Technical BODY, TECH Bondo 101 (Magic dent erasing compound)

Was tricky for this amateur to get the roof even...
Summer '03...

 

After various hurdles that put the project on hold, I'm still at it last November... constantly at it with metal etch. At first I mistakenly decided to wait 'til ALL the corrective bondo work was done. Then it became more apparent my outdoor project should be covered in primer ASAP (sins of a beginner, helped by HAMB'ers).

 

Filled the cab corners, kept the doorjambs paintstripped and the rust away...

 

Perfecting level planes on the front hood... (rubbed out the 8-month old primer last week, worked around the bondo)...

 

SUPER PICTURES!! That's just what I was looking for. Also great info on working batches and layers. Thanks 60's Style and Humboldt Cat. Your projects are NOT in the beginner class. The work looks exceptionally good! Your projects and Nads are tributes to the talent of the people who hang out on the H.A.M.B. I LOVE IT!!! overspray

 

Glaze putty for touch-up on the front hood, where I'd smoothed over the center emblem holes... gf's son Luke did that teardrop (just below the blanket) out of a big lump o' bondo.

 

Glad you like 'em... '60s is right, it's hard to summarize it. My attempt at etching primer didn't work out, last month (when this shot was taken), so I rubbed most of it out, rust-neutralized the body and shot it again (with a MUCH better air comp) the other day. Got the etching in there... and then the next day it rained. Waiting for the weather to clear before filler primer.
Thanks for all your help on defining the differences in primer (mine's Transtar self-etching, not epoxy), it helps to figure out how best to proceed, considering the elements (had I garage to work with).
That's it for now- hey cool shots, '60s Style! How recent are those?

 

One more for the road... aside from the front fender, this part around the gas filler neck has been trickiest, because of the spacing, a classic teacher in different ways to work your hand or block for an even sanding. That's all.

 

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'60s Style! How recent are those?

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I took those pics this morning at about ten o'clock.

overspray, thanks again for the info &

Humboldt Cat, looks like you've come a long way, lookin' good!

thanks for the kind words guys,

now where's Nads' current pictures?

you find your camera yet?

hey, maybe soon we'll have a PAINT TECH post??

Paul

 

PRIMER INFO--I'm going to mention types of primers and not so much specific brands because everyone will have different brand names available in their area. --Timebandit-- I hope you are still following this post because you brought up some very good questions and concerns I want to address. I'm a firm believer in the 2 part primers. There are so many kinds and I'll try explain the basics of most. Urethane based 2 parts are probably the most universal. They are based on resin that uses an isocianate hardner (health concern here). Most epoxy primers are 2 part based on epoxy resins. Polyester primers are based on polyester resin (fiberglass/bondo resin) and use the same chemical as a catalyst as fiberglass and body filler. These primers all bond with mechanical adhesion--they grip to scratches in the surface of the panel (metal-fiberglass-plastic-bondo-etc). Self etching primers use an acid based activator/reducer to convert with the metal and form a chemical bond as well as mechanical adhesion. For resistance to moisture both the type of resin and the amount of solids (filler material) in the type of primer are factors. A good 2 part resin that provides good mechanical bond along with dense filler material that does not absorb moisture will be better as a rust inhibitor. There are some really good systems available in everyones price range. You should do some research and ask questions about the system you are interested in and make sure to get thorough product information reference sheets to insure you use it correctly. In the product information for any particular primer, it will tell you-what kind of surfaces it can be applied to-how the surface should be prepared (sanding/cleaning)- how much it fills per coat (mill thickness)-what chemical or solvent resistance it has-and what topcoats should be used. READ these and ask questions if you don't understand. Most companies have a web site or an 800 number you can reference. You will find a huge variety of primers for filling and sanding-sealing and protecting. Another thing I really like that both 60's Style and Humboldt Cat referred to is POR-15. Sealing the backside of your panels and neutralizing corrosion on the inside will make the repairs last so much longer. Moisture can seep through tiny pinholes and ruin your body filler repair or primer and paint. POR-15 together with a paint or under coat can probably seal most tiny pinholes in the panel. I don't know if it is possible to get them all but this is a good way to start. In areas where panels have been welded I like to seal the inside of the weld with POR-15 and maybe a layer of seamsealer and paint. One thing on DP primers. If used as a rust inhibitor read the tech sheet to see the mills (thickness) per coat. These primers are usually used for tie-coat sealers and should be topcoated with another product. For use as a "storage" primer you may need several (more than 2) coats to get good moisture protection for an extended time. overspray

 

Haven't used POR-15 as much lately, have been mostly doing metal etch and Loctite's deep rust neutralizer. Initially got the front part of the truck good 'n plenty with POR 15, but not with the other half (still time to do that with the bed and rear fenders, though). My help recently went as far as to cover the bondo as well as the bare metal with the Loctite, am not sure if that would help or hinder things. 'Neath the primer the whole cab's covered in Loctite, just to be on the safe side. Is this good or bad?
I'm glad yer progress on to primer, since (of course) that's what the project's evolving into. Also, you'd mentioned doing POR-15 on the inside as well as outside of the panels, hadn't thought of that, I've only done it on the outside o' the panels. Well, what's done is done, we'll see from here (at least for the cab).

 

Humboldt Cat--if I remember the directions on both the Loctite and POR-15 say it is OK to put body filler/bondo over it after it has cured. You should be doing everything according to the specifications. The pictures of your truck are exactly what REAL "Magic dent erasing" is about. overspray

 

Yes Overspray, Im following with great interest.
I`ve always thought there is a chemical substance in all rust inhibiting primers that protects the steel from moisture.Even when cured. I have noticed that steel surfaces with primer only will rust after a while.
I have also noticed that bare steel with just automotive paint and no primer will rust fast. I therefore reasoned that no paint is absolutely sealed and will have pores on a microscopical level.
But the combination of the two will last for decades if taken care of. Then there must be a mechanism in the primer that takes care of the moisture that seeps through the pores in the top coat.
One other thing. I have had some problems with long lasting finish on sand blasted parts. Even with two coats primer, two coats paint and clear on top I have had rust showing through the surface after a while.
I belive the cause of this problem is that the primer sinks down in the "valleys" of the pitted surface and the "peaks" are left with almost nothing. Next time I will sand the surface first, and then again between coats to be sure everything is protected.
At least in this part of the world the main problem of getting a long lasting finish is rust and not adhession. Most of the time I have noticed loose, cracked bondo it is caused by rust on the surface beneat.
You have some very good recommendations on sealing the back side of the panels.Thin penetrating rust inhibiting oil is good in hard to reach places such as doors and rockers.
Where in Norway did your family come from btw?

 

Timebandit-- I wish my Norwegian was 1/10 as good as your English. I'm amazed how well you command and understand American English especially with the technical information I giving. One part of my family came from Numedahl (Numedal) and my Grandfather (Dad's dad) came from Sogn North of Bergen. I know I have relatives in Bergen but I haven't corresponded with them or even met most of them. Back to primer and rust. In the opening of this post I mentioned pre-WARMing (NOT HOT) the panel in cool humid conditions (which you and I both share because of climate) to evaporate the moisture that condenses on the metal. The metal will be 10-15degrees Farenheit cooler than the air and moisture will condense on it. If you put filler on a cold panel in humid conditions you trap a thin film of moisture under the filler. That is ONE of the causes for rust under the filler. This is the easiest to avoid by simply warming the panel to slightly above the air temperature (which should be above 70 degrees F.) Grinding or sanding the panel just prior to applying the filler will also help. When spreading the first batch of filler to the bare metal, extra pressure should be used to force the material into the metal as thoroughly as possible. This helps the mechanical adhesion of the filler to the metal. An even cure temperature until full cure is reached will also help with expelling solvents and humidity from the filler as it cures. You are on the right track about primers. The material most used for rust inhibiting and protection against moisture is Zinc-Chromate. This material has a large molecule that is dense and when used as a filler material in primers helps stop moisture from penetrating. There is a health concern with chromate based products and we are starting to see "chromate-free" products. Lead based paints give the best protection but due to health concerns they are being replaced with other less dense materials. Most old and probably new ocean vessels are painted with lead based primers and paint to ward of the corrosive effects of salt water. When you are buying primers compare the weight of the can. High solids primers may weigh up to 5 pounds more per gallon. Always read the information sheet to see if what you are buying is right for the job you have planned. I like self etching primers on my sandblasted (old car parts) and yes, sanding the sandblasted steel to smooth out the high spots is a good idea. The etch primer's activator (acid) chemically bonds with the rust to form iron phosphate. If I'm not doing body filler work soon I leave this primer on for protection. For really long term storage I use a dense urethane 2 part primer on top (wet on wet) per manufacturer's directions. When this is fully cured I prefer to grind, the areas I am going to fill with body filler, to bare metal. I could actually put filler over the FULLY-CURED primer system (after sanding and making sure it's clean) but I usually find some more metal finishing I can do and it's easier to grind that area off to do the work. If I have areas that are bare for a time in between work sessions and surface rust seems likely, I use a small sandblasting gun to re-clean the areas. I hope this information helps, but everyone reading this has to do some research themselves on the specific products and systems they are going to use. overspray

 

Thanks Overspray. I have actually never been in an english speaking country.( will be soon, heading for Paso this year) but we learn it in school from early age on. But I think Ive learned most from american car mags and books tho.
So infact I find the technical terms somewhat easier than the casual slang often used here. But Im learning...
Thanks for clearing up the primer/ bondo issues. I think I understand the procedures now.
-Thomas

 

Overspray, I, like probably alot of us, Would like to thank you. Your info is really appreciated. I am just getting started with bodywork. I planned on using Vari-Prime on all my baremetal first. Can I use the Rage filler right over it? Do I have to wait a certain amount of time or can I start to use the filler right away. I have a fairly pitted frame that has been blasted and I wanted to attempt to hold back any rust if possible. Thanks for being so helpful with rookies like me.

 

Fantasic post - many thanks!!

 

Overspray: Excellent tech post. This has to be the most concise and well written post I've seen on the subject. It seems like everybody I've talked to in the past has had a different opinion if to lay the filler directly on the sheet metal, or over the primer, but offered less then stellar reasoning for their point of view. Your explanation lets me understand why there are divergent views, however your recommendations sound extreamely sound to me.

 

BTTT

 

Curbspeed, the Vari-prime has an acid based reducer/activator. You should NOT put the Rage over the Vari-prime if there is any chance it is not fully cured and the acid has not completely converted. This is hard to determine in cooler and humid conditions which slow the process down. I like to let it dry, then before I apply the filler I remove the Vari-prime by grinding the area first. This also gives better mechanical adhesion for the filler. Another option is a rust encapsulator like POR-15 or similar product. Clean or sandblast the rusty areas then apply the POR-15 (or similar product) let it dry per product information and rough the area up and apply the filler. Anytime you apply filler over something that has a solvent (thinner/reducer) base it has to be dried and cured enough so all the solvents are evaporated and still roughed up with abrasive. There are solvents in the filler that could soak into the layers underneath and cause shrinkage later. Self etching primers (acid based reducer type like Vari-prime) are still soluble and can absorb thinner or solvents. Thin layers, maybe 1 coat, will be less likely to cause problems. Thick layers, like multiple coats, can act like a sponge to soak solvents which can remain until after the filler cures, possibly causing problems later on as they try to escape. So even with this information, the best is still to apply the filler directly on the cleaned (sandblasted-wirebrushed-abrasive ground), warm, dry bare metal. overspray

 

I usually apply a coat of Fix-a-dent to the damaged area at night before I go to bed and the next morning the whole dent is usually gone except on the really deep ones they will need a second coat.
I also like the minty taste of Kentucky Jelly on my biscuit or toast for breakfast.

 

Overspray, Thanks! I'll take your recomendation. Keep this thread going if you would please. I realize you might have to repeat some of the same info a couple of times but this stuff is helpful. Dale

 

Well done!

Many great tips, and the unravelling of a few urban legends.

Thanks!

 

Overspray... What are the correct sand paper grits
to use from prep of the bare metal to working down
the filler, applying the primer and before final color.

Also what do you recommend for a suede finish?

Great read!
TIA,

 

A lot of the sandpaper grits are a matter of preference. Basics are: 16 to 36 grit for grinder discs for paint removal and bare metal bondo prep- 24 to 36 grit for roughing out the filler with an air file sander or hand board- then 60 to 80 grit for smoothing out the rough scratches from the previous operation and shaping finer contours-then 80 to 180 for further smoothing in preparation for "high-build" catalyzed primers (with hardner)-or 240 to 320 grit for lacquer based (non-catalyzed) primers-320 to 600 grit for final sanding prep before paint, following the manufacturers guidelines on their product information sheet-and finally 600 to 2000 grit for sanding clearcoats for recoating clear or removing minor surface imperfections prior to polishing and buffing. PLEASE-ANYONE ELSE CAN DIVE IN HERE WITH GOOD IDEAS AND TECHNIQUES. The last shop I worked in was a Cadilac/Oldsmobile shop and we used AKSO-NOBEL/SIKKENS paint and primers. This is high dollar top line product. Our production system was- bodyman finishes the filler work to 80 grit- then a quick trip over the filler and old paint edge with 180 grit on a DA sander (lightly to not destroy the shaping)-then featheredge the surrounding repair with 320 Grit DA sander-red scuff pad (scotchbrite) a little past the area to be primed-prime with 2-4 coats of high build catalyzed urethane primer- after the primer is cured any areas needing slight block sanding are done with 240 to 320 grit on the primer-then use a "finishing DA" sander with 320 grit on flat surfaces and 320 to 400 grit DRY sanding on most of the rest of the repair-for Base/Clear paint the rest of the panel was "wet scuffed" with an abrasive cleaner/sanding paste and a gray scuff pad (scotchbrite)-certain colors, mostly some types of metallics, would need a little finer prep on the primer area, maybe 500 to 600 grit light wet sanding-then clean-mask-sealer (a lot of times not necessary with this system)-and paint. For those of you not familiar with a finishing DA (dual action orbital) sander, a regular DA has a slightly bent shaft that helps cut better for featheredging and removing paint. A finishing DA has a straight shaft and with practise produces a very smooth and flat surface without waves or ripples. Now, my favorite suede finish is a very good quality single stage urethane enamel flattened to about 75 to 80 percent. Some colors won't stand up with this much flattener in the mix, so some experience with the pigments used in the mix is a must. A big part of the durability in any paint system is in the undercoats (primers). overspray

 

Overspray,I'm sorry to repeat what so many others have said,but DAMN...this is great stuff..Tried printing it all last night,ran out of ink,tonight the printer is cutting the ends off of all the lines,so I've spent hours reading,and writing in the missing words..Worth every minute of it ! I've got body/paint books and articles from the 50s til today,tons of them,and your info is the best I've ever read.THANK YOU for spending what has to be shitloads of time typing this for all of us.
My wife will cook,and you can have the kids room whenever you need to get away and help me do the bondo work on my Merc.OK,you can have the wife,too

 

Reed ("overspray"), you are a real asset to this place. I've saved your posts on this thread because you've given us a lot to digest, and this information needs to be understood by everyone who does bodywork.

If Ryan has no intention of saving this thread in his Tech section, I would like to ask permission from him and yourself to put your posts in this thread as an article credited to you on my site, http://www.roadsters.com/

If you don't mind, I'm going to paste another of your posts (from the Fiberglass Horror Stories thread) in here as a way of keeping this thread from sliding off into oblivion.

Thanks for taking the time to share your knowledge with us. Here's your post on fiberglass.

Quote:

A friend of mine was restoring an old Corvette and the owner opted to buy a one-piece front end and then install the bonding strips to make it look original. I can't remember the company that made the front end, but it looked nice when it showed up. The installation went well, and the paint looked real nice. This was in late winter early spring. The first time the car got some serious sunshine the seams and thicker areas of the glass started to bubble. He thought it was the paint, but when we inspected closer and I made a couple calls to my mom's cousin's husband (who has a Masters degree in industrial plastics), it confirmed what I suspected. The part was laid up in January (cool shop temp, probably below 60 degrees F.) They must have heated the outside to set it up, but the resin didn't reach full cure inside. After sitting in the sun, some of the curing process continued, which expells styrene (a powerful solvent in polyester resin) and gasses, and caused bubbling in the areas mentioned. It was a mess!

Fiberglass resin (polyester resin) is basically the same as what's in bondo. In pure form it is like water, but usually the stuff we see is like syrup because it is thickened to make it easier to handle. The same basic ingredient (MEK peroxide) is used as a catalyst in bondo and fiberglass resin. Mixing the correct ratio of liquid hardener to liquid resin is difficult and you need practice and experience. Temperature is extremely important!! Below 64 degrees F the resin won't cure properly with the correct ratio of hardner. You can add a little extra hardener but too much and it cures unevenly and can trap gasses and styrene in the part or crystalize the resin and make it brittle. Over 95 degrees F. it cures real fast and thicker areas can easily cure too hot and crystalize. It starts crystalizing over 140 degrees F. It's best if you can work between 75 and 85 degrees F. (the temperature of the mold or part), maintain some air flow, and the correct hardner ratio for a nice slow even cure. Different companies thicken their resin in different ratios, which proportionately affects the hardener ratio. It takes years of experience and knowledge to get real good at this, and the best "glass men" will screw up a batch.

 

This needs to be saved in the Techomatic!!!!