main spar primer

[GT280flyer]

I am nearing covering on my wings and noticed on a build site that the builder has primed the spars and drag anti drag tubes with epoxy primer. I can not find a section in my build manual about this procedure. I plan on using the Stewart system for gluing and painting but is it necessary to prime the spars etc. before covering?

[Geowitz]

Kitfox doesn't say it is required on the spars, but it is suggested in high humidity areas(and if you plan on using floats) so it's up to you to decide, but if you're at the stage in building where it's easy enough to do I would definitely do it as it can't hurt.

The poly fiber epoxy primer is neccessary if using the poly fiber because of chemical compatibility issues but would also work with the Stewarts system. Stewarts has their own version of an epoxy primer for metal as well. It is also my understanding that with the Stewart system you could also just use regular old zinc chromate primer which is a much cheaper option.

Of course in any case ensure proper prep. If you look up "wing spars" there are several posts explaining corrosion protection.

[akflyer]

The local repair shop has been using this primer for years. It was about half price of the poly fiber primer and you can get it at about any auto parts house that sells paint.

[HansLab]

PolyFiber warns in the manual not to use anything but their product due to cchemical risks (I would've done the same if I were PolyFiber...)
Have you thought of that? Or are you into chemicals (and can you help me with these same questions... Long live Internet)??

hansL

[akflyer]

All I can say is that we have been using it for years, and it works fine. If it looks like a duck, walks like a duck and quacks like a duck, chances are its a duck.

I used both the PF and the Omni epoxies during my rebuild. They mix the same, thin the same and spray the same.

[HansLab]

...and did you prime all framework? Or just the wings?

[Geowitz]

Just to clarify for GT280flyer. He is using the Stewarts system, so he is most likely fine with any primer he chooses.

[akflyer]

If you are asking me, I primed about 90% of the fuse (the parts I had to replace or weld on), the new lift struts, new landing gear legs and the wings. On the fuse sand blasted all the tubes I replaced and then wiped the remaining powder coated sections down with acetone, then shot the primer over that. I had to brush on alot of the primer in the tail cluster because I could not get the spray gun in all the areas. It leveled out nice and did not look "brushed" on.

[Tom Waid]

I confess, I'm presently covering the right wing and, before doing this, I primed the metal parts with white Poly-Fiber primer. In spite of it not being a brushable paint I applied it with a brush since none of the surfaces will be visible on the finished airplane. Spraying would require the worlds supply of masking tape. In Florida life is a continuous struggle against rust and corrosion. Painting the spars with primer is part of my obsessive struggle in this cause.

[szicree]

I intend to prime the spars with sprayed on epoxy, but I have what may be a dumb question: Can I prime things first and then glue on the ribs? That is, will the Hysol stick well to the epoxy or am I required to glue to bare metal? Thanks.

[Dave S]

Your build manual provides instructions for prepping the spars and similar before bonding ribs and other parts with the hysol - that means prepped metal to hysol to ribs - I'd follow the instructions......

Dave S

[szicree]

I appreciate the advice. I have been flipping through the manual while waiting for my kit and am unclear about the use of Hysol. I understand the tail feathers are powder coated but need to have their ribs glued in. The manual says to scuff with Scotchbrite and I assume they mean scuff the powder coat. This would mean that Hysol sticks well to paint. So...couldn't I prime my spar inside and out before gluing the wing ribs in place? If this is not the way, then can I assume that the spar is primed after all the ribs, stringers and drag/antidrag tubes are in place? Seems like a major masking headache. The manual seems to indicate that many slosh the inside of the spar but makes no direct mention of protecting its exterior. Seems awful silly to slosh the inside and leave the outside naked to the world. Any thoughts/experience is greatly appreciated.

[Tom Waid]

The manual seems to indicate that many slosh the inside of the spar but makes no direct mention of protecting its exterior. Seems awful silly to slosh the inside and leave the outside naked to the world. Any thoughts/experience is greatly appreciated.

About the inside of the spars. My plan is to wait until the airplane is assembled and do not anticipate any more gluing and painting. At that time I'll treat the spar interiors with Corrosion X or similar product.

[GT280flyer]

E-mailed Stewart systems this morning about using other products with theirs. I have poly fiber epoxy primer that came with the kit, Stewart systems said they have no incompatibility problems with other products. I am NOT endorsing the use of differing products and it is at the builders own RISK if they chose to do so. This post is only for discussion and future reference. To answer a earlier post I am not in to chemicals nor do I have a lab. Just a garage with a beautiful kitfox under construction in it :D

[Dave S]

Hi Steve,

Just wanted to try to answer a couple of your questions. I do want to be clear that every one of us probably has some personal ways we prefer to do at task - but here is my reasoning on the wings/tailfeathers/ribs/hysol/primer deal. Certainly others may look at it differently. In the end - if a person follows the manual they will be fine - it's good.

1) Bonding the wing ribs to the spars is more structurally significant in my opinion - the ribs and the drag braces are what hold the spars in the proper place - for that reason - I wanted the best possible bond between the ribs and wing spars.

2) Powder coat is not the same as epoxy primer or any other paint

3) For the tail feathers - the horizontal stab, elevator, vertical stab and rudder are all structurally accounted for with the steel tube frames/spars and and ribs welded together - the wood ribs we bond into these parts pretty much serve only to define the airfoil shape and hold the fabric - consequently, I feel that the process of bonding the tail feather ribs to the steel structure is way more than adequate if a person scotchbrites the powder coat/cleans up and bonds the wood ribs into the tail parts right on the powdercoat.

4) masking and painting spars.....I have attached a photo - basically I did not concern myself with masking anything - reasoning I am not going to be inside the wing looking at it anyway; and, overlap/overspray is a good way to seal up between layers of epoxy varnish on the ribs, the hysol and cover the spars & drag tubes with primer - sealing is what this is all about anyway - overspray was not actually all that bad - you guys be the judge. The polyfiber tech guy said the epoxy varnish and epoxy primer & hysol are all 100% compatible in any case:) (there is some epoxy superfil in places too.)

Sincerely,

Dave S
KF 7 Trigear

[szicree]

Dave,

Very clear info and very much appreciated. Looks like a good plan. So, I gotta ask what all those hemostats are for. You doing surgery in the shop?

[Dave S]

Steve,

Ah..yes....the artery clamps...... I found that they were very useful when doing the rib lacing (which was going on with another part of the tail at the time of the photo) - actually - found them useful for lots of stuff during the build - holding washers, wires, rivets, small nuts and lots of small parts during fitting and assembly. Buried with the artery clamps in the photo is my pinking shears and a large tweezers - also used during covering & rib lacing. Guess I left a few things laying out in the shop....;)

Dave S

[flypdx]

Dave-

Why couldn't a person just spray seal the entire wing (including the spars) when finished and prior to covering? Just like you did but hit the spars also.

Or are the wood portions better off varnished? I guess it could add quite a bit of weight maybe?

[Dave S]

Hi Jeff,

The intended use for the varnish is to use it on wood parts - whereas the epoxy is pretty much intended for everything else - my angle on this had more to do with compatibility between the two as advised by the polyfiber rep. and therefore seeing no need to mask off the two when painting the spars. I think the fact that varnish is transparent also gives a person a chance to see the condition of the underlying wood during inspections and eventually when recovering.

Sincerely,

Dave S

[flypdx]

Yep, seems like primering everything would be overkill. I think I'll plan to do it the same way you did.