الموضوع: دوكووووووو

ملخص العملية .. من خبرة Matt

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Ahmed, I was able to translate a little bit but it still didn't make much sense. I have my hands full here in America anyway, "huuuuuu", lol. Lots of mechanics seem to need advice on paint and I like to help because one day I hope to build a wicked engine.

One thing- the primer is not good. I suggest using the Kapci 625 or 630 instead, if quality is what you want. Using 1K primer will look bad soon.

Here is some good reading for you, from me. I wrote these for others but you need to read them if you want to know the American way! I think you will appreciate it.

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Whatever posessed me to do this, well here it is ...

Junkman's sanding for dummies, no pics. Not too specific but maybe timely if you are considering tackling a paint job or just have never done this before, or if its been awhile and you're wondering about currently popular methods. Not that they change much in the sanding world, ha! Anyway this is just me walking you through how I like to sand cars. Its pretty general and is just intended to give you the basic order of steps and some grit guidelines. I dunno- read it and see what you think. Its an educational post but feel free to discuss any questions with myself and the group here, I am always curious what questions something like this will generate, and I usually learn something new from the input. It is my goal to just help everyone understand better, and be empowered to fix a Pontiac up. Thank you.



Remove existing finish, filler, and rust-

Any type of specialty stripping disc or rough sandpaper will work if theres a lot of material to remove. Refrain from using a grinder like a 5, 7, or 9 inch. If you use something really agressive like that, stop right before you hit ....l.

If the car does not have a lot of paint on it, 80 grit will get you there nicely on a 6" DA sander but you need a lot of air and a whole roll/box of sandpaper to do the car. I recommend heavy weight sandpaper, it lasts longer. Such as 3M # 1506, the sticky green stuff. E-weight paper (thick). That roll will outlast two of another kind but its a hundred bucks. Nothing I've found compares to that part # when it comes to putting the final finish on the ....lwork before filler and primer. But any 80 grit will get you there eventually. If you're "bucks down" ask your paint store whats available.


Once the bulk of the material has been removed with a stripping disc or 40 grit sandpaper on a 6" or 8" DA (thats how I like to do it), then switch to the heavyweight 80 grit and make the ....l pretty and clean. If you use 40 grit for that, it just doesn't clean off the ....l as well although 40 grit provides good bite for bondo. If I gotta wipe thick mud on a spot, I like to just smooch it with a grinder to give the ....l some real "tooth" where it will be thick.

Upon stripping the existing finish, you may find that the paint or primer doesn't want to sand off. Makes clods on the sandpaper and kinda melts and smears where it gets hot. The grinder does even worse! Boys, thats lacquer and its gotta come off because it will squirm around under the new paint, probably crack and peel later. If some cases I have had best luck going down to 180 grit and working slowly. Ugh. In other cases, I have been able to wipe the stuff off with strong lacquer thinner and a Scotch Brite pad. I have seen stripper work on it, and I have seen stripper make it worse. I say if you can't sand it off, wipe it off. Yer on your own, trial and error, every one is different on that.

Now that the ....l is clean and has a nice uniform 80 grit scratch pattern, clean it by first blowing and dusting it off. Then wet the panel with degreaser or thinner and wipe dry. Allow any remaining solvent to evaporate. Now we can-

Wipe and sand

Mix up your bodyfiller and apply. Be sure to "stuff" the putty firmly against the panel, and into any low spots. It can't stick if it don't touch. Pile the mud into the dent, make a hill and scrape the putty thin around the edges. Clean your stuff up and let it dry.

Alright, go ahead and knock off the tops of your putty wipe area with your DA and 40 or 80. If you have a large area to work, put 40 grit on a long block and go to town on it. Stop short with the 40 grit. Just barely rough in the shape then switch to 80. Every time you step down grits like that, your hand will be able to feel whats going on with the panel a little better and you'll feel where you need to keep sanding. I like to step down again, to 150 or 180, still on the longest applicable block. You're pretty close by that time. Usually if you need to add more filler, you'll know by the 80 grit stage.

After it feels fixed, in 180 grit on a block, then I lightly buzz it with 180 on a DA and pay attention to the edges of the filler. It is important to the final appearance to not have any heavy straight-line sandscratches because they are more visible when they swell, than the random orbital (tiny circles) pattern you get from the DA sander. Now blow off the bondo thoroughly and get all the sanding dust out of the filler. No need to wipe down again.

Then its time for glazing putty, to fill pinholes, scratches, and featheredges. Mix it up and drag a thin coat, again scrape the edges of the coat thin and cover the whole area, extending past the bondo. Let it dry real good, wait until its not sticky.

You can start again with the 80 grit on a block, followed by 180, and 180 on a DA again. It should look marvelous, lol. On with the lesson-

Prime and block-

OK so you just shot primer on your fix and now its dry. You put the first coat or two just over the putty then the last couple coats over the whole area, half a foot out past the mud. And you're ready to block it. Reach for some 240 grit and start off but keep moving. Kinda like before, we are gonna step down so just rough it in with 240 then switch to 320 and make it look like you want it to look. Just like before, we are using the same "longest applicable" block to sand with.

Final sand-

Now we stand at a crossroads. Will we be using sealer before paint? If so, we can stop here or just lightly go over it with 320 on a DA and she's ready to shoot. OR- if applying basecoat or single stage color directly over the sanded primer, use 400 on a DA or 600 wet to finish out the surface, taking away all the 320 scratches then stopping. Careful, don't put any waves in what you just blocked out.

The choice of doing it one way or the other can involve several factors. Sealer (applied wet-on-wet, without sanding before color) adds a tiny amount of ....ure because it fills. Color alone won't hide much but lays flat. For me- drivers get sealer, show cars get color directly on sandscratch. But my boss seals show cars so its up to the individual and the job at hand. The slight ....ure goes away in the clearcoat when we sand n buff, if sealer is used. Probably the finest way to do it is to re-prime after the 320 blocking and then final sand but that gets expensive.


idrivejunk

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Thanks for the help with my raw .... there Tuff, I felt like a few folks were wondering about this type of thing right about now. Actally a mechanic at work keeps wanting me to write up some notes for him. Anyway theres not enough hours in any day so yeah I'll whittle away at the details some more.

Actually, Rum thats a good question but blocking technique is hard to describe. It requires every bit of a human's skill to do straight work. Experience is the best teacher. There are rules of thumb but between minding the pressure applied, the direction, and the tilt on a rounded surface (they almost all are), its too delicate to describe. You have to sense what part of the block is making contact. Much like an ordinary guy with a trouble code reader, he is still screwed if he ain't a mechanic. So you gotta pick up a block and give it a go. But yes, when you are out in the middle of a large panel, it is best to alternate strokes in an X. Most folks just sand for a moment this way then switch hands and go that way. Your elbow will tell you when. Its an operation where the procedure matters less than the result. On any given day at some point you could catch me bending the rules of proper blocking!

So since I didn't really make a proper tutorial out of that post, howzabout I show you everything I use to sand with? The tools anyway. Should provide some clarity, eh? The discussion can continue from there if y'all want. I know that lots of folks wonder about primers and sealers and what to use, and I'll try to brew up something similar for that.

This is my sanding arsenal, below. I don't own the expensive tools, just use 'em. I can make mirrors out of your quarters with whats here, fairly quickly.

Note- there is one important item not shown- my "long board". Its a wooden board about 2 3/4" wide, 1 1/2" thick, and four feet long, too long for the pic. I stick continuous roll sandpaper on it and it tells no lies.



From top left:

Plastic tubing, about one inch diameter and twenty long.

Cardboard from a roll of DA paper, wrapped with tape.

My trusty Hutchins 9" hand file.

A five inch grinder.

3M soft block, #5442

3M rubber block, #5519

Hutchins "Hustler" inline air sander. I use clip on 40 grit paper.

An 8" Dual Action sander (spins more than it orbits)

A 6" DA sander (orbits more than it spins, finer finish)

The almighty DuraBlock, a two footer. Hard rubber. They make a 30". Beware, even this block can tell lies, thats why I have the board. Block has to be longer than the repair or you will lose the contour out in the middle of a big one.

3M 18" block, #5444

3M 7" block, #5441

Yes I have had all those 3M blocks forever but the Hutchins is by far the flattest and most accurate. The 3M ones come into play when I need a little "give". The bright yellow ones are rigid plastic.

Oh heres a couple things I forgot-



Whats under all that sanding dust is (aside from my current favorite hammer) is a stone on a die grinder. Don't ask about that or the hacksaw blade, I was grinding a weld and this ain't about that. But theres my yellow rubber 9" block, which also has it's purposes, obviously. What looks like junk is the little pieces of sandpaper all around. Well, one of them is wrapped around a 10MM drill bit. One has a slice of a bondo spreader inside. One has a piece of a paint paddle in it. Stick sandpaper to whatever works, man.

Until next visit, heres the stuff I live and breathe (not, I wear a mask, usually) . Bodyfiller and glazing putty.

Thanks for stopping in.



Heres the paint stripping discs I like to use in small areas and in dents and creases, they also get into rust pits pretty good without badly thinning the ....l.

See the dust mask? USE ONE!




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Primer basics

My purpose with this thread is to clear the fog surrounding primers and sealers using plain language. Just my own words and opinions, if I have left something too vague, please point that out.

Primers each have a specific purpose, mixing ratio, etc. Always read the technical data sheet of any product you will be spraying. Paint manufacturers make these readily available, both online or from the store you buy the product at. Required personal protective equipment is outlined on them, as well. Material Safety Data Sheets are also available from those sources. Those describe precautions specific to the product, and tell what to do in case of emergency. Have the MSDS for all products you own handy, and read them before you store them. A fireman or EMT may need them, plan for safety. Seriously, protect yourself.

Dried primers are porous and have no UV resistance. Water can penetrate them and sunlight destroys them. Don't expect primer to serve as paint. Primers that do not use hardener aren't good for exterior work, don't leave them on your job (except in the case of single component adhesion promoters for plastic, see below). Temporary bare steel protection between work sessions can be provided with aerosol stuff. Clean with solvent, use self-etch then spray paint for that.

Primers are designed to do these things:

Provide adhesion. (sticks to whats underneath)

Provide fill. (fills imperfections in the surface)

To seal. (to isolate or obscure whats underneath)

Catalyzed primers need hardener to dry, and sometimes reducer (AKA thinner) to thin for spraying. A catalyzed product cures when it dries, turning into a substance that will not turn back into a liquid no matter how much you soak it in solvent. Uncatalyzed products dry by evaporation mostly, and oxidation after that. They don't use hardener (sometimes also called activator). You can rub those off with thinner. Avoid using uncatalyzed products on your vehicle's exterior, they do not perform well enough, or last long enough to be worth the labor of applying them. I use them on exteriors only as temporary indoor protection on bare steel.

Basically, there are three substrates we will encounter while working on cars: ....l, plastic, and existing finishes. Anything dried and sanded qualifies as an existing finish, such as old paint, primer, or bodyfiller. My recommendations and preferred techniques follow, and are generalities rather than references to specific brands when possible.

Lets look at substrates first and the special considerations and products for each.


....L:

BARE STEEL, DIE-CAST, STAINLESS AND ALUMINUM:

For bare ....l, theres only two things that get to cover that. Epoxy primer and bodyfiller. Either is good and sticks to an 80 grit sandscratch, even 180 on softer stuff like die cast or aluminum. You will hear self-etching primer mentioned but these days, you normally only see it offered in uncatalyzed aerosol form. Back when you could get it, it was the best. It is acid based and physically bites into the ....l, whereas epoxy primer is more like glue. Stick to epoxy, real etch is a killer anyway.

A film of epoxy primer does not contain as much air as a coat of bondo, on a molecular level. So naturally, epoxy is a better protector of ....l, from moisture. Not to mention the fact that the curing of filler generates heat and thereby condensation, and the fact that the lower viscosity of the primer will penetrate scratches and rust pits better than a wiped-on putty. This is why you see me use epoxy primer over bare ....l and bondo over that. Either way, my filler is sticking to a clean 80 grit scratch.

CAST IRON-

Parts made of this are rarely (never) exterior surfaces. Use the same technique as steel if it is a smooth, body colored part. I normally use specialty aerosols for cast iron, and believe that the less material I can apply, the longer it will look good. Thick peels easier, thin allows better thermal transfer to the air. I think everything cast iron should be black or silver engine paint. Lots of folks have had great success painting engine blocks with exterior finishes after much smoothing and priming, and even using ....l-reinforced bodyfillers. I haven't, so I don't recommend it. I like using the high-heat paint directly on the bare iron.


PLASTIC:

FIBERGLASS-

Fiberglass and gelcoat are both made of polyester, same as bodyfiller. Gelcoat can be treated like old paint, just an existing finish. However if it is broken (bare fiberglass showing) thats another story. Bare fiberglass needs a layer of polyester over it before you apply urethane primer. Either gelcoat, bodyfiller or 2K (with hardener) glaze putty, or polyester primer. The porosity of bare fiberglass will just soak up good primer like a sponge, plus the glass strands still stick out where its been sanded. So you need fill, plus to seal it. The three things I mentioned are all thats acceptable over bare fiberglass. I have encountered some bad problem panels as a painter. New OEM hoods that have bubbles that won't go away. Often these troubles won't appear until the hood is hot. When dealing with new gelcoated fiberglass parts I like to get it hot, cool it down, and clean with both water and solvent based cleaners before I sand on it. If you can heat cycle it a few times after sanding too, thats even better. I'm talking about hot sunlight, an infrared lamp (careful), or in a bake booth. It helps to purge impurities from the panel, such as mold release.

BARE PLASTIC-

Well there are two different kinds. Keeping it simple here, there are two basic groups as far as primer is concerned, polyurethanes and polyolefins. If you don't know much about plastics, thats OK. The yellow stuff from Bandit Trans Am bumpers, Endura noses, and such is polyurethane. Not used much anymore. Black slippery plastic is usually the other type. ABS, Polypropylene, etc.

Plastic identification normally is done by looking for the two or three letter abbreviation cast into the backside of most modern parts. But there is also the float test and the burn test. If it floats in water and makes ash when burned, it fits into the polyurethane group. If it sinks in water and disappears in heavy smoke when burned, it fits into the polypropylene group. There are in-between plastics, too.

As a general rule, the urethanes remember their as-cast shape and don't respond to heating until it burns, whereas the greasy black stuff can melt and be re-shaped. Anywhere you read up on plastics, the main distinction between types is thermoplastics and thermoset plastics. Thermosets melt once, in the mold. They are the ones I'm calling urethanes. Thermoplastics melt and re-mold indefinitely, and can be repaired by melting ( AKA plastic welding). Thats what I'm caling greasy black stuff.

Sorry, spending way too much time on plastics. Theres really no need for great understanding of them, in the old car world.

So you have a plastic or vinyl part you need to spray- buy adhesion promoter or just use regular primer?

Well, it depends how correct you want to be. I say identify your plastic and research the instructions for the product you are considering, then decide from there. Only time I want to use a "plastic primer" or "adhesion promoter" (usually clear and watery, disappears when dry) is when I paint a bare thermoplastic. Not a common situation in old cars.

So you can probably just use regular primer. Plastic primer for polyurethanes is pretty much obsolete at this point, and modern catalyzed primers are designed for modern cars with lots of plastic so they have a good amount of flexibility built in. However, consult the technical data for the primer in question, a flexible additive may be needed for very soft plastics.


EXISTING FINISHES:

ACRYLICS-

LACQUER- Oh boy, you gotta strip this stuff off if you find it on an exterior. It is reversible. Meaning that when it comes into contact with solvent (like when you spray primer on it), it re-wets. Catalyzed products can seal it but cracking is likely later. Lacquers are defined as something that dries by evaporation only.

ENAMEL- This stuff is like lacquer except it has "drier". Not a catalyst which causes molecular crosslinking, but an agent that cures by oxidation. Enamels become harder to rub off as they cure. Cured enamels have some chemical resistance (gasoline, ATF) but will still rub off with thinner if you rub harder. I don't suggest priming over this stuff but its not quite as unstable as lacquer.

URETHANE- As with the others, these can be single stage or clearcoated. Acrylic urethane is and has been the standard auto refinish paint for decades, and its normally what you find on any car thats been repainted and still looks good. The only consideration here is thickness. If you sand into it and find that a panel has been repainted once, generally you can go one more paint job over that if its in good shape. If its been repainted three times you definitely need to thin that out, sand most of it off. Most OEM paint jobs are around six thousandths thick. Keeping a refinish job under ten is great, it will live long. Excess buildup causes cracking and contour swelling over time.

Identifying these existing paints is as simple as rubbing with a thinner rag. If it rubs off, thats lacquer. If a little rubs off, thats enamel. If nothing happens, you can prime over that as long as its not too thick.


POLYESTERS-

BODYFILLER- Normally sanded with 80-180 grit, just has to be clean before primer. Blow thoroughly with compressed air to dislodge all dust trapped in pinholes, and let degreaser fully evaporate before priming. This applies to polyester bodyfillers and glazing putties that use cream hardeners. Anytime I find specialty fillers such as Kitty Hair, Dura-Glas, All-....l, etc, I remove it. There is always rust underneath and/or a crack at the edge. Fix ....l problems with welded ....l instead and use good bodyfiller if you want the paint to look good and last.

POLYURETHANE PAINT- You won't run across this much! Remember Imron? Polyester urethanes are like acrylic urethanes except they take it to the next level with durability, at the expense of workability. Even brake fluid has a hard time messing up polyurethane. It is so hard compared to other finishes (as measured on the pencil lead hardness scale) that you pretty much can't sand and buff it. Needless to say, it would be fine to paint/prime over. But you might wear out a lot of sandpaper trying to scratch it!


AVAILABLE PRIMERS AND THEIR PURPOSES:

What to use? I will only discuss here the products I use in typical pre-1980 jobs. Really theres not much to tell.

ETCH- Due to the acid base of this industrial product, it has been phased out of the market. Bad dangerous. But like most bad for you stuff, it worked great. Today, all you see is rattle cans of it. The only place I use it is to temporarily cover bare exterior steel, or as an internal panel coating.

EPOXY- When the etch primers went away, an alternative was needed. Glue technology to the rescue. Now we have epoxy. Alas, the EPA got ahold of this, too. Lead-free epoxy can require more coats to provide the same protection as leaded stuff. Check the instructions and protect yourself always. The purpose of epoxy primer is to grip ....l. Period. Any fill you get out of the deal is a side benefit, its a one-trick wonder. Normally if using a urethane primer-surfacer, it is applied wet-on-wet over flash-dried epoxy, if the substrate is bare ....l. Epoxy can also sometimes substitute as sealer, such as in the case of a new bare ....l part that needs no repair.

PRIMER/SURFACER- Most commonly, a catalyzed acrylic urethane product. This is what most folks are talking about when they say "primer". It sticks, fills, and seals. But it has to be sanded before painting. Its main job is to build up thick so you can sand it flat. It is not intended for use over bare ....l and doesn't bite it well. OK for small spots of bare ....l though, like sand-throughs on the epoxy. Can be applied over stable existing finishes and fillers.

PRIMER/SEALER- Can actually be the same product as primer/surfacer, mixed differently. See technical data for your primer. Lays down smooth and is intended as a wet-on-wet coat applied over sanded primer surfacer and/or existing finishes, just before painting. Useful when repainting a whole car with many primer spots but mostly good paint, it creates an even tone and ....ure, and aids color coverage and fade/bleed-thru resistance of the paint applied over it.

HIGH-BUILD POLYESTER-

Typical urethane primer/surfacer builds about one mil per coat. So in a normal application, you get maybe four mils of buildup once its dry. Polyester primer/surfacer, also referred to as "spray on bondo" builds about four mils per coat. Four times what urethane does. It uses MEK hardener (clear liquid, small amount) and acetone as thinner. Polyester primer, glaze coat, bodyfiller, fiberglass and gelcoat, all these things are pretty much polyester resin and talc, mixed in varying proportions.

The down side(s)? You must prime or seal over it (There is one called slick-sand, that you are supposed to be able to paint over). And you shouldn't wipe bondo over it, although glaze putty is OK after sanding.

The high build makes it ideal for restoration projects. Multiple applications of urethane primer are a very costly alternative to polyester primer. Even the roughest surfaces can be smoothed with one or two applications of this stuff.

WATERBORNE-

I live in the central US and have little experience with waterborne products, but I'll tell you what I know. I did use waterborne flexible primer extensively in Dallas in the early 90s and it wasn't bad stuff. Great for plastic (I was shooting reman bumpers), not so great around steel.

Nationwide, there is an effort to transition all production body shops to waterborne primer and basecoat color. Don't worry, those are good products now. Drying is much more dependant upon airflow but the stuff works. But the primer don't have hardener in it and I don't like that. A little old school there, they will have to drag me kicking and screaming into the waterborne auto paint world. I hear theres primer now that cures with UV rays. Bah, humbug. Maybe later, for me.

Bare ....l primer (epoxy) stays the same, as does clearcoat, in a waterborne paint system. That is to say- whats on top and bottom still has solvent and hardener in it. The epoxy has to grip the ....l and the clear has to keep out the sun and water, but everything in between can be water-based! Solvent-borne base color doesn't have hardener in it either, so waterborne is a lateral move there, not a downgrade.

This concludes our lesson today. Hopefully, now you can make more informed inquiries when you shop for primer and are more familiar with some of the associated terminology. Questions about specific repairs and additional input are welcome, I just wanted to lay down the basics as I understand them.

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