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nheng
12-04-2003, 12:28 PM
For you guys who have painted old machinery, how many have done so successfully without primer, over bare (stripped) metal. I know ... the primer gets a grip into the surface and provides a better surface for the paint but for home use with spray cans, I can't honestly say that primer has ever given me a more durable and chip "resistant" surface. Heat always seems to improve the end result though, driving off the solvents.

Also, what is your favorite spray can paint that gives good results and is readily available ?
Den

G.A. Ewen
12-04-2003, 12:35 PM
I am by no means a professional painter but from my limited experiance I have found that primed surfaces make it much easier to get a uniform color as an end result.

Evan
12-04-2003, 12:51 PM
Primer really does help, especially on aluminum. Zinc Chromate primer for aluminum also works on iron. It bonds chemically to the metal and also prevents rust. Favorite spray paint is Tremclad. Baking the parts until it no longer has the solvent smell sure does improve the durability but it might not be advisable to bake a lathe or similar. http://bbs.homeshopmachinist.net//biggrin.gif

lynnl
12-04-2003, 01:24 PM
At what temp should the baking be done?

Evan
12-04-2003, 01:46 PM
I bake at about 150-180 degrees F. Right about at the point where it is too hot to touch for three seconds. It's not critical but don't get it too hot. Let the paint air dry fairly well so you don't boil the solvent and make bubbles. I will use an infrared radiant heater or sometimes place longer parts over an electric portable baseboard type heater. Been known to put parts on top of the wood stove but that stinks up the house pretty good. I don't dare use the kitchen oven http://bbs.homeshopmachinist.net//eek.gif

[This message has been edited by Evan (edited 12-04-2003).]

nheng
12-04-2003, 01:55 PM
G.A.Ewen: I forgot about color uniformity ... it definitely does that !

I've "baked" with a 150W Halogen boom arm lamp played on the surface. When a region of the surface gets moderately hot to the touch, I let it sit like that for an hour or so and then move on.

This really shrinks the thickness of the paint. Parts that are clamped on to painted surfaces without baking will "sink" into it for days. Clamping onto baked parts acts like there is a firm shim under it.

Den

nheng
12-04-2003, 01:56 PM
[QUOTE]Originally posted by nheng:
[B]G.A.Ewen: I forgot about color uniformity ... it definitely does that !

I've "baked" with a 150W Halogen boom arm lamp played on the surface. When a region of the surface gets moderately hot to the touch, I let it sit like that for an hour or so and then move on.

This really shrinks the thickness of the paint. Parts that are clamped on to painted surfaces without baking will "sink" into it for days. Clamping onto baked parts acts like there is a firm shim under it.

Evan: I used the kitchen oven for paint baking when I was a teen. That's probably why my parents moved away while I was at college http://bbs.homeshopmachinist.net//eek.gif

Den

nheng
12-04-2003, 01:58 PM
G.A.Ewen: I forgot about color uniformity ... it definitely does that !

I've "baked" with a 150W Halogen boom arm lamp played on the surface. When a region of the surface gets moderately hot to the touch, I let it sit like that for an hour or so and then move on.

This really shrinks the thickness of the paint. Parts that are clamped on to painted surfaces without baking will "sink" into it for days. Clamping onto baked parts acts like there is a firm shim under it.

Evan: I used the kitchen oven for paint baking when I was a teen. That's probably why my parents moved away while I was at college http://bbs.homeshopmachinist.net//eek.gif

Den

What's with this HTML "quote stuff" on edits ? Anyone know ?

nheng
12-04-2003, 01:59 PM
Sorry about the doubling up there ... something has changed with the edit function.
Den

nheng
12-04-2003, 02:21 PM
<font face="Verdana, Arial" size="2">Originally posted by nheng:
Sorry about the doubling up there ... something has changed with the edit function.
Den</font>

Looks like UBB code, not HTML, my mistake.

thistle
12-04-2003, 02:44 PM
i happen to have lots of 2 part epoxy and polurethane for marine use so prime with the epoxy primer followed by a few coats of polyurethane - nasty stuff but it works .lasts for ever out side should work inside.

for rusty parts like around the base weremetal is in contact with the damp ground i sandblast to bare metal -use rust converter then spray on a bit of cold galvaising zinc .then epoxy over the top.

zinc chromate over any aluminium.

hammered finish spay paints like hammerite are good- but difficult to get an even finish over big areas




[This message has been edited by thistle (edited 12-04-2003).]

CCWKen
12-04-2003, 11:52 PM
Primer is to give you an even color holdout (even coverage). It's really not necessary for bare metal, if the metal is prepaired properly. If you do use primer, make sure it is compatible with the paint you plan to use. Also, check to see if the primer must be sanded before top coating (painting). Most do and if you skip this procedure, your paint will flake and chip off with the slightest bump. There are some epoxy primers that can be top coated without sanding if you paint it within 4 hours.

Primer also fills small imperfections and voids. If you have any filler (Bondo, etc.) on the machine, you sould use a primer and make sure the primer is compatible with your filler. I'd go with an epoxy primer. It sticks good and covers anything. By the way, forget the SPRAY CAN epoxy stuff. It has way too much solvent. It can cause checking and poping over fillers later. (Usually right after that final color coat)

Forgot: THE best color in a can is Krylon. Forget the famous rust-o stuff unless you can let it dry for five to seven days between coats and for 20-30 days after the final coat. Baking this stuff can help but 120-130* is plenty. Too hot and you seal the top surface too fast and you'll get "curtains" on the next coat. (That's those little saging wrinkles.)

[This message has been edited by CCWKen (edited 12-05-2003).]

SJorgensen
12-06-2003, 04:38 AM
Nheng,
I'm not the expert here but I do agree with you that I find paint directly on pristine surfaces is often better than primer on pristine surfaces. This is because paint is harder than primer. I like paint as the initial bond to pristine metal and then a filler like primer for fixing surface imperfections because it is more sandable. Primer is not a solution to surface waxes or oils but is often used that way. Also primer is very porous and is no protection from moisture or the resulting rust. When doing bodywork if you paint the bare metal before you primer and sand you will have more protection from rust. Primer isn't as good as a having a clean surface and then painting with a good enamel.

Just my two cents.

Spence

Evan
12-06-2003, 11:28 AM
Spence,

Have you ever used zinc chromate primer? That stuff is hard as nails, and actively prevents rust as the zinc acts as a sacrificial anode. The chromic acid reacted with the zinc makes it bond with the metal to the point the stuff won't even come off with paint stripper well.

ibewgypsie
12-06-2003, 03:32 PM
Some primers are made to etch into the metal surface bonding with the bare metal, Some primers are made to smooth out irregularities in the surface over the base primer ( High-build looks like pigpen's dustcloud when you sand), Some primers are made to give a color base to a see-through top coat ("house of color" opaque finishes).

I didn't know there was so many different primer functions till I started painting bikes.

Powdercoat does not require a primer coat, it is by far the cheapest form of coating. If you can do it yourself. Most people use oven elements in thier powdercoat outfit. You can either spend money on lots of elements or money on insulation. Fiberboard is the best, good to 600 degrees. Getting a radiant system to heat evenly is a problem.

I want to build my next oven with silicone cloth curtains stuffed with cerwool. be suspended via wire.

David