Problems with high gloss finish

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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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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.
 
diyAudio Member
Joined 2004
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.
 
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
 
diyAudio Member
Joined 2004
jarros said:
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.
 
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
 
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.
 
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
 
For what it's worth, I *hate* orbital sanders for this kind of work. I don't like to use them past the glazing & spot putty phase (right before sealer/primer). [Caveat again - automotive experience only!]

Can you get it off with a sanding block (not just free paper - invest five bucks in automotive paint aisle at Crappy Tire) and 125 grit?

If it's really high, you might be able to cheat-start with a sharp knife.

Wes
 
PS - metal polish may actually damage your finish. I don't know Mibro, but Brasso would probably kill it. Metal polish often contains de-oxidization compounds.

I would strong recommend buying the 3M stuff. 3M Fine Cut Rubbing Compound. The easiest place to get it is WalMart (Crappy Tire doesn't carry it). Of course, if you live in Vancouver, Wally World is not an option. Chumps! :)

Wes
 
yes you get brush strokes using a brush, but thats ok, you use sandpaper to remove them. Dont try and get it perfect with a brush, that is impossible.

I find you can use high grades of paper, like 400+ for your smooth sanding if using an orbital because you have the aid of a machine, makes it quicker. You need to take your time and be careful throughout the sanding and polishing stages, as you dont want to remove too much in any area, or burn any areas.

Most everything that everyone else mentioned is also good advice, especially that of the car finishing, as its not that different. The biggest difference is that poly is not as hard as car paint.
 
Sounds great. I should be able to sand it down enough with my sanding block. I'm getting real tired of sanding by now, but I'd rather have it done right than ruin it by using a powered sander after I've come this far :) I'll also go and pick up the 3M Rubbing compound so I don't have to take any chances with the Mibro stuff.

I think I've got a good idea of what I need to do now. Thanks again for all the help, and I'll be sure to let you know how it all turns out!

Jared
 
Sorry to join this party so late but on future projects I'd recommend prepping with a good quality lacquer based sanding sealer before applying color or poly. I like the Deft brand.

I make a lot of things with veneers, veneered plywood and hardwoods and sanding sealer is well worth it. It fills the pores very quickly and doesn't raise the grain like some other finishes do. On a tight grained wood like maple I usually finish sanding at about 220/240. Then a coat of sanding sealer. I'll sand that at 320/400. What I look for is a uniform matte finish at this point. Anything still glossy is below the sanded surface. If I see this I repeat the sealer/sanding. Open pore woods like oak will take a few more coats if you're going for a 'glass' surface.

The good thing about lacquer is that you can sand in minutes if you spray and in about 30 minutes if you brush it on. The other nice thing about a lacquer base is that it accepts subsequent finishes like enamels and polys without any problem. If you're staining something though you need to apply stain before the sealer.

I've tried the water borne sealers and have been disappointed.

One other tip that prevents heartache is to really clean the surface after sanding. I'm fortunate to have a compressor so I blow off the surface and then vacuum before applying the next coat. Its amazing how a little dust particle will make itself known to you when it all dries. Especially if you're a perfectionist which I bet you are.

Lastly, except for your disappointment in the gloss over black finish its really beautiful work!
 
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