished it after that, but there seems to be a slight bluish/white cast to the finish. It didn't get back to the actual glass-like look that it had before I sanded it down.........it seems that it marks very easily in the state that it's in. Should I let it sit for another week or so before using it? Will the polycrylic get harder over time? It just seems soft......
Lets start off with sanding. Always start with a grit that will actually flatten your surface and keep it lubricated. Water should work just fine for that. Some people use mineral oil, but I dont know what will or will not react with Polycrylic. Once your surface looks flat and level, move up about 2 notches on the grit scale and remove ALL the previous sanding marks. keep doing that untill you get to about 5,000 or 6,000 grit. Then use any automobile rubbing compound to remove the scratches you cant even see from the 6,000 grit. This should give you a low luster. For a deep mirror shine, step up to a good automotive polish. The mirror finish is dependant on all of the stages of sanding. That is, if you started with 400 grit and next jump to 1,000 grit, the 1,000 may not get out all of the 400 grit scratches.
Ok, now for problem solving. Lets start with the bluish/white cast. Since you put on the Polycrylic too thick it is probably still somewhat soft. It is conceivably possible that the surface absorbed some of the wet/dry sandpaper backing dye or maybe reacted with the rubbing compound. The softness, again, is attributed to the heavy coating. As stated earlier, part of the drying process of the first coat is evaporation of solvents. The solvents in the finish are trying to work their way out so the finish could dry and it has a lot of layers to penetrate.
let me state that I am not familiar with Polycrylic so anything I say is just an educated guess. I looked briefly on the Minwax site and didnt get much info on the Polycrylic as to what it is so I am guessing that it has a high acrylic base. Acrylics are relatively soft compared to most varnishes and lacquers but should still be OK. Next.......Min-wax is a fa cocta brand of finish. Ask someone who speaks Yiddish to translate although you can probably figure that out yourself. If a product is sold in Walmart or Home Depot, youcan bet it is bottom of the line.
Back to your finish...... let it harden another week or so and then start with the sanding procedure all over again and I think you will be just fine.

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post #9 of 11 Old 11-01-2009, 06:29 PM Thread Starter
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Lets start off with sanding. Always start with a grit that will actually flatten your surface and keep it lubricated. Water should work just fine for that. Some people use mineral oil, but I dont know what will or will not react with Polycrylic. Once your surface looks flat and level, move up about 2 notches on the grit scale and remove ALL the previous sanding marks. keep doing that untill you get to about 5,000 or 6,000 grit. Then use any automobile rubbing compound to remove the scratches you cant even see from the 6,000 grit. This should give you a low luster. For a deep mirror shine, step up to a good automotive polish. The mirror finish is dependant on all of the stages of sanding. That is, if you started with 400 grit and next jump to 1,000 grit, the 1,000 may not get out all of the 400 grit scratches.
Ok, now for problem solving. Lets start with the bluish/white cast. Since you put on the Polycrylic too thick it is probably still somewhat soft. It is conceivably possible that the surface absorbed some of the wet/dry sandpaper backing dye or maybe reacted with the rubbing compound. The softness, again, is attributed to the heavy coating. As stated earlier, part of the drying process of the first coat is evaporation of solvents. The solvents in the finish are trying to work their way out so the finish could dry and it has a lot of layers to penetrate.
let me state that I am not familiar with Polycrylic so anything I say is just an educated guess. I looked briefly on the Minwax site and didnt get much info on the Polycrylic as to what it is so I am guessing that it has a high acrylic base. Acrylics are relatively soft compared to most varnishes and lacquers but should still be OK. Next.......Min-wax is a fa cocta brand of finish. Ask someone who speaks Yiddish to translate although you can probably figure that out yourself. If a product is sold in Walmart or Home Depot, youcan bet it is bottom of the line.
Back to your finish...... let it harden another week or so and then start with the sanding procedure all over again and I think you will be just fine.
Thanks for the informative post :) My sanding went as follows... 400, 600, 800, 1200, 1500 then the compound. I followed the posts above and only went to 1500, and I honestly don't know where I'd even get anything over 2000. I had to go to the auto parts store to get even up that high as far as the grade.

I was very nervous about sanding *too much* off and getting down to removing the stain (happened before!). This whole process probably took me upwards of 2 hours +. I'll take your advice though and try again in another week. Your educated guess about the polycrylic was probably right. a few points on higher spots I noticed the sand paper clogging slightly from soft (not totally dried) finish. Thanks again for the lengthy reply!
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post #10 of 11 Old 11-01-2009, 07:47 PM
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Thanks for the informative post :) ...I was very nervous about sanding *too much* off and getting down to removing the stain (happened before!). OK, but you wont get a cherry on that...... Your educated guess about the polycrylic was probably right. a few points on higher spots I noticed the sand paper clogging slightly from soft (not totally dried) finish. Thanks again for the lengthy reply! You are quite welcome.
Just Google "6000 grit paper" and you will get some results. That is the highest I have ever used. I normally use pumice and rottenstone for my final buffing. I get it in a kinda wet paste where the pumice is suspended in an oil and the same with rottenstone. I'm not sure but I think pumice is equivelant to about 50,000 grit and rotenstone to about 60,000 grit. Not sure and too lazy to look it up. Automobile compound and polish should be close enough I would think. You can go to an automotive supply store and ask what to use to get that 'wet look'.

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post #11 of 11 Old 11-01-2009, 08:07 PM
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Thanks for the informative post :) My sanding went as follows... 400, 600, 800, 1200, 1500 then the compound. I followed the posts above and only went to 1500, and I honestly don't know where I'd even get anything over 2000. I had to go to the auto parts store to get even up that high as far as the grade.

I was very nervous about sanding *too much* off and getting down to removing the stain (happened before!). This whole process probably took me upwards of 2 hours +. I'll take your advice though and try again in another week. Your educated guess about the polycrylic was probably right. a few points on higher spots I noticed the sand paper clogging slightly from soft (not totally dried) finish. Thanks again for the lengthy reply!

IMO, this schedule is sufficient. I've never had to go beyond 1500x - 2000x on any film finish. The trick with waterbase finishes is that it takes more applications than say lacquer or oil base poly. You have to have a sufficient build to sand and buff. It's imperative that each and every application is allowed to cure. It's easy to jump the gun as each application seems to dry so fast.

I would also suggest to use a hand block with the wet-or-dry and water. I would not use a ROS or any powered sander. Likewise with using compounds after sanding. Using a power buffer could by virtue of a spinning pad, create enough heat to cause the surface to get hot and deform. It may appear hazy and not get clear. This will also happen if the finish isn't cured. Using a power polisher can also collect the compound and create a scratching by mixing the compound with buffed off material from the finish.

In selecting automotive compounds, check closely their rating for abrasiveness. With some the whites are fine and the reds are coarse. That may not be the case among different brands. The container should have the numeric grit equivalent.






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