I'm assuming a conventional suction feed spray gun. An HVLP is a little different. Set your air
pressure first. The gauge at the gun should read approximately 55 lbs with the trigger pulled far
enough to allow air and not fluid. Point the gun at a piece of masking paper, and pull the trigger
a bit further to allow fluid. The pattern should be convex, with slightly more paint in the center
than the edges (I'm going to have to put some pictures on my page since this is a commonly asked
question). The idea is with a 1/2 overlap, to evenly distribute the material.
Theory and practice are like apples and oranges. Does a compressor really put
out it's rated delivery, and does a paint gun really require only 10cfm? Or does it
meet VOC requirements if you spray at 10cfm? I've been spraying paint for a long time,
more than twenty years, so I suppose I'm just asking you to take my word for it.
I generally use acrylic enamel (uncatalyzed and
reduced to a very thin viscosity) for air brush work, although I admit I don't do much of
it anymore. It might be a good idea to get your base color finished with a urethane clear
coat so you have a nice base to work with. After you are happy with your design, clear over
the acrylic enamel with the same urethane clear. It sort of goes against the rules, since
uncatalyzed acrylic enamel SHOULD wrinkle when clear is applied over it, but maybe because it
is so thin it doesn't (or at least it hasn't for me). Lacquers dry too quickly and plug up on the
tip of the air brush, and catalyzed paint cannot be stored. Acrylic enamels are cheap,
and you'll only need a few basic (bright)colors to tint with blue red yellow black and
white to give you all the colors. Oh yes, one last thing, don't buy tinting colors, buy
mixed colors. The tinting colors don't have driers added and may not work properly.
Duco is Duponts old lacquer system. It is very inferior
to their current line of paint products, so unless you absolutely insist on original paint, use
the newer urethanes.
Japanese Varnish: In the early years, between 1900 and the 1920's, Japanese varnishes were used.
The varnish was applied by brush. Nitrocellulose Lacquer: in the 1920's, several paint manufacturers
were involved in the development of nitrocellulose lacquers. This paint had rapid drying and low
viscosity properties, and was applied with air pressure through a spray gun
leaving a hard dry finish in approximately one hour. When rubbed, polished, and waxed, it far
surpassed in durability and appearance the qualities of the Japanese lacquers. Synthetic Enamel:
In the mid 1930's, a new and completely different type of paint was developed, the alkyd or
synthetic enamels. It proved to have superior qualities in film strength, adhesion, luster,
flexibility and durability over all previous paints. The resin base was developed from the reaction
between phthalic anhydride and glycerin, with gums, oils and plasticizers added during the
manufacturing process a drying oil such as linseed, a polyhydric alcohol, such as glycerine,
and a dibasic acid, such as Phthalic Anhydride. It dries by solvent evaporation, like the lacquer
paints, but the resin remains soft and sticky when no solvents are present. It cures to a hard
finish by absorption of oxygen from the air. The curing process can be accelerated by heat, and
several methods of baking enamel were developed. Unlike lacquer, when dry, it needs no polishing
to produce a high luster finish. Acrylic Lacquer: As time passed, chemists developed a substitute
for nitrocellulose lacquer, using an acrylic resin as a base. The resins used in acrylic lacquer
tend to be slightly brittle. This deficiency is overcome by the use of a plasticizer ( a liquid
that is a solvent for these resins and softens them slightly). A cellulosic resin is any resin
derived from cellulose (pure cotton). Acrylic lacquer was used extensively by General Motors.
Acrylic Enamel: During the late 1960's and early 1970's, technology brought on the development
of acrylic enamel, which was harder and more durable. Chemically, it is a cousin to synthetic
enamel, but is modified with acrylic resin, and is not soft and sticky with no solvents present.
It cures further with the absorption of oxygen from the air. Unlike the lacquers, which remain
soluble in solvents, the enamel family is insoluble in solvent when cured. An acrylic resin is
chemically any polymer whose basic monomers are chemical derivatives of acrylic acid.
Polyurethane Enamel: In the mid 1970's, polyurethane enamel was developed to withstand the
severe stress of high speed airplane surfaces, which are subject to rapid temperature changes
and flexing. This paint was much more durable than the acrylic enamels. Acrylic Urethane Enamel:
Acrylic urethane enamels were developed to withstand environmental elements, such as acid rain
and ultra violet rays. It is the most durable paint to date.
Use the acid wash and zinc chromate primer (it
is usually green) on the bare metal before you seal and paint. Any of the name brand paints are
good quality.
Use a zinc chromate primer which is essentially a metal
treatment. Follow this with a good quality primer surfacer (a brand name that requires a catalyst
(urethane or epoxy)). All the major manufacturers use a form of a seven stage process before
priming.1. Hot detergent wash to remove grease and oils. 2. Water rinse to remove the detergent,
since the detergent interferes with acid. 3. Acid wash to remove scale and open pores in metal.
4. Water rinse to remove acid. 5. Zinc phosphate acid treatment for corrosion protection and
paint adhesion. 6. Water rinse to remove acid. 7. Bake dry.This is followed by a primer coat
of melamine polyester resin (Japan), polybutadiene (Europe), or a polyester or epoxy ester system
(USA).
No, you can apply the clear much later if you like. There seems to be a difference of opinion
on the maximum time frame; I've heard anything from 72 hours to infinity. I asked the Dupont techs
on their tech line, and they don't seem to know either, and it isn't listed in the technical manual.
I've done it three days later with no apparent ill effects.
One of these days I have to check into the chemical composition of bird feces. It
is very hard on paint. If it is rusting it will have to be repainted.
I've answered this somewhere else in this FAQ, but the short answer is,
blending, use the lowest pressure you can, as long as the material is atomizing
properly.
Good question, since the majority of paint repairs are blends. We will use acrylic enamel for
this example (others are similar). After you have repaired the area (body filler, polyester putty,
primed, etc.), you must clean the surrounding area with soap and water and a good scrubbing with a
final wash solvent (mild, silicone free). I cannot stress the importance of this step enough. It is
the singular most important factor in your blend. Clean to the edges of the panel (where the
masking starts). After the area is sufficiently cleaned, follow with a thorough compounding of
the area (my personal preference is #4 or #2 McGuiars and a wool pad). This will remove old
oxidation, and disturb the surface enough to promote adhesion. Clean off any polishing residue.
Reduce the air pressure to the gun to around 15-20 psi (siphon feed), and spray the repaired area.
Wait for the coat to tack sufficiently, then apply successive coats until full coverage is achieved,
slightly extending the coats each time to melt in any dry spray from the previous coat. On the
last (blend) coat, reduce the paint in the gun (you may have to pour some out) 100% with blending
solvent. Carefully blend out the dry areas. Further addition of blending solvent may be necessary,
or if you are very careful, you can lightly blend the edges with 100% blending solvent.
** Note** If you don't have blending solvent, you can use medium reducer, although it doesn't
work as well. Don't use fast dry or slow dry solvents, as they contain additives which are not
conducive to good blending.
Perhaps a couple of beers would get rid of those really weak brain cells that you
seem to be thinking with. And since I am explaining things to you, that too, was a joke.
All major brands
of paint perform well and it is not my intent to recommend any one particular brand. However,
certain paints are better for the first time painter, although they may have inferior qualities
in other areas. A novice or first time painter might try Dupont acrylic enamel (Centari (tm)).
It is one of the most forgiving paints, as it dries quickly, melts in over-spray well, and does
not run easily. These positive features outweigh the negative effects of quick dry times, which
are mentioned elsewhere in this FAQ. I don't know if they still make it, but Deltron(tm) by PPG
is also an excellent product for a first time attempt.
No. A professional spray gun is an expensive precision tool. With today's mica's and pearls,
the finish has to be finer than 320 grit, or the particles will not orient themselves correctly.
The paint gun has to provide a fine, even mist to enable the correct transfer of material which may
be less than 1 mil (one thousands of an inch) thick for some base coats. As for applying these coatings
correctly with a paint brush there would be a better chance that a random collection of atoms in
outer space could gather together to form a Nike running shoe.
I have never dealt with them, but I'm sure they provide a good budget
service. Most shop rates here are close to $50.00 an hour, so divide that
by the cost and you get how much time they can spend on your car and still
show a profit. No one should expect a complete restoration for a budget price.
If you are doing the restoration yourself, you will receive a great deal of satisfaction in
painting it also. All the trials and tribulations will be worth it in the end, and it will be an
invaluable educational experience.
You should, to speed up the
curing time of the paint. However, acrylic enamel will cure over time by absorbing oxygen from
the atmosphere to complete the molecular cross linking needed to create the polymer. The addition
of a catalyst accelerates this process greatly (a few days versus a few months without a catalyst
agent). Most catalysts contain isocyanates which can be a health hazard if inhaled. A fresh air
supply is strongly recommended. And warning labels are often not as adequate as they should be.
Methylenedianiline is used primarily as a chemical intermediate in the closed system production
of isocyanates and polyisocyanates and is also a curing agent for epoxy resins and urethane
elastomers, a dye intermediate, and a corrosion inhibitor.
Everything depends on the type of paint on the vehicle. If it is a urethane then a solution
of muriatic acid (household name for hydrochloric acid) should work. Try a weak solution on a small
area first. The concrete should foam and turn yellow. Then wash off with water..
I
Most shops use gun wash, a cheap blend of strong solvents used exclusively for clean up. Varsol is not strong enough to dissolve most of the newer paints.
The expensive and best way is to use powder coating. A less
expensive way is to use a product called Egyptian Lacquer which is manufactured
by the Egyptian Laquer Company in Lafayette, Indiana (765-447-2136).
I'm not familiar with the product, it was referred to me by a paint chemist.
If the old finish is of
poor quality (enamel or lacquer), you must use a sealer to separate the two finishes. Sealer is
an inexpensive insurance policy to prevent COLOR bleeding, which was quite common with enamel
reds during the sixties.
Of course, painting the
jambs, door posts, and underneath the deck and hood will increase the labor hours. Other than
that, pigment is the determining factor in the cost of paint. Blue, for example, is made from
cobalt, which is relatively inexpensive. Red pigments are by far the most expensive, perhaps three
times the cost of whites (titanium dioxide).
The flex additive used in the paint on plastic parts often darkens the color. This is quite
common, as most of the plastic parts are painted separate. A painter in a body shop will blend
the paint from the bumper into adjacent panels to camouflage the change in color.
Unfortunately it is very common for paint not to match the original finish. If you don't have
a tinting system, you'll have to set up the job to blend into the adjacent panels.
You can, but it will be awkward. When your
pressure drops the paint will not atomize well, and will orange peel. If you wait for the pressure
to build up, the paint will dry and you will have dry spots. Maybe if you do it in sections?
Although the manufacturers may void any product warranty if heir paint is top coated over
another manufacturers sealer or primer, they have essentially the same characteristics. The
urethane and epoxy based primers are extremely durable, and to my knowledge can be top coated
with anything. However, the reverse is not true. Urethane and epoxy paints cannot be applied
over some primers (nitrocellulose based lacquers for example). And, the strong solvents used in
urethanes can cause sand scratch swelling or feather edge lifting in air dry primers. Of course
there are exceptions to this rule (e.g. using urethane over an enamel sealer) but these are special
circumstances and I'm not going to get into that now.
The color of the primer isn't important, but you can choose one that is close to
the top coat color. That will help with coverage. But, remember, fiberglass stores
a lot of static electricity, so be careful when wiping it down with final wash. Use the
plastic type of cleaner or one small spark could cause a nice fire, and if you are holding a
paper towel soaked with solvents things could get unpleasant.
Fish eyes are caused by contamination usually containing silicon, that screws up the surface
tension of the paint. To prevent them you need a very clean surface and a clean air supply.
As a last resort you can use some fish eye eliminator, but use caution since it might result
in loss of adhesion.
After sanding, ensure the surface is
clean by washing with a final wash like Dupont 4105, and check your air supply. You need a good
water trap and clean lines. Acrylic Enamel is prone to fish-eye easily. If you must you can use a
little fish-eye eliminator, but only if you absolutely need to.
Flash refers to
the waiting period it takes the solvents to evaporate from the paint before applying another coat.
When using base coat, the paint will look lose it's shine.
If you cannot bend the parts easily, you can skip the flex agent. If it is bare plastic,
you will have to use plastic prep and plastic primer before painting.
You can. I suggest applying a clear coat before you color sand. this will
cut the masking edge of your flames, and also eliminate the chances of sanding
through one of the colors.
Crank the pressure up on that gun so that you have about 50 psi
going into it. Higher if you want. the manufacturers give specs that meet
environmental regulations for low over-spray, but aren't practical in real life.
A High Volume Low Pressure system designed to increase transfer
efficiency by eliminating excessive over spray, which creates high VOC emissions and material
waste. They've had a bad rap in the past because the early models didn't work well, if at all,
without a sufficient volume of air. Physics dictate that to move a certain volume of mass requires
a specific amount of energy. To do it with less air pressure should require a greater volume of
air, which should produce the same amount of total energy. Of all the models I've tried, most
were poor, some were good, and one was so good I bought it.
OK.. so many people have asked me this I am going to break one of my rules about
being product specific. I'm not employed in sales, and don't want to promote one
product over another, but the paint gun I use is a Sata NR95. I found it to be
superior to the other models I tried. Excellent compression design, and good weight
balance.. The trigger isn't long enough for me, but then again, neither were the others. Or
maybe my fingers are too fat.
It depends on the size of the
vehicle, and the type of paint used. There are formulas for sq. ft. coverage, but in my
experience are not always reliable. Let's take a 92 Cutlass Ciera for example, which would
be a fairly common size. In a base coat /clear coat (BC/CC) application, I would mix 2 quarts
of base coat, (perhaps one quart with an HVLP) which thinned to spraying consistency would give
me a gallon of spray-able material, and should provide adequate coverage. However, some are more
transparent than others, and additional or less material may be required. Paint booth lighting
is essential to ensure proper coverage. After applying the base coat, I would mix two quarts of
clear, which reduced would give me three quarts of spray-able material (two coats at approx
1 1/2 quarts per coat). An additional third coat could be applied if desired, but be sure to
watch for excessive film build which can lead to dulling or solvent popping problems. If you
don't have access to a paint mixing system, then buy more than you need. There is no way to
fix a paint job that does not have adequate coverage except for repainting the entire car.
Good question. I wish I knew the answer. Most of the people in the trade have been exposed to
a lot more than you plan on, myself included, and most of us seem to have escaped any ill effects.
I don't recommend using laquer for any reason. It is, and I've mentioned this
several times in this FAQ, the least durable of all the paints made. It does not
last long, has no uv resistance, and is not resistant to solvents. And, to make things
worse, if you want to repaint over it after you decide its not what you wanted, you
have to strip ALL of it off. Every tiny speck. The new urethanes don't agree with it
and will blister if there is a small trace of it left on the vehicle. I didn't know it was
still sold, since it does not meet any of the new VOC emission rules.
I am doing sectional repainting on a motorhome with OEM gloss laquer thinned
at a 1 to 1 ratio.
Lacquer is unique, as it does not undergo any
molecular changes when it cures. It dries by solvent evaporation alone. The reason for applying
several thin coats is that the solvents may become trapped, and the paint may appear dry on the
surface, but will be wet underneath. Also, piling on heavy coats may result in checking problems.
Nitrocellulose lacquer, or acrylic lacquer will dry to a dull shine (satin). It has to be polished
to get a good gloss. Fortunately, although lacquer has many drawbacks, it is very easy to work
with. Apply it, wait till it dries thoroughly, and polish it.
Mercedes makes perhaps the safest car in the world. It deserves a good
high end quality paint job. The Princess Di accident is a good example of how safe this car is.
A direct impact with a cement wall at 80mph, and the body guard in the front seat survived.
Had the Princess been wearing her seat belt in the back seat she might have walked away.
You will have to apply a couple of coats, then sand out the flake
nibs that are above the surface so it is smooth, then re-apply another couple of coats of clear.
The paint and catalyst are the important ratios, and should be displayed on
the containers. This is VERY important. As for the reducer, if you aren't familiar
with spraying, add some until it takes about three or four seconds to drip off
the stir stick.
Yes. With metallic colors high pressure tends to lighten the color. And, when blending,
try to use the lowest pressure that you feel comfortable with. It helps to eliminate the over spray
which can be a problem.
Usually I don't answer questions concerning brand names, because I want
to be as neutral as possible. But, the short answer is, it depends where you live.
If you live in a northern climate like Canada, where the temperature has drastic changes
then use PPG.
Paint chips from a loss of adhesion to the substrate. This can occur as a result of several
factors. First, poor prep work before painting, inferior product, or sometimes from a sharp impact
from a hard object, which might abrade the paint. (Hail does not chip paint, but gravel will).
Perhaps if you were wearing a ring it may cause the paint to chip. It is very unlikely that the
impact from a hand would cause properly applied paint to chip.
All paints consist of pigments resins, and solvents. The resin provides the coating material,
with the pigments creating the desired color, and solvents reduce the material to a workable viscosity.
The only thing I can think of would depend on the type of epoxy you used.
If it contained an acid (e.g. phosphoric) etch, you CANNOT wet sand it because
you will re-activate the acid, and this will affect he top coat.
Wet sanding is probably the only viable solution, and even that will not have
satisfactory results. The problem is not in removing the stripe, but in the inevitable color
mismatch. the paint underneath the stripe is protected from weathering and will be
a different color than the rest of the paint. If you feel they have to come off, then wetsanding
and polishing afterward will give you the best results.
It seems every good auto body person enjoys tipping back a few, and over there in the UK
it seems the same as here in Canada. I know a lot of guys in the auto body trade, and most of them
have had similar experiences, but I don't recall that defence ever working for any of them. I hope
that the police conducted themselves in a courteous and polite manner, because as we all know,
their vehicles eventually end up in the body shop at some time or another :)
Painting in a garage is very dangerous,
and perhaps illegal. There should not be an open source of heat inside the paint room since the
atomized paint is very explosive. But, to answer your question 70 to 75 degrees F should be the
correct temperature range.
Sounds fine, if the bumper you are working on has some kind of existing
coating already. If it is bare plastic you will have to wipe it with plastic prep, and spray on a
coat of plastic primer or adhesion promoter before top coating. If the bumper is very flexible you
might want to add some flex agent to the paint but it is usually not necessary.
At the end of the day, you will have turned your air pressure way past
the recommended levels to get an acceptable spray pattern from your HVLP,
so there will be plenty of over-spray. I'm not saying don't do it, just use caution.
You can, but there are a couple of drawbacks to
painting in this manner. This is an operation where the sum of the parts
are greater than the whole. It takes more time to paint individual parts, than to paint the
complete vehicle. I would suggest assembling the vehicle first, ( sometimes assembling later
damages the paint) and doing some meticulous masking. Make sure the car is prepped to your
satisfaction. Get everything ready, and leave the painting for one Sunday. The actual spraying of
the car will take you about two or three hours. Then another hour for cleanup, etc. The rest of
the day you can spend admiring your work, or wondering how you are going to fix any imperfections
that may have occurred.
Pearls do not usually go well with acrylic enamel paints. Not that putting them in the paint
will create a problem.. you just won't be able to see them because of the high hiding quality of
acrylic enamel paint. Most formulas that use pearls have a translucent quality.
Pearl is a material that reflects light (like metallic) but also allows some of the light to pass
though and reflect back from the surface below. The light reflected may be un-obstructed, or may pass
through another particle of pearl, adding the illusion of depth, and altering the hue. Paints
containing pearls usually contain a higher resin to pigment ratio and require more coats of
material to obtain full coverage. The newer tri-coat systems involve a base coat, a clear/tint
coat, and a final clear coat. This creates a very nice effect, but makes spot repair more
difficult.
The technical term is delamination.
There are two methods of paint adhesion. Chemical and molecular attraction. Properly prepared
surfaces and substrates, and properly applied coatings should have excellent adhesion. Why then,
are there so many instances of peeling paint in recent years? The problem seems to be in the
quest to meet increasing VOC (volatile organic compound) emissions by using water borne or water
based low VOC products. The topcoat should slightly penetrate into the substrate and bite into
it with a good chemical adhesion. Unfortunately, this does not seem to be the case when working
with incompatible solvents. Notwithstanding all precautions, poor adhesion may result because of
faulty product, which happens occasionally. The reps are usually quick to recall it when the
problem is discovered, but I remember a few years ago spraying a couple dozen or so that you
could peel the clear off in sheets.
You will need a 7 grinder (something that runs at about 1000-1200 rpm, no faster or you will
have many problems. Panhead wrote and chastised me for neglecting to mention this important tidbit
of information), McGuiars #4, #2, #7, #9 compound, a bucket of clean water, a stiff foam sanding
block, and some sheets of 8 micron (1500 grit) or 10 micron (2000 grit) wet sandpaper.
Do not attempt to polish in direct sunlight. If the paint is non-metallic or clear coated,
then wet-sanding is recommended. Do not attempt to sand a metallic paint that has NOT been
clear coated as you will disturb the metallic pattern. Wash the car thoroughly. Use 8 micron
(1500 grit) or 10 micron (2000) grit wet sandpaper, and fold three or four sheets into three
sections so that none of the abrasive sides are touching (from the back, left side in two
thirds, right side in one third) and put it into a bucket of CLEAN water. Have a coffee or
cold beverage and do nothing for about twenty minutes. This will allow the sandpaper to
become soaked and flexible. If you omit this step, you will likely put deep paper cuts into
the paint that won't polish out.Use a firm foam sanding block, keep the surface wet and sand
the surface, squeezing the water off every once in a while with the sanding block to check
for imperfections in the surface. Stay away from edges or high crown lines, as the polishing
wheel will burn through these areas very quickly.Once you are satisfied, put a clean wool
polishing pad on (if it has old polish on it, then spin the pad and clean it with a
dressing tool or something that's clean and not sharp), and apply some #4 McGuiars
onto the pad. If you have used 2000 grit to sand the surface with, you might try #2 first.
Polish the surface, moving the pad steadily to prevent heat build up (except for lacquer,
which can be re-flowed). In a few minutes you will see a good shine develop. Continue
with the remaining panels. Put on a foam pad, and use #9 , followed with #7 compound,
to bring up a deeper shine and eliminate any swirl marks. Wash off any compound
residue when finished and have another cold beverage.
I want to be cautious dispensing advice on this subject, since it is easy for someone who is
inexperienced to create more work by attempting to do too much them selves. Body shop costs are
calculated from the hourly rate the shop normally charges multiplied by the hours required to do
the work based on Mitchell Guide Flat Rate manuals. Let's say the hours required to re-finish a car
is quoted at 23 hours, multiplied by a shop rate of $42.00/HR, plus an additional charge of
$19.00/HR for paint materials, we would arrive at a cost of $1403.00 plus any applicable taxes.
Body work is extra, usually quoted at the shop labor rate plus an additional charge of $9.00/HR
for shop materials. To reduce some of the labor time, one could remove all chrome and trim that
has to be removed for painting. If the sheet metal is straight, then sanding with 180 grit or
finer would also cut down the labor costs. But then again, putting additional divots with the
sander, or denting the sheet metal while removing the trim will only increase the labor hours.
I would suggest consulting with the body shop that you intend to use, as to what you can do.
How much and what you decide to do is at your own discretion.
Start with a low pot pressure, approx. 5-10 lbs, and air pressure at about 40 psi to the gun
(this is measured with the trigger pulled). Adjust your fan width so you have an long oval shape
(thickest in the center). Overlap 1/2 on each pass. Oh, first do the trouble spots like the wheel
openings and edges on the panel you are painting. Don't stop the pass on the edge of the panel or
you will get a large accumulation of paint on the edges. The first coat should be light, and don't
worry too much about how it looks, although it should be fairly even. Let it tack up to almost dry,
and follow with a heavier coat. The first coat will act like glue, and hold the second coat from
running. On your final coat ( probably your third or fourth) reduce the paint a bit more and
increase your air pressure to the gun slightly and move you hand back a couple of feet from the
vehicle and spray a light mist coat in all directions to even out your metallic (I'm assuming you
will have a lot of striping). Do this immediately after spraying the last coat or the mist coat
won't blend into the paint and will look dry.
You'll have to check with your local area shops to find who
is the cheapest, but remember, you get what you pay for. Quality paint materials are expensive, and
are not used on cheap paint jobs.
If your prep work is good, you shouldn't have a problem. Use some etch primer on the bare metal
areas (you can do this in the booth just before top coating). I would recommend a quick coat of
sealer though, as it is cheap insurance.
Good question, and one which may have several causes. First, it may be environmental.
Since it is confined to the lower part, do you drive near an industrial manufacturing area or
a rail yard. Fine metal particles may be on the ground, and may cling to the car, rusting when
they get moisture. It could be a problem with the paint (I've known of cases where the paint can
lining dissolved and contaminated the paint). And then again, I've seen cases where someone has
cleaned the chrome on their vehicle with steel wool, and the particles of steel wool that cling
to the car rust. Sorry I can't be of more help.
Aliphatic hydrocarbons (Mineral Spirits- V M P, Naphtha) Aromatic hydrocarbons (Toluene, Xylene)
Esters (Ethyl Acetate, Butyl Acetate) Ketone (Acetone, Methyl Ethyl Ketone (MEK)) Various
combinations are used along with other additives (retarders, accelerators, and levelers) to reduce
the viscosity of the material to a spray-able consistency and accommodate climatic conditions.
In general, the smaller the molecular size of the resin (high volume solids), the less reducer
will be required. Some products require very little or no reduction. I recommend following the
manufacturers directions unless you have extensive experience in spray painting automotive finishes.
However, in a pinch, the general rule is that reducers are downward compatible (i.e. you may
substitute acrylic enamel reducer for enamel reducer, but NEVER vice versa. The solvents are
weaker and you'll end up with an ugly curdled mess in the bottom of the paint gun).
I will post some reference shortly. I can't remember the publication we used
in school off the top of my head, but it is the Bible of auto body repair.
Corrosion is caused when an area of metal has a positive charge and
another has a negative charge. Water acts as an electrolyte, allowing current to flow between
these areas. During this process the metal absorbs oxygen from the water and forms iron oxide
(rust). Salt water conducts electricity better than fresh water so in areas that use salt on
the roads, this process is greatly accelerated. The objective of applying a protective coat of
paint is to insulate the metal from water. To ensure that no rust is present before we coat the
metal, we clean the metal with an acid (phosphoric based, which leaves a thin film of iron
phosphate or zinc phosphate that prevents flash rusting), and then apply a zinc phosphate
coating which neutralizes the acid, and promotes primer adhesion. Zinc (galvanized and zinc
rich primers) competes with the iron for oxygen, and becomes the sacrificial metal which
corrodes, leaving the iron undamaged.
As for the rust, it should be removed completely (usually this requires
some sand-blasting). The conversion coatings only work to the depth they penetrate, and some
rust may still exist below the converted coating. It appears you are looking for quick fixes,
and there aren't any.
These products promote a rust conversion process. Most contain some phosphoric acid which
reacts with iron oxide (rust) which is chemically converted to an inert material. Sold under
many different brand names, they are a common product on auto body shop shelves.
Some red
colors are notorious for pigment separation. I don't know why, but to my knowledge, it is something
that affects only the reds. Sort of reminds me of the time I decided to wet sand a small spot of
Martin Senour etch primer before I painted a quarter panel. The technical notes said in large
capital letters, but I did anyway since it tends to load dry paper. Nothing happened. What the
heck do those guys know anyway? I blended in the repair. The next day there was a large green
stain in the orange paint. It turns out that the etch is acid based, and likes water, so the
green pigment was free to bleed through to the surface. Seems those tech notes are worth reading
after all. Anyway, back to the red problem. If you're not sure, lay a couple of coats of clear
over the paint. That will leave you some meat to sand (just don't go through to the color),
and it polishes nicely.
Sealer is usually designed as a "wet-on-wet" application. Spray it on, let it
flash off, then paint. It is designed to seal the substrate from the top coat so wet sanding may
impair its ability to seal.
That is the basic procedure. Remember tig or mig welding as acetylene will create warp-age
problems. I recommend letting the pros do this type of repair as there may be legal and safety
concerns.
It depends on the type of paint. Some paints (urethanes or epoxies for example) do not
depend on air to cure, so they will store well, in some cases indefinitely. Other types such
as enamels utilize the properties of air to cure (solvent evaporation and oxygen to induce cross
linking) and have a relatively short shelf life.
Soldering parts is not something that
is done often. Like brazing, the flux and the electrolysis between two different metals creates
problems, usually affecting the adhesion of the body filler that covers it. Try and clean the
area well before using metal prep and etch primer to remove any trace of the zinc chloride flux,
although I can't honestly say what effect, if any, it will have on any coating applied over it.
On the technical data sheet, volume solids refers
to the percentage of actual film formers in the paint. The remainder is lost to evaporation.
(e.g. 32% solids means that 32% of the material applied forms the coating; 68% is reducer or
thinners).
Spray cans usually contain uncatalyzed enamel. It would take something
like six months of air dry time before you should consider applying a chemical
as harsh as clear coat over it.
The most common methods of paint removal are sand-blasting, plastic blasting, chemical
stripper or sanding. Sand-blasting is not recommended as the high energy tends to create
heat and warp the sheet metal, which creates a whole new set of problems. Plastic blasting
is good, but expensive. Chemical stripper is fairly inexpensive and fast, but it is quite
messy and be sure to mask or remove all the trim and plastic lens coverings. Additionally,
caution must be used to avoid skin or eye contact which could result in severe injuries. A
dual action sander (set to strip mode) with 80 grit paper will do the job nicely, although
it may take a while. Follow with 180 in oscillating mode to remove the circular patterns in
the sheet metal.
Residue from hard water, un-rinsed soap or dried wax or polish, usually require power polishing to
remove. If you haven't had experience doing this yourself, I suggest speaking with the local auto
detailers. A polisher can cut through the paint on the crowns rather quickly which will mean a trip
to the body shop for some expensive repairs.
You're in the paint booth, and you've used compressed air to blow dust from the panels, edges,
beneath the mouldings and lights, and from the masking paper and the wheel covers ( You do this outside
the booth first, then again in the booth with the exhaust fan running, starting furthest away from
the fan). You then have washed the vehicle with a Final Wash or Prep Wash (other washes contain
silicone which cause fish eyes). You finally wipe the vehicle with a clean tack cloth and you're
ready to spray. Occasionally, even after reducing the paint to the manufacturers specifications it
may be too dense to spray properly. The usual specs is about 15 seconds in a #4 Ford viscosity cup. Translated into English, that means about 4 seconds to stop dripping off the end of the stir stick. Turn your regulator to about 50 lbs, and get a nice oval pattern. Trigger the gun so that air passes through the cap, but no fluid comes through. Holding the tip of the gun about 8 - 10 inches perpendicular to the surface, start your pass along the panel at a hand speed of about one foot per second and squeeze the trigger to allow fluid. At the edge of the panel, release the trigger to stop fluid but still allow air. This constant air flow ensures that the air is not pulsing with bursts of pressure. This could cause excessive build up at the ends of you pass, leaving runs and sags. Don't stop at the edge of panels either, as this will also cause build up of material. On the back stroke, overlap half the first pass (the edge of the paint should appear dry, and the center wet. This is known as a medium wet coat), triggering the gun as before. Always begin painting furthest away from the exhaust fan, so that you are painting over the over-spray. Otherwise, over-spray will settle onto the painted areas and may not blend in, leaving the surface dry and dull in appearance. With base coats, wait until the coat of paint is DRY before applying the next coat. Otherwise wait until it is almost dry, but a little sticky (the directions are usually close). If you get runs, drips, sags, don't try and fix them while you are painting. You will likely create more problems. They are easy enough to repair after the paint has cured.
When catalyst is added to paint, the paint cures very quickly. In a few hours it would be have
the consistency of Jello-O, and in a few days it would be rock hard. At any rate, you would have
to use the paint within a couple of hours at best. Acrylic enamel will cure without hardener by
absorbing water vapor from the atmosphere, but the process is very slow. I don't know if you would
be happy with the results of painting a section of a fender with a spray can. The paint is quite
thin, and will require many coats for coverage. The edges will be dry, and the color probably will
not match. It seems like a small job that your local body shop shouldn't charge too much for.
Acrylic Enamel is still used these days. It
is recommended that you use a catalyst, but is not absolutely necessary. Fairly easy to work
with, and most of the newer colors are available with the exception of some pearl and/or mica
colors.
Nearly all the materials used in automotive
re-finishing are hazardous to your health, the paint especially so. The catalysts usually contain
Diisocyanate Prepolymer, and it's the that is the main concern. It attacks the central nervous
system, and can cause permanent injury. A good air flow, and a fresh air mask should be used.
If you don't have any bronchial problems, then an activated charcoal mask can be used. I have
used the charcoal mask for years, but now my lungs seem to have an asthmatic reaction to the
fumes and I strictly use the fresh air system. Also, some paints contain lead, which may have
negative effects on your health when painting or sanding,
Vinyl Wash primers are used over properly prepared bare steel. The basic function is to promote
adhesion of the paint to the steel. Metal wash is a low concentration of phosphoric acid (sometimes
with fluorides) that is wiped onto bare steel, and removes oxidation and slightly etches the metal.
The vinyl wash primer is sprayed on after, and followed with a primer surfacer. The metal etch wash
(that is wiped on) goes a long way, as does the vinyl wash primer (since it is used only on bare
steel and applied lightly as it has no filling qualities). There is no need to buy large quantities
of either. Of course there are other uses for the metal wash like cleaning mineral deposits from
the kitchen taps (phosphoric acid cleaners are often sold under trade names such as CLR).
You really can't skip the metal wash sequence over bare steel or the primer surfacer will have
poor adhesion.
Machine polishing works. Those sodium spots are a nuisance, so you
must hand dry the vehicle immediately after washing it. I have the same water
problems in my area.
Wet sanding involves using a specific type of sandpaper. The benefits are less loading of material
in the paper, a better visual view of the sanded area (the sanding dust is rinsed away), and allows
the use of a much smaller grade of sandpaper than dry sanding (anything over 400 grit tends to load
the paper almost immediately). The drawbacks are that is is a bit messy, and that the surface has to
be thoroughly dried before painting, as water can become trapped in seams and moldings. Wet sanding
isn't very complex. Water, some 600 grit wet paper and a lot of elbow grease. Sand until you don't
see any orange peel (it shows up well when the water dries) and small imperfections are feathered.
Use the block to squeegee off the excess water. If the water you are using has a high mineral
content, don't let it dry on the car. It could leave spots which may bleed through the new paint.
