Prepolish wetsand or not?

[swebster]

my understand on this is that you should run water over the area to be sanded. The water acts as a lubicant between the surface and the paper and also helps to move away residue and keep the paper from fouling. I used a hose, but I've seen low specialty hoses with little suction cups on them which attached to the body and spray a nice little shower onto a larger area through little pinhole in the hose.

I'll stick with the garden hose but I think you could use a bucket and sponge as well.

[64GT]

I wet the sandpaper and then had a sponge that I used to wet the area and then to keep it wet.

[uwe]

I only run the hose periodically. I use a wet rag in one hand to clean the sanded are, and dip the paper in a bucket to clean the paper and keep it wet at the same time.
The aluminum might require a different technique, not sure yet. I put the project on teh back burner, because I have camping reservations and don't want to go with a half finished trailer...

[Rog0525]

I really don't expect it matters much so long as you keep the skin and sandpaper wet.

[surf'n safari]

I think you are all on the something here. I've been using a dewalt slow speed drill with wool bonnet and Nuvite. I'm in it about 60 hours...its a very, very slow process. I've used $100+ of product. Well, I bought some 800 and 2000 grit sandpaper and tested a small section. It appears to be a much faster and better for trim then the Nuvite alone. My opinion to this point, use the best of both methods. - because the Nuvite is a great product. I will polish today and try to post some pictures of my results.

[Ken J]

You may be using too much product - use sparingly - more is not better in this case

Ken

[Will Ackerman]

I have a 69 Safari, how can i tell if there is a clear coat or not on my trailer?Just replaced the window gaskets.Ready to begin with the polishing hum?

[Safari Tim]

Originally Posted by surf'n safari

I will polish today and try to post some pictures of my results.

Good luck. Its a very satisfying project. Look forward to the pictures

[Safari Tim]

Originally Posted by Will Ackerman

I have a 69 Safari, how can i tell if there is a clear coat or not on my trailer?Just replaced the window gaskets.Ready to begin with the polishing hum?

I am sure someone will correct me if I'm wrong

I think you can test with a small amount of polish, some also say toothpaste. Rub it on the trailer and if it turns black, you don't have a clearcoat.

[Ken J]

Safari - you are correct - take some toothpaste if it turns black, you don't have clearcoat. My guess is that on a 69 trailer you have clearcoat unless someone has stripped it. The fact that your not sure tells me the clearcoat may be in good condition - little bit of Walberize is all I would do if the clearcoat is all there.

Ken

[greg176]

I've been trying to remove some fairly deep scratches by wet sanding.My problem is that the wet sanded area requires a great deal of polishing to get a mirror shine in the sanded area, even after sanding with #2500 paper and polishing with Nuvite F7.Most of the lower panels on my trailer are heavily scratched and pitted and it looks like they will all have to be replaced. Have any of you had better luck getting rid of scratches.

[Safari Tim]

What I learned on my trailer is that you have to go much slower with the compounder than you would think. I had to make a consious effort to go slow, like one inch per second from right to left.

I also found that I had to go over the same area as many as 10-15 times. I was primarily using F7.

Here is a picture of what I was dealing with.

[greg176]

Thanks Tim, that's what I have found 10 to 15 times with the F7 is about right.

[53flyingcloud]

While Tim has a point, some selected area might clear up easier if done by hand..(Instead of using the machine)..
Wait until you see what I have on the 64GT to clear..WHEW..
(This is gonna be one heck of a project)
Just a thought..
ciao
53FC

[uwe]

Also, if you're sanding, then you are removing material from the top layier of the skin.
Now you essentially end up with "different" material from the reast of the skin, as the top layer is removed by the sand paper. It will polish to a slightly different finish, i was told.

[Ken J]

Uwe

Think what you are referring to is removing the Alcad - yes it will still shine up, but as you say its different material.

Ken

[fireflyinva]

I did a bit of library research into polishing (see my previous post here: http://www.airforums.com/forum...1&postcount=15 ) --and frankly, based on what I read in the books I found, I think removing the alclad layer may be pretty much inevitable.

Here's what I mean--the patina you see on a dull trailer is a very thin layer of molecules where oxidization has changed the molecular structure of whatever metal is at the surface (I don't know what kind of plate metal was used in alclad, but according to what I've read, this part is true of all metals). These molecules are in fact chemically changed and cannot be easily changed back to their original chemical structure (ie, the original metal).

So, to regain the shine, you have to remove the chemically altered material ("polish"). Regardless of what product you use, this generally done by abrasion. The trick is to "cut" out the smallest layer out--no more than absolutely necessary. This can be done by removing less than necessary until you come to the non-oxidized layer. Finally you buff the surface material--actually melt down the metal--to smooth out the "cut" marks into a smooth reflective shine.

But back to where I started--knocking off the alclad layer is pretty much inevitable. Every time you remove patina, you remove metal, regardless of what product you use. How fast you remove the alclad layer is a question of how thick it is. I think the trick is to find a polishing product that balances the tradeoff between a high abrasive that cuts off the patina fast but will take off more metal--and a low abrasive that does less metal damage but works slower--and may drive you crazy!

I don't know what I'll do!

Mary

[Ken J]

Its my understanding that Boeing did a test on its aircraft, using I believe a polish similar to Nuvite S - did the polish 300 times and did not take the alclad off.

I've always been concerned about removing alclad myself and used only Rollite S because it was a zero cut polish, I'm now using Nuvite S which has a very lite cut after reading about Boeing.

My understanding is that polish kinda rearranges the metal as I understand it.

Ken

[fireflyinva]

Please understand that I do not claim to be an expert, just that I went to a local university library and looked the subject up in some technical books. Granted, these books went quickly into chemistry and formulae--which I do not understand much at all---but the premise of shining is basic to all metals and made sense even to me. It's a pretty basic process to get a handle on--and I think understanding it will make us all smarter at doing it.

The surface (patina) layer must be removed, or you will essentially be embedding tarnish further in your metal structure. That won't get you much reflectivity (a subject for an entire chapter, might I add). That is done by abrasion--either physical or chemical. The chemical processes, as I recall, can involve ionization of molecules, complicated processes and in some cases, can get hard to control, depending on the chemicals and metals involved.

That all is polish. So, there cannot be a true zero cut polish, since the point of polishing is to physically remove patina (bear in mind, I am using the technical verb "polish", not the coloquial use of this word).

As mentioned previously, melting the metal surface (or, as you say, Ken, rearranging the metal) is buffing.

The tricky part is that both processes can be performed with the same shining product. With physical abrasives (I can't really write about the chemical ones), slow movement will dig small (or microscopic, depending on the abrasiveness of the product used) grooves in the patina level (or beyond, if the abrasive is too coarse). Using the same abrasive at speed will create higher friction and heat, causing the exterior molecules to melt and settle down into a smoother surface. With a coarse abrasive, more heat will need to be generated to get to buffing--however, when this happens, the surface will be melted deeper.

Smoother surface=greater reflectivity. Rougher surface (due to either oxidation or polishing) means there are more surfaces to capture light=less reflectivity. Interestingly--a shinier trailer should be a cooler trailer, since less solar energy is captured (someone should do a science experiment on this at a rally).

Different metals require different levels of heat to get to the buffing point. I'm not sure what the metals involved here are--in the patina (tarnish) layer, in the plated (alclad) layer, or in the base metal.

That said, and I think this is important, it is possible--especially with small amounts of patina/tarnish--that the same level of effort will polish off (ie, remove) a patina/tarnish layer of metal with a high melting point and SUBSEQUENTLY buff off an underlying layer with a low melting point. This change in activity may not ever be understood by the person doing the work--but it is in fact, a whole different process.

That's what I believe happens when folks touch up the shine on a trailer that had been "polished" fairly recently. That's also why buffing cloths also get blackened (from abrasively removing the final layer of tarnish before really buffing).

Whether the products you describe is best or not is a personal choice, I think. You want something that will remove sufficient metal (yes, tarnish/patina is a metal, just a different one) so that you don't go crazy with the process--and is sufficiently fine (low abrasion) to not erode the layer under the patina. This should not only extend to the substance used, but also to any cloths and pads used to do it.

I am going to make a hypothesis here (and I hope nobody misinterprets this as a fighting argument in the polish war, but rather a logical consideration of the physical process). I have concluded that the slower techniques use finer abrasives. It's not clear to me whether the faster effectiveness of the coarser abrasive is going to eat too far into the alclad layer (there may be enough plating there) or make an inconsequential difference (maybe we need Boeing here again, lol).

No matter what technique is used, it's going to end up that it's probably the alclad layer that ends up getting buffed in either case. It's the metal getting shined that determines the reflectivity--and how far the item is buffed (or how well the surface irregularities are melted down--aka the elbow grease factor!). That's why I don't think the photos are really going to be evidence of how the techniques/products stack up in the end--although they are fun to look at for armchair polishers like myself!

Mary

[Ken J]

Mary

Very good research. Perhaps thats why the courser Nuvite polish indicates that it starts out course, then as you polish the courseness breaks down to a finer course polish. Were as the medium polish remains a consistent courseness.

Yes the zero cut, stills turns very black when you polish. However Rollite claims zero cut - perhaps it just melts the metal surface?

Over the years, I've learned that sanding takes off too much too quickly.

Ken