[VAC] Re: Orbital sanders & the Holographic effect

["Robert / Susan Harper" <rharper@xxxxxxxxxx>]

>Don't let the sandpaper touch the skin.  When someone used sandpaper or
>coarse scotch brite pads to remove the clearcoat on our trailer, it left
>fine little scratches in the Alclad layer that polishing & polishing
>couldn't totally remove.  That is what I'm sure created the "holographic
>effect" when I mirror-polished the Caravel using the Rolite & the Cyclo.
> The tiny scratches weren't  on the top, where the clearcoat would have
>been missing when they stripped it.  >RJ

My experience contrasts this. I'm using a 7" circular buffer (not orbital),
and in some areas I have used wet sandpaper on scratches. I first used 2# of
green-ox polish (did entire trailer), and did not enjoy the experience much.
It took off a lot of oxidation, but I found the paraffin based polish very
messy and hard to wipe down.  The green-ox was not agressive enough to
remove sanding scratches unless I did the entire routine very carefully:
600/800/1000/1200/1500 grit, all wet, changing water and wiping down repair
area at each step to avoid transfer of grit particles between stages.  With
each change of grit, you need to increase the area being sanded slightly to
get all of the previous grit's scratch patterns (always a linear pattern,
although I did find that when I got to 1200 grit, I could do a ver careful
"cross-grain" step and spot any imperfections before moving on to 1500).
Unfortunately, a 1" x 3" area quickly becomes a 3" x 6" area after going
through all of these steps. This was followed with the green-ox via the 7"
circular polisher, and it was VERY difficult (if not impossible) to bring
the sanded area up to the shine of the surrounding non-sanded areas.  These
grits are VERY fine, and don't remove much material if used carefully.
Always with clean water.

Then I switched to Rolite pre-polish, and have used about 3# of it so far. I
am very close to going to the Rolite metal polish step, but 65+ degree days
(a must) are sporadic, and I have a little more work to do on vents/solar
panel anyway.  In my opinion the Rolite pre-polish is MUCH better when
dealing with scratches than is the green-ox (using the 7" circular buffer -
mine is the Milwaukee v.s.).  In all fairness, Jim Weston advised right up
front that the green-ox would not be easy using a circular buffer, and that
swirls would be a b****.

The Rolite pre-polish with a 7" circular polisher is capable of handling a
lot of scratches without any sanding, and it easily brought back the full
mirror shine to areas I had wet-sanded to only the 1000 grit stage. It takes
multiple applications and firm but careful pressure, & watch the heat.
Aggravating as it is to have to keep washing these pads, do not let them
load up with gunk.  The gunk is abrasive, and when it hardens in the pad it
will damage your work surface.

As RJ has said, there is definitely the risk of going through the alclad
layer.  I have one small area that was dinged/dented on a rear corner which
I suspect is showing some alclad wear-through. The insidious thing about
this problem is that it's very difficult to distinguish between the
appearance of having gone through the alclad -vs- not having worked hard
enough at removing the scratches.  I've focused my most extreme efforts on
the most visible areas: near the entrance door and at eye level all around
the trailer (say 4 1/2' to 7').

>
>If I had to remove heavy oxidization again (I'm sure I will - I'm
>looking for the next project now), I'd use my PorterCable variable speed
>orbital and the coarse buffing pad from Lake Country Mfg.
>(800-648-2833).  RJ

I have done some experimenting with my Porter-Cable 6" random orbital
variable speed sander (using a buffing pad), both with the green-ox and the
Rolite pre-polish, and found it to be too timid.  The orbital action of the
head robs much of the power of the circular motion.  I will try this again
at the next step (Rolite metal polish), but from the tests I have done so
far with the 3-stage Rolite system and the 7", I think it will work out OK
using only the circular buffer.  This is not to say it is easy, far from it.
And as the trailer gets shinier and shinier, flaws become much more evident.
That means dings, scrapes, minor pitting, polishing patterns, even
directional wipe-down lines.

RE: the "hologram" effect, I have to disagree with RJ.  Or maybe more
correctly I should say that you don't have to use sandpaper to get the
"hologram" effect.  I made a "mounting plate" for my script and nameplate
(to cover some pitting on the skin) and cut the part from the panel under my
rear window on the inside.  Since this is a painted interior panel in my
trailer, and I had it off to work on floor problems, I'm replacing it with a
non-alclad piece which will also be painted. The old piece was raw on the
inside. Never painted, never sanded. I used the pre-polish on my 7" x 12"
piece (3 or 4 applications) and brought up a great shine and a great
hologram effect.  I move on to the metal polish stage, and improved the
shine, but still had the hologram effect. Only after 3 applications of the
metal polish and total wipe-downs was I able to make this effect 95%
disappear.  I then did the AP-300 (twice), did it again in a linear
direction by hand, then one more time (all AP-300 work using Lake Country's
0-cut buffing pad), and finally the hologram effect was gone. I think.  (I'm
almost positive that this part is alclad both sides.)

At this point this finish is VERY finicky and I think very fragile.  Just
the direction of a wiping action (soft cotton wet with paint thinner) leaves
lines which show under bright focused light.  This is very, very shiny, but
it is still very soft aluminum.  Is it worth it?  Jury still out ....  Still
a long ways to go to produce this kind of shine on the whole trailer.


BH62GT/SC