Body Filler basics

[K13]

I created this post for the HAMB about a year ago but at the time posting pictures was such a chore here didn't post it. But Franks has made all these fantastic changes so i thought I would throw it up and hopefully some of you can get some use out of it. I hope it's not too picture heavy for the site but if it is, Frank, I won't be offended if you have to take it down or maybe it belongs in a different section of the forum. I just wasn't sure how much people look at the other sections.

There always seems to be a lot of questions surrounding body fillers and putties so I thought I would put together a thread to cover some of the basics. I will give some general info about fillers and putties make up, differences, etc. and then a few tips. I apologize if some of the pictures aren't the best as I was making some panels for work and just did the stuff for this quickly while I was working on those. Keep in mind that all these products are designed for the Collision Industry and are formulated to increase production and reduce problems not for ease of use for hobbyists.

Pretty much all body fillers and putties in North America are what are known as lightweight products. They consist primarily of 3 components: Polyester resin, Talc and Microspheres. Different companies then add different components to increase performance aspects but all contain these three basic components.

Resins: The vast majority of fillers and putties use polyester resins. There are a few exceptions where hybrid resins are used but I won't get into that here. Generally more expensive fillers will use more expensive resins that will flow better and sand better. Putties use a unique resin that cures to a tighter and denser film which provides a more stable and more solvent resistant surface which is why they were developed to provide a better surface for primer application than what most fillers can provide.

Talc: Talc is the main body of a filler. Think baby powder as a common talc product. The are different sizes and shapes of talc used in various products. There are two basic shapes of talc used in body filler and putty: Spherical (top) and Platelet (Bottom).

Round talc is what is used in body fillers. It is easier to sand due to the fact that you are generally sanding a smaller area of the mineral.

Platelet talc is usually used in putties because it is easier to spread and gives a smoother finish and a denser surface structure. The easiest way to think of the differences is think of trying to cover the bottom of a box with balls or sheets of paper. You will get more spaces between the balls than the sheets of paper and thus not as dense a surface. Combine this with the special resin used in putties and you get a surface that does not absorb nearly as many solvents as body filler during primer application.

Microspheres: Mircospheres are tiny hollow glass or plastic bubbles that are added to fillers and putties. These are what makes a filler a lightweight product. Micropsheres main purpose is to increase sandability. Cutting through the hollow sphere is much easier than the solid talc particles. But there is obviously a trade off in they are not a solid particle that will add stability and density to a surface like talc will. Filler companies use this to their advantage to make cheaper fillers that sand really well without having to use more expensive resins and finer talc grinds by adding more microshperes which sand better but don't provide as dense or hard a surface.

 

[K13]

Ok now we will talk a bit about mixing and applying. With the exception on one product all body fillers are a 50:1 mix ration or 2% weight by volume. You should always kneed the hardener tube and stir your fillers before using to ensure everything is mixed up as they will settle and separate over time. The easiest way to eyeball the correct amount of hardener to use is with a simple ribbon method. Place your filler on your mixing board and let it self level. You can bang on the bottom of the board to speed this up. Then depending on the size of the puddle you run a ribbon of hardener across the puddle. A 2" puddle you run the hardener half way across, a 4" all the way across, 6" all the way across and 8" all the way across and then another strip half way across. This method has been tested with a scale and is well within the accepted ranges of hardener use.

Note: Do not use porous surfaces like cardboard to mix fillers or putties on as they will absorb the products and can change the ratios.

Over and under catalyzation are the cause of the vast majority of issues with filler. Too much can lead to filler becoming brittle and cracking. It will also increase the chances of pinholes forming. Under catalyzation can led to shrinking and movement later on down the road which can lead to mapping of the repair area. so make sure you try and keep pretty close to the about ratios.

The best way to mix the product is to try and fold it over itself rather than stirring. This tends to add less air to the mix. You want to mix it until you get a uniform looking product. You do not want streaks of hardener in the mixed product. It should look like this

Always use the hardener that is provided by the manufacturer. About 3 years ago there was a world wide BPO shortage which is the active ingredient in hardener and some companies adjusted their formulas to compensate so using a different brand hardener could result in over or under catalyzation even if the above method or a scale is used. Also other than one Evercoat product that uses different speed hardeners there is no difference in different colour hardener. They are made different colours so they can be easily seen in different coloured fillers.

Now you are ready to apply the filler. The surface needs to clean and sanded. 80 grit is now pretty much the standard recommendation for all filler companies as body shops are trying to eliminate coarse grit paper so this is what fillers are being designed to go over. There is some belief that coarser grits mean better adhesion but that is no longer the case and some of the newer filler will actually perform worse over heavier grit scratches so 80 grit is the best bet. Blow the surface clean. If you want to wipe it down with a solvent make sure to use a fast evaporating solvent like acetone so there is no residue left on the surface.

A little tip when you have finished mixing your filler is to spread it out over your mixing board rather than leave it in a pile like the picture above. This will do two things. It will slow the catalyzation so you will have more working time and it will let any air you have added during the mixing process escape.

When applying your filler to the surface you want to make sure that the first pass is pressed right into the metal. We call this a wet coat. The idea behind this is it ensures you get the filler pushed down into the sand scratches. This will obviously help with adhesion but it will also reduce pinholes as air doesn't get trapped between the filler and the bottom of the sand scratch grooves. Don't just glop the filler over the area. Once you have pressed it into the surface you can build on top of that. This isn't a great picture but your first pass should look like the one on the left not the one on the right. You don't have to let it cure like that before adding more but you don't want your first pass to look like the right.

A little closer look.

Let it dry and sand, reapply as needed. Once you have filler down you should not use solvents over top of it as they can be absorbed and then kicked out later causing failures. Just blow it off and reapply.

Fillers should not be applied any thicker than 1/4" and putties 1/8".

I missed adding this the first time but I wanted to make sure it was here. It is NOT ok to use regular fiberglass resin to thin fillers and putties. The resins are not the same and required different types of hardeners to catalyze. Using fiberglass resin will almost always result in shrinking as the resin does not get fully cured by the BPO style hardeners. The only ways fillers and putties should be thinned is with specific resins designed for thinning (Plastic Honey, Super Charger) or mixing a thinner product with a thick like using a putty to thin filler.

EDIT: I should have added this yesterday these are only guidelines you should ALWAYS read the technical data sheet of any products you use for the best information on what is recommended by a manufacturer.

 

[K13]

Now a little about reinforced fillers. (Allmetal/Metal2Metal are slightly different so I will cover those after)They substitute the talc and microspheres with some other type of fill material to product something that is stronger. They also can be used in areas where corrosion is a concern as they will not absorb water like a talc based filler will. They are classified as heavyweight fillers because they lack the mircospheres. There a basically 4 types of fill material used: long strand fiber glass fibers, short strand fiberglass fibers, and either fiber pulp or Kevlar pulp. These materials can be used individually or in combination to produce different products. They use the same BPO style cream hardeners and mix ratios as regular body fillers.

Long strand fillers will be the strongest and best able to bridge gaps, holes etc due to the length of the fibers. They would be used when the most strength is required. They are not the easiest to work with as they are thick and don't sand well but short of using resin with mat or cloth they are your best bet if strength is required. They can also lose strength when used in thin applications as the fibers get push out and you are left with mostly resin. The fibers look like this:

Short strand fillers are essentially the same but use a shorter strand of fiber which gives them less strength and less ability to bridge. They are however easier to work with as like with different sized talc they move around better and you are sanding a smaller strand. So these would be used where you still want some strength. Short strand tend to be the most popular reinforced products as they are a good compromise between strength and work-ability. There are also some short strand based products that are mixed with filler to make them even easier to work with but they will not be as strong and will absorb water. The fibers look like this:

Finally there are multi strand or compound products. They mix the above two types of strand with some sort of pulp either fiber or Kevlar. These types of products are kind of the best of all world as the different sized fibers will kind of spread themselves out as you apply and give you strength regardless of how thinly you spread them. The biggest drawback to these is usually cost. The pulp fibers look like this:
Fiber Pulp:

Kevlar Pulp:

Allmetal, Metal2Metal are kind of a unique category as they use a different style of resin that requires the use of a liquid MEKP type hardener. This is the type of hardener used with stand alone polyester resins. BPO and MEKP type hardeners are NOT interchangeable. They may seem to cure the product if used in products not designed for them but it will not be a full cure and can lead to failures down the road. Basically these products are resin and aluminum powder. They were developed as a replacement for factory lead when the use of lead started being frowned upon. Because the hardener is a liquid the above mixing method will not work and you will need to count drops and or use a scale for proper mix ratios. The ratios are still 2% weight by volume. These products don't sand well but do create a good hard surface. Aluminum powder looks like this:

Something I should have mentioned in the filler discussion and I will go back and add it is not ok to use regular fiberglass resins to thin fillers and putties. As mentioned above they use different types of hardeners and adding resin to filler will almost always result in shrinking due to an incomplete catalyzation.

Some of you probably saw this on the other board and it's kind of just the basics but if you have any questions please feel free to ask and I will do my best to answer.

 

[PG409]

Wow. Thank you so much for the excellent tutorial. Have not done fillers or sanding for a few years but this post is most helpful.

 

[PG409]

This needs to be kept at the top.

 

[Scotty]

That was an awesome tutorial with lots of great info. Was in the bodyshop trade for 25 years before moving to the insurance side. Now only putter in my home garage. Definitely witnessed some of those errors being committed by others and myself over the years. Thanks for the current information. My biggest takeaway was that it appears I've been using too coarse of grit to prepare the metal. (Old school 36 grit).

 

[ssmustang]

K13: Lots of great information, I have not seen this anywhere else. You certainly know more than anyone else I have talked to and I have some questions on fillers.
Long story short, car was stripped (chemically) in 1983 white lightning filler used painted with single stage.

Forward to 1999 was going to update the graphics, lady ran a stop sign and broadsided me, car was repaired and updated to base/clear, not sure what filler/s may have been used?

Car was also undercoated with rust preventative (I think ACF-50). All work was done in Saskatoon, car was shipped to Hawaii and a few months after started seeing 'bubbles' all over, didn't seem to have any rhyme or reason to where it was happening. Kept getting worse to the point I cut one open to see what was going on. Out goozed and smelt like the resin from old white lightning. Had the 'repair' shop look (he took samples), PPG rep here look (took samples) but no one could figure out what happened. Any ideas??? I thought maybe new type filler put over the old white lightning that caused some kind of reaction? Tried to keep this short but could supply more if it might help.

 

[Sassy]

I never knew that car got hit.
Sure looks good today!!
His name is gone,,, Bruce? but what a great auto artist!!
What intersection is that?
Fred

 

[JohnnyBgood]

A few years back a friend was redoing some fender bender repairs. The fender was dinged several years before and now again in the same spot. 6 months after the fix the paint bubbled...Turns out it wasn’t the paint bubbling it was the old filler...The new filler ended up reactivating the old stuff. When the paint bubble was broken there was a sticky substance underneath... Smelt like bondo. Ended up taking the fender off and stripping..New repair and repaint and never a problem again. I think you hit the nail on the head when you said you thought the new affected the old.

 

[K13]

K13: Lots of great information, I have not seen this anywhere else. You certainly know more than anyone else I have talked to and I have some questions on fillers.
Long story short, car was stripped (chemically) in 1983 white lightning filler used painted with single stage.
View attachment 1503

Forward to 1999 was going to update the graphics, lady ran a stop sign and broadsided me, car was repaired and updated to base/clear, not sure what filler/s may have been used?
View attachment 1504

Car was also undercoated with rust preventative (I think ACF-50). All work was done in Saskatoon, car was shipped to Hawaii and a few months after started seeing 'bubbles' all over, didn't seem to have any rhyme or reason to where it was happening. Kept getting worse to the point I cut one open to see what was going on. Out goozed and smelt like the resin from old white lightning. Had the 'repair' shop look (he took samples), PPG rep here look (took samples) but no one could figure out what happened. Any ideas??? I thought maybe new type filler put over the old white lightning that caused some kind of reaction? Tried to keep this short but could supply more if it might help.

So a few questions. You said the paint bubbling was all over and no rhyme or reason to where it was happening so did it only occur over areas where there was filler? Did it only occur in areas that had new filler over old? Only areas where it was just the old white lightning? Was it between filler layers or was in between filler and primer? I guess the big question is if new repair work was done why was the old filler not completely stripped off in that area, so why was new filler put over old? It is pretty difficult to get properly catalyzed filler to reactivate or soften without using a lot of certain chemicals. More than should be present in any newer style fillers if properly catalyzed. 99% of problem I see like this usually happen when something is added in between two products during the application phase that causes problems. It is usually some type of solvent wiped over the old filler, absorbed, then the heat of the catalyzation of the new product pulls it out of the existing filler and it hinders the proper catalyzation of whatever is put over it filler or primer.

Now having said that White Lightning is a heavyweight filler that predates anti clog formulas and my time in the industry so they may react completely differently to what I am use to dealing with. If I remember I will run it by our tech the next time I talk to him and see if he has any insight.

 

[ssmustang]

Fred: Yes, Bruce Williams, my go to graphics guy! Our Canadian Foose I call him, we go way back to the track days when he worked for Les. He was still working on 60th street and that's where I was heading when I got hit. I had already booked the Fairlane on a boat from Seattle that fall. Intersection of Highway 11 and 60th where there is service roads parallel to the highway. She said she stopped at the sign them proceeded to hit me, Bruce said that had to be the hardest accelerating Buick he'ed ever seen! In the second and third picture it's the silver car turned back toward the intersection. usually I am cautious when driving the 'good' stuff but never saw her, cop couldn't do anything as he did see it!

 

[ssmustang]

K13: Sorry I don't have some of the information you seek. I believe that the areas where it 'bubbled' could have had new filler over old filler (and I know for sure it was white lightning used on the car), sail panels, rear quarters, truck. The body work was repaired while I wasn't there over the winter. More of the story... SGI would only fix the front end, painter/repairer guy said he could not match the single stage with base/clear and SGI would force him to use base/clear so ended up paying him extra to paint the whole car. There was no bubbling or any other funky looking stuff going on with the old paint at that time.

I was only going to update the old 1983 graphics with something more up to date and a little Hawaiian per Bruce. I do not know for sure what the painter/repairer guy used or how far he took the old paint down when he did the new but I assume as little as possible so guessing about 'new' filler? I know Bruce and I did the graphics at his shop with candy colors over silver base the next spring and all the body work had all been completed by then and the new burgundy was done after we completed the graphics. I only mentioned the acf-50 because it was brought up when we were trying to figure it out but I don't think it had anything to do with it. Here, we took it down back to base metal but was hard to tell where there was different 'layers' of filler but it did seem 'softer' than I remember it being. I had never hear of the old white lightning ever breaking down before (painters defense) but the smell of the resin was unmistakable so to me something effected it and broke it down that was put on with the new paint? Maybe more related to some kind of solvent used like you speculated? Thanks for any insights, no one ever gave me any explanation of what the samples they took and checked out showed or didn't.

 

[ssmustang]

Sorry again K13 but have remembered more. My excuse is I'm old and usually try to forget this whole episode! Painter/repairer guy did call or contact me somehow through the winter to tell me of 'old damage' he found that had been done on the Fairlane passenger side behind the door. Paid more money for him to 'fix' it properly, agreed and on it went for the rest of that winter. This is the area where the worst of the 'bubbling' occurred and what we have repaired here. Knew there was something about new filler over old in this story! So maybe he did not take that area back to bare metal? I wasn't there at the time so do not know exactly what he did. That was a couple of computers back as I did take pictures that may help you and I will try to find them. Thanks again for any info.!

 

[Bash and scratch]

Bob I have seen fillers turn to mush after rust check being applied. Usually though it comes from a pin hole/rust hole in the metal from the back side. Turns it to grey mush. And that stuff is designed to wick everywhere.

 

[ssmustang]

OK Neil, what product(s) have you seen do this? I do seem to recall that is what the company that did the rust proofing was called. I am guessing on it being ACF-50, as I ran into that product here years after when I was flying with the CAP (Civil Air Patrol) and doing some airframe/paint work on members airplanes. When all of this was going on I seem to remember the rust proofing was discounted (by the PPG rep here who came over from Oahu to look and took samples) and the new filler over old was more suspect or at least something attacking the filler(s) used. I am trying to find some pictures of the bubbles as some of that seemed to be in areas where the rust check stuff wouldn't have gotten to (sail panels)? I wouldn't say the filler had turned to mush but when we dug everything out it seemed 'softer' than what I remembered it set up as. The bubbles were caused by the resin or oil being pushed out of the filler between the paint layer and the filler layer, when we cut them open the raw resin/oil came out. I will try to get some pictures as it may help you guys figure it out? Thanks everyone!!

 

[ssmustang]

OK, couldn't find the pictures but I did make a little video back then which I have been able to take snapshots off. Quality is low but you can see where we did repairs. There were probably one or two bubbles each in the sail panel areas, same for trunk/below back window area and 4 or 5 throughout the quarter panel area kind of random scattered. This is the area where he did some 'repair' work. Besides the new area that has now come up there isn't any other panels bubbling up anywhere. I think the door work was alignment issue chip repair not a bubble.

This is a new area that has bubbled up since we did the repairs years ago. It is very representative of what the rest looked like, spots here and there no reason or pattern to it? As you can tell from the pictures this new area is just below areas we fixed which were worked out quite a ways from the actual original bubbles. I have not cut this one open yet but it has cracked open on it's own. Hope these pictures help...

 

[K13]

Wow there could be all sorts of issues there. The first thing that comes to mind is was the original 1983 paint a catalyzed urethane single stage or was it an enamel? That is pretty early on for urethanes to have been used and spraying/spreading any catalyzed product over an enamel without completely removing it is a crapshoot. This kind of leads to the second point, if I am seeing these pictures correctly the above bubble doesn't appear to even be where a repair was undertaken. It's a little hard to see in the small pictures but it doesn't look like that area was even touched when the repair was done to the quarter panel. It looks like the primer stops right above the body line and starts again right around where the trim would sit. Finally you said that the goo was between the paint and the filler so that would indicate to me that something caused an issue with the new filler not the old. If the new filler had created problems with the old it would have separated between filler layers not between paint and filler. I wouldn't be surprised if multiple issues cause the failures but unfortunately, without knowing exactly what products were used with all the repairs, how the repairs were made and getting a good look at one of the failures it's pretty much just a guessing game at this point.

I hate to say it but I feel some shortcuts were taken just looking at those pictures and what you have told me ,not removing all the paint on that quarter when he had already repaired 3/4 of it, not removing old filler before reapplying etc. More often than not these kind of things lead to problems especially when you are talking about time periods when there were a number of technology changes and compatibility issues are highly probable.

 

[ssmustang]

K13: Thanks for you input and as I remember the 'all sorts of issues' came up more than a few times. I can clarify some things, the car was originally painted in '83 with single stage enamel. You are correct that the 'new bubble' is below where the original repairs were done here in Hawaii. I can't imagine there was anything there and we wouldn't have dug it out and repaired it at that time. When I said the 'goo' was between the paint layer and filler that was an observation when we cut it open and the goo was pushing the paint layer away from the 'base' and causing the bubble. I am only guessing on what the shop in Saskatoon (fillers, etc.) did with the accident repair and the prep and repaint in '99/2000, I was not there to watch. The 'bubble repair' was done here in Hawaii once the Saskatoon shop wouldn't do anything or help. The areas in primer in the pictures were all taken down to bare metal prepped and worked back. The 'bubbles' were only in small areas within this 'repair' area and as most of the graphics were fine we didn't do the whole rear panel. I know lots of things may have gone wrong but I believe because of the smell (you can't mistake white lightning smell when you opened a can back in the day and that is what came out when it was cut open) it was something used over the original bodywork that caused that filler to break down? As the worst of the 'bubbles' were within that area I paid the Saskatoon shop to 'repair' along with the base/clear repaint I feel it was something that happened there? I was hoping your obvious expertise with fillers might at least give me a better idea on what happened. Thanks again for your comments.

 

[Bash and scratch]

Bob I couldn't tell you exactly which filler it was, as I was not the one who applied it. But It was whitish, like white lightening, some of the fillers back then were pinkish, I suppose it likely had to do with what color cream hardner was used? Now adays a lot are yellowish with a blue cream hardener. And yes it was Al at Rust check who had done the rustproofing, not sure what the product was he used? But it did turn the filler to a grey mush, having said that I believe that the filler was directly exposed from the back side to the rust check? Via a rust or pin hole in the metal which doesn't look likely on yours, especially on a trunk lid?

K13 correct me if this is wrong btw, I was told years ago that the hardener was already in the filler in the can, the "cream hardener" in the tube was mearly a catalyst? One of the product reps (not a salesman) told me this years ago.

 

[ssmustang]

Thanks Neil: I am pretty much guessing at all of this. I know what the final result was but as K13 and others have said it is complicated. The rust check was discussed but seemed to be dismissed early and it may have been like you said about areas being exposed from the back side? That being the theory, I would think it would have come through at all the molding holes along the quarter panel, doors, fenders, etc.? It bubbled in the middle of panels which seemed odd? It would be nice to know but in the end as K13 stated unless you know all the products used, order, and so on there are just too many variables. Thanks all for your insights and experience. Just have to suck it up and strip the car again at some point and start over.