GHA
Well-known member
And the zinc turns to powder lifting the paint around the dink, leaving more bare steel to corrode than would have happened with just epoxy.
Steel degreasing prior to painting
- Thread starter Jegs
- Start date
And the zinc turns to powder lifting the paint around the dink, leaving more bare steel to corrode than would have happened with just epoxy.
KellysEye
Active member
>And the zinc turns to powder lifting the paint around the dink, leaving more bare steel to corrode than would have happened with just epoxy.
It's Zinc rich EPOXY I though I made that clear. The epoxy stops the zinc corroding and it can't turn to powder. As for putting acid on after grinding I suggest the person grinding goes to Specsavers.
It's Zinc rich EPOXY I though I made that clear. The epoxy stops the zinc corroding and it can't turn to powder. As for putting acid on after grinding I suggest the person grinding goes to Specsavers.
GHA
Well-known member
Have you tried acid etcing after grinding? Obviously not, if you had you would see the popping and fizzing as the acid reacts with rust in the unseen pits.
As for zinc rich epoxy, a moments google comes up with a well known process. see here..
http://resource.npl.co.uk/docs/scie...ns/online_guides/pdf/structural_steelwork.pdf
"
When exposed in either marine or highly industrial
environments, zinc epoxy primers are prone to the
formation of insoluble white zinc corrosion products
which must be removed from the surface before
subsequent overcoating"
Just because you had success (above the waterline?) it does not mean your preferred method is the one and only way to keep corrosion at bay.
Pasarell
Well-known member
Both KellysEye and GHA are right, and wrong, in parts of what they say.
The best way to prepare steel for coating is to abrasive blast but, as the OP has stated several times is not possible so compromises have to be made. Second best way is to grind and if that is done well then it is worth putting a high performance primer on such as Interprotect. If grinding is not possible then it is probably only worth applying a conventional primer such as Primocon.
Before grinding was with fresh water as thoroughly as possible to remove salts and other contaminants on the substrate. The purpose of preparation is to remove as much contaminant as possible and if salts are still there when you grind then they will, to an extent, be forced into the micro grooves in the surface of the steel caused by the act of grinding. Pressure washing is ideal if possible.
When grinding try to get into all the pits and clean them out if possible otherwise corrosion materials will remain. This is about the only time when phosphoric acid has a place in steel preparation but it still has drawbacks in that the powdery residue needs to be removed before priming. If you can clean the pits out then acid brings no benefit.
After grinding the steel is still likely to be greasy so you are right to tackle it. Nothing water based however. White spirit is not good and nor is acetone because, as VicS says, it is too volatile. Your acetone soaked rag will pick up grease but then, as the acetone flashes off, it re-deposits the grease elsewhere on the surface. Best to use the solvent for Interprotect or if not available something like xylene. There is actually an ISO standard describing the way solvent wiping should be done!
If your surface is really clean then Interprotect is fine as your primer. If the steel is still contaminated then a zinc rich primer is probably better as it will inhibit the onset of new corrosion. Adhesion of Interprotect should be slightly better than a zinc material so you have a trade off depending on cleanliness. Zinc rich doesn't have to be epoxy. Urethane base is also very effective and is more tolerant to ambient condition, especially low temperature.
Getting your primer on quickly is important but not as critical as suggested. Modern high performance primers are tolerant to a little flash rusting provided it is ginger, not black, and any powdery residue is brushed off first. More important than rushing the primer on is to ensure the surface is salt and grease free, dust and debris free, and dry.
Good luck. Your original plan is pretty close to ideal
The best way to prepare steel for coating is to abrasive blast but, as the OP has stated several times is not possible so compromises have to be made. Second best way is to grind and if that is done well then it is worth putting a high performance primer on such as Interprotect. If grinding is not possible then it is probably only worth applying a conventional primer such as Primocon.
Before grinding was with fresh water as thoroughly as possible to remove salts and other contaminants on the substrate. The purpose of preparation is to remove as much contaminant as possible and if salts are still there when you grind then they will, to an extent, be forced into the micro grooves in the surface of the steel caused by the act of grinding. Pressure washing is ideal if possible.
When grinding try to get into all the pits and clean them out if possible otherwise corrosion materials will remain. This is about the only time when phosphoric acid has a place in steel preparation but it still has drawbacks in that the powdery residue needs to be removed before priming. If you can clean the pits out then acid brings no benefit.
After grinding the steel is still likely to be greasy so you are right to tackle it. Nothing water based however. White spirit is not good and nor is acetone because, as VicS says, it is too volatile. Your acetone soaked rag will pick up grease but then, as the acetone flashes off, it re-deposits the grease elsewhere on the surface. Best to use the solvent for Interprotect or if not available something like xylene. There is actually an ISO standard describing the way solvent wiping should be done!
If your surface is really clean then Interprotect is fine as your primer. If the steel is still contaminated then a zinc rich primer is probably better as it will inhibit the onset of new corrosion. Adhesion of Interprotect should be slightly better than a zinc material so you have a trade off depending on cleanliness. Zinc rich doesn't have to be epoxy. Urethane base is also very effective and is more tolerant to ambient condition, especially low temperature.
Getting your primer on quickly is important but not as critical as suggested. Modern high performance primers are tolerant to a little flash rusting provided it is ginger, not black, and any powdery residue is brushed off first. More important than rushing the primer on is to ensure the surface is salt and grease free, dust and debris free, and dry.
Good luck. Your original plan is pretty close to ideal
GHA
Well-known member
Pretty much agree with all that, but not meant in a confrontational manner - how do you know? How does anyone know?
For individuals you need on have several pieces of identical steel,, do your different prep and paint. Leave them in identical conditions. And check again about 6 years later.
Personally I rate this book.. http://www.amazon.com/Metal-boat-maintenance-A-yourself-guide-ebook/dp/B0070QRME4
As as good a guide as there is IMHO , and he's pretty vague as well
Acid etch - only shows in the hot tropics, but I've spent forever doing the perfect grinding cleanest metal you can ever hope for, bit of ospho and pop fizzle in the pits. Still rust in there. So I prefer acid and Ameron sealer as a primer , which takes ages to kick and so far seems as good as it gets. Especially in the bilges where prep is a nightmare.
Bottom line I think is there are so many variables that if you find something that works then stick with it, then tell everyone on a net forum "this is the way you must do it!"
Pasarell
Well-known member
Jegs
Well-known member
My sincere thanks to all who have responded to my plea for help; it's been both interesting & informative.
AllTheBest,
John G
AllTheBest,
John G
coenvanwyk
Member
A few observations, if I may: I was advised to degrease just before sandblasting, because there may be oil or acid (Acid rain, atmospheric contamination from a nearby galvanising plant) which had to be removed. Industrial degreaser, applied with a Karcher, then hosed down several times with clean water ubntil no suds showed.
After surface preparation (And try to get the metal as rough as possible) I would consider using phosphoric acid, but some paint companies feel this would interfere with their paint systems. There are amazing zinc- and aluminium rich primers available, but usually in large quantities.
Best of luck!
After surface preparation (And try to get the metal as rough as possible) I would consider using phosphoric acid, but some paint companies feel this would interfere with their paint systems. There are amazing zinc- and aluminium rich primers available, but usually in large quantities.
Best of luck!
D&T
Member
I have be reading this thread with interest. I have an area to do along the top edge of my keel, which is quite pitted, so may be hard to grind perfectly flat. I note there has been no mention of using a Rust Convertor prior to using a primer, is this not recommended?
Pasarell
Well-known member
The acid mentioned by various posters above is the active ingredient in a rust converter.
If you can avoid using a rust converter it is best to do so as they usually have a negative impact on adhesion of the primer. Often on small boats you cannot do the surface preparation very well so rust converters have a role to play provided they are used correctly. Probably your job along the top of the keel falls into this category.
After the acid has dried any powdery residue should be removed with a stiff brush before priming, otherwise your primer will just be sticking to a loosely adhered powder rather than the underlying metal and corrosion will come back pretty quickly.
All primers work by forming a closely adherent bond to the substrate they protect so any rust converter will have a negative impact, even when properly prepared. This is why you will rarely see rust converters recommended by coating manufacturers. Also rust converter manufacturers avoid the subject like the plague.
If you can avoid using a rust converter it is best to do so as they usually have a negative impact on adhesion of the primer. Often on small boats you cannot do the surface preparation very well so rust converters have a role to play provided they are used correctly. Probably your job along the top of the keel falls into this category.
After the acid has dried any powdery residue should be removed with a stiff brush before priming, otherwise your primer will just be sticking to a loosely adhered powder rather than the underlying metal and corrosion will come back pretty quickly.
All primers work by forming a closely adherent bond to the substrate they protect so any rust converter will have a negative impact, even when properly prepared. This is why you will rarely see rust converters recommended by coating manufacturers. Also rust converter manufacturers avoid the subject like the plague.
dolphin
Member
this is how i do the painting
usually, before to start any painting work, the boat is well fresh water washed
the surface preparation is first hammering to remove the big pieces of rust if any, second chipping with the small hammer, after grinding and depending from the result at the end, rough sandpaper. well clean of the surface with rags and final clean with acetone. soonest possible apply the first coat epoxy resign , followed by 3-4 coats.
after if needed sand the surface for the two component primer and apply 3-4 coats. final is the two component paint also 3-4 coats.
the result after 6 years - the cockpit is in the same condition as the first year with only one place need an attention as the rust have found his way out
the same way for underwater surfaces
usually, before to start any painting work, the boat is well fresh water washed
the surface preparation is first hammering to remove the big pieces of rust if any, second chipping with the small hammer, after grinding and depending from the result at the end, rough sandpaper. well clean of the surface with rags and final clean with acetone. soonest possible apply the first coat epoxy resign , followed by 3-4 coats.
after if needed sand the surface for the two component primer and apply 3-4 coats. final is the two component paint also 3-4 coats.
the result after 6 years - the cockpit is in the same condition as the first year with only one place need an attention as the rust have found his way out
the same way for underwater surfaces
Brent Swain
N/A
A needle scaler works well. I sharpened the needles on mine, a big improvement. First it turns the steel black . Hold it on for a while, and it gradually goes a clean , shotblasted gray colour.
Wet blasting also works, if you do it in hot weather, and dry and paint it quickly .
TSP is great for degreasing. Cheap too.
Wont help, if you don't get rid of the rust before painting.
Acid is a big mistake, as it accelerates corrosion, eventually .
Wet blasting also works, if you do it in hot weather, and dry and paint it quickly .
TSP is great for degreasing. Cheap too.
Wont help, if you don't get rid of the rust before painting.
Acid is a big mistake, as it accelerates corrosion, eventually .
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lw395
Well-known member
Fairy Liquid and scotchbrite pad or wet'n'dry works for me on many things.
I then often use a hot air gun to get it properly dry.
I then often use a hot air gun to get it properly dry.