Light Aircraft Association

Hi everyone, I am in the very early stages of a Vans RV7 build - I have ordered the preview plans, started converting my garage, boring the wife with the details etc.

My biggest question at the moment is whether I need to prime the Aluminium parts. The Preview Plans have an interesting section about this. They point out that there are some 50 year old aircraft out there that have not been primed and they are showing no signs of corrosion. They also state that all their parts are made from Dural so are aluminium coated and 'should not' need priming.

All the above is great if you live in Oregan where I believe the weather is always fine. What about here though?

Well, while ALCLAD should be OK against surface corrosion you'll be breaking that aluminium skin at each rivet hole and on every edge. So if you don't live in an arid country the routes are there and many for moisture to get in and get to work.
Consider too, your investment. Not saying your building to sell but at some time you may want or need to sell so how (un)attractive would an unprimed airframe be to a buyer in a maritime climate?

Keep an eye on the mag sure there was mention of an up coming article on priming. Also I believe a new TL coming out on the subject.

Also discuss with your inspector as they have to be happy with the airframe construction to sign off on it.

I would most definitely prime! There are quite a few RV's in the UK with some extensive corrosion on them. If you talk to some of the painter guys like Mick Allen etc they will tell you the same.
Also after you have spent a hell of a lot of money building your RV7 do you really want to have that nagging thought in your head for evermore of 'I wish I had primed it'?

There may well be some 50 year unprimed aircraft in good condition, but what about the tens of thousands that have rotted away or needed extensive and/or expensive repair. And the thousands of primed airframes that have corroded. Go with the odds and improve the chances of longevity by priming.

If you are not already a member, get on the RV Sqdn forum, apply to [email protected] . Posting questions there will get replies from experienced RV builders.

John
RV6A
G-TJDM

Further
The thinner sheet components will be Alclad. If you can guarantee not to scratch through this surface at all while building it should protect the base ali. The thicker plate parts and angle material are not Alclad and must be primed according to the manual.

Remember, there is nowhere in the UK more than 70 miles from the sea and salt air.

John

Colin,

Priming is quick, easy and well worth the trouble, however, you are entering the area we refer to as 'primer wars'....

Panic not, it is not a bad area, it is just that everyone has a different opinion.

We have built, or are in build with a total of 5 RV's and use a simple but effective automotive etch primer called Tetrosyl Etch Primer.

It is a 50/50 mix with a splash of thinners to suit, no chromate, no cyano, so a good 3M carbon mask - 4251 is suitable.

The base aluminium has no idea whether it is being used for an aeroplane, a boat, a car or an ornament so do not be hoodwinked into 'special' aircraft primers. What you are trying to achieve is protection, scuff resistance and ability for the primer to accept a top coat if needed for say the interior paint.

Here is a reference to the product.

http://www.ebay.co.uk/itm/201846560513? ... EBIDX%3AIT

If you want more info and a chat about it, get in touch off line and welcome to RV building. I am in Harrogate if you would like to visit our workshop.

M

Many thanks everyone for you replies. In addition to posting the question here I also consulted my 84 year old Dad who served 30 odd years as an engineer in the RAF. He didn't even pause for breath and said I should definitely prime.

I like the idea of the Tetrosyl Etch Primer so will go with that.

I will be writing a blog once I get properly started, I am just waiting on news of a suitable hanger to complete the build in before I do.

Regards
Colin

Make sure the primer you choose will be compatible with what ever paint you are going to use for the topcoat. Randolph make an excellent epoxy primer for steel and aluminium that is available from LAS.
Tony Nowak

Thoroughly degrease the Al surface then only handle with clean gloves.

Apply Phosphoric Acid based treatment to etch the Al and then clean off excess. If not degreased first the P will not be effective.

Spray with an Epoxy Primer immediately after etching.

The Al coating is there as the Alloy beneath has dissimilar metals, e.g Cu, and is not corrosion resistant. The Al will break down in service especially on exposed edges.