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mv1371

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I see references to wet sanding in several posts yet I am still not clear as to how this process works. It does not make sense (to me anyway) to put water on a cardboard tube. Can someone please give a clear explanation for this paint finishing technique?
 

troj

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First, you need wet/dry sandpaper for it -- standard sandpaper will disintigrate if you get it wet.

Have a container of clean water nearby (old cottage cheese containers, margarine tubes, etc) and dip the paper in, then sand for a bit. After a while, you get a feel for how often you have to go back and re-wet the sandpaper. It can be useful, especially with cardboard tubes, to have paper towels or old towels handy to periodically wipe off the moisture.

With cardboard tubes, as long as you don't sand through the finish, you're fine.

It takes patience, and a little bit of practice, but you can get a much smoother result with wet sanding. In addition, the sandpaper lasts a lot longer, because the water keeps it from clogging.

Like conventional sandpaper, not all wet/dry sandpaper is created equal. Buying a quality sandpaper will make your life much easier.

-Kevin
 

Marlin523

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After 1st coat of primer I dry sand and recoat. I moisten the paper and sand the second coat. Before the final paint coat I do the same thing. I simply don't saturate the thing. It works. Of course each step needs to be wiped clean. I use isopropyl alcohol.
 

Micromeister

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I see references to wet sanding in several posts yet I am still not clear as to how this process works. It does not make sense (to me anyway) to put water on a cardboard tube. Can someone please give a clear explanation for this paint finishing technique?
Wet Sanding is not a proceedure used on raw cardboard. it's a finishing technique used to remove or reduce Paint dam lines and other defects in the completely painted and Dried finish.

You'll hear some Misrepresent dipping there sandpaper in water to unload it as wet sanding...it is NOT. Wet sanding in the painting industry is done with a running hose, wet/dry sandpaper and lots of elbow grease:)

It's is possible to completely remove orange-peel, dust, dirt, masking paint dam lines and other imprefections in a painted finish with this technique but you have to prep the model for use around lots of water. and have some way of catching the runoff slope and slurry created by the process.

PS: Primers are NEVER to be wet sanded, it's porus allowing mositure to penetrate the coating causing problems with adheasion down the road.
 
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luke strawwalker

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Sure... glad to help if I can.

Here's how I do it. Once I have the rocket constructed and I'm ready to start finishing it (any filling/rough sanding all done, or fins papered, etc.) then I shoot the rocket with a couple good coats of a sandable primer. I'm kinda fond of the regular old Walmart Colorplace primer myself, because it's cheap and it works well. Of course IF you're going to use a lacquer based paint, or a different brand, it's always best to use a lacquer primer or the same brand and type of primer as the paint brand and type you plan on using, for compatibilities' sake.

Once your primer is dry, start by sanding the rocket DRY with 220 grit. I 'free sand" (without a sanding block) as it's easier for me-- I've done a lot of car sanding and farm equipment sanding and I'm used to doing it that way, but most folks get better results using a sanding block). Thing to remember with sanding, is ALWAYS KEEP MOVING, NEVER SAND IN JUST ONE SPOT, and sand in CIRCLES and NOT STRAIGHT LINES if you can help it. Sanding in a straight line tends to cut grooves into whatever your sanding and leave deep sanding scratches. Another important thing to remember is, LET THE PAPER DO THE WORK. Don't use a lot of pressure or "push down" hard on the paper-- light pressure works just as well if not better, heavy pressure only clogs your paper, makes sanding scratches, dulls the grit of the paper, and generates heat which makes the primer gummy. Make a couple passes around the rocket, sanding the whole thing. Hold it up to the light and let the light "glint" off the rocket, and wipe it down periodically with a paper towel to remove the sanding dust. Look for any obvious high spots, low spots, or imperfections, and sand them as smooth as you can. It's likely you'll wear through the primer and down to the original glassine coating on the tube in places... but you should have SOME primer left on the rocket when you're done... If not, you probably sanded too much. Reprime any bare spots if needed and resand them to get them smooth and even. A few bare spots are ok for painting over, but it's better to have some primer under the paint, so repriming the bare spots is a good idea.

NOW, we come to the wet sanding. I actually prefer to call it 'damp sanding', because, unlike the wet sanding typically done on cars, you actually need FAR FAR less water to do a good job, and as you said, with the absorbent and rather delicate nature of things like cardboard tubes and balsa fins and nosecones, which tend to warp or dissolve in water, you DEFINITELY don't want to use too much water. You only need enough water to keep the sandpaper from clogging up.

I get a small bowl of water (like an old Tupperware or something like that, preferably retired from the kitchen and used 'for sanding only' since you WILL get primer or paint particles in the bowl from the sanding process. You'll also need some paper towels, a regular old cloth towel (worn out bathtowels are handy) and some 600 grit wet/dry sandpaper. I usually start sanding dry, just to take out any sanding scratches or other stuff that needs a little more dressing from the 220 grit sanding before I start. When I start damp sanding, I dunk the sandpaper in the bowl (I usually sand with a small piece of paper about 1.5 by 3 inches or so) and then 'shake off' the excess water. The first time you'll probably have to rub the paper with your fingers a bit to get the water down into the grit of the paper. Shake off the excess over the bowl, and starting with the dry rocket, start sanding in small circles, gently turning the rocket constantly in your hand as you do. I start at the top of the tube and work to the bottom, sanding about 2-3 inches of the length of the tube at a time, all the way around, and then moving down to the next section of tube below it. The sandpaper will start sanding off the primer dust and mixing it with the water, leaving behind a fine 'sanding mud' behind the paper on the rocket. The more you sand, the drier the paper, rocket, and sanding mud will become. Periodically dunk the paper in the water and shake it off and sometime daub it on the old towel to remove excess water. Look at the grit side of the paper, and if it starts to get clogged (paint 'spots' clinging to the paper) rub it gently underwater to release the trapped paint. Periodically wipe the 'sanding mud' off the rocket to get it out of the way. You really don't want it to dry on the rocket, as it's hard to get off and messy and defeats the purpose. Things don't have to be sloppy wet (water dripping off the rocket) but it does need to stay moist-- usually a drop of water from a finger dipped in the bowl will give enough water to continue sanding if the sanding mud starts to become more of a 'paste'.... but then it's probably about time to rinse and clean the paper again anyway, and wipe the sanding mud off with a paper towel.

It's surprisingly easy to do... I wash the paper about every minute or so of sanding, and wipe the rocket down about the same. Damp sand the whole rocket, then hold it up to the light and let the light 'glint' off it, and look at the reflected 'stripe" of light. If it's smooth and even, you know you're there. If you can see imperfections in the reflected glint of light, like pock marks, scratches, dimples, holes, broken or unstraight 'lines' of the "glint" of reflected light, then you have low spots, high spots, unfilled pores or grain or dimples or uneven-ness and depending on how good a finish you want, you may want to go back and correct these problems now. Going back to using some spot putty to fill a low spot means starting over (at least on that spot, as you'll have to resand with 220, reprime, resand again with 220, then re-damp sand with 600 grit, but if you want a flawless finish, that's what you need to do, and NOW'S the time to do it! Once your satisfied with your sanding job and the surface appearance, use a pretty damp paper towel (wet but not dripping-- dipped and squeezed out pretty good is about right) to wipe all the remaining sanding mud off the rocket, fins, nosecone, etc. (actually I usually do the nosecone seperate-- it's just easier that way)
Wipe the rocket down with a clean dry towel to remove any residual moisture, and let it air dry thoroughly. If you want, you can clean it again with a tack rag to remove any residual paint dust before you do your color coats...

If you do it right, you CAN make primer actually SHINE. Getting a great finish on a rocket is 95% in the prep work-- the better you do at filling, sanding, priming, sanding, damp sanding, and cleaning, the better the rocket will look when it's done. Using these methods, I haven't had to color sand yet and still I get very nice finishes. If you go to an automotive type finish, you may well have to do a little wet color sanding to really get the deep deep lustre that those finishes are meant to achieve... but that's usually the exception rather than the rule... and besides, the more work you put in ahead of the color coat, even if you DO have to wet sand the color coat, you'll have a LOT less color sanding to do to get a 'perfect' finish...

As far as the water is concerned, I haven't had any problems with damage to the tubes or fins. You don't want to use a LOT of water. The glassine coating on the tubes seals them from the water, so as long as you don't sand through the glassine (you'll know it if you do because you'll get an instant case of the "fuzzies"!) the tube won't absorb any water on the outside of it. True, primer IS slightly porous and will absorb a bit of water, but it evaporates readily because the primer coat is very thin. Balsa fins CAN absorb water, but if you used filler on them and have them coated with a good layer of primer, and don't use TONS of water, it shouldn't be a problem. I typically either paper my fins (most all) or wick CA into the fins and then fill and sand them; both methods seem to work fine with this method. When wet or damp sanding, you're not removing a LOT of material anyway-- the finer the paper the less material you're actually taking off. The idea is to SMOOTH the existing surface, not to remove large amounts of unwanted or unneeded material.

Good luck and hope this helps! OL JR :)
 

dave carver

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The water is for lubrication, cooling and to carry off residue. The cooling part is why the paper doesn't clog up wet sanding. The friction of sanding can cause a heat buildup with a slight melting of the paint and it's this semi liquied(sp :p ) that when it rehardens clogs the paper.

There is a 5 pack of various wet-dry papers from 3M that has 220, 320, and 400 grit in them. Think I got mine at Ace Hardware but I know that there are more places than that to find it.
 

mv1371

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Thank you to everyone for your quick responses! Luke, you must have just finished one of those energy drinks based on the speed and length of your post!:D
 

MarkII

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Thank you to everyone for your quick responses! Luke, you must have just finished one of those energy drinks based on the speed and length of your post!:D
Nah - he composes those posts ahead of time, and keeps them in a big file. He can pull one out at a moment's notice. :p

Actually, achieving smooth finishes on rockets is a popular (and perennial) topic for discussion here on TRF. Many forum members are quite accustomed to talking about various aspects of prepping and painting rocket components and so they can post detailed descriptions of their favorite techniques with ease. L_S has a lot of relevant experience that he can draw from for such discussions.

MarkII
 

luke strawwalker

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Nah - he composes those posts ahead of time, and keeps them in a big file. He can pull one out at a moment's notice. :p

Actually, achieving smooth finishes on rockets is a popular (and perennial) topic for discussion here on TRF. Many forum members are quite accustomed to talking about various aspects of prepping and painting rocket components and so they can post detailed descriptions of their favorite techniques with ease. L_S has a lot of relevant experience that he can draw from for such discussions.

MarkII

Hehehe... not quite... where I pull them out of you don't want to know...

(think about it) OL JR :)
 

rokitflite

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Actually Ol JR is sponsored by a computer keyboard company. He goes through about 2 a month...
 

luke strawwalker

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Actually Ol JR is sponsored by a computer keyboard company. He goes through about 2 a month...
Funny, funny...

The ONE class I flunked for the year in High school?? TYPING!!!! (I was learing "proper" two-handed typing and then we had some stupid exercise where we each typed a sentence and handed the paper to the person in front of us to type the next sentence, making "stories" as we went along... Well, not having a book to look at, I watched my hands and never could type right again... I just ended up missing so many of the speed/accuracy landmarks we had to hit to keep our grades up I finally quit doing ANY of the exercises in there and did other classwork instead, like an extra "study hall".

Of course, that was before the miraculous development of internet dating... Once I started meeting girls online, it took me awhile, but I got REALLY good at typing... I can type now about as fast as I can talk, and even though my accuracy sucks, I KNOW instinctively when I make a mistake and can back up instantly and correct it. I don't know what my exact typing speed is, but I typed all this up in about 90 seconds...

Later! OL JR :)
 

Micromeister

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While I can agree with 98% of Ol Jr's long post. I have to strongly disagree where he goes just a tad off the path promoting the use of even "damp sanding" of our lacquer, or acrylic lacquer primers. I also use walmart colorplace Cheapy .88cent a can grey primer.

I too am an Old painter/finisher from way back. Being in the sign business we paint all manor of vehicles and objects from small sheet metal signs to Motorcycles, Trucks, boats, Trains, even Aircraft....and an occasional tractor. We use (or have used) just about every brand and major manufacturer of Automotive and other currently available coating systems on the market and with a very few exceptions these companies instruct that we do not use water when sanding primers UNLESS it's in the last SEALED coat. OBTW Spary-can primers are not sealed until a color coat is added.
One exception suggests, If their epoxy primer is wet sanded it be allowed to air dry a minimum of 24hours or be heated to 140°f for 2 hours prior to painting to ensure no water vapor remains trapped. Which can cause bubbling and other paint adhesion failures.

All that said to say: Primer sanding to a very fine finish is very important, but Wet or Damp sanding is totally unnecessary. You will get the same highly shinny surface on your rattle can primer by dry sanding with 400 or 600grit papers so holding the model up to a light source to spot blemishes stand out. The only difference is you might use a second small bit of sandpaper in the process.

It's been my long standing experience that unless you have some major flaw your trying to work out in a models surface primer sanding beyond 360 is generally unnecessary to obtain a babies butt smooth "Flawless" finish.

I am a strong supporter of lengthy Dry Sanding primer preperation and of wet sanding finial Painted surfaces particularly where multi-color masking paintdam transitions, orange-peel removal or repair feathering are a concern or required.

I've heard it said that Damp or wet sanding of primers is a matter of personal choice. While this statement is true, the point is your not gaining anything by the use of water on your primers.
 
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MarkII

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For me, wet-sanding has been quite useful with some surface treatments, but none of them involve paint or primer. Applying paint in smooth, even coats is the best method. Products like liquid rubbing compound, applied sparingly with a rag and worked with some elbow grease, can help in many other situations.

MarkII
 

1974_Trident

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I have been "Wet Sanding" my sand and fill primers since I started driving 20 something years ago and I've never experienced any adhesion problems.

I see that what I always called wet sanding is more appropriately called "Damp Sanding." I use the plastic container of hot water method except I have always rubbed the warm wet sand paper on a bar of soap before sanding and periodically during. I forget where I learned this but I have found that my sandpaper lasts longer and doesn't clog.

I am under the understanding that our favorite rattle can colors are not sandable as are many of the modern automotive finishing systems. I've been told that the only sandable paints are acrylic lacquers. Is this so?

Anyway, I have been getting-glass smooth finishes on my recent rockets by spraying two coats of color and two coats of clear over a sanded smooth primer.

I tried damp sanding when I built my G-Force and the tube ends softened up to the point that I had to trim a quarter inch off. So, from my experience I will never again damp sand another paper tubed rocket.
 

luke strawwalker

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I've been doing this awhile and I've never experienced any adhesion problems either. Not denying what Micromeister is saying is not possible, but just saying I've had no problems with it myself. I'd say the results greatly depend on what materials your using and in letting everything dry thoroughly before painting, which is a good idea no matter what you're doing. I generally don't paint until the next day after I prime and sand in most cases anyway.

BTW, the W/M Colorplace is NOT a lacquer, but a standard alkyd enamel. I've had NO problems damp sanding, allowing to dry, and then painting over it. Primers CAN (and do) absorb moisture, as the primer itself has 'pores' or a microscopic structure to the finish particles which can allow water to be absorbed, but a some drying time seems all that's necessary to allow the moisture to 'wick out'. The fact that our substrates are usually hygroscopic and porous as well would tend to help by allowing a secondary path for moisture to escape, if need be, unlike typical steel or fiberglass nonporous substrates which would trap any moisture remaining in the primer. At any rate, from experience, it hasn't been a problem. I'd say it's one of those things that probably is reportedly a bigger problem than it actually is... IMO...

Anyway, there's more than one way to skin a cat, so whatever works for you, go for it. I don't like color sanding because of the possibility of messing up the color coat. It has it's time and place, sure, but I look on color sanding as more of a 'rescue treatment' for a bad finish than a finishing technique in itself.

I'll say it again-- a paint job will NEVER be ANY BETTER than the surface prep you've put in beforehand. Yes, you CAN ruin a great surface prep job by messing up applying the paint, or having the paint 'go wrong' on you, but if you've done your surface prep right and do a good job shooting the paint on, it'll look terrific. If you did a shoddy prep job, no matter how good you lay the paint on, it's STILL going to be suboptimal. PERIOD. You can color sand, cream and buff, and clearcoat and wax or put other 'shiny' finishes on it, but that's just 'work arounds' so to speak. Do the work up front or do it later, it doesn't matter, but you WILL have to put the time in to get a great looking finish.

Later! OL JR :)
 

SCIGS30

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I know people like the .99 primer from Walmar Colorplace, and I have a can sitting in my work shop. The problem is the back of the can says to recoat within 4 hours or after 7 days. Is that because they just use a generic label? Also when can you start sanding?
 

MarkII

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I know people like the .99 primer from Walmar Colorplace, and I have a can sitting in my work shop. The problem is the back of the can says to recoat within 4 hours or after 7 days.
That's what keeps it out of my shopping basket.

MarkII
 

Handeman

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I've use a wide variety of rattle cans for top coats. For primer, I've gone exclusively to the Rustoleum Filler Primer from the Automotive section at Wal-Mart. It's a high fill primer that cover almost anything is a couple of coats.

It does say on the can, Dries to the touch in 10 minutes. When dry, can be immediately re-coated, top coated, or wet sanded. Wait 2 - 4 hours before dry sanding.

That is why I "wet sand" primer, because I can do that hours before I can dry sand. I don't wet sand the first coat, and sometimes the second coat on cardboard tubes.

As for cardboard tubes, I buy the CA in bubble packs at the dollar store and run a bead of CA on the ends and inside edges of all my cardboard tubes. It hardens the tubes, makes them last longer, and prevent soaking up water when I "wet sand" the tubes while finishing.
 

Pat_B

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Timely post. I too just bought some Rustoleum Filler/Primer from an automotive store. I liked the 'filler' aspect of it and it dries rather quickly. I'm building a HP rocket and didn't want to use FNF for the entire tube. Figured I try to hide most of the grooves with a good quality filler. So far, so good.

I've been wet sanding it, per instructions, and generally like wet sanding due to the water providing a slippery surface which helps the sandpaper glide across the surface of the primer and not dig in as much. It's all a matter of preference, but I've bought a number of primers over the years that had instructions allowing for wet sanding.
 

Micromeister

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I know people like the .99 primer from Walmar Colorplace, and I have a can sitting in my work shop. The problem is the back of the can says to recoat within 4 hours or after 7 days. Is that because they just use a generic label? Also when can you start sanding?
I don't like the 4 hr /7day lable either but I couldn't NOT try the stuff at .88 a 12oz can.
it's always been my feeling that for hobby purposes the Cheapest sand away primer is often a blessing. Used to use K-Mart Fresh-N-Easy but they raised the price to 1.30 a can even in bulk orders so Poopus Nunie on them. Back to looking for a cheap reliable primer. ColorPlace Alkyd Enamel is the current cheapest stuff If found.
Actually the material is sandable in about 20-40 minutes, I generally let multi-coats dry about an hour before sanding. I've recoated after 24hours with no problem using rustoleum and old formula Krylon. I've only been using this stuff a short while so I don't have a huge number of success models to show but it's not shown any bad signs with any other paint then new formula Krylon which it didn't like after a week of drying:( corse new formula krylon doesn't even like itself:)

Yes luke" I am aware colorplace is a alkyd emamel, I don't always type every possible combination when making a point. the MAIN POINT I would like everyone to understand is surface preperations is paramont to the finial finish to a POINT. Sanding Primers beyond 360-400grit can actually cause an adhesion problem by removing the very tooth we are applying the primer for in the first place. Excessive "polishing of a primer could cause the color coat to lift having only surface tension holding it to the polished surface sort of link paint on glass.
I have to admit this might only happen in the worst cases, but more then one professional Auto paint artist has advise me against the use of many of the finer grit paper on the primer coat.

Luke & I Fully agree: DO correct any defect, bump, blemish or nasty thing seen in the primer coating before applying a color coat but do it DRY and you'll be better serviced to check the surface by applying a coat of White finishings primer after sanding your underlaying grey primer (whte primers have the fines solids) then Polishing the surface of your grey primer with those super fine 600 to 4000 grit papers. 360 well give a very high to the surface that will show shadows of anything you missed.

Folks have ask why then are such papers and the wet sanding method around. and I AGAIN answer these technique is a FINISHING technique specifically used on masking paint dam line transitions areas, top coat/clear coat issues and fine dust,debris and scratch removal. Not ment at all for use with primers.

Spend your time removing the major and minor blemishes in the surface of your models but save yourself a bunch of time and useless effort by limiting any beyond 400grit sanding use to very tiny areas after the paint is applied. Personally I'd much prefer spending an hour leveling masking paint dams the a little finessitt-II and a damp rag and spending that same time polishing primer.
 
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luke strawwalker

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I know people like the .99 primer from Walmar Colorplace, and I have a can sitting in my work shop. The problem is the back of the can says to recoat within 4 hours or after 7 days. Is that because they just use a generic label? Also when can you start sanding?
As soon as it's dry-- I've shot it and sanded within an hour or so. I've done the color coat later that day or the next day. No problems whatsoever.

I REALLY like the stuff. Just wish they offered it in more colors.

Later! OL JR :)
 

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