What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

SEM Self-Etching Primer vs. EZ Coat

jls32

Member
I'm just getting started and would like to prime my parts if I can do with a rattle can. So I had settled on SEM Self Etching Primer. When looking at prices on AS, I saw this in the Q&A section:

"Q: Would SEM self etching primer be suitable to use on interior aluminum wing parts by itself for corrosion protection without any top coating?

A: Per supplier, I have spoken to many customers about this application and although it seems to work for them, Self Etching Primer is not intended to be used as a topcoat. My recommendation would be to use our EZ Coat product. It is a direct to metal and aluminum topcoat that has excellent adhesion and is available in 6 colors (Black, Olive Green, Light Green, Gray, Tan, Olive Brown)"

Has anyone used EZ Coat? They say it's "direct to metal" so I assume it's self-etching as well.

Both products say to clean the surface with a cleaner then sand with 320 grit. Is this how everyone is prepping for SEM Self-Etching Primer?

Thanks,
Dan
 
Last edited:
SEM

Oh yes. This should be fun.:D
Sorry, welcome. Just kidding. SEM is good stuff if you're settled on rattle can.
Prep is key to painting aluminum. Feel free to read my blog (link below) I get on my soap box about paint prep. I'll save everyone here another diatribe.
On another note...
I manage a Google Group, Colorado RVs
If you would like to join, send me some info (address below) from a G-mail account.
Full Name
Phone
CIty
RV Model
 
Not sure about ez coat but I used SEM self etch primer throughout and really like it. Super easy with rattle can. All about proper prepping!
 
Etch primer

I believe that AS is correct and an etch primer alone does not provide any protection from corrosion unless it has zinc chromate in it, which most currently don't.

The etch primer is intended to give a top coat something to stick to and it is porous.

If you want a primer that gives corrosion protection via an impervious barrier then 2-pack epoxy will do this. It obviously doesn't come in a rattle can. Sorry I don't know anything about ez coat.

There are some good historical threads on VAF that explain all of the corrosion protection options and opinions.
 
Last edited:
We used the self-etching for some small parts with a top coat but for the interior we used the 2-part epoxy primer setup with a sealer per SEM's instructions, made for a really durable and easy to maintain flat finish that doesn't chip like paint.
 
Here in this part of Colorado, primer is not needed. My 65 year old Cessna, unprimed, has minimal corrosion, and all that came from 6 months parked outside near Philadelphia.

I'm only priming my RV-3B for the benefit of a future buyer.

I used SEM for the bulkheads and small parts. SEM works fine as a barrier but really isn't intended for a rigorously brutal environment. It goes on easily, is reasonably durable, and can be removed if needed with lacquer thinner and some rubbing. I like it a lot.

I use the maroon Scotchbrite, followed by cleaning with lacquer thinner or denatured alcohol, for prep. Sanding is not required.

I've used the water-based Stewart Systems Ekopoxy for a few parts where I wanted something more durable. It sprays easily and is a nice finish. I used it for the baggage area and seat, to get more light in there.

I'm up in Boulder if you'd like to see for yourself.

Dave
 
Many years ago when building my RV-10, I did a coupon scratch test using various rattle primers. The SEM self etch primer won hands down.
 
I contacted SEM and this is what they said:

"Due to the heavier solids content, the EZCOAT will be better for corrosion protection. Although there is no acid in the EZCOAT, it will adhere to clean, sanded aluminum as well as SELF ETCH PRIMER. It also handles UV better than the primer. Etch primers do not have a high solids content so do not provide a significant film build and will not handle abrasion as well as EZCOAT."

EZCOAT is a bit more expensive than the etch primer.
 
The more I read these primer threads, the less I understand.....

So you're telling me the self etching primer has no corrosion proofing value??

So literally if I'm using the self etch primer from SEM (which I am) I'm wasting my time??
 
The more I read these primer threads, the less I understand.....

So you're telling me the self etching primer has no corrosion proofing value??

So literally if I'm using the self etch primer from SEM (which I am) I'm wasting my time??

It?s a question of degree. In some sense all paints are porous. Primers more so, as the tiny pores give the top coat a place to grab. But depending on where you live, it might go like this (I?m just making these numbers up-it really depends on environment): nothing, lifetime=10 years; primer only, lifetime=50 years; primer plus sealing top coat, lifetime=200 years. You decide.
 
Primer

JMHO but I think any primer is better than none. However, no primer will probably survive plenty ling. Preparation of the surface before spraying is as important.
VANs has an aluminum sample outside for over 15 years with SW P60G2. It's not intended as a corrosion preventative either but it hasn't shown any corrosion.
 
....So you're telling me the self etching primer has no corrosion proofing value??....

Download the MSDS and see if there is any chemical in the paint which, on aluminum, will inhibit corrosion. Usually, if there is, it acts as a sacrificial material. And also read the data sheet to see if the paint is recommended for corrosion protection directly or if it needs a top coat of some sort.

Dave
 
JMHO but I think any primer is better than none. However, no primer will probably survive plenty ling. Preparation of the surface before spraying is as important.
VANs has an aluminum sample outside for over 15 years with SW P60G2. It's not intended as a corrosion preventative either but it hasn't shown any corrosion.

Over 17 years now.
P60G2 has chromates in it but Sherwin Williams will also tell you it provides no corrosion protection unless top coated.

I have 17 years of testing that shows that it does provide corrosion protection.
 
Decision time

I have really struggled with this corrosion protection issue. The more I read about it the more I struggle. I live in the state of Utah which is second only to Nevada as the driest (water) state in the nation. I will be doing my entire build (-12iS) inside my home and garage. I have no facility to safely apply primer during our cold winter months.
My current plan is to not prime alclad coated surfaces at all. After the plane is finished and the exterior is painted I will rely on Corrosion X or ACF-50 for long term corrosion protection. Is this a reasonable plan or am I setting myself up for disaster due to something I have not considered. I'm sure I'm not the first to consider this approach. I've got to decide quick as I'm ready to start assembling parts.
Your advice will very much be appreciated.
 
No worries.

My 1955 C180 was not primed. It's entire life was mostly in Colorado or South Dakota, and it has very, very minimal corrosion - and that came from the six months it was tied down outside of Philadelphia. Even the three years it spent in Southern California, in a nice hangar, didn't cause additional corrosion,even though the ocean was just three or four miles away.

I'm only priming my RV-3B for resale value. It doesn't add any practical value in my area.

Dave
 
I’m reading the label on a can of SEM Self Etching Primer: “Provides excellent adhesion and corrosion resistance to properly prepped steel, aluminum and stainless steel”
 
Back
Top