SANBLASTING!!! Good or BAD

[rad006]

Hi Guys

Im rebuilding a bike for a mate and need to strip his old paintwork is it ok to just sandblast the frame???

 

Also seeming as its alu and its rusts on contact with air do I need to prime it right away after sandblasting???

 

If so is there a special primer or can I just use normal metal primer???ie that brown/redish stuff

 

Bike will be painted with normal 2k afterwards so would like to know if my thinking is fine

[rad006]

Oh also should I paint or powdercoat if its going to be 1 colour???

[AndreZA]

Don't sandblast but rather beadblast it with wallnut shells.

 

 

 

If you are going to do one colour and don't mind the stickers to be put ontop of that then go powder coat. Otherwise have it painted with base colour and clear coat.

 

 

 

I think you would need alu primer.

[rad006]

But is Powder Coating better??? Its on an HT so no bearings to worry about and little scraping needed.... I mean whats more tough

[Capricorn]

sandblasting wont be an issue really: just protect any threaded portions.

 

 

 

Also, aluminium does 'rust', but not in the sense that the word rust conveys. It forms a very thin oxidised layer that actually protects the aluminum underneath, so there is no real danger of huge amounts of material loss as one expects when mild steel or iron oxidises.

 

As long as it's not exposed to the elements, you can leave the primer off: choice is yours really.

[rad006]

Thanks Capricorn

Cos there will be a delay between sandblasting and painting and im worried that if I dont prime it then I will have some serious issues later down the road

[Bos]

Powdercoated Is a bit harder I think but you can also go for a 2 part automotive paint which is mixed with a hardener.

 

prime it right after you sandblast it so that "layer" mentioned above dont form, the paint will bond better with raw ali.

[rad006]

So u saying dont prime BOS???

[Bos]

No, sorry, You still prime, what I ment to say was just dont wait for the layer of oxidation to form before you Prime ( I said paint )

[rad006]

Ok so sandblast then prime right away...

 

but now is there a different primer ie steel to alu???

[IanJ]

Ok so sandblast then prime right away...

 

but now is there a different primer ie steel to alu???

 

Yes Alu needs a self etching primer, can get it from auto paint places.

 

[RodTi]

Does the above apply to an old steel frame as well?

[RABUBI]

sanblasting?

 

 

 

Almost thought you want to go bushmen hunting????

 

 

 

You forgot the d in sand

[rad006]

Thanks Ian

[Capricorn]

Does the above apply to an old steel frame as well?

I would have to hazard a guess which says No. Old steel might not be a of the exotic/near-aircraft grade steels/aluminums they use today, thus them being more prone to very obvious corrosion, which will require some work removing.

Keep in mind, that stressed portions of a piece of metal acts as an accelerant wrt corrosion. That's why, on items that have been pressed to form a shape, such as car bonnets and bootlids, the corrosion in older models of cars tended to occur at these bent sections, all because of the stresses incurred during the shaping process.

 

Similarly, your bike's welds and sharply curved portions might be stressed if not properly heat treated to relieve these stresses. On older steel frames, this more than likely the case. So leaving exposed steel surfaces to even air, much less more aggressive conditions such as outside in varying temperature and rain, those stressed areas will start corroding the fastest. Note: stresses also occur over time in parts of the frame that are not that obvious. Check elsewhere on Thehub for some thread which clearly shows a Cannondale almost shearing off mid way thru one of its tubes. Cannondale calls it 'normal' fatigue failure. (frankly, i would luv to simulate that particular frame using some finite element analysis software to determine if that area is prone to fatigue, and compare it to frames from competing manufacturers. Might point to a design failure on behalf of Cannondale)

 

So corrosion can be accelerated almost anywhere depending on where residual stresses are highest.

 

I would recommend slapping on some primer on steel frames as soon as possible after removing it's protective layers of paint.

Capricorn2009-05-13 04:09:06

[slowtwitch]

I'm out of my depth on this topic, but....

 

DON"T SANDBLAST!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

I just had an old steel frame sandblasted with "old shot" as they call the "sand" already used, primed and painted.

 

I was there when it was done. The problem is even if they use old shot and even if the blast it only "lightly" the frame comes out like sandpaper which the primer, paint nor clear coat hide.

 

If you want that smooth finish don't sand blast