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Bondo Before Primer Question


 
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Duane WI
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PostPosted: Tue Jan 01, 2013 8:20 am    Post subject: Bondo Before Primer Question Reply to specific post Reply with quote

I have been working on a 1947 IHC Pickup. My plan was to strip the paint (using wire wheel)from the body parts, weld in the patch panels (bottom of fenders and such) and work out the dents. Since my shop isn't heated I was then going to bring them into the basement, treat with phosphoric acid and do the bondo work. My shop isn't heated so painting is out until May. So right now I have a bunch of body sheet metal parts in the basement ready for bondo but after reading several posts about primer before bondo I am not sure this is a good idea. What are your thoughts? It is 2 degrees this morning so my desire to work in the shop is definitely low but I want to keep making progress. No way my basement is well ventilated enough to even think about painting. Thanks for your help.
 
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CNKS
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PostPosted: Tue Jan 01, 2013 9:34 am    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

Where do you live? In a dry climate it is not a problem, people in humid areas say it can be a problem. I have a heated shop in a dry climate and have 0 problems with rust--I currently have parts that have been bare metal for over 6 months, there is no rust on them or in them. I don't recommend doing body filler in your basement -- with no circulation you will have fine bondo dust everywhere when you sand it, unless you have a way to keep it cleaned up. It can also get in your furnace and get into your living area, if a gas or electric furnace be sure you have a good clean filter and wear a charcoal mask with dust filters.
 
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Stephen Newell
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PostPosted: Tue Jan 01, 2013 9:35 am    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

The only reason primer is recomended before bondo is the primer will protect from rust better. If you were to get a nick to the metal right next to the bondo, water could travel under the bondo and rust a hole where the bondo is. Its pretty unlikely to happen and if you keep nicks like that repaired you wouldn't have a problem with rust anyway. Its the person that once has a vechile is painted never touches it again that gets in trouble. If a nick occured on a vehicle that was epoxy primed and not tended to the rust would be isolated to the nick and not spread.

Bondo is not real good to work with in winter either. Unless you can get your basement 75 to 80 degrees you should allow a lot more drying time for the bondo to cure. Otherwise you can fix a dent, sand it flat and when it cures it can shrink on you bringing the dent back.
 
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Duane WI
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PostPosted: Tue Jan 01, 2013 10:25 am    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

At this point I have all sorts of time to wait between coats to sand. My basement is about 55F. The can of bondo I have says 45F. I live in Wisconsin so humidity is a concern. Thanks for the advice.
 
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MO8N4ME
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PostPosted: Thu Jan 03, 2013 6:16 am    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

Duane WI wrote:
(quoted from post at 13:25:32 01/01/13) At this point I have all sorts of time to wait between coats to sand. My basement is about 55F. The can of bondo I have says 45F. I live in Wisconsin so humidity is a concern. Thanks for the advice.


From what you say here, I think you'd be OK temperature wise. You might want to check manufactures labels, cause you might have a problem with bondo over phosphorous. If you are going to bondo right away, I'd clean the area you are going to work, down to good clean bare metal.

FWIW, I done bondo work in body shops that were colder than 55F. Didn't have a choice. Far as I know, it never fell out. LOL
 
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Chief 83
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PostPosted: Fri Jan 11, 2013 7:15 pm    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

Put a little fiberglass resin in the bondo. Mix it in when you put in the hardener. Add enough that the bondo is easily spread. You don't need to use any more hardener than you normally would. This works great and dries in about the same time as regular bondo. I've never added too much but I guess you could. Don't want to make it runny. Really helps in the cooler weather.
 
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Mike M
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PostPosted: Tue Jan 15, 2013 8:00 am    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

I would use all metal by USG ? it is an aluminum filled body filler. Goes on good over sandblasted bare metal and sticks really good too. I have even patched gas tanks with the stuff.
 
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MO8N4ME
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PostPosted: Tue Jan 15, 2013 10:58 am    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

Here is an excellent post on body fillers from the "ALPHA BULLETIN BOARD"

This should at least define some things for you.

Quote:
Body Filler and Lead: One Man's Opinions

--------------------------------------------------------------------------------

What is the best filler to use on my vintage car? I see this question many times over on many different sites, so I thought I would add my two cents in as a professional restorer.

First of all, let me explain that body filler, be it made of lead, aluminized reinforced polyester (i.e. All Metal or Metal-2-Metal), fiberglass reinforced polyester (i.e. Kitty Hair or Glass Lite), polyester filler (i.e. Bondo, Z-Grip, or Rage), or a glaze (i.e. Metal Glaze or Ever-Glaze) are all designed to do the same thing; smooth out small imperfections in sheet metal work. Each of them has there own strengths and weaknesses, which I will get into in a moment.

None of them are intended to fill large dents, more than a quarter inch deep. All of them, except glaze, are designed to go on top of bare metal. As well, some restorers apply them over epoxy primer with good results. Excepting glaze, they are not designed to be used on top of paint or most primers.

As in most things related to automobiles, the quality of the underlying work defines the quality of the final repair. Most horror stories regarding filler (i.e. Bondo) come the misuse of the product. You cannot use it over rust, existing bodywork, or apply it too thick and have a lasting repair. When used as intended, all fillers will last the life of the car.

In order to have a long lasting repair, they must be applied according to directions (I know, I know, but seriously, read the directions) and ALL rust must be removed. Any of these products used over rust will only buy you a few weeks or months and then the rust will return.

The manufacturers recommend no more than a quarter inch of applied filler. So, the sheet metal should be as straight as practical. What does practical mean? Well, if someone is doing a $2,500 complete paint job, it means doing as little sheet metal work as possible and slathering the car with filler. If someone is doing a $5,000 complete paint job, practical means all metal is finished to within a quarter inch overall. This is within the published limits of the polyester based fillers. If someone is doing a $10,000 paint job, it means getting the panels as straight as possible and using less than a 1/16 of inch of filler in small areas. While, I don’t do it, I have seen shops use a reinforced filler to build up half-inch areas over a 2 foot x 2 foot section and have the repair last for several years. The manufacturers, and I, are not recommending it, but I have seen it work.

There are several classes of filler: lead, polyester, easy-sanding, reinforced, and glaze.

Lead is the original filler. It is a non-ferrous metal (i.e. won’t rust and a magnet will not stick to it) that melts at a low temperature and relatively (compared to other metals) easy to work. It’s advantages are: when the paint is removed from a car, one cannot tell whether the repair was done at the factory, before 1970, or by someone who used original materials. For some, it comes with bragging rights, "my car has no Bondo, only lead." The disadvantages of lead are: it work hardens as the car vibrates and becomes brittle over time; it is less flexible and has less adhesion than modern polyester fillers; it is more expensive; it is more difficult to work than modern fillers; and, the fumes it puts off while being applied are toxic. Personally, I see no reason to use lead, other than someone wants to be original and recognizes that the repair will be more expensive and less durable than one done with modern materials. Unless you are painting your car in lacquer for originality sake you should really not be using lead.

Regular polyester filler (i.e. Bondo, 3M Lightweight Body Filler, etc.) is made of polyester and a bonding agent. It is light, easily malleable, flexible, and has a low tensile strength. The repairs will typically have pinholes and need to be glazed before finishing. When applied in a thin layer, it is extremely durable and strong. However, it gets its strength from the underlying sheet metal.

You can think about it this way, it is very hard to poke your finger through plastic wrap once it has been vacuum-applied over a product you buy. But, it is very easy to poke a hole in a roll of plastic wrap. The strength comes from the substrate.

Easy sanding fillers (i.e. Evercoat Rage Extreme, Z-Grip, etc) have hattonite or talc added to them to make them easier to sand and have fewer to no pinholes. Trust me, get this type of filler, it is much less work, even if it is more expensive.

Reinforced filler is a polyester-filler that has some sort of strengthening compound added to it, generally aluminum beads or fiberglass. All Metal and Kitty Hair are examples. This filler has a much greater tensile strength and is suitable to use in places where lead would have been used by the factory. There is a bit of a religious war as to whether fiberglass or aluminum beads are a better, but both are very strong and flexible. Neither product will leave a finished surface and will need to be skim coated by another filler and or glaze.

Glaze comes in a tube and is designed to fill very minor imperfections. Glaze unlike other fillers, can be used on top of existing paint and primer, so it can be used to fill small surface imperfections (stone chips, etc,) before a car is painted. It should not be used in large areas or as the basis for a repair.

The way I approach the work is as follows. I do not use an epoxy base coat. I repair and work the metal to within 1/32 of an inch overall, with the occasional 1/16 inch problem area. I apply All Metal (aluminized reinforced filler) in the problem areas and for covering weld seams and factory panel issues. I may or may not use some All Metal to slightly change the shape of panel openings (trunk area, door openings, etc). This is dictated by how perfect the car is to be. I personally prefer to not fix factory gap issues, but to each their own. After I finish with the All Metal, I will use some Z-Grip (easy sanding filler with hattonite) in areas with small undulations that I believe will not block out during sanding. I then prime the exterior surfaces of the car with a high-build polyester primer (I like Sherwin Williams primer). This is essentially like spraying 30 mils of polyester filler on the entire surface of the car. I block the living daylights out of the car, and hope I don’t need a second application. I will then use Metal Glaze (glazing putty) on any small areas as necessary and then seal and paint.

I hope this is helpful for those trying to navigate the world of fillers. This is just my experience, I am sure others will chime in.

Good Luck,

 
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neblinc
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PostPosted: Wed Jan 16, 2013 6:23 pm    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

And remember, body filler is pretty potent smelling and will stink up the whole house.

Randy
 
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MikeinKy
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Location: Milton, Ky

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PostPosted: Sun Jan 20, 2013 4:10 pm    Post subject: Re: Bondo Before Primer Question Reply to specific post Reply with quote

Bondo should go on bare metal. It doesn't stick to paint as well.
 
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