Wet sanding??????

Crank729

I'm in the middle of a pepakura project, and pretty soon I want to wet sand the helmet. I understand what wet sanding does, but I don't know how to wet sand.



I just don't know, and I feel it's a pretty important part of my project. Any help is greatly appreciated.

Thank you very much!!!!!

Jannix Quinn

Wet Sanding Part 1 of 5 - YouTube

Crank729

Thanks man!

exoray

Some hints, that work well for me...

Use only cool or cold water, hot water has a tendency to make some surfaces sticky and thus creates a negative effect when sanding... And if you want you can mix in a little (or a lot) of dish soap (Dawn) as I find the added lubrication helps glide across the surface, and you are cleaning it as well, the soap also helps the water sheet and stick across the surface vs just running off...

I also find that doing it under running water in a slop sink or kitchen sink to be beneficial if the part is small enough as the constant stream of fresh water doesn't clog the sand paper and immediately washes away the sanded particles... And for real small parts you can do them completely submerged in a bucket under water...

j0wE

I usually use a 5 gallon bucket(for helmets) filled 3/4 full with cool water with a little dish soap. I always start with 800 and go up to 1500. You have to remember to keep the piece and sandpaper wet for lubrication or else the sandpaper will get clogged up.

EDIT: I pretty much said what exoray said lol

HadronMM

I'm not sure what you're plan is with the painting, but I'd be really surprised if you need to go up to a grit any higher than, say, 320. Wet sanding at grits of 400-1500 is for achieving very high degrees of polish on metal. Paint, especially spray paint from a can, will effectively conceal any marks that are left once it's been gone over with 320. In fact, I routinely sand only to 220 grit with an orbital sander only before painting, and I'm highly doubtful that a surface that has been sanded to 400-800 and then painted the same way would be distinguishable to the eye or to the touch in any way. So I guess I'm suggesting that wet sanding, which is usually reserved for 400+ grits, probably isn't necessary.

Matt

Maelstrom

Incorrect.

It depends on the finish that you are trying to achieve. If you think sanding a Vader helmet with 220 and then painting it is going to give you the same gloss effect that wet sanding up to a 1500 grit and then painting will I highly suggest that you try a home comparison for the two methods.

Hfuy

I routinely wet sand unless there's a reason not to, mainly because I find it helps the paper last longer. his seems to help mainly with clog avoidance, butil I get the feeling that the lubrication also extends the life of the abrasive particles.

One safety tip: it seems to be possible to rub a hole in you own flesh without any warning pain when wet sanding. I did this a couple of days ago to the outside edge of my right thumb while flattening off the back of some cast resin rank insignia (as mentioned elsewhere on this fine forum) and they were somewhat too small to grip easily. The first warning was when the slurry of white resin tailings in water started to turn pink. Now the wound has dried out of course it's enervatingly painful out of all proportion to its microscopic size, and I shall be enjoying today's traditional roast dinner with the cutlery in a rather awkward grip.

I find the idea that spray paint will fill in the surface to be rather hopeful. It depends exactly what you're using, of course, but my experience with rattle cans is that, properly used, they are capable of an extremely fine finish which will not fill in any but the very tiniest hints of a scratch. Even the yellowish stuff sold as "spray filler" seems reluctant to fill in rubbing marks for some reason. Of course an airbrush is even less likely to lay down a thick enough coat, and you may have more luck with the full size compressed-air guns and the rather higher-viscosity paint used to finish cars, which I get the impression is more designed to act as a fairly thickly-applied coating with a deep gloss finish, but I don't have much experience with that. Ultimately I think that any paint thick enough to obscure detail you don't want is also risks obscuring detail you do.

-HF

exoray

Don't forget wetsanding is not only a 'prep' step before painting it can be used after the final paint job to remove any surface or orange peel effects, using a quick buffing to bring back the shine after that final wet sand...

And I agree if you are going for a deep high gloss finish, you need to go down much further than 300 or 400 grit, 300/400 is OK for some things with sloppy top coats but not if you are looking for a mirror finish... Also different paints will fill better than others, for example lacquer will show 300/400 sand lines with other paints will fill them...

Finhead

When I wet sand (bodyman by trade) I wont even both with anything heavier than 600. No point before that, whole point of wet sanding is to get a nice finish (smooth sand no cross hatch) for your paint surface. Most base coats will show sand scratches with anything less than 600.

Crank729

I just thought I would tell you now that I am working on a thomas bangalter helmet and I would like to paint is silver/chrome.

Thanks for all the tips though, really helpful!!!!!!

Rebelscum

I'll take a modified bet on the quote above...

Agreed, you have to go higher than 220, but 1500 is unnecessary unless you aren't actually at 1500, but think you are. This is a very common mistake when sanding because sanding at any grit doesn't make it finished to that grit until all the scratches left by it are uniform. Knowing how to actually determine this is harder than you'd think, but easy to misjudge if you are skipping any grits or going up in too large of increments of grit.

The resolution of essentially all paint is much less than 1500. Even if you're shooting lacquer, you'd finish the paint itself to 1500, or more, but not the substrate before you apply paint.

When painting plastic, metal, bondo or other similar things, as opposed to staining or finishing wood, it can't hurt to go to 1500, but it can be a lot of effort for no benefit, so even if you think it's required, you're not going to harm your final product.

I work with almost every type of finish you can think of, on many different materials, but sanding prep is exactly the same on everything. Understand the finish requirements, and don't do any more prep work than necessary for your finish to be perfect.

kurtyboy

I always wet sand at least 600 or 800 between coats too. Really helps achieve the final glossy finish if that's what you're after.

Rick Hanson

Possibly important question - what surface or finish, exactly, are you wet sanding? I can think of a dozen ways this could end in tears and sadness for you if you're getting a Pepakura-based item wet before it's really ready. No offense intended at all, but the very fact that you're not sure how to apply the process leads me to believe that maybe it's not quite the right thing to be doing yet.

BTTFSpencer

When I wet-sand my models, I go from 180 grit, to 240, 400, 600, 800, and then 1200. After I've finished sanding sometimes I'll even grab a bit of Meguiars scratch X polish to clean any little surface scratches up. I find this method makes a really clean crisp surface for the primer, and the paint. The smoother the surface, the better the paint finish.

Just my two cents.

nick daring

Good thread!

When is dry sanding better than wet sanding?

The benefits of wet sanding sound numerous.

Nick

Maelstrom

Well...let me step back on that a second. Yeah I probably have never gone up to 1500 on primer coats, but I have gone at least 1000-1200


Also...as to what Rick Hanson was asking earlier I have to admit I was wondering the stage you were at also. Wet sanding won't be an issue until after you have fiberglassed/resin'd your pep and gotten all your angles smoothed out with Bondo or whatever you are using. Wet sanding won't be worried about until you are at final primer coats before painting

Crank729

I completely agree with you, I dont want to do this process unless it is neccesary and I am completely confident how to do it.

Here is the lowdown on my helmet.

It is a completely fiberglassed, completely bondo'd pepakura helmet, the thomas bangalter file from dung0beetle. I am basically done sanding, only about 2 more little pinholes to fill. I need a very smooth look, because chrome/silver paint looks crappy on rough surfaces.

There ya go. Thanks for the discussion guys, really helpful for me!!!!!!!!

If you got any more questions, shoot!!!!

exoray

[QUOTE=nick daring;2063706]When is dry sanding better than wet sanding?
/QUOTE]

You usually dry sand 150/200 grit or bigger... There is no need to wet sand the bigger grits as it's just rough in work, and due to the size clogging shouldn't be a big issue...

Wet sanding happens in or about the 220 range as you aim to finalize the prep and achieve the final smooth surface... This happens usually after the item has been primed or immediately before priming if the surface permits... You can say wet sand plastics and metals before primer, but you can't (or shouldn't) wet sand bare wood (or another surface that absorbs water and causes issues) before primer/sealer...

FYI: I place an arbitrary number in the 220 range, it's not an exact science across all jobs there are many times I will dry sand in that range and other times I will choose to wet sand, it simply depends on the job and what I'm trying to achieve... You might find the 320/400 range to be a better transition for your wet sanding needs depending on the job, or even vice verse where you are wet sanding 80/100, for the simple purpose of keeping the dust down... It's more of an art, and finesse you will learn from experience, with the important rule don't skip around the grits, work it down in steps, or else you are only going to create more work for yourself...

In all cases if you are wet sanding the paper should be rated for wet sanding or else it will likely just fall apart...

elro

The later hundreds is where is start wet sanding - Likewise as jowe , I do it submerged and with dish soap. the paper lasts way longer that way.

Rick Hanson

Thanks for the clarification, Crank. Sounds like you're actually *nearly* ready. I'll defer to the real experts for a final judgement, but in my experience as a hobbyist, you'll probably want to wait until you get some good quality primer on the helmet before you start the actual wet sanding process. High-build automotive primer (Dupli-color is what I use) will cover well and fill in all the tiny imperfections in the Bondo. You will still want to get the helmet itself as smooth as possible beforehand. The idea is to gradually build layers of primer, wet sanding in between each coat, until the whole surface is uniformly smooth and even. It may take two coats of primer or it may take ten...it all depends on the quality of the initial raw surface.

Again, I am not an expert, but this process has worked well for me in the past on cast resin and fiberglass items. The more experienced guys who've been posting here can probably give you some better detail on how to prep for something like chrome.

Crank729

Thanks rick!!!! Lots of great ideas in this thread!!!!