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Old 15th October 2005, 10:25 PM   #1
jarros is offline jarros  Canada
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Unhappy Problems with high gloss finish

Hey everyone. As some of you might know, I'm working on a 2.1 system for my computer consisting of a pair of B3N's (design by Zaph), a dayton 8" DVC with a 70W plate amp, and a slightly modded T-amp.

All the boxes have been made and I'm down to the finish. After 3 months of painting and sanding, I'm trying to nail down a technique for applying the high gloss finish over my black paint. I'm using Polyurethane and have tried applying it with both a foam brush and a paint pad. Both times I ended up with streak marks, so I did some more sanding to get ready for another shot. I've tried to do a lot of reasearch on the best technique for applying the polyurethane, so I gave it another try this afternoon.

I was probably getting streaks because the poly was too thick, so I thinned it by about 20% using Mineral Spirits. This time around I tried applying it with a natural bristle brush. Before using the poly, I loaded the brush with paint thinner and pressed all the excess out (I read that this prevents the brush from soaking up too much of the poly).

It didn't work.

I applied the poly nice and smoothly, being careful not to over brush. What I ended up with looks blotchy in places, almost like putting water on oil. I've included a picture of what it looks like, although it might be a little tough to tell.

Any ideas what I'm doing wrong? Did I not apply a thick enough coat? Was using paint thinner in the brush before hand a bad idea? Any comments would be appreciated, like I said I've been working on the finish for over 3 months now and I'm very eager to hear the speakers again!

Thanks in advance,
Jared
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Old 15th October 2005, 10:27 PM   #2
jarros is offline jarros  Canada
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Here's another pic that hopefully gives you a better idea.

Jared
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Old 15th October 2005, 10:39 PM   #3
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so you painted it... and then polyed it...

why are you trying poly over paint... I'm fairly certain it doesn't work

if it does work... you should just it a rattle can... you will ALWAYS see the streaks on urethane unless it's wood underneath
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Old 15th October 2005, 10:49 PM   #4
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I can't tell you that my way is perfect, but it might work. First, It looks like water was spilled on it, is that the urathane, or did you put water on it. If thats the urathane, then I think you made it too thin, or the finish of the black is too shiny and has oil on it.

Start by getting the base finish, that black finish, as smooth as possible. I assume you have done this, but since you have some finish to smooth down or remove, I will just mention it again. I would probably sand it down to about 4-600 grit paper. Smoother if you want to take the time, but that is probably fine. I then usually apply the first coat full strength, without thinner. Oh and I always use natural bristle brushes. I also order my urathane from an internet source, as its hard to get good urathane at any store locally. I also get a thinner specially made for the urathane. After the first coat is dry, I then go back over it with some very fine sandpaper. I usually use a piece of wet dry sandpaper, I believe at about 800 grit. This is to get out any slight imperfections like fisheyes or dust. I then thin the next coat to about 10% thinner maybe, and try again. I let that dry, and once again go over it with the sandpaper. I do this till I have built up 4 or 5 coats. Also, be careful with the sanding, it can make the finish look dull if you aren't careful of the grade and how much you do.

Once my last coat is on, I take an electric buffer I have and use a very heavy automotive polish for removing paint drips. The stuff I use is from Menzurna, though I am sure that Meguiers makes a similar product in their proline. I go over the finish many times and gradually keep reducing the polish until I am using basicly a final polish like is readily available in auto stores. I go through between 3 and 4 stages now.

I will say, you will never achieve a proffessional like finish by hand without this final prep work. This kind of finish is normally sprayed on with high quality sprayers, and even then, is usually buffed afterwords. I have seen some people put on a very nice finish by hand without much post finishing work, but I have no idea how they manage it. I did once see someone put on a very thick super shiny finish using a kind of epoxy and spreading it on about 1/8" thick, but I dont know anyhting about how thats done.
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Old 15th October 2005, 10:59 PM   #5
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The simple fact is that you've got to put more effort into the finishing.

Sand what you have back flat with 1200-1600grit wet sanding and then buff out with a fine cutting compound. Afterwards wax and you should have a nice surface without all those ripples.

The reason you have the ripples is because your using cloths/sponges to apply the finish - that means lots more hard work to get it back to a uniform and flat planar surface. The real way to do it is with a compressor and gun. Save you lots of time in the finishing.
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Old 15th October 2005, 11:09 PM   #6
jarros is offline jarros  Canada
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Thank you for the replies.

I used Krylon gloss black spraypaint for my base color because I read that this would give me a more even finish (as opposed to painting it with a brush/mini roller). I also tried using the Krylon tripple-thick glaze, which worked fine on the veneer (I have a veneered front and the sides/top/back are black), but it ended up speckled and textured on the paint.

pjpoes, don't you get brush marks if you don't thin the first coat? When I brushed the non-thinned poly on, I got brush strokes that I could feel when I ran my fingers across. Did you get this too, or did you just not worry about it until you used the buffer and polishing compound?

This being my first DIY project, I'm not expecting a totally perfect mirrored surface, but the brush strokes I saw aren't acceptable.

Also, I don't have a heavy duty buffing tool, but I do have a polishing attachment for a drill. Will this do the trick? I've also got a mouse sander that I might be able to stick a buffing pad on to.

Final question here, what do you recommend I do after I sand the surface smooth again? I have been wet sanding all along, but I was sure to let it totally dry for over an hour before I applied the poly. Should I wipe it down with a rag with a bit of paint thinner (or mineral spirits) on it?

If anyone can help me find the answers to any of these questions it would be greatly appreciated. Thanks!

Jared
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Old 15th October 2005, 11:15 PM   #7
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Quote:
Originally posted by jarros
Final question here, what do you recommend I do after I sand the surface smooth again? I have been wet sanding all along, but I was sure to let it totally dry for over an hour before I applied the poly. Should I wipe it down with a rag with a bit of paint thinner (or mineral spirits) on it?

If anyone can help me find the answers to any of these questions it would be greatly appreciated. Thanks!

Jared
Use an orbital sander to flat the finish back. Don't apply any more coats of urethane!!! What you're trying to do is get a perfect finish in your final coat without and finishing work and to top it off your doing it with a sponge or similar - never going to happen.

What you need to do is simple sand it flat with wet sanding using 1200-1600grit, make sure you don't go back to basecoat, then simply buff it out with rubbing compound and wax afterwards. Its a lot of work but its the only way you'll do it by hand without a compressor and gun - even with those I still have to flat back and buff out but to a lesser extent.
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Old 15th October 2005, 11:17 PM   #8
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I don't know squat about woodworking, but I know a fair bit about automotive finishing -- and base/clear is what automotive is all about! (Car clear is usually polyurethane).

So -- I'll pretend that you're painting a car. You can adapt whatever changes you think are appropriate!

Anyhow -- long story short -- not matter what you're doing, your goal is SMOOTHNESS. Shine comes from smooth. If you can spray, do so in thin coats. WAY easier to get shine from spray than brush-on.

Frequent sanding, up to at least 1000 grit, is required for mirror finish. Use wet sand paper (3M brand is preferred), because it helps to wash away the grit and keep your work piece from getting scratched (and dull).

If you have bad bumps, you're best off to use a fairly coarse sand paper on a sanding block (300grit), then work your way up. If you start too fine, you'll wind up sanding the lower part of the surface way too quickly.

Once it's SMOOTH, it may be dull, but that's from micro-scratches. To get rid of micro-scratches, you need a rubbing compound, sometimes followed by a polishing compound. The difference between dull at 2000 grit and polished quickly is INCREDIBLE. Like flat to gloss finish.

If you are rubbing by HAND (not machine!), I would suggest using 3M fine cut rubbing compound. It costs $7.50 CDN per bottle at Walmart. It is EXCELLENT. It works well, fast, and is very easy to get good results with.

Wes
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Old 15th October 2005, 11:35 PM   #9
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All good advice so far.......

.....The last smooth finish I did, I had to put on 5 coats of poly. Between the first three coats, I sanded lightly with 220-grit. On the 3 and 4 coats I sanded with 220, then with 400. One the last two coats I sanded with 220, 400, 600 and then wet sanded with 1,000.

Wes bet me to it, the secret is to complete the 1,000-grit sanding with 3M Super Fine Rubbing compound. Apply with a cloth. Should be super smooth!

The best finish is applied with a spray gun, but I got just as good results with a high-quality brush. I alternated the direction I applied the finish. First coat was up/down, the second coat was side to side, etc.
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Old 15th October 2005, 11:41 PM   #10
jarros is offline jarros  Canada
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Thanks again for the replies, I really appreciate it! Let me make sure that I've got this strait:

I need to sand this back down to as flat as I can get it using an orbital sander (any grit recommendations?). Once it starts flattening out, I will need to wet sand, starting at 320 or 400, then 800, and then 2000 (this is what I have now for wet sand paper). Once I've removed all the imperfections I move on to the polishing compound to polish the finish back to gloss.

I bought some Mibro high gloss polishing compound from my local hardware store a week or two ago. The stuff is designed for polishing metal, but it should be fine for this, right? Also, what kind of cloth should be used with the polishing compound?

Jared
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