elementary engine tin primer question

[audi]

I had my engine tin media blasted today, and have already purchased Wurth high temp black paint from our host for it. I don't want to powdercoat it.

I've searched and can't seem to find a clear and concise answer as to whether or not I need to use a primer?

I wasn't going to prime it, as the surface post-blasting looks pretty etched; I was going to just paint it with the Wurth, and have assumed this would be fine.

Anyone know the definitive answer, to prime or not to prime, and if it is necessary, what's a good primer to use underneath the Wurth that would be compatible?

Or am I overthinking this?

Thanks,
Audi

[gtc]

Originally Posted by audi

Or am I overthinking this?

Yes.
Just grab some rustoleum primer or something similar from home depot.

[timmy2]

There is high temp primer available as well.

[A horse with no name]

I have over time completed five ground up restorations in which one was a 911. Being that you have media blasted the tin work you will want to achieve the best look that you can- Use a proper primer/ undercoat.

It will fill any imperfections in the tin, including it will make the top coat 'stick'. It's hot under there and it will prevent it from flaking off in time.

A most important procedure is to do is to make sure that metal is very clean, including the primered tin. You can purchase A Silicone- Wax remover from any automotive paint retailer. Fish-eyes in paint work is a result of a unclean surface. (oil-wax)

Keep in mind that the oil from your skin when handling will adhere to the tin or primer. It's good for cleaning numerous other things so it will not go to waste.

When using a spray bomb, start by putting on light coats of the primer or paint.

Primers flash pretty quickly so make sure you don't wait too long before you put on another coat. Put as many coats on that you need so as to cover it well. Then you will be able to sand it.

Let it dry completely then use 400-600 paper and sand it very lightly until it smooth- Don'tsand through it, If by chance you do- not to worry- just spray it again.

Before painting your top coat, make sure that you have allowed enough time for the primer to have properly dried. Before top caoting clean the primer'd metal well.

When applying the top coat, so as to not get any runs, put quick light wet coats on..Don't be in a hurry. When it 'tacks' apply another light wet coat and repeat these until you have have a few good coats on the tin.

If you warm the tin up a bit before painting, the paint will flash quicker and you will have a much lesser chance of getting any runs.

On your last coat make a quick pass that will provide a wet looking coat over the entire piece.

When the pieces are painted make sure you put them in a dust free area to dry... A simple small poly tent over the pieces will work.

Dust, including unclean surface's, are the two things that can ruin what would have been a 'great' paint job.... Again, take your time so as not to load the tin up with so much paint to where it will run. IF you do get a run you can wash the paint off with the Silicon- Wax remover.

When painting one of my cars, I unfortunately ended up having to wash down a large portion of the job- One HUge mess and one massive PITA but unfortunately that's what you have to when you apply too much paint and or are too impatient and do not wait long enough for the first coat to flash.

[audi]

Thanks for the replies so far - prime it is.

Originally Posted by miglenda

Use a proper primer/ undercoat.

Any suggestions as to brand/type, acid-etch, etc.; what would be considered proper?

I normally use Rustoleum rusty metal primer for everything, just wasn't sure about what heat would do to it in the long run. I normally also topcoat with Rustoleum so compatibility isn't an issue, but I didn't know about using Wurth on top.

I'm not going for a concours finish by any means, but I don't want to have it peeling in a year, either (I saw mention of that in the archives here while searching this topic).

[Jack Olsen]

The real benefit of self-etching primer is the zinc it contains, since media blasting generally removes any galvanization or previous layers of primer.

[A horse with no name]

Hi...Etching primer is a very good product to use on bare steel and particularly aluminum. Aluminum is a must because without the proper build up of aluminum etching primer, and a primer undercoat, the top coat would flake off.

The etching primer 'etches' into the bare metal and becomes an adhesive for the undercoat which in turn seals and acts as an adhesive for the final top coat.

You are correct in the fact the because it has been media blasted it already has a very good 'etch' that a primer undercoat will adhere to. If say the paint had been paint stripped with an Automotive-Aircraft paint stripper, then the smooth surface would have to be sanded with 180 to 'rough it up' for the primer undercoat to adhere to.

Just go to a automotive shop that has a automotive paint division or has a good selection of spray bombs and purchase a good quality primer/ undercoat that is sandeble.

As a matter of interest Wurth (German) is more know for it's excellent fillers than it's paint in N/ America. More or less any of the major paint companies products are more than exceptionable.

E.g - PPG / Ditzler/ Dupont to name but a few- Glasurit (German) has an excellent product but you will find that more show class street rods are painted with PPG.

Point is that because our machines are German does not mean that one has to use German paint as there are many other non German products that will do the same or even better job at a better price point. e.g. PPG.

Ferrari as a matter of fact switched over to using PPG from Glasurit in the mid 1990's. Engine tin work can be painted by all of the above products plus many others that will to the same job

Because the paint manufactures all have their own type of reducers and hardeners that only work with their 'system', painters will get used to the way a particular brand works for them and they stay with it.

Etching primer is very seldom used on normal collision damage. The metal is sanded with a 150 paper for the fillers to adhere to prior to undercoating.

The truth is surface preparation is the key to a good paint job. No matter who squeezes the trigger, what brand or color, or what make or model vehicle it is going on, if the surface preparation is less than "perfect," the paint job can't be greater than the preparation.