DIY Spray Finishing Tutorial - AVS Forum
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post #1 of 27 Old 04-15-2008, 12:17 AM - Thread Starter
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I got a few pm questions, so I started this thread to give a visual of spray finishing at home. I have access to a spray booth, but will do this in my garage to show results in a DIY setting. This will be for solid color mdf finishing.


This test box will be a gloss black.




A little background on me, I own a trim carpentry company, I am not a spray finisher by profession. But I do it out of an occasional necessity, and as a hobby. Very little audio theory knowledge though, and been here the last few months learning.

I skipped the box building, as from what I’ve seen, most of you guys get there w/o help. Just a tip, don’t leave your panels short on your corners. Better to leave them long, and trim them with a flush trim bit on the router. Less prep work.


*** Keep silicone out of the area. Silicone will mess up all finishes, if using it to seal inside the box, be careful what you touch!

PREP WORK:
Most important step. Don’t rush it. The higher the sheen (gloss), the more imperfections will be seen.

I’d start with bondo work. Regular automotive two-part, buy the gallon (well, I have other uses for it.) I’d go for a skim coat on all surfaces if you’re going for a gloss look. Raw MDF will finish differently than a filled one. I didn’t go into detail on Bondo work here, I’m sure there are plenty of auto body sites with step-by-step.

For sanding, random orbit sanders work, but the paper clogs quick with bondo. And you just end up following waves with the random orbit sander. You can use an 80 to take out the ridges, but I would not do all my sanding with a random orbit, just my initial clean up.





Don’t take it more than 1/3 past the edge, if you tip it you can round your flat surface. For a high gloss, ulltimate goal is the surface in the same plane.





For sanding without dropping $ on an inline sander, you can get the same results with some elbow grease with a wood block. I use one that is about 3 x 10 inches. That lets you use 9” x 11” in ripped in half. Start with coarse 60 – 80 grit if you have a lot of leveling, 100 if minor. Stop at 100 – 120 if you are doing a second Bondo coat.





After your first pass of sanding, I spot fill any scratches with 3M Acryl-Blue Glazing Putty. It’s blue, so it contrasts nice on the red bondo. I’d give it a quick shot of primer here, the different colors help with leveling and seeing where you need still work.


HAND SANDING:
Level in long strokes in all directions.

Front - Back




Side – Side




And diagonally, work it both directions diagonally for best leveling.





If no dents or scratches, work up through a 180 grit in all directions, no real need to go to a 220 before primer. Watch the edges or round-overs on corners. Hold a light at a very low angle to the surface you're working on, it will highlight any bumps or scratches.

It's way late, gotta be up in 4 hours... Primer next time...
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post #2 of 27 Old 04-15-2008, 12:17 AM - Thread Starter
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In my assembly, I used glue and 18 gauge brads, then pre-drilled and countersunk screws to pull it tight. (That's the carpenter coming out in me). Glue and clamps only will save some filler work.

Shinobiwan makes some good points I will bring up before getting to the spraying. As the title states, no roller finishing here. No spray cans either. Need to get a gun if you want to get serious into this hobby. To get enough air (i.e. big compressor) and a good gun is some $$. For one-timers, here is a good time to consider just paying a finishing shop to do your box.

I have a DeVilbiss PRI Gravity HVLP Primer Gun - 1.4 mm Fluid Tip. It is a nice gun, but an air hog. It needs about 16 cfm to run continuously. A 1.8 mm tip would be better for primer, but I use the 1.4 because it's a nice size for the lacquer.






HVLP - High Volume Low Pressure. Don't get a conventional, siphon feed, high pressure gun. You'll get more spray in the air - overspray, blowback . You get a higher TE with HVLP - transfer efficiency. More of your expensive finish stays on your project and not on the floor.

Other nice guns:
  • Sata
  • Iwata
  • Binks
  • Asturo Eco.
Buy a good one it you plan on doing this often with good results.
Here is a site for suggestions and price ranges.

Atomization is the process in your gun that turns liquid into mist. It's the air that breaks up the paint/finish. It's all about the gun. A Harbor Freight, Depot Husky gun (paint spitters, cough, cough) will do it, but not nearly as well as a good gun. More air will do it better, but there are low-air/low cfm options that will do a good job.


Air is next.

You don't need a compressor with the rated CFM higher than your gun will draw. If your compressor only puts out 5, but the gun draws 10 = just means more waiting-time for the compressor to catch up once you empty the tank. You still can spray, but a bigger tank and more CFM is better. I have an 220 volt Energair, I think it's a 25 or 30 gallon tank. I never wait for air, and it's not running all the time.






Also, make sure you have an air/water separator. Most finishes don't like moisture in the compressed air - good cheap investment. (At the shop we have a rotary screw compressor and a refrigerated air line dryer with a secondary filter - almost hospital clean air!!) Not needed though for this discussion.






I run full pressure in the hose to the gun, I added a regulator at the gun to control the pressure there. Not only for control, but you get too much of
a drop if you only run 25 -30 psi in the hose. (See above gun pic)



OK, Finally to the primer!!!

For this I will be using a two-part, polyurethane primer. It is a high-solids primer, 65%. It will build nice, dry to the touch in minutes, sand to a powder in just a couple hours. My favorite is an Italian one - Vernici Egidio Milesi.








This box is about 5 cubic feet. I will need about 12 oz of combined finish to hit it. Use the graduated plastic mixing containers. Easiest way to measure. (Cheap if you buy bulk, not sure the deli potato salad containers are solvent resistant )





This 1st Batch = 7 oz poly, 3 ½ oz. hardner, +/- 2 oz. thinner.
When I say thinner, not Lowes mineral spirits! The thinner supplied with your poly (of course purchased separately). This Milesi one is some what picky, the thinner runs about $20 gal.


Tack the sub, use the (very little bit of) thinner and a new clean rag to remove dust. As for spraying technique, easier to show than describe. Just trigger in the air off the sub, and release once past the edge. Car guys will hold on and spray almost non-stop. Don't be triggering on/off too much.







After all nice and black, I hit it again with the wood block, and 220 grit this time. This is your last shot for major fixes it you missed anything. You are looking for the whole surface to get scuffed and powder evenly. Here is the top with real good prep. Front baffle looked good too. Just a few high spots.







Here is a side that had somewhat poor prep for a high gloss.
Um, well, you see, yeah... I rushed through the bondo work / sanding on purpose for photo demonstration purposes yeah, that's it! I was sloppy for your benefit!!

(OK, caught me. Just rushed )

Ended up doing some more sanding and 3M Acyl-blue.







Since a good portion of that 1st coat got sanded, I gave it two more coats of primer, 90 minutes apart.

Here it is, waiting for the next step. I took the shot right off the gun, so still drying. Plus the flash added something funky. But it looks nice - flat, smooth consistent black.

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post #3 of 27 Old 04-15-2008, 12:18 AM - Thread Starter
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SPRAYING BLACK LACQUER:

My gun has a few knobs for adjustment.
The top is for the width of the fan spray, bottom is the fluid flow rate.
This is where I’m still working on my skills. After spraying this box, I talked to the finisher at my friend’s cabinet shop and found I had a few things off.

My pressure was a bit high. I was shooting at 30 -35 at the gun. About 28 psi was the sweet spot for my gun.

I also was using too little thinner. I only had 5 %; when I upped it to about 15%, the lacquer flowed out and went down much smoother off the gun.

I was spraying too low of a flow rate. I was over-atomizing – combined with too little thinner - thus the lacquer was almost drying in the air before it hit the surface.

This is where you need to practice. You need to find the right mix of 4 things.
Fan width and distance from work piece
Air Pressure
Thinner : lacquer ratio
Fluid Flow rate.

Whenever possible, it is best to spray horizontal surfaces. You can lay down a bit thicker coat without sags. Then again, when pros paint cars, they don’t rotate the car to spray flat. This box I just sprayed as is in position upright.

I got a new lacquer this time. It is by Valspar. 90% Sheen. I put down 5 coats of black, about 15 – 20 minutes in between coats.
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post #4 of 27 Old 04-15-2008, 12:18 AM - Thread Starter
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Same procedure for spraying clear lacquer as black. Just get the settings and mix right, and the finish will be better than my before pic in post #19.
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post #5 of 27 Old 04-15-2008, 12:19 AM - Thread Starter
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Reserved For Polishing
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post #6 of 27 Old 04-15-2008, 12:35 AM
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Nice. I'm glad to see someone doing a step by step procedure with pictures. I'm keeping my eye on this. Thanks Kubbie.
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post #7 of 27 Old 04-15-2008, 04:40 AM
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nice thread, peaked my interests!

I can win a game of connect four in three moves.

Room V Theater Construction Thread

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post #8 of 27 Old 04-15-2008, 04:45 AM
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There are some good tips given so far.

It's never over, it's never finished....it's never cheap.

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post #9 of 27 Old 04-16-2008, 02:06 PM
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Very interesting. Want more!!! Thanks for taking the time to do this too. It really helps out.
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post #10 of 27 Old 04-17-2008, 01:37 AM - Thread Starter
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I copied this info here from another post I made, to keep finishing info in one place.



Many off-the-shelf finishes don't "dry" by evapration, they cure by a reaction with the oxygen in the air. Just because a finish is dry to the touch, does not mean it is cured. Other types, mainly professional finishes, use a catalyst (or hardner). Pre-cat only refers to when the catalyst is added. It comes pre-mixed, and has a limited shelf life. Other type, you add right before spraying, and has be sprayed in minutes to hours.

A few definitions when you go talking to someone to finish your boxes:
  • Nitrocellous lacquer, aka nitro or N/C lacquer. Not good for kitchen cabinets, ok for speakers. It yellows, and faster in sunlight. But great for touchup, new coat just melts into old.
  • CAB (Cellulose Acetate Butyrate) is a clear and non-yellowing, but still has the weak durability of N/C. There are CAB blended with acrylic resin, which are better, but not as good as a pre-cat, which is a good choice. (To add more confusion, there are also water-based acrylic lacquers)
  • Pre-cat is Pre-Catalyzed lacquer. Usually, the catalyst is added at the factory, sometimes your supplier. This catalyst starts a chemical reaction when sprayed. But you have somewhere between 30 days to a year pot life(Some claim 18 or 24 months in the can, don't know...) Can be clear, or tinted to give you any solid color you like. Overall my favorite finish. Easy learing curve, durable, recoat in a short time, best characteristics overall, many cabinet companies use this.
  • Post Catalyzed lacquers, you add the cat/hardner yourself before spraying. Some say that because this catalyst is hotter, you get a better finish than pre-cat. Again, I dunno...But whatever you mix up and don't use, you have to dump.
  • Moving past the family of post-cat, you have CV = conversion varnishes and catalyzed polyurathane. The are rated higher by the AWI in performance compared to pre or post-cat. IMO catalyzed poly is one of the best finishes, but not too user friendly and more toxic.
  • There are catalyzed vinyl sealers, polyester, 2k Polyurathane, UV cured epoxy...

But don't jump in without good research. These are professional products, CV use xylene and formaldehydes, 2K urathanes contain isocyanates which are absorbed through the skin (ie tyvek suit, goggles, fresh-air-system and not just a respirator). Not to mention you could burn your house down.

For this reason, there is a unstoppable trend towards waterbased finishes, there are waterbased 2K urathanes. There are some real nice and user friendly low VOC waterbased CAB and acrylic lacquers/poly (not Depot Polycrylic).

If you care to learn more, I can send you to other DIY-friendly forums that are specific to wood finishing:

To give you a start go to woodweb.com The finishing forum is great and do some browsing.

They archive some of their useful posts in the Knowledge Base

Another site is painterschatroom, but it is slow, although some spraying info there.

 

SprayableFinish.pdf 5.53515625k . file
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post #11 of 27 Old 04-17-2008, 07:28 AM
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Wow thanks Shinobi and Kubbie for taking hte time to do this. I have 2 of the guns mentioned but never even used them. I will definitely use this tutorial to work on my boxes.

Thanks again
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post #12 of 27 Old 04-17-2008, 07:32 AM
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I'll try to keep posting to a minimum in this thread, as not to muddy it up. I'm getting issues with your pictures Kubbie. All but one are showing up as red X's.

Something I didn't see mentioned was environment (garage) prepping. The only garage I have access to for a long period of time is my parents and they live on a dirt road. It's impossible to seal it off and if anyone drives by and the wind is blowing towards the house, it'll come right in the garage. I'm assuming I'd only be able to do something like this after 2am when the wind is done and no one's driving.

Quote:
Originally Posted by NO1B4ME View Post

Wow thanks Shinobi and Kubbie for taking hte time to do this. I have 2 of the guns mentioned but never even used them. I will definitely use this tutorial to work on my boxes.

Thanks again

Think you may want to sell one of them off? Enlight of this thread, new potential buyers will likely pop up.

YID DIY
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post #13 of 27 Old 04-17-2008, 12:21 PM
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Wow also, thanks Kubbie and Shinobiwan. my cheesy compressor blew, and I'm about to get this one below and looking to upgrade in terms of gun and matieral.
Love the pdf and refs to finish sites.

[IMG][/IMG]

Prolly have enough air

can't find anything but Becker Acroma pre-cat--dont like it, or maybe I just need to get better gun, or get better at pressure setting, etc.
This is what I need to know about.
Looking forward to more here!

Thanks again.

Dave
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post #14 of 27 Old 04-17-2008, 06:22 PM - Thread Starter
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Ditto!
If you see my post 11, I posted almost the exact information:

Quote:
Originally Posted by Kubbie View Post

But don't jump in without good research. These are professional products, CV use xylene and formaldehydes, 2K urathanes contain isocyanates which are absorbed through the skin (ie tyvek suit, goggles, fresh-air-system and not just a respirator). Not to mention you could burn your house down.

Although the 2k urethanes are some of the best finishes available and safe when cured, they are hazardous to the person spraying.

I should show a more user friendly primer. And maybe some more legal mumbo jumbo - Do not spray any finishes without reading MSDS, understanding all risks and hazards involved, and don't come back saying Kubbie said "it's ok, it's a DIY project" without taking the proper precautions.
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post #15 of 27 Old 04-17-2008, 08:05 PM - Thread Starter
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Quote:
Originally Posted by Looneybomber View Post

I'll try to keep posting to a minimum in this thread, as not to muddy it up.

Hey, not my thread - post away. That's why I reserved the first few for myself, but any other finishes others have used with success, techniques or tips, please share.

This piano, gloss black on a flat surface is one of the hardest of all finishes to do. Expert finishers will tell you it's not easy. It's me going to the plate and trying to hit a homer off of Zambrano - rookie trying to get a pro result on the first attempt.

P.S. - Speaking of expert finishers, Chip Foose is in town Saturday doing a meet-n-greet for kids, I'll have to take my kids so "they" can meet him. Anyone see Overhaulin' and some of those paint jobs? That's where the real "WOW" is due...

Off to spray some lacquer.
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post #16 of 27 Old 04-21-2008, 06:31 PM - Thread Starter
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Update - got real busy. I didn't abandon the thread, I'll finish the write ups on the lacquer and compounding probably after the weekend...

Just a little tease of how its coming along - I don't have the skills to leave a high gloss of the gun, I'm sure the car painters would rib me some...


Before:




After:

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post #17 of 27 Old 04-21-2008, 11:53 PM
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Just to add a few points...

The sandpaper that you have problems with clogging ( with filler ) is not stearated... get actual 3m paper ( or norton, etc ) designed for sanding paint and filler. It will work much better and it is not that much more expensive.

Buy a good block ( or several ) and block by hand, yes this is a definate must for a flat surface.

No need to tack the surface before priming. ( as it will be sanded again in the future after priming ) With MDF, I have found the need to wipe down the bare surface with a wax and grease remover. ( have found oils from hands on sheets and such ) Wipe with one really wet rag ( full of wax and grease remover ) and then wipe with dry rag on each surface. Repeat with another clean wet rag and dry on each surface. ( wipe twice )

Nitrile gloves ( or a doubled up pair of latex at least ) are a must when playing with solvents, paints etc. 9 seconds after you have solvent on your skin it is in your blood stream.

As was mentioned primer guns need a larger fluid tip as the materials are thicker. ( high viscosity ) Good advice on the HVLP, I have a Sata NR2000 with a 1.3 mm fluid tip for topcoats, a beautiful piece. For primers I have a cheap 1.7mm HVLP gravity fed gun. ( still has a nice pattern, but not a production grade tool )

Cleaning your guns will require quite a bit of thinner after each use. Plan on having a gallon of lacquer thinner ( or gunwash ) for the first timer.

Solvents are flammable!! Don't ever try to spray in an environment with open sparks ( pilot lights etc.. ) this is like playing russian roulette.

"You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the rabbit-hole goes."
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post #18 of 27 Old 04-22-2008, 08:46 AM
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Fantastic guide
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post #19 of 27 Old 04-22-2008, 10:00 AM
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Awsome thread!!! Glad I found it.

I have a small 20 gallon compressor and a Harbor Freight gun... Really really entry level gear but I am going to give this a shot once I get my box built. Ive always had some interest in painting with a gun but never experienced it.

Got iSCSI?
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post #20 of 27 Old 04-22-2008, 12:17 PM
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Kubbie,

Great work ! I am impressed with the before and after pics...I have to buy the Mirror Glaze and a good polishing tool.

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #21 of 27 Old 04-22-2008, 02:51 PM - Thread Starter
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Quote:
Originally Posted by TheEAR View Post

Kubbie,

Great work ! I am impressed with the before and after pics...I have to buy the Mirror Glaze and a good polishing tool.

Thanks, just that's a middle step of a few. There are a few steps of sandpaper, that's the 1st cutting compound, and then a two others after it. I'll go into details... just have to go pick up the kids, off to baseball practice - and who are all these neighbors that I haven't seen in 4 months?

Hard to get anything done once we finally hit 60's and 70's here!
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post #22 of 27 Old 04-22-2008, 02:56 PM
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Quote:


Just a little tease of how its coming along - I don't have the skills to leave a high gloss of the gun, I'm sure the car painters would rib me some...

Glad to hear this! I know my troubles here. Judging by pic#2 that's not a deal killer.
Keep this coming!
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post #23 of 27 Old 05-03-2008, 11:03 PM
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The rough finish out of the gun could be caused by several factors - wrong air pressure, too thick paint/thinner mixture, too far from material when spraying, etc. While it may not look the best out of the gun, it really just means a little more work for you with the sanding process.

That said, you ought to be able to get the initial finish much smoother than that. Keep practicing and you'll get it.
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post #24 of 27 Old 05-08-2008, 04:56 AM
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Yikes, that "before" pic makes me think I could have done better with a spray can. I do want to read your polishing section though so keep it coming.
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post #25 of 27 Old 05-08-2008, 11:09 AM
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Quote:
Originally Posted by Kubbie View Post

Hey, not my thread - post away. That's why I reserved the first few for myself, but any other finishes others have used with success, techniques or tips, please share.

This piano, gloss black on a flat surface is one of the hardest of all finishes to do. Expert finishers will tell you it's not easy. It's me going to the plate and trying to hit a homer off of Zambrano - rookie trying to get a pro result on the first attempt.


NO CAR BONDO ALLOWED IN WOOD!!!!!

I have sprayed a LOT of wood cabinets to a paint finish and you are missing what I consider the most important step - epoxy resin - save the bondo for the car.

Bondo will shrink in wood after about 6 months, its the way the heat of the cure reacts with the wood. What starts off as a smooth finish 6 months later will have all sorts of divits from shrinkage, don't ask me how I know..........

The best way to fix this I learned is to stop by a marine supply store that has 2 part epoxy, the type for fiberglass. Its benign and easy to use as well. You basically mix it and brush or pour onto the entire wood surface, let cure, then sand. Then you can apply any paint you want to it.

Its the "secret" that few want to tell since its really quite simple............

You can also mix additives with it to make it into a bondo like paste. Its all I use on wood now and I also use it a lot on the cars I work on. Person who taught me about it used it on fiberglass airplane assembly (he bought it in the 55 gallon drum).

Learn from my mistake, no bondo in wood.


Nick McKinney
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www.aespeakers.com
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post #26 of 27 Old 05-08-2008, 01:20 PM - Thread Starter
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Quote:
Originally Posted by 2Below View Post

The rough finish out of the gun could be caused by several factors - wrong air pressure, too thick paint/thinner mixture, too far from material when spraying, etc..

2Below nailed a few things I had off on this spray job. I detailed some of them in post #3 wich I edited.

I used a lacquer by Valspar, before I had always sprayed with Milesi with 5% thinner and didn't have this problem. Turned out that the Valspar needed about 15%. It was too hot off the gun.


As for the polishing, got a bit of the delay there. My 7 year old son liked how shiny the top was, so he thought he would make it "more shiny" by taking some 220 sandpaper he picked up in the garage and sand the top.
Didn't get too far, but far enough before I saw and stopped him.

To get to the polishing, you need to leave it for about a week to cure good and hard. I need to figure out how deep he went - if I can sand it down and just hit it with clear, or start with some black first...!! (And then wait another week to cure...)

Quote:
Originally Posted by nickmckinney View Post

NO CAR BONDO ALLOWED IN WOOD!!!!!
Nick McKinney

Nick, is this over wood, or MDF substrate that you saw shrinkage? I've done it over MDF before and not seen it. Then again I haven't done much with a 90 sheen with this high of a gloss. Do you have any pics of the shrinkage? I'd like to know so I don't lead people in the wrong direction, have them put a lot of time and $ into paint to have it look off in 1/2 year...

What do you use for filler Shinobiwan?
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post #27 of 27 Old 05-08-2008, 02:26 PM
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Quote:
Originally Posted by Kubbie View Post

Nick, is this over wood, or MDF substrate that you saw shrinkage? I've done it over MDF before and not seen it. Then again I haven't done much with a 90 sheen with this high of a gloss. Do you have any pics of the shrinkage? I'd like to know so I don't lead people in the wrong direction, have them put a lot of time and $ into paint to have it look off in 1/2 year.


Have seen it in both MDF and Baltic Birch. I still have a pair of auto finish cabinets that show little spots from where I filled in the staple holes.
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