What ever you think
chaskuss said:
George,
Have you ever actually read the application instructions for the various brands of polyurathane paints? If you actually had, you'd know that they call for a 6 mil coating (2 coats) of finish paint. Assuming a MilSpec (1 mil) application of primer, that means the primer is only ONE SEVENTH of the weight of the complete paint job. Let's see, ... 30 pounds divided by 7 equals 4.29 pounds of primer on the exterior. If we assume that priming the interior will add twice that 4.29 pounds, that's quite a bit less than your guesstimate of 25 pounds. 25 pounds of primer sounds reasonable for a sea plane, but not most RVs.
I think you really are overstating what portion of the total weight can be attributed to the primer. If you live in Florida or New Zealand, you had better treat it like a sea plane, because it is. Down here, we have 4 year old RVs (always hangered) which have significant corrosion because the builder didn't use Alodine under the primer. FYI, MilSpec epoxy primers only stop 7 of the 8 types of corrosion. The only thing which stops filiform (the most insideous type) corrosion, is a chromate conversion process (aka Alodine, Iridite and several other brand names). Alodine will prevent 4 of the 8 types of corrosion. Most of this info is available on EAA Chapter 1000's web site.
Charlie Kuss
Not sure what your point is? It decidedly sounds like you are telling me I am not only wrong but ignorant,
"Have you ever actually read the application instructions for the various brands of polyurathane paints? If you actually had, you'd know......"
Clearly you are looking for a fight and I am not playing. You don't like my SWAG, OK. Second please don't lecture me about corrosion. I was a lead structural engineer for Boeing at one time. I know more about finishes and corrosion in aerospace materials and structures than you think. I am not going to argue with you. Prime to you hearts content Charles.
I don't buy your 5 lbs, 1 mil thickness for a true protective (sealing) primer by the way. No 1 mil thick primer could stand up to the "Mil Spec" salt spray test that I know of. The Grey Lesonal (german) primer I use recomends min 3 mil build to seal surface.
If you would read my post carefully it starts with SWAG - Scientific Wild A** Guess. Second, I only quote what a FINISH paint job weighs as a data point. Not a trying to make any comparison, except that primer, paint and clear can add 30 lbs, fact. Yes primer alone is lighter, no kidding. Primer is at least a quarter of teh 30 lbs.
So Surface area outside < Surface area inside structure (including sub structure)
This is my point. How much more area inside? I don't know. 100% more? So if primer alone on the outside is 7 or 8 lbs than the inside would be 14 to 16 lbs. OK so my 25 lbs is too high by a factor of 2. I don't really care, but your 4.29 lbs (high precison number) is off by a factor of 3. In a 100 years it will not matter.
If you would have read my post, there are many brands and types of primers. Wash primer is translucent, low solids. Filler primers are applied to greater thickness and weight. What Van uses, wash self etching, does not add much weight. I am not going to get into wheather Van's wash primer is OK as a final coat. I think it is fine and adds some protection, especially since the aluminum is already clad. However other true sealing primers go on way thicker than 1 mil my friend.
For the record, I gather you don't like my comment about float planes. Yes, I don't think Alclad needs to be primed unilateral. Overkill priming is one of the contributing factors to RV's that have 1,250 lb empty weights. Some builders have never seen an extra pound of weight to add they said no to. My RV-7 in a hanger. Even on a coastal city is going to last longer than I need it to. Will any of this matter in a 100 years. Relax. It is not critical like you make it sound. We are not using exotic high strength materials in harsh conditions. Just 2024-T3 clad sheet. Ho hum. You are eggagerating the corrosion issue, even in Florida or new Zealand. You have a better chance of your RV being destroyed by either a hurricane (FL) or a goat eating it (NZ), than getting significant corrosion damage in your life time. But do what makes you happy.
To each his own brother. If you want to prime that is your business, but you are adding weight, more than you think.
There are too many variables to say for sure, but a true primer that is designed to be top coat protection (thick) and "fully priming" ALL THE structure inside a RV can add up to 25 lbs IMHO. May be its half that? Most people apply paint and primer too heavily. There are too many variables.
Clearly you don't like my guess. OK. We agree to disagree. I am going to take a wild guess your RV is primed inside. Right. What is the empty weight of your plane? Respectfully disagree. Have a nice day. Cheers