Painting preparation: keep the filler or sandblast it off? - Page 2
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  1. #21
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    Glad to see you didnt strip/blast off the old paint, pretty pointless unless youve got stability problems with it (cracking / peeling / mapping etc).

    As Mark said, using a guide coat over filler, before/after primer is a good idea, it lets you know visually where youre at, all the better if you dont trust your 'feel'. A cheap can of satin black is fine.
    Dont bother with the 'air dry' fillers btw, they move all over the place, not stable.

    The finish you got looks nice to me. I you feel its a little tight then give it a decent denib with 1200 before a final coat. If youre worried about runs you can wind the needle in a touch and go over it a few times instead of one heavy pass. Ie lite coat, wait a minute, second lite coat, wait a minute to see how its flowed out etc. Repeat till youre wet enough. Can get it like glass when you get a feel for the paint.
    Or you can chill out and wind out that needle and go for the finish. Its no Bentley

    I like youre extractor wall type setup. At 1 metre per second could almost do without the mask. Can mix your paint and fillers next to it for a fume free experience.

    Good job sir

  2. #22
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    Hi Mark,

    thanks for the tip. This wasn't needed, as I didn't need to remove much, a couple of wet passes of 1000 wet-or-dry did the trick. After 15 minutes of sanding each piece I then laid on another coat, this time going much thicker than my previous coat. No runs, and this flowed out nicely. I'll let it cure for a couple of days, then kiss it with some 2000 grid and rubbing compound. Here are the three parts (color is the same, lighting is different):



    This long arm is the part that I did NOT sandblast, I just wet sanded until I reached firm material.



    I sandblasted this sheet metal cover.



    I also sandblasted this head. I think that was a mistake, in the future I'll only blast areas that have lost all paint and filler already.

    Here's a shot of my painting area. I made a cardboard cover that goes over the (open) window, but it's not shown here because the window is closed. The arm is on a lazy-susan bearing to make it easy to spin around while spraying it.



    The purpose of the plastic sheet is to increase the air velocity at the opening below, but to let in some light so I can see better.

    Air velocity calculation: fan moves 1500 CFM = 42 cubic meters/minute. The opening below the plastic has a cross section of about 2 x 5 feet = 10 square feet = 1 square meter. Hence the air velocity is 1500/10 = 150 feet/minute = 2.5 feet/second or 42/1 = 42 meters/minute = 70cm/sec.

    After reading about isocyanates, I would never use them without a mask, and do not recommend that anyone do this, no matter how good their spray booth is.

    Cheers,
    Bruce
    Last edited by ballen; 03-21-2016 at 07:32 AM.

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  4. #23
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    Not recommending you dont use use a mask Bruce. Just pointing out that with your setup, your mask maybe doing no work. Youre standing up wind of the gun all the time spraying in this way and providing youve enough extraction, the vapours are only going one way. Easy to check, with no mask, put some thinners (no isos in the thinners) in the gun and have a blast. Hand on heart can you smell anything? If not you can ask yourself the question , or not .
    Im guessing you have a single fan, the one shown on the exhaust side, which would make the air intake passive. I get the the maths, and from what I can see youve no exhaust filters to get plugged (good for airflow), but the flow rate will depend greatly on your air intake size. 300mm x 300mm window? - 2m x2.5m garage door? Big difference.
    Location of the intake and exhaust are also kinda important.



    Nothing to fear but fear itself eh.


    The guide coat you only really use when taking down fillers and primers
    In my time ive tried it on a finish, once lol. Found no benefit over a squeegee n eyeballs.

    Seriously Bruce, thats a nice looking 9/10 finish you got right there. Unless its chock full of nibs that dont show in the pics would probably be best to leave as is. You can colour sand and buff up with 3M's n Farecla's finest and go for glass. Just be prepared for the heartbreak when the chips start to fly.

    Cheers
    D

  5. #24
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    Hi Demon,

    The mask is absolutely necessary. The strong odor of thinners is everywhere without it.

    My air inlet is the main door, which is 2m high. I block it open about 20cm, so cross sectional area is 0.4 square meters, much bigger than the fan which is 50cm diameter.

    The main door is located diagonally across from the window, so the internal airflow is directly across the room, and externally there is no flow-back.

    I think 9/10 is right. There are a couple of embedded dust particles here and there, so it's certainly not better than 9/10. I agree that this is good enough, if I was refinishing the entire machine I'd be happy and stop. But I want it to match the original machine finish for the parts that I am NOT redoing. And those original Deckel-finished parts are perfect, new-car quality finish (apart from chip scratches and handling wear. Yeah, it won't last long but it's will match what is there.

    Cheers,
    Bruce

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    Understood Bruce. My general view is that if you can smell it, mask or no, theres a problem.

    With a passive intake I found that big is good, biggers better. You might find your odour situation improves greatly with the door wide open. Especially if the fan is a low power unit.

    Re dust contamination. With the fan on and the door wide open, you can take an airline and blast the door frame, room, yourself and extraction box down. Just before spraying, is a good idea to wear clean overalls, blast work and box with air and tack wipe off before spraying.

    If nibs are still a problem, you might like to try a nib file before the 2000. Sounds horrendous but after youve a feel for it, in practice theyre nice to use , give a better result on large nibs than just paper. Runs cut down well too.

    Anyways, youre doing fab by looks of it. Better than some of the 'new car' finishes ive had to work with.

    Cheers

  7. #26
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    Hi Demon,

    I experimented with having the door open more, and it didn't increase the airflow measured from outside the window with the fan in it.

    Indeed being sensitive to solvent smells is important, because the isocyanate is low/no odour. So the clue that something is wrong with the mask is when you can sense regular solvents.

    I eliminated dust just before painting by putting an empty sprayer on my HVLP air supply and then blasting in and around the paint booth with that, while the extractor fan was running. I did not want to use a regular compressor because I am worried about oil and other impurities in the air from that compressor. I am pretty sure that these nibs came about because when I cleaned the gun, there was one seal with I did not realise could be taken off. That had some hidden flecks of cured paint behind it.

    I have never heard of a nib file. Scary looking! All the nibs will come off with wet sanding @1000 grid or greater, so no worries there. There is about 1 nib per 150 x 150mm patch, so perhaps 50 per square meter. Too many for car painting but OK for small machine tools. All in all, I might have 5 or 10 nibs in total across the 3 pieces that I painted.

    Your comment about new car finishes made me wonder, are you a pro at this? No question that experience here counts. I am sure that someone who does this day-in and day out would have done this job much faster and better than me

    Cheers,
    Bruce

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    Well ive had around 15 or so years painting cars / motor bikes and a few odd balls, mdf kitchen units were different. Its the only real experience I can offer the forum. Been a few years since ive layed hands on a gun though.

    Yeah the hardener is usually pretty low odour, but the paint and thinners you mix it with are high odour. Its the wet uncured airborne vapour thats the main problem with the 2K stuff.

    Nib files are nice for cutting runs and if you want preserve the 'peel' of a finish. Important when trying to match a peely finish. When just using paper things always smooth out, when using 2000 to cut down before buffing, nibs can appear as a slight lump amid a flatter finish.

    Nibs can truly come from anywhere, even the paint youre using.

    strain.jpg

    Anyways im waffling

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  10. #28
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    I'm ready to close out this thread. This past weekend I got a couple of hours free, and wet sanded the paint (3000 grit) then rubbed it out (3M black compound). I think this is pretty close to factory original. Bottom line: if the old filler is sticking, keep it.









    Cheers,
    Bruce
    Last edited by ballen; 04-05-2016 at 03:54 PM.

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  12. #29
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    Very nice.....I would say even beautiful!

    One of these days I need to get around to painting a couple Deckel items that have seen better days.....

    Kevin


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