To scuff or not to scuff (tanks)

When I built my RV-7 tanks, I dutifully scuffed the alclad off the skin where ribs, stiffeners, etc. mate up.

Now I'm building my RV-10 tanks and considering skipping the scuffing. I'm trying to grok a tangible benefit.

All the tanks I've seen online where builders scuffed the skin -- they don't scuff the *opposite* surface. Just the skin. The rib flange, the stiffener face, etc. weren't scuffed -- plain old undisturbed alclad on those. And if you get right down to it, I've never seen anybody scuff the area around dimples where we surround each shop head in sealant. Hm. Maybe these omissions are down to oversight on the builder's part?

Or maybe all this scuffing is much ado?

My thinking is -- if the sealant is sandwiched firmly between the skin and the other part, where's that sealant going to go? Is there really a chance of it debonding in that tightly mated area, and working itself out somehow? And is scuffing going to make the difference?

Or is scuffing more about giving the fillets and overlap in surrounding areas better grip?

I don't mind taking the extra effort to do this scuffing business -- as I said, I did it on my RV-7, and I've had zero leaks. It's not difficult, and it's not even that time-consuming. But I'd like to understand something rather than just do it blindly. Can you help me understand this better?

I scuffed everything when I did my tanks. I even spun a little square of scotchbrite in the dimples if I forgot to scuff a line before dimpling.

I think of it in similar terms to painting; you'd never see a recommendation to paint without roughing up the surface. I don't think of it as 'where can it go', so much as 'how easily can it bond to the surface'.

But I'm no proseal (or painting) 'expert', so take it for what it's worth.

Charlie

Forgot to add: No proseal on interior ribs, except little 'donuts' around each rivet & then over the shop heads. Not my idea; learned it from a repeat offender. Tanks look great (no skin ripples) & 1 can of proseal did both -7 tanks, plus a pair of leading edge aux tanks.

Scuffing keys the surface. If both surfaces haven?t been scuffed then it was an omission that should have been done.

Scuff

rv7charlie said:

I scuffed everything when I did my tanks. I even spun a little square of scotchbrite in the dimples if I forgot to scuff a line before dimpling.

I think of it in similar terms to painting; you'd never see a recommendation to paint without roughing up the surface. I don't think of it as 'where can it go', so much as 'how easily can it bond to the surface'.

But I'm no proseal (or painting) 'expert', so take it for what it's worth.

Charlie

Click to expand...

+1
Leak free too.
I scuffed too but not terribly agressive. Both sides of ribs flanges and skin areas were scuffed. I cheat a bit. I scuff parts before dimpling, while the parts are flat, because it's almost impossible to scuff the dimples inside and out after. It's kinda sick but I also masked off the skin so proseal was only where I wanted it. I used the fay sealing method so both surfaces of any two parts were coated.
I also scuff all interior parts before dimpling so the primer sticks better. Maybe that's why my build hours are so much longer than others.

I scuffed both mating surfaces prior to application of proseal on my tanks as well. I thought the reason for scuffing both surfaces was to increase the grip of the proseal. I would think if you only scuffed the skin and not the rib, it would not have as good a grip on the flange.

Scuffing ain't fun...

...but IMHO you should do it.