I've just been reading quite an in depth leaflet about primers, it was geared towards fabrication but still a worthwhile read and it's raised a few questions in my mind. The leaflet subdivided primers into epoxies, silicates and acrylics by zinc and aluminum.

 

It said lead based primers are the most tolerant of rust and scale however they are being phased out. Do you know of a modern primer type that can handle a bit of forge scale/oxide after manual cleaning?

 

Are there primers that don't require industrial surface preparation? I.e sandblasting.

 

Are primers needed for handrails?

 

How reliable are the All-in-One primer and top coat paints?

 

Ultimately I'm thinking ahead to exterior projects that'll need painting, probably by brush, after being cleaned by hand.

 

Cheers

I have never used any primers for blades or the fixtures. What do you have in mind that needs it ? Dont expect to have a good edge with primer on it.

Joel,

 

Coating systems are a science unto themselves. Simple metal prep involves getting down to the base metal, i.e., no scale or rust. Either will undermine your coating job.  You can mechanically clean the metal via scraping or wire brush. You can etch the surface with acid in any number of ways. A common technique is to use vinegar or citric acid. This releases any residual scale that may be present.   In the end you want a clean bare metal surface. Be sure to wash the acid solution off with soap and water. Always dry the surface to be primed.

 

Primer or undercoating is essentially a porous coating that serves to prep the metal surface for the finish coats. Primer by itself will not prevent rust. Spray coverage is generally better than a brush application because it's more consistent.  A simple primer procedure is to use two different colors so that you can see any places you may have missed when you apply the second coat. Two coast of primer at a minimal are a good idea. Now you have the base for the finish coating. Pick the one you like and have enough of the batch on hand for your project.. If you buy decent paint you will get good results.  Use light multiple coats. Let the coating dry between applications. It will not do you much good to flood it on. Remember you are creating a continuous seal on the metal surface, your objective is to preclude water from interacting with the iron. If rust is present under your primer it will break the paint seal and water will find its way to the metal surface.

 

Our outside ironwork is generally painted. The rusted look is favored in some art projects but anything you are going to grab onto likes paint. Rusty surfaces aren't really that hand friendly.   I oil finish some door hardware (knockers) but after a few years you have to service the pieces because they start to rust up. I always paint the plant hangers and the decorative grills because I think they look shabby when they rust up. Also rust will leach onto stone and wood surfaces and leave a stain.  Check out the ironwork in old cities and you will see that the iron handrails of old are generally painted. Brass and bronze weathers to a likeable patina and it hand polishes if its used a lot.

 

Good luck,

 

Peter      

I wondered why anyone would want to paint a blade when I saw the title,,,,now I wonder if it was meant to be in another area.

Unless of course he didnt want to know about blades, in that case I  will reloacte this to a better place.

Do you trust the owners to maintain it?  If not go for a professional job on finishing it and build that cost into the quote!  Or make it from stainless and build that cost into the quote!

Joel check out aircraft primers. Like Petere said light coats over CLEAN metal.  You must have complete coverage and spraying works best. Then cover with your top color with good drying time between coats.

I wondered why anyone would want to paint a blade when I saw the title,,,,now I wonder if it was meant to be in another area.

Doh! I didn't see this was a bladesmithing section. I'll see a mod can shunt this thread over to a better area...

 

Already has been...

Joel check out aircraft primers. Like Petere said light coats over CLEAN metal.  You must have complete coverage and spraying works best. Then cover with your top color with good drying time between coats.

 

How clean is clean? Cleaned back to a silvery finish?

Joel,

 

Clean usually means bare (white) metal, no slag, no scale, no grease;  essentially a smooth uncontaminated surface.  This definition translates into time spent on surface prep. This is a the big time consumer in the shop.  We spend a lot of time cleaning and prepping ironwork before it is coated. Big iron operations have separate shops that just blast and coat. Small shops have a guy with a wire wheel, emery cloth and a good work ethic.    

 

 When you estimate projects on a shop time (hour) cost basis, prep comes down to some serious labor time. True cost of anything you turn out has to cover everything involved. Materials, transportation, design, tooling, shop costs, etc. it all goes into the gross estimate.   Sometimes I see folks selling at fairs and I wonder how they can produce the product and cover costs for what they are charging.  They all seem happy though and that may part of the profit component.  

 

Peter    

Cheers Peter.

Now I'm curious to read the claims and ingredients on a tin of "paint straight over rust" metal paints DIY shops stock. Should be a good laugh!

If it contains phosphoric acid you can paint over rust! It ''converts'' rust!

Yes Joel clean is down to bare metal.  Then an evaporating degreaser like acetone on a clean rag. Clean is basic to a good paint job it is what makes primer and paint last for years. Handle only with latex gloves while priming or painting.

So I take it that the life expectancy of the "all-in-one paint over rust" paints is much less than the traditional paints that go onto clean surfaces, or sandblasting companies would be out of business?

Incase this sounds like I'm looking for a shortcut to cleaning the steel & wanting to paint my work on the cheap, I'm not! I'm just curious about the processes.

Hammerite =all in one ,good stuff though not cheap here.

When I clear coated metal, I use a two step process that I get from an automotive paint store.  Two cleaning solutions to clean it and no bare human hand contact during and after cleaning.  Immediate drying, and spraying the clear coating. Otherwise you will get rust from the oils on your hand or you gloves.  It will show up soon or later.  Even when I do primer and paint, I still clean the metal the same way.  Good luck.  

I lost a fair amount of money on a job 5 yrs ago for 2 reasons. (1) I did a last minute quick fabricated railing for a new construction that had a loan deadline for certificate of occupancy. I worked 18 hours a day for 2 weeks, lots of lineal feet. It had square tubing framing members, and 1/2 sq pickets. Turns out the sq tubing was so slick from factory rolling, primer and paint peeled off in sheets. Now I rough up all sq tubing with 80g sandpaper. (2) I had a professional industrial paint guy match my railing paint to the house color. After 6 months, it all chalked up, and looked like a 20 year old job. Paint guy called corperate, and found out that my super industrial paint didn't like all that much tinting...they covered the new paint cost, but not the week of sanding the old stuff and re-spraying in place.
In summary, ya just never can tell what's going to happen.....

The steel yard/fabricators I buy from don't have their stuff sandblasted, they just roll on red zinc phosphate primer. They reckon it lasts about 4-5 years. Obviously their stuff hasn't got forge scale & oxides on it though.

Think about giving Dulux a call, they are very helpful.

I have heard some good things about aluminium impregnated urethane for sealing boat trailers, I would love to try it but its hard to get here. Apparently it is difficult to store once the lid has been opened once. Even spraying some argon or butane in the can may not be good enough to let the lid come off a second time. Best to use the whole lot in one hit.

AFAIK nothing will chemically remove it, so its old clothes, gloves and brushes to work with it.

 

Nice matt grey/silver finish.