The Priming Process explained (Priming Wing Ribs)

I split the wing ribs into 4 batches of 7 - which allowed me to keep the smaller items (the aileron torque tube brackets & flap brackets etc) apart from each other so they didn't get mixed up - this saved having to label them with tokens. The wing ribs themselves were labelled with the wing rib number (i.e. L12, or R3) on a stamped token so the number would hold up through the priming process.

Here a rib label has been transferred from the token back to the part flange, before dimpling and fluting etc.

The Preparation Process

Prior to priming, the parts are cleaned with EkoClean, which is mixed 10:1 with normal tap water in a spray bottle and sprayed on. This gets off any oils from my hands etc, and also takes off most of the red ink that is left on the parts. I do not rinse this off, but go straight into using EkoEtch, which is mixed 2:1 with normal tap water, also in a spray bottle. This is sprayed on and i find i need a dust mask if doing this inside, as the smell gets you in the throat. The whole part then receives a scrubbing using 3M Scothbrite 8447 pads, which are a bit coarser than the normal 7447 pads and make the job go a bit quicker. I cut the pads into little squares and wet them down with the etch. I am looking for a uniform level of dullness on the part. Once this is done, i used a normal hose and rinse off all the cleaning and etch. If you have done it right, the water will lay on the surface in a uniform sheen, and not ball up into water droplets.

I wear gloves throughout this whole process to avoid oils from my skin getting on the parts. The parts are then left to dry naturally - i do not use compressed air to dry them, as this can spray minute oil droplets on the parts, however i do sometimes steal the bosses hairdryer!

These parts are drying - you can see the "uniform dullness" i look for. 

The Priming Process

I had made a previous post which can be seen here, where i had some issues at the start with the Stewart Systems paint seeming too thick to spray. I was thinning it quite a bit at the start, however now i have the process down pat i felt the need to clarify my comments on the paint.

As a reminder, the primer being used here is Stewart Systems EkoPoxy, in Smoke Grey color.

Firstly, this paint is not like other paints which i have used. It seems to be a very high solids paint, which settles fairly quickly over time. If you try and mix it together with a stick (as i did originally) you have almost zero chance of getting it thin enough to spray (or even get out of the can). To combat this, on the advice of Stewart Systems, i found a couple of things that worked:

• The paint doesn't like being cold: I was keeping the paint can in my shed, and it was just too cold in winter for get it mixed together properly. Once i started keeping it in the house i found it a lot easier to mix and use. 
• The paint needs to be mechanically agitated: A stirring stick is not going to cut it - on the advice of Stewart's, i purchased one of the mixers shown below and it works a treat. About 30-60 seconds of mixing (ensuring i get the stuff off the bottom) is like magic - not only does the paint mix together into a uniform consistency, but it thins but a significant amount, perhaps like cream. 
• It can't be mixed easily in the can: I found it almost impossible to mix the paint in the can using the mechanical mixer shown below as the paint just flies out everywhere - so when i get an order of paint (say 2 quarts), i decant it into a container shown below. This allows it to be mixed much more easily. 

I use a pail like this to decant the primer into

This is the type of mixer that is used to mix the paint before thinning etc. 

Once the paint is mixed up to a uniform consistency, I used a 60ml horse syringe to take out the required amount into a paint mixing up on scales. I then thin it with 13% of denatured water and 18% of the Part B hardener by weight. This is mixed up with a stick and poured through a paint strainer into the HVLP gun. After thinning, it turns to the consistency of milk. 

I set the gun as per the instructions that came with it - about 35PSI at the regulator (maybe 25-30 PSI at the tip). The paint sprays very easily and goes on in one coat, and very very rarely runs (unless i put it on too thick). I can spray one side of the parts and after around 5-10 minutes, the parts can be flipped and the other side sprayed. 

Wing Ribs before and after priming

Check out those guns!

So far i am very very happy with the paint - easy to spray by an absolute novice, dries fast and stands up to dimpling after the priming very well. The best part is that it is non-toxic, has almost no over-spray (what is there just falls as dust) and can be cleaned up in normal tap water.