Blasting and powder coating a fillet brazed frame

[klunkrider]

Chatting to the lads in my local bike shop yesterday and posed the question in conversation. It's not a Giant Concept store but a pretty oldschool shop I may add.

Is it safe to blast and powdercoat a fillet brazed frame, I'd always thought it damages the brass.

One said no problem, one said no way

What's the consensus?

The heat in the oven isn’t what you need to be worried about, it’s the heavy handed operator of the blasting equipment who is more used to smashing his way through thick layers of paint and rust on a handrail that’s made of tubing that’s about 10x as heavily walled as bicycle tubing. He’ll **** your day/frame up in a heartbeat.

Also I’m of the opinion that powder coat is about the most harmful thing you can do to a steel frame but I know that’s an unpopular opinion.

 

[widowmaker]

I'm using a Powdercoater that's done loads of bikes before and well known and pretty sure they will take care of it. Fellow Retrobikes have used them.

Don't want to start a bun-fight but I'm m interested as to why it's the worse thing I can do. Getting wet paint is expensive and powdercoating will give it decent protection doni can use it in anger ?

 

[klunkrider]

I'm using a Powdercoater that's done loads of bikes before and well known and pretty sure they will take care of it. Fellow Retrobikes have used them.

Don't want to start a bun-fight but I'm m interested as to why it's the worse thing I can do. Getting wet paint is expensive and powdercoating will give it decent protection doni can use it in anger ?

I repair cracked frames and a ‘kind of recent’ powdercoating job seems to be a common denominator in these frames that develop cracks.

I’ve spoken to people in other industries who have told me that if they blast one side of a sheet of steel it’ll become concave/vex and the other side must be blasted in order to restore it to flat, this tells me that the blasting is introducing stresses and tensions into the steel and this is something that you strive to avoid as a builder so why would you be happy subjecting a complete frame to it? I definitely feel like this might be a contributing factor in the failures I’ve seen. Yeah, some places will be careful with media and pressure but the majority are more used to doing the handrails and gardens gates. There was a post on another forum I use from someone who had their frame blasted in preparation for wet paint at a place that specialises in bicycle restoration and they appeared to have blown through the tubing in several places.

It used to be said that a good framebuilder would/should never do just a clearcoat on a steel frame as clear lacquers generally aren’t impervious to moisture and they have no anti corrosive properties so they don’t really do a proper job of protecting steel from the elements. I think that at least with clear coat you can see the patina (rust) develop and can do something about it whereas powdercoat still (generally) lacks the anti corrosive properties but does a really good job of hiding what’s going on underneath.

I think maybe on an aluminium frame which would (I think) have thicker walls which would be more forgiving of this stuff then it’s alright but I’d always recommend against it for steel.

 

[widowmaker]

Thanks for the info, much appreciated.

 

[minor_LEGEND]

https://www.retrobike.co.uk/threads/british-steel.188154/page-23#post-1549572
My grey freshly powder coated & fillet brazed frame as photographic evidence. Sorry I can't post the pics directly.

 

[Old Crank]

It used to be said that a good framebuilder would/should never do just a clearcoat on a steel frame as clear lacquers generally aren’t impervious to moisture and they have no anti corrosive properties so they don’t really do a proper job of protecting steel from the elements. I think that at least with clear coat you can see the patina (rust) develop and can do something about it whereas powdercoat still (generally) lacks the anti corrosive properties but does a really good job of hiding what’s going on underneath.

Spot on!
Powder coat has the misconception of providing corrosion resistance, it offers no better protection than wet paint.
It is classed in the industry as a decorative coating, the only way to guarantee corrosion resistance is with galvanizing.

The quality of finish of powder coat compared to wet paint is poorer imo.

 

[Stressed]

Good to know

 

[klunkrider]

Spot on!
Powder coat has the misconception of providing corrosion resistance, it offers no better protection than wet paint.
It is classed in the industry as a decorative coating, the only way to guarantee corrosion resistance is with galvanizing.

The quality of finish of powder coat compared to wet paint is poorer imo.

Afaik, most people doing wet paint on bike frames will be using a primer with some sort of anti corrosive property. I am certainly not a pro painter but I use a zinc rich primer which gives anodic protection so that even when chipped or scratched enough to expose bare metal, it still shouldn’t rust.

Frames can can be dipped or otherwise coated with an anti corrosive agent before powder coating but a) the handrail mob definitely ain’t doing this and b) I expect the cost implications would render it uneconomical for a one off job.

 

[widowmaker]

It's all too much for my brain

The concern I have is that to get a decent wet paint is going to be several hundred pounds and for a frame worth around £300 it's almost uneconomical.

Obviously I'm not going to leave it with the handrail boys, and with someone who has done many before and for fellow Retrobikerd.

 

[klunkrider]

Pretty much the reasons I started painting stuff myself.

As I’ve said, I’m definitely not a pro and my paintjobs are an acquired taste but with the combination of zinc primer, a pigment heavy paint and a heavy duty lacquer I’m satisfied that they are anti corrosive, durable, affordable, quick and I like the looks I’ve managed to create.