Conductive paint questions

Discussion in 'Hardware, Setup & Repair [BG]' started by DiabolusInMusic, Mar 17, 2014.

  1. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    I have a bass with some hum that has some extremely tight pickup routes. Tape is not going to be an option, it will just get bunched up and pushed down. There is basically zero clearance from pickup to body. I am hoping to use some conductive paint but I have never used the stuff, when I have seen it done it was from Fender and didn't work since it was poorly done. This is a rather expensive bass so I am really not about to route it.

    Does the paint build up any kind of texture? Will it work in a zero clearance situation? Is there a local source that might carry it instead of ordering the stew-mac stuff? I have seen the homebrew method with graphite but I would probably just buy the real stuff than try to concoct my own. Has anybody used copper foil to conductive paint to solder a ground as opposed to installing a ground screw? There is a grounded brass plate under the pickups, I am assuming that connection would be sufficient to touch the conductive paint but just in case.

    Thanks in advance for the help.
  2. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    I've used both conductive paint and copper foil extensively for many years. It used to be that the copper foil alternative was considered to be the best, but times have changed along with technology. Now a decent quality conductive paint like you would find at Stew-Mac can out-perform a job done with copper tape. It's worth noting that most (if not all) of the high-end builders use a quality conductive paint these days. But you need to be thorough in it's application.

    Not only do you have to give a full thick coating on all the cavities, you also need to coat the inside of the drilled tunnels between the routs. And you have to ensure that the underside of the pick guard and cavity cover plates are well coated and that the coating (or foil) makes contact with the cavity shielding paint. None of this is difficult - it just requires attention to detail.

    If done carefully, you will have a very effective shielding without the hassles of tack-soldering the foil joints and the hassle of the folk not sticking well in the difficult areas.

    I still wil do foil if the customer insists. But I prefer the paint - not because it is easier, but I have also found it to be more reliable in the longer term.
  3. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    The basses I build all have complex shaped control cavities. Years back, I used to shield them with copper tape, which was a huge amount of labor. I've also used the Stew-Mac paint, and never really liked it. It's carbon based, so it has higher resistance. You have to put it on thick, and it tends to flake off and leave conductive powder floating around in the control cavity.

    About 5 years ago, I switched to SuperShield, from MG Chemicals. It's available online and from most good electronics stores. SuperShield is nickel-based, basically nickel powder floating in a polyurethane base paint. It's very low resistance; a cavity is typically only 1-4 ohms across it. It's available in spray cans and small touch-up bottles. I use the spray cans. Usually two thin coats are all that's needed; I spray them 15 minutes apart and let them cure for 6 hours. Nice and neat and simple; a silver-gray color. It dries hard and doesn't flake off at all. In fact, it's fairly hard to remove. You can't just scratch it off.

    SuperShield isn't cheap; about $35 per spray can, which will do about 15 cavities.
  4. CrashClint

    CrashClint I Play Bass therefore I Am Gold Supporting Member

    Nov 15, 2005
    Wake Forest, NC
    DR Strings Dealer
    In situations I can't use tape I use conductive paint. I will put two coats of conductive paint and I will normally still put tape at the bottom of the cavity and solder a wire from the tape and run it to ground in the control cavity.
  5. bassbenj


    Aug 11, 2009
    I try to NOT use conductive paint if I can avoid it. But sometimes (as in your case) you can't avoid it. As you can see by comments, paint is great if someone else is paying and you are doing the work because it's much easier to use but expensive. And it's also very variable. Sometimes it works well and sometimes it does not. And that goes for commercial builders like Fender too! Some of this paint is excellent. Ever see the coating on picture tubes? You can't get that off no matter how hard you try! And yet stuff you buy for guitars will flake like mad sometimes. It's all about the BRAND of paint. So listen here for good reviews and pick one of those. I recommend the metal paints (silver is best but VERY expensive).

    And remember that paint needs to be grounded too! I'd recommend a couple of grounds (wood screw and lock-washer lug that "bites" paint). Put them at opposite ends of the cavity. For pickups in tight routs they'll have to be down in the bottom away for obstructing pickup adjustement range.

    A problem with copper is after some time the glue can dry out and the copper lining become loose. This is why I don't like conductive glue copper.
  6. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    Thanks for the help so far. I found MG chemicals Super Shield from my local suppliers, but I can only see spray cans on their site. I am hoping they can order a touch up can as well. Should I use something different than painters tape to mask off areas when working with this super shield?

    Do I really need to line the wire holes? I have never needed to do this with copper foil and still had great results. I would rather avoid removing all the wiring, but I suppose I probably will have to anyways.
  7. I use the Super Shield and just spray it into a disposable cup and apply it with a small disposable brush.
  8. I use cupro-cote from a company called less-emf, it is copper in an acrylic suspension I think, it comes in a small can 4oz and is about 40 dollars when shipping is factored in. It is pretty conductive, see picture, not sure about scratch resistance and flaking off yet since it is the first time I use it. I stopped using foil after a piece came off when I was playing live (damn south Louisiana humidity) and shorted my output jack. :mad:

  9. bobalu


    Oct 1, 2004
    above the 49th
    I have used the Stew-Mac shielding paint with excellent results but it was expensive even back then (several years ago). Judging by the postings here, technology has advanced in the paint field. I've used the copper tape as well, but it was tedious work.

    Notwithstanding what brand of paint you use (if you go that way), the only way to be sure of applying the proper amount (ie: creating the most effective shield) is to test it for conductivity with your multi-meter once the coat dries. Paint 1 coat, let it dry, test it. Repeat if necessary. It will ensure that you use the minimum amount of paint while still achieving a proper shield. With the stuff I used from Stew-Mac several years ago, I think I had to apply at least 3 coats before I achieved full conductivity over the entire cavity. Maybe the newer stuff out there now is much better? IMO, paint is the way to go.
  10. Matthew_84


    Nov 7, 2010
    Has anyone tried applying the paint to the inside of the plastic cavity plate used to cover rear-routed basses?


    I'm thinking of doing this, and attaching a grounding wire with screws from the plate to the inside of the cavity.

    I've never used the paint before myself, and I don't know if it will dry properly to the plastic, or if I'll need to apply a primer of some sort.
  11. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    In the case of plastic cover plates, adhesion can be a problem. It's far easier to use aluminum foil. Use some spray glue to cover the inside surface of the cover, wait until it gets quite tacky, then lay a sheet of aluminum foil over it and rub it on smoothly. If the glue was tacky enough you can trim it up right away. Use an Xacto knife or similar to trim just inside the edge of the cover. It's easy and fast.
  12. Matthijs


    Jul 3, 2006
    I shielded cavity covers with conductive paint. Works just fine. If the cavitiy is shielded and grounded it will make a connection to the cavity shield and ground without the need of an extra wire.

    A cheap alternative is glueing aluminium foil with sprayable photo glue. You spray the cover and place it, glue side down, on a sheet of foil. Copper foil looks better, but this will work too.
  13. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    Just make sure the cavity shielding contacts the foil or paint on the cover when it's screwed down. Bring the cavity shield (paint or tape over the cavity lip and around a screw hole so good contact is made.
  14. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    I acquired some supershield from my local suppliers. I needed some 250k CTS pots but they did not stock CTS at my local supplier. My L&M currently only has split shaft in stock, I don't know if I am going to wait or just screw the knobs onto the split shaft. Where are my fellow Canucks scoring CTS pots from?

    Back to the supershield.

    I will be applying this stuff to nitro basses, do I need to prep the cavities first or can I just spray away? If I did do a poly bass, same procedures?

    Will normal painters tape work to mask off areas where I do not want it? Can I just wipe away any excess? Do I need a special type of brush to apply the stuff?

    I will probably be following Bruce's advice, allowing 15 minutes for the first coat to dry before adding another. I will probably wait a full 24 hours for it to dry though. Good idea? Bad idea?

    I have shielded a dozen basses or so, so the process is not foreign to me. I am always down to collect more tips though, so spout 'em if you got 'em. I am not doing this until next weekend from the looks of it, so if I think of anything between now and then I will ask but I think that is all I need to know.

    Thanks again!
  15. Matthew_84


    Nov 7, 2010
    Regarding CTS pots, I got mine from Stewmac.
  16. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yes, normal masking tape works fine with the Super Shield. Cover your external painted areas. Super Shield is sticky and dries fast. Overspray is tough to get off. I think that the base paint of Super Shield is about like Krylon.

    The Super Shield bonds well to pickguard vinyl, in my experience. It also bonds well to either bare wood or finished wood. On my new basses, I first spray the base coats on the bare wood, including the inside of the control cavity. I do all the sealing and basic level sanding. Then I mask off and spray the Super Shield in the control cavity. Then I cover over the control cavity and do the color coats and top coats. So the Super Shield has a layer of base paint to bond to, which is probably better. But I've sprayed it right on bare wood cavities to, and it's bonded fine.

    The Stew-Mac shielding paint is about like latex house paint. It doesn't bond well to many surfaces, and it scrapes and chips off easily. I gave up on it many years ago. Maybe they've improved it since then, but I think it's still the same stuff. I like Stew-Mac, and they have many great tools and products, but their black conductive paint isn't one of them.
  17. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    Great. Saves me some prep work, although I will still have to rip out of all the copper foil that is in there now first. I was debating spraying the pickup covers, although I might just leave them in copper tape so I can ground them easier.
  18. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    That's the Super Shield in liquid form, for brushing on.

    Here's the aerosol cans, which I use:

    One spray can will shield maybe 20 of my basses. You have to clean the nozzle carefully. I've lost several cans where the nickel particles jammed the valve down in the can, and then the pressure and contents slowly oozes out over the next few days.
  19. Rano Bass

    Rano Bass

    Sep 9, 2006
    Tijuana Mex.