Paint & humidity

[Brandish]

Hey guys,

Let me first state that I'm pretty much clueless on painting at this point, but I'm hoping to expand my knowledge a little... I currently work as a car audio installer, so my bodywork skills are pretty limited. I've been working on a fibreglass sub box presently that I've decided to try painting myself...



That's an older pic. Since then I've re-sanded the entire thing starting with 40 grit, to 80, 120, 220, and finally 400. I'm filling in all the pin holes with glazing putty, and then spraying it with high-build primer so I can wet-sand it sometime in the near future. So... I went to a local autobody supply store and bought some acrylic-enamel paint (in aerosol format) to finally finish this thing. My only concern is with the final finish... I was testing out the look of the paint on a small part, and it looked fine during the process, but after it dried I noticed a number of small bubbles had formed on the surface at some point. I'm just wondering if this had anything to do with the humidity in the air at the time (it was about 39 celcius with humidity that day), or if it's just something I'm doing wrong. I'm also debating whether or not to clear coat it, and if I do what the process would be for that. I'd like the finish to be as shiny as possible. One other thing... I used to always just buy the crappy paint from the auto parts store that you could scratch off with your fingernails after it had dried. I was really hoping that this paint would give me a harder finish, and although it was much better than that crappy paint, I found I could still scratch the surface if I dug my fingernail in hard enough. I'm just wondering how you gurus get that glass-hard finish that is more resistant to scratches.

Thanks in advance for any help, it is muchly appreciated!

[mike@af]

Acrylic-enamel, personally I hate it. Its especially a rather soft paint out of an aerosol can. With enamels there is know cure time what so ever, the paint never cures completely.

For a harder finish you should get some Acrylic-Urethane. Its some of the most durable stuff on the market. I also reccomend against aerosols and spending the money on a spray gun, and by a half gallon (sorry dont know the metric) of some PPG K36 High Build primer, about 3 pints or so of PPG acrylic-urethane base, and about half gallon of PPG acrylic urethane clear. Of course you will have extra.

That glass finish is achieved by wet sanding the base coat, wet spraying the clear, wetsanding the clear, using rubbing compound on the clear, and high quality paint.

I never paint outside because of the humidity. Humidity is one of paints worst enemies. I always paint in a booth, so see if you cant find one, or make one.

[Brandish]

Thanks for the info!

We actually do have a spray gun in the shop I work at and a small compressor. I bought the aerosol cans because they're obviously cheaper, but I'll definitely try the urethane in the future.

[mike@af]

Forgot to add, your fiberglass work looks very good. One fiberglass user to another, did you use the draping cloth that you just "paint" the resin over, or did you actually use real fiberglass?

[Brandish]

Thanks for the kind words!

I actually used fleece as a medium to stretch over the MDF framework, and then I painted a few layers of resin over the outisde, one on the inside and then the rest of the strengthening was done with kitty hair. It's over 1/2" thick in some spots and is very solid. You can see some more pics here, and a more thorough explanation.

Another qestion actually while I'm here... When wetsanding for the polished look, I'm assuming I'm using really high grit paper, like 2000+? And I'm also not sure what you mean by "wet spraying" the clear coat...

Thanks again!

[mike@af]

Originally Posted by Brandish

Thanks for the kind words!

I actually used fleece as a medium to stretch over the MDF framework, and then I painted a few layers of resin over the outisde, one on the inside and then the rest of the strengthening was done with kitty hair. It's over 1/2" thick in some spots and is very solid. You can see some more pics here, and a more thorough explanation.

Another qestion actually while I'm here... When wetsanding for the polished look, I'm assuming I'm using really high grit paper, like 2000+? And I'm also not sure what you mean by "wet spraying" the clear coat...

Thanks again!

That kitty hair works wonders, though I havent used it. I have seen it done, normally I use just some 9oz. fiberglass cloth, or bi-directional carbon fiber whatever the case may be.

Yes, wet sand using a water-dishwashing soap mixture with some 2000 grit paper. The dishwashing soap acts as a lubricant, only add a little to the water. Wet spraying as in, dont mist coat. Put a lot on, but not to much. Its hard to explain really. Basically make sure you have a nice smooth layer after spraying. Just make sure it isnt thick, as it will crack or run.

[Markgase2000]

I also like the quality of the fiberglass job keep it up dude. I have a phobia it seems when it comes to fiberglass fabrications. What would you suggest I try practicing on for a beginner , I would like to learn how to make it mould perfect and dont know any nice enough peoples to show me just pros who laugh when I say I dont know how , I hate that lol.
The closest I got to working with fiberglass is painting it and I got pretty good at that. How do you come up with/make molds?

[Markgase2000]

I dont mean to sound dumb but wouldnt the enamel work for painting the sub box since its flexible it wouldnt crumble apart with vibrations or is that non applicable in this project?

[mike@af]

Originally Posted by Markgase2000

I also like the quality of the fiberglass job keep it up dude. I have a phobia it seems when it comes to fiberglass fabrications. What would you suggest I try practicing on for a beginner , I would like to learn how to make it mould perfect and dont know any nice enough peoples to show me just pros who laugh when I say I dont know how , I hate that lol.
The closest I got to working with fiberglass is painting it and I got pretty good at that. How do you come up with/make molds?

http://www.automotiveforums.com/vbul....php?p=2091083 theres a post from the new fabrication forum asking about the same thing. I just went through it.

Originally Posted by Markgase2000

I dont mean to sound dumb but wouldnt the enamel work for painting the sub box since its flexible it wouldnt crumble apart with vibrations or is that non applicable in this project?

The sub-box will be minorly flexible. I suggest using acrylic-urethane. Sad to say my uncle (who is an excellent pilot, has flown a few thousand hours, built several planes) hit a runway light on the bottom of the fuselage during take-off. We painted his plane in PPG Acrylic Urethane. There is little bit of a gash in the bottom, but the paint is absolutely unharmed.

[Integra06]

I have to agree and say to use acrylic urethane as it offers the most durable finish. With acrylic enamel, you get a really slow drying finish that I have heard also scratches easily due to the drying time. I've never really done any paint work myself, but I've got a spray gun that I'll be learning to use sometime in the near future. In the end, even though a spray gun finish costs more, you'll be very pleased with the results and realize it to be worth the time and effort. Like anything else, it just takes a little practice to get it down. Good luck and nice fiberglass work also.

[Brandish]

Originally Posted by Markgase2000

I also like the quality of the fiberglass job keep it up dude. I have a phobia it seems when it comes to fiberglass fabrications. What would you suggest I try practicing on for a beginner , I would like to learn how to make it mould perfect and dont know any nice enough peoples to show me just pros who laugh when I say I dont know how , I hate that lol.
The closest I got to working with fiberglass is painting it and I got pretty good at that. How do you come up with/make molds?

I had the same phobia when I tried it for the first time... It's just one of those things you have to keep working at to get good at it. I guarantee you'll botch your first project, or it'll look so unbelievably horrible that it's probably not even worth painting, but that pretty much comes with the territory. Live and learn, try again and do a little better...

Anyways, I don't make molds for mine, that's just way too much work and I don't plan on putting any designs into production really. If you're interested in molding techniques, JL Audio has a pretty detailed overview here (Adobe Acrobat needed), but it seems like a whole lotta work. I normally buld the frame out of MDF (cuz it's cheap, strong) to stretch the fabric over. Basically with that project I built a rectangular frame for the base, cut out three 10" rings for the subwoofers and made some mouting "arms" to fasten the rings to the frame. I used glue and screws to hold the whole thing together. I've found that building a strong frame is absolutely essential, because you'd be surprised at how much pressure is put on the frame when you stretch your material over. It has to be stretched super-tight to get the curves to conform properly. So, I used fleece for the material. You can use anything from fleece, to grille cloth, to pantyhose, but I find fleece is the best because it's cheap (especially the butt ugly colours), it's flexible, and it absorbs a ton of resin on the preliminary coats. This avoids having to add more layers of mat/resin underneath for strength. I used an air stapler to staple it down, which is pretty much necessary for firing into MDF. Spring-loaded staplers don't really have the balls to flush the staples down properly. After that, I used the leftover circles from the MDF rings to hold the fleece down over the odd angles on either side of the center ring. I just screwed them down temporarily, but forgot one important thing: I didn't tape them off or cover them in some kind of mold release, so of course after the resin cured I had to essentially break them off, and that left some repair work for me. See, you learn a new thing every time. Once that was done I got my bag of dollar store paint brushes and latex gloves and started painting the resin on. One thing about the resin, it's best not to use it on really hot humid days. A lot of small bubbles formed in the top layers, and had to be filled in later. Also, if the resin is fairly thick, you can add some thinner to thin it down so it will absorb into the fleece better. And make absolutely sure you mix the resin thoroughly with the proper amount of hardener. If you skimp on mixing, you'll end up with little pockets of uncured resin (like mine did), and they're a pain to deal with afterwards. Resin usually cures completely in about 1 1/2 hours, so take your time. After that dried, I started underneath with the kitty hair. This was an exploratory thing for me, as I had never used the kitty hair before. It lays up nice and thick and cures faster, but isn't as strong as resin/mat would be of equal thickness, so I guess it's a trade-off. It's pretty strong, but I think the resin/mat is the better way. After your box is firm, be prepared for 99.9% of the work... sanding. Start with 40 grit to knock it down, and don't be shy. Trust me, if you're not meticulous about sanding, you'll see the imperfections as soon as you lay the primer on. So... use the 40 to rought it up real nice. After that point your basically just sanding your sand marks, so go down to 80, 120, 220, and by that point it's usually safe to lay on your high-build primer, or you gould sand with 400 before that, your call. Cover the whole thing with a coat of primer, and then find an area with good lighting because you're about to see every little pinhole and divot that you thought never existed. Fill those in with spot putty, and fix whatever areas need fixing (there'll be lots ), sand it all back down to 220 and then prime again. A good idea at this point might be to test it out with a guide coat, so just go to any automotive store and get some glossy paint of any colour. Spray your surface with it and look over it again with good lighting, and you'll probably see more imperfections. The gloss finish (which is eventually what you want) will show everything, and it's real disheartening sometmes because you think to yourself... sh!t, I've sanded this thing for hours and I'm still seeing imperfections, but that's the way things go with this kind of work... Anyhow, if you do do the guide coat, it might be easier to just to that even before the primer because sanding enamel is harder than sanding primer. So... once your satisfied with your surface (or just plain fed up), lay up a decent amount of primer, let it sit for about 20-30 mins and then wet sand with 400 grit to smooth it all out. Wash off all the residue and then decide whether you want a professional (like GTMike) to paint it with the proper tools, paint and environment to paint it, or if you want to tackle it yourself. If you're doing it yourself, heed all the advice you can get from the experts here. Get a proper spray gun/compressor, learn how to use it, buy some decent urethane paint, find a relatively cool/dry/well-ventilated/particle-free area to do your duty and then go nuts. A respirator probably wouldn't be a bad idea either because the fumes will eventually kill you.

If you want to see some phenominal work with progressive pics, check out this page. This guy is an animal, and his fabrication skills are out of this world. If I could be 1/2 as good as that, I'd be a happy man. For the record, he's been doing that for 15+ yrs and still gets his painting done by a professional.