Primer for ribs and spars etc.

[Barry]

Everyone,

Thanks for all the replies and opinions. This being my 3rd build, I totally understand how many different opinions there always are on many different subjects. Thanks Dan for giving the factory opinion as well.

I have decided not to prime due to climate and also my old age, as many have stated, it takes a very long time for corrosion to do enough damage to make an aircraft non airworthy. It will also speed up the build a bit.

I will use primer for areas for aesthetics, but not on ribs etc.

Happy building!
Barry

[ykachuro]

For the acoidance of doubt, I didn’t mean to disparage the “factory priming”. I have no doubt it works for what it is intended. I understand it is not meant to be the finish layer.
And like many things in life, the beauty of priming (or the lack thereof) is in the eyes of the beholder.

[danweseman]

As a note the 'factory primer" is SEM etching primer. It is "lacquer based" so it can easily be softened and wiped off with various chemicals. I It has really good adhesion properties but is not a "tough" primer in terms of handling. If it is coated with a Polyurethane it is very durable. It is mainly applied to the factory spar to help with corrosion between the various layers. In this respect it is a excellent choice as it ins not susceptible to damage from handling.
It is not really necessary and our own aircraft do not have it.
The biggest reason we prime it is that it looks nice....We have the SEM available in "spray cans" for touch up as it is somewhat easy to damage with handling especially if it was applied to thick. We did have this happen some with the "green" primer as one of the shop guys (he will remain anonymous... Pat whooops) is a bit vain and likes them to look nice and have a thick coat ..... We switched to the grey SEM as it seems to cover better over the aluminum and look good at the appropriate thickness.

As a side note be very careful using bonding agents other than "polysulfied based" (pro seal etc) sealants as some are reactive with aluminum, and can actually cause corrosion.

The VAF forum referenced will make your head hurt with opinions. Please dont get bogged down in the "great primer debate".... If you spend more than 1 hr deciding on primer or not what kind etc you spent to much time on the decision!

Dan

[ykachuro]

Barry, I should note that the spar I ordered pre-built came primed from the factory, but the primer was more for long term storage, I assume, as it started to flake off in places almost as soon as I unpacked it. That factory primer comes off easily with acetone.
I should also note that I epoxy most of the rivet joints at the time I rivet them, but that’s a different story (not approved or recommended)... although it may add corrosion resistance to the joints (not that I think it is needed).
If you haven’t done it yet, you may want to check out the wealth on priming info on VAF forum.

[MyronNCallaham]

Barry, I am priming just the mating surfaces with SEM self etching grey , 39683. It is the best of the rattle can primers I have found. Expensive , at $20 per can. TEMPO also makes a good product at about half the price, but has been hard to find. I have some back ordered for months. In all honesty, it’s probably unnecessary, but I chose this as a conservative approach. Most of the cheap primers you find at big box stores are in my opinion worthless. The SEM and TEMPO etch and adhere well.

[ykachuro]

Barry, my 2 cents:

I’ve decided not to prime because (1] 6061 aluminum is very corrosion resistant. It is the grade used in salt water marine applications, among other things, (2) even other grades of aluminum that have less resistance to corrosion (2024 ~ the most common type used in aviation) often show no signs of corrosion degradation over the life of the airplane, (3) priming adds time to the build and weight to the airplane (not to mention $), (4) i knew i wouldn’t enjoy the process, (5) no one lives forever; the resale value of the airplane will be a fraction of my out of pocket expenses and priming won’t make a measurable difference in that respect, (6) i plan to keep the airplane in CO (where people pay money to get iron/steel artificially rusted as an architectural/design feature...), but I wouldn’t prime it even if I kept it near a sea.
I thought about spraying some corrosion inhibitor inside the steel cage, but I probably won’t do it. I will instead pay attention to sealing the rivet lines well with an adhesive of my choice.

[Barry]

Hello,

I am getting prepared to prime some internal parts. I was wondering what everyone was using for primer. Advantages of various brands and methods of application. Prep that works fast and easily? I live in Colorado where there is low humidity, but it may be a good thing to do. Thoughts?

Any tips welcome.

Thanks,
Barry