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Author Topic: Priming after sandblast advice  (Read 546 times)

Offline JMPUK

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Priming after sandblast advice
« on: Oct 08, 2017, 16:43:35 »
Hi all

I have have a couple is small pieces sandblasted a couple of weeks ago.

I have kept them wrapped in a dry micro fibre cloth in a dry place however I think from initial contact with them they have developed very slightly rust spots.

The question;

Can I use a metal, grey primer rattle can straight over, followed by a metal paint to finish or is that not the right method?

Albeit very slight will the small signs of surface rust spots be okay if so?

Thanks


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« Last Edit: Oct 08, 2017, 16:59:59 by JMPUK »

Offline VonYinzer

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Re: Priming after sandblast advice
« Reply #1 on: Oct 08, 2017, 17:28:10 »
Use some scotch-brite pad and clean the surface up. Get rid of the rust. Then use a self etching primer to help treat the metal.
Like a river that don't know where it's flowin'
I took a wrong turn and just kept goin'

Offline JMPUK

  • Posts: 24
Re: Priming after sandblast advice
« Reply #2 on: Oct 08, 2017, 17:48:21 »
Use some scotch-brite pad and clean the surface up. Get rid of the rust. Then use a self etching primer to help treat the metal.
Will do - Cheers!

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Offline jpmobius

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Re: Priming after sandblast advice
« Reply #3 on: Oct 08, 2017, 17:59:59 »
Probably going to be pretty hard to actually cut away every bit of rust - sand blasting makes for a pretty rough surface.  If you can't remove ALL the rust, you need to convert it and stop the oxidation process.  There are lots of products that do this, and also paint that contains tannic acid which is what converts the iron oxide into iron tannate which ends the trouble.  Pretty much all the paint I've seen says "rust converter" or something to that effect on the can.  Rustoleum and Plasticoat both make such paint.  For future reference, unless you live in the desert, you should paint pretty much immediately after sandblasting.  Sandblasting makes an incredibly rough surface with vastly increased surface area which is why blasted parts rust so badly and quickly.  These days I only sandblast frame and chassis parts and have my painting operation planned and set up before hand.  That way I get everything protected straight away and don't have rust issues down the road.  I use epoxy straight onto the blasted surface after an acetone wipe down and thorough air blast.  It's too much trouble for small parts, but worth it for things you really want to last.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline JMPUK

  • Posts: 24
Re: Priming after sandblast advice
« Reply #4 on: Oct 08, 2017, 18:50:14 »
Probably going to be pretty hard to actually cut away every bit of rust - sand blasting makes for a pretty rough surface.  If you can't remove ALL the rust, you need to convert it and stop the oxidation process.  There are lots of products that do this, and also paint that contains tannic acid which is what converts the iron oxide into iron tannate which ends the trouble.  Pretty much all the paint I've seen says "rust converter" or something to that effect on the can.  Rustoleum and Plasticoat both make such paint.  For future reference, unless you live in the desert, you should paint pretty much immediately after sandblasting.  Sandblasting makes an incredibly rough surface with vastly increased surface area which is why blasted parts rust so badly and quickly.  These days I only sandblast frame and chassis parts and have my painting operation planned and set up before hand.  That way I get everything protected straight away and don't have rust issues down the road.  I use epoxy straight onto the blasted surface after an acetone wipe down and thorough air blast.  It's too much trouble for small parts, but worth it for things you really want to last.
Thanks for your message. You are right in what you say. I used these bits as a tester to see the finish of sandblasting as they were badly rusted and came up well. I have determined however that aqua blasting with the paint process set up immediately for the frame and engine etc is the way I will go as is less abrasive (although never done it) ... What are your thoughts?

I was toying with the idea of chromimg the top of the carb cover but will probably juts finish these parts in black.

As the guy before said, and I think will work just fine is that I will sand and smooth down the surface and remove rust that has formed and then grey prime, and paint? Would that be okay? Will do these parts only myself with a couple of cans....

Thanks again

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Offline J-Rod10

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Re: Priming after sandblast advice
« Reply #5 on: Oct 08, 2017, 20:28:35 »
Scotch brite, spray with carb cleaner, prime. Carb cleaner will get all the dust from scotch briting it off, along with oils.

Offline jpmobius

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Re: Priming after sandblast advice
« Reply #6 on: Oct 08, 2017, 22:08:51 »
Not too sure what you mean by aquablasting.  If you mean vapor blasting (as it is commonly called in the US), a frame is mighty big for the cabinets I have seen.  I personally don't want any moisture whatever involved in prepping bare steel.  Dry glass beads are fine for small parts and with some dedication can produce parts nearly as nice as vapor blasting.  Certainly you can sand or scotchbrite parts to a sufficiently smooth and rust free condition, but you guys must have some sort of bad-ass scotchbrite or some much finer abrasive than I typically see used for sandblasting!  Regardless, I reckon the key point here is how long you expect the parts to last, i.e. how long before unattended to corrosion shows back up through the paint, and what you require as an acceptable finish in the first place.  No doubt you can simply prime and paint your parts as is, and they will come up pretty good.  If you want them to last a while, you need to get the majority of corrosion off first.  If you want a 20+ year part, you will need to get ALL the rust removed and a fairly carefully prepped surface.  You also need to consider the environment the parts will live in.  Carburetor parts get handled a lot more than most parts on bikes, and get attacked by gasoline as well.  That is why the manufacturer typically plates steel parts on carbs.  Most people find chrome plating prohibitively expensive in the US, but that would certainly solve the problem (if you can find an acceptable plater!).  Paint on carbs is really hard to make last unless you go to a fair amount of trouble and either use epoxy and/or urethane paint or powdercoat.  Sometimes it is useful to look at the overall scope of the project to determine how much trouble you need to go to.  If the project is a blank check or museum caliber job, obviously you spare no expense.  Otherwise, small parts like these can be "good enough" with a "90% of the effect for 10% of the trouble" approach.  If those parts were mine and I was putting them on a bike I was going to use, I'd sand them, spray them with converter-primer, and paint them and bake them to make the paint as durable as possible.  I'd live with the results and touch them up if they start to suffer.  Down the road, you can always take them up to a higher level if you can't live with them.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline JMPUK

  • Posts: 24
Re: Priming after sandblast advice
« Reply #7 on: Oct 09, 2017, 03:04:11 »
Scotch brite, spray with carb cleaner, prime. Carb cleaner will get all the dust from scotch briting it off, along with oils.
Cheers!

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Offline JMPUK

  • Posts: 24
Re: Priming after sandblast advice
« Reply #8 on: Oct 09, 2017, 03:07:04 »
Not too sure what you mean by aquablasting.  If you mean vapor blasting (as it is commonly called in the US), a frame is mighty big for the cabinets I have seen.  I personally don't want any moisture whatever involved in prepping bare steel.  Dry glass beads are fine for small parts and with some dedication can produce parts nearly as nice as vapor blasting.  Certainly you can sand or scotchbrite parts to a sufficiently smooth and rust free condition, but you guys must have some sort of bad-ass scotchbrite or some much finer abrasive than I typically see used for sandblasting!  Regardless, I reckon the key point here is how long you expect the parts to last, i.e. how long before unattended to corrosion shows back up through the paint, and what you require as an acceptable finish in the first place.  No doubt you can simply prime and paint your parts as is, and they will come up pretty good.  If you want them to last a while, you need to get the majority of corrosion off first.  If you want a 20+ year part, you will need to get ALL the rust removed and a fairly carefully prepped surface.  You also need to consider the environment the parts will live in.  Carburetor parts get handled a lot more than most parts on bikes, and get attacked by gasoline as well.  That is why the manufacturer typically plates steel parts on carbs.  Most people find chrome plating prohibitively expensive in the US, but that would certainly solve the problem (if you can find an acceptable plater!).  Paint on carbs is really hard to make last unless you go to a fair amount of trouble and either use epoxy and/or urethane paint or powdercoat.  Sometimes it is useful to look at the overall scope of the project to determine how much trouble you need to go to.  If the project is a blank check or museum caliber job, obviously you spare no expense.  Otherwise, small parts like these can be "good enough" with a "90% of the effect for 10% of the trouble" approach.  If those parts were mine and I was putting them on a bike I was going to use, I'd sand them, spray them with converter-primer, and paint them and bake them to make the paint as durable as possible.  I'd live with the results and touch them up if they start to suffer.  Down the road, you can always take them up to a higher level if you can't live with them.
Great stuff, thanks very much for your advice and time in responding to me on this - I will certainly follow. Cheers

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