Damaged dimple on a skin, is it fatal?

[rv6builder]

I don't think you've flattened the hole, but actually ground it down. Thats why you're seeing the larger hole. As the skin would now be pretty thin around the hole, I would replace the skin if there was more than a few. I'd suggest just scuffing by hand next time.

Alex

[Taltruda]

Looks like you?re scuffing with a powered DA and not by hand?

[Tom Martin]

Oops rivets are not likely going to work as the hole is now too large. Larger rivets might work but unless you do all the skin with them it is going to show.
As this is you first part I would replace the skin. Keep this skin for parts if you need some small pieces of aluminum later in the build. Set this part aside and move on to something else you can get a skin shipped with your next order to save some shipping costs.
Scuffing should be done by hand with a red Scotchbrite pad. Very little is required, just enough to see some light etching.
I see that you are based in Israel. You might consider not scuffing and priming as pictures of your country would lead me to think it is very dry. However I do not know the effect that Mediterranean has on local cars and equipment. Go and talk to a local aviation shop and ask their advice on priming.

[BrianDC]

Personally I would recommend looking at a new skin. Based on your picture you were using some decent sand paper with your orbital sander. I would highly recommend a visit from an EAA Tech Counselor or possible the EAA Sheet metal class.

I would not recommend sand paper to scuff before priming, but red scotchbright pads. Also as others have stated, Scuff before you dimple (I would go farther and say scuff and prime, then dimple after primer has fully dried). If you REALLY want to use your orbital sander, just remove that sand paper and put a maroon scotchbright pad on it and use LIGHT pressure. You are just trying to scuff, not sand any thickness off.

Maybe give us a photo of the area so we can get a better idea. Could be it just sounds worse than it is and OOPS rivets may be fine, but hard to tell.

[N804RV]

An old-timer I know and respect a whole lot told me that virgin alclad does not need to be scuffed. You're either going to use a conversion coating, and primer. Or, you're going to use a self-etching primer. With clean, new alclad skins and extrusions, just wipe with acetone using a lint-free cloth to remove ink and oils. Then, wipe again, just before priming with denatured alcohol.

He was emphatic that scuffing compromises the alclad and is just not necessary, unless the area is already compromised by salts or corrosives (like when you find corrosion under the blue plastic around the edges of alclad that has been stored a long time).

[nzrv8]

The goal of the scuffing is to provide a key for the primer to help it 'etch' into the surface. This only requires a quick light scuff by hand with Scotchbrite as others here have mentioned. Just enough to lightly scratch up the surface - not so much that all of the shiny Alclad layer is removed. The shiny Alclad helps prevent corrosion, so you want to retain it, but you also want the primer to stick to it.

PM me if you would like to Skype and I can demonstrate a few things for you - I know the feeling of building in a country where you can't just get another builder to come over and have a look.

[bkervaski]

alclad does not need to be scuffed

The parts definitely need to be scuffed and cleaned with Acetone or MEK to provide an oil-free non-smooth surface for a primer to grab onto, otherwise it's going to eventually flake off.

[jacoby]

Originally Posted by BrianDC

If you REALLY want to use your orbital sander, just remove that sand paper and put a maroon scotchbright pad on it and use LIGHT pressure. You are just trying to scuff, not sand any thickness off.

Would an interface pad help as well? I've used them cutting clear on cars and they really save you from cutting through sharp corners and following curves. You end up with a lighter touch than by doing it by hand.

[CJ in EP]

I've used a quarter sheet finish sander with the red scotch bright pad (instead of sandpaper) with great success. I always tried to scuff before dimpling, but the times I've forgot the thickness of the pad and very light pressure (not much more than the weight of the sander) allows the pad to conform to the dimple without any material removal.

[wirejock]

Originally Posted by CJ in EP

I've used a quarter sheet finish sander with the red scotch bright pad (instead of sandpaper) with great success. I always tried to scuff before dimpling, but the times I've forgot the thickness of the pad and very light pressure (not much more than the weight of the sander) allows the pad to conform to the dimple without any material removal.

Same here. Maroon scotchbrite on the pad of a random orbital. I just guide it around with no pressure very quickly.