Author Topic: Filler for powdercoat  (Read 2825 times)

rogerzilla

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Filler for powdercoat
« on: 08 February, 2019, 06:48:26 pm »
This is a new one on me.  I bought a rather tired-looking (but perfectly straight)  frame and took it off to be powdercoated.  The powdercoaters have blasted it clean but say there is some filler under the paint (covering small dings, presumably) and this will leave a mark if the frame is powdercoated. 

Apparently some fillers can take the 200 deg C temperature used to cure the powder and also have good conductivity to allow the powder to stick.  Any ideas which?  I have four options:

1. Sand out the existing filler and use something more suitable
2. Get them to blast it out and coat it, leaving the dents as they are
3. Fill it with normal body filler and do a rattle can job (will have to wait until much warmer weather)
4. Get it enamelled instead - not economic, as it's a gift for someone

EDIT: some alloy wheel filler (not expensive) claims to do the trick.  Very high metal content and resistant to powdercoat temperatures.  Makes sense: the professionals fill kerbed wheels all the time before powdercoating them (not the guys who do it in a van, the big workshop-based outfits like BJV Engineering, who are excellent by the way if you're within reach of Chenies/Hemel Hempstead).
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.


Torslanda

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Re: Filler for powdercoat
« Reply #2 on: 11 February, 2019, 09:07:56 pm »
Wurth also sell a high temperature filler which gets good results in a powder coat.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

rogerzilla

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Re: Filler for powdercoat
« Reply #3 on: 12 February, 2019, 02:32:41 pm »
Turned out to be silver solder rather than filler.  Sloppy framebuilding, Holdsworth must have used dented tubes to avoid scrapping them.  At least, I hope it's not ordinary electrical solder, as that melts at about stoving temperature instead of 650 deg C!

They're going to shove the bare frame through the oven at 180 deg C  just to check it doesn't melt, before applying any powder.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

rogerzilla

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Re: Filler for powdercoat
« Reply #4 on: 13 February, 2019, 01:17:19 pm »
And...it was crappy electrical solder!  Looks as if this will be a rattlecan job for the summer, unless anyone knows a surefire way to remove all traces of solder from the frame (I'm thinking a blowlamp and desoldering braid, but it could be super-laborious).
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

jiberjaber

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Re: Filler for powdercoat
« Reply #5 on: 13 February, 2019, 01:26:03 pm »
And...it was crappy electrical solder!  Looks as if this will be a rattlecan job for the summer, unless anyone knows a surefire way to remove all traces of solder from the frame (I'm thinking a blowlamp and desoldering braid, but it could be super-laborious).

gental blow lamp to get it flowing, hanging upside down from the dent then flick out with a screwdriver.... (obvs being careful etc)... should reduce the amount of braid you'd have to use.  I think you will still end up with some coating where it has flowed on to the metal.  ???
Regards,

Joergen

Re: Filler for powdercoat
« Reply #6 on: 13 February, 2019, 01:33:41 pm »
old electrical solder is a eutectic composition and wouldn't be used as a filler. Higher lead content solders have a broad 'mushy' range and in the past were used for 'wiped' soldered joints and as body filler in car repairs.   It is most likely that you have that kind of solder, used in the same way as 'lead loading' would be used in car body repairs.

If you used something other than powder coat to finish your frame, you could leave it be. As it is you have a potentially toxic problem.  The lead loading should just wipe off (eg with a piece of leather) when molten; it needs encouragement to wet onto a steel surface and will soon de-wet unless there is flux present.

cheers

Kim

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Re: Filler for powdercoat
« Reply #7 on: 13 February, 2019, 01:44:14 pm »
And...it was crappy electrical solder!  Looks as if this will be a rattlecan job for the summer, unless anyone knows a surefire way to remove all traces of solder from the frame (I'm thinking a blowlamp and desoldering braid, but it could be super-laborious).

Not sure if it'll help, but super-low-temperature solder removal alloys are a thing:

https://www.chipquik.com/store/index.php?cPath=200

The idea being that you dilute the solder with the magic stuff, then it stays molten for *much* longer than usual - primarily helpful for removal of large SMD components that are difficult to keep at soldering temperature without damaging the board.

rogerzilla

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Re: Filler for powdercoat
« Reply #8 on: 16 February, 2019, 03:12:39 pm »
It's off now - blowlamp and a damp sponge.  There may still be traces on the surface, so it'll be a rattle-can job.  I'll rotary wire-brush it (it's been blasted already), fill the dents and prime it for now.  No point spraying colour or lacquer until the weather is warmer.

I'm thinking VW L50B Diamond Blue, which is that baby blue you get on old Beetles.  Dark colours are harder to spray at home, as are metallics.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

Re: Filler for powdercoat
« Reply #9 on: 20 February, 2019, 12:55:36 pm »
If you're going the rattle can route, take a look at that Spraybike stuff. I did a frame in it last year and it's such a joy to use compared to regular rattle cans. Limited colours unfortunately.

rogerzilla

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Re: Filler for powdercoat
« Reply #10 on: 20 February, 2019, 05:30:05 pm »
I might get a Pantone colour mixed up.  I want a light turquoise or lavender (haven't decided).    Acrylic is what I want, isn't it?  It'll be acrylic lacquer over, and Isopon Zinc 182 primer.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

Re: Filler for powdercoat
« Reply #11 on: 20 February, 2019, 07:13:36 pm »
182 primer is basically cellulose, I think. This is OK with a layer of acrylic on top but what you shouldn't do (I think)  is use cellulose over an acrylic layer; this is what causes cracking/crazing to occur.  So I think you can use 182 primer, either type of colour coat, and acrylic clear coat.

However if you have to go back and do repairs, you have to think carefully if you used a mixture of paints. There are two common circumstances;

a) you need to feather back all the colour coat when spraying primer locally, (i.e. so that no colour coat sees any primer overspray) if you used acrylic colour coat. Similarly

b) if you used a cellulose colour coat, you need to remove the acrylic clear coat completely if spraying a small repair area with fresh colour coat. This is less easy to do well, because you can't always see if there is clear coat remaining.


FWIW 182 primer doesn't give quite such a nice finish as a standard cellulose primer, plus it dries slowly and it costs more. Thus I often use a couple of thin coats of 182, then spray with a standard cellulose primer. The latter is usually slightly lighter in colour and dries a bit faster too. This means that when rubbing down if you see the darker 182 colour showing through you know the metal is not far away, and maybe you should quit rubbing in that area or spray another coat or two of primer.

With a bit of elbow grease you can get a DIY paint job that is mirror-smooth even using aerosols for the colour coats, provided you can cut the colour coat back.  However it seems that most aerosol acrylics stay soft for ever; thus the finish chips through to the primer quite easily. If the primer is cellulose this part eventually dries very hard indeed, so rust from minor knocks is at least unlikely.

 One of my plans is to try a two-pack clear coat, (now available in aerosol form) hoping that it will be both tougher and it will resist a type b) recoat problem, since once two-pack is cured, you can spray anything over the top of it.

cheers

rogerzilla

  • When n+1 gets out of hand
Re: Filler for powdercoat
« Reply #12 on: 20 February, 2019, 08:57:01 pm »
I've done cars with rattle cans and got a good finish.  The tricks are to only spray in warm dry conditions (primer is less fussy) let the colour and lacquer coats dry really hard (2 weeks for lacquer) and cut back with 2500 grit wet and dry, used wet.  Final polish of lacquer with a really mild compound like Meguiar's ScratchX.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.