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Technical Filler Over Guide Coat?

Discussion in 'The Hokey Ass Message Board' started by Porttownsend119, Mar 25, 2016.

  1. Porttownsend119
    Joined: Nov 19, 2012
    Posts: 35


    I've been looking for a while, but can't seem to find any info on this. I've done a ton of body work on my 55 Mercury fenders (pulling dents, leading seams, brazing, filler) and epoxy primered over everything. I spread powdered guide coat over the panel and blocked some of it out for a while when this occurred to me: IMG_3327.JPG Now I can clearly see lows that still need a bit more filler or glazing. I would think that I'd need to remove all of the guide coat before adding filler, but that guide coat really shows the lows well over the white primer. If I completely remove it, I have to rely on a photograph to remember where all of the lows are at. But If I leave some, it would leave me with a clear and easy visual of where I need to add filler. So my question is: will leaving guide dust keep fillers from adhering properly? And if so, could I wipe most of it off with wax & grease remover, leaving a little bit for a reference point? Also, should I be using like a long strand fiberglass filler over places where bolts are going to be tigtened down over the painted surface to keep cracks/chips from forming and inviting rust there?

  2. midroad
    Joined: Mar 8, 2013
    Posts: 270


    If you use a guide coat on the filler before priming you shouldn't have to fill over primer. I have watched an old school body man straighten out my '37 Ford coupe and these guys can feel with their hands to find high and low spots. So far once he has told me a panel is ready for hi-fill primer it is.
  3. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,951


    you may be over thinking things.

    Irregardless, the most important thing to remember is this:
    Stick with one manufacturer or brand when doing coats, fillers and paint.
    Learn to trust your fingertips as they are capable of feeling elevation changes of less than 1/100th of an inch. At some point you will get very tired of flipping the panel over or looking underneath to find the high/low spots.


    Up here we will strip a panel and immediately spray with acid etch primer, it's black (fresh unprotected steel alarms me) Although it's not uncommon for us to start with a regular grey primer over bare steel....

    This goes a long way in keeping the entire panel protected instantly and for the next 20 years irregardless of whether you work it today or loose interest next month.

    It also gives you your initial/first working guide coat.

    As you work the panel, you can use a block (flat plane) where applicable with fine paper (400 is good) to reveal highs/lows.


    In an active body shop, there is Always something in the spray booth and always something being sprayed.

    If the painter has primer in the pot then ask him to respray/coat your panel which in essence,
    gives you another protective layer and a new guide coat.
    If the painter has color (paint) in the pot he can spritz your panel giving you a new guide coat.

    In your home shop, you can use a flat black rattle can to spritz your area depending on your needs.
    -Don't use glossy/shinny rattle cans, they are to hard to (gently) block sand thru and may gum up paper or cause paint problems when that time comes..


    Body work hierarchy;

    From bare steel...
    :Acid etch primers bite metal hard, excellent adherence. (your 1st guide)
    :Quality primers adhere to etch primers or directly to clean steel, excellent adherence. (2nd guide)
    :Quality Brand name fillers adhere to clean steel and/or the above primers, excellent adherence. (3rd guide)
    :Quality branded Flat black rattle can "spritz" adhere well enough to all the above in layer/combination.
    :The above flat black spritz shows the fine -400 grit- lines from your block sander, your 'guide'.
    :Repeat as necessary
    :Finishing with epoxy Primer is a good choice for last or sealant coat.


    In a body shop, As you work a panel, you are always varying the color between coats...
    Steel - black/etch - filler/putty - grey/primer - putty/filler - green/primer - filler/putty - high build primer - repeat as necessary and finish with epoxy primer.
    The above layering eliminates the need for flat black spritzing - and that of course is up to you as it is your choice to spritz of not if/when you are building layers..
    Layering brings the surrounding panel up towards high areas and
    builds low areas up toward surrounding steel/body work. (we are talking microns here).

    In layering, as you block/sand, you will find your highs/lows and can tell how deep you are by seeing down thru each and every color change/layer. Seeing/sanding down thru 4 or 5 layers also can be called a guide (-learning to work without a flat black spritz)

    It is not unrealistic to have 7 or 11+ different colors/layers before you seal it with a final epoxy primer.
    The epoxy primer seals and protects your body work and all layers from moisture/oil/erroneous dirt/spatters/oversprays/fingerprints/contaminates/dog piss/beer/taco bell etc.
    -it locks in your finished bodywork and readies it for -eventual- paint while locking contaminates out.

    And remember, cleanliness from steel to clear coat helps ensure little to no mysterious paint problems -(as does sticking with a reputable brand name of paint/primers).
    ---If someones being using wd40 in the vicinity, don't hesitate to use wax and grease remover before applying or working the next layer of primer/filler/paint.

    In a quality body shop where show cars exit the doors, 'guests' are often reminded to
    'please don't touch the body work' even if it's just raw steel. I don't care and certainly don't want to know where their fingers have been.

    And Projects on hold are covered with plastic even if it's just for a day or 2.
    This protects against dust as much as it does fingers and oversprays.

    But Honestly, If I were you the first thing I would do is wash all the contaminants off that fresh fender using wax and grease remover and start with a quality etch or grey primer.
    ...Clean and Seal that fresh steel from your own finger prints before doing anything else.

    Last edited: Mar 25, 2016
  4. Moondog13
    Joined: Sep 7, 2006
    Posts: 729


    Awesome write up Moe! Thank you for it!
    Register now to get rid of these ads!

  5. chopolds
    Joined: Oct 22, 2001
    Posts: 5,653

    from howell, nj
    1. Kustom Painters

    If your existing primer is the right type to put filler, or glaze over, I usually take a piece of 80 grit (if low spots warrant body filler) or 180 (if shallow enough for glaze) and do a quick scuff right before applying filler. Of course, a quick blast with shop air to blow off the dust first. If you mix your filler right, and it isn't too hot, I sand immediately before putting it on.
    I don't see putting it over a slight amount of guide coat, as being the problem, for me it is the fact that the primer in the low spots has not been scuffed or sanded. I always give epoxy a light sanding before applying filler, so it has some rough ness to adhere to. Epoxy dries with a bit of glossiness that would prevent 100% adhesion of anything on top of it, unless applied when wet.
    I dont' like using wax and grease remover right before filler, especially on primer, as it can absorb into the primer, and may cause issues later on. If you DO have to remove greasy fingerprints of contamination, do so, and wait an hour or 2 for it to evaporate completely (or use a hot air gun) before continuing.
    rod1 and Hackerbilt like this.
  6. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,231


    Theres gonna be tons of opinion and personal experience in a post like this.
    There are MANY roads to success and each successful person will swear by their personal experience...and why not? It worked for them! LoL

    Here's a couple of links to filler manufacturer FAQ's.
    They will answer some of your questions...
  7. Thanx Moe,I'm gonna save this info as I am not a pro.
  8. john worden
    Joined: Nov 14, 2007
    Posts: 1,456

    john worden
    from iowa

    Remove all traces of powder in the low areas. Mark lows lightly with a pencil and fill. Reprime with epoxy.
    Any filler can crack if stressed.
    kevin31 and Paint Guru like this.
  9. williebill
    Joined: Mar 1, 2004
    Posts: 2,415


    Good advice here. Overspray has written many posts/threads on this subject. Is he still active on the HAMB?
  10. Fortunateson
    Joined: Apr 30, 2012
    Posts: 2,438



    The OP stated that the fender is in white primer. I like the sequential process tips you provided. Thanks.
    Last edited: Mar 25, 2016
  11. john worden
    Joined: Nov 14, 2007
    Posts: 1,456

    john worden
    from iowa

    Anything other than a paint product over self etch is high risk for failure.
    Hackerbilt likes this.
  12. mikhett
    Joined: Jan 22, 2005
    Posts: 1,398

    from jackson nj

    SELF -ETCH bit me once.NEVER AGAIN IM in the Epoxy Primer camp!
  13. I work for a filler company and the vast majority of problems I see are when filler has been put over etch primer or some type of acid wipe. Problems over Epoxy are almost non-existent. Most problems are admittedly procedure errors but etch has a much greater chance of producing them compared to epoxy.
    Hackerbilt and metlmunchr like this.
  14. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,951



    Ya, Fuckin Dupont Shit Anyway.

  15. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,951



    Ya, Fuckin PPG Shit Anyway.

  16. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,951



    And Fuckin Shit 3m and Fuck Napa who sold it to you too anyway.

    Its all their fault.
  17. overspray
    Joined: Jan 14, 2003
    Posts: 1,228


    Yup, I'm here. Some real good info in this thread and some misguided info. moefuz, chopolds, john worden, read like the "Books of the Bible" for body and paint prep.

    Now, most of the metal prep and primer posts leave out some very critical information.

    1) What are you doing to prep rusty metal before bodywork?
    Even back before WWI automotive steel sheet metal panels were phosphated, which is one of the first major steps in corrosion protection.


    The Phosphating process is a conventional process since long time in automotive paint industry.This provides the strong adhesion and better corrosion protection by sealing the substrate with a layer to stop the contact of surface to environment.

    [​IMG]There are different type of Phosphating process in terms of metal combination –

    1. Monocation – Zn
    2. Bication – Zn/Mn
    3. Trication – Zn/Ni/Mn
    If we categorize it in terms of industrial use.Then it will be categorize as following –

    1. Iron phosphating (Non Layer)
    2. Zinc Phosphating (Layer)
    3. Manganese Phosphating (Layer)
    Non layer term is used for Iron Phosphating. It doesn’t mean that no layer is deposit.All these coating deposit a layer on metal surface but because of having thin layer it is termed as Non Layer.Details of all Phosphate Coating is shown in following table –


    Significance of Phosphating –

    • It neutralizes the residues of alkali that could harm the adherence of paint and which leads to corrosion.
    • It has crystalline structure which provides the excellent base.In which sharp edge and corners are evenly covered.
    • It also increases the surface area of substrate which provides good adherence for the next coat.
    • It forms capillaries and micro-cavities which a) promote bonding of layer to metal b) Improve adhesion , better absorption of lubricants and anti corrosive oils.
    • It provides the cushion for the base against the scratch and electro-chemical corrosion.
    • It also prevents the reaction of paint ingredients and sensitive base material.
    • It reduces the speed of corrosion.
    If I start with a Model A body found in a pasture, covered in a nice layer of rust, how do I remove all the rust and replace the phosphate corrosion protection? This information is usually missing in these threads--in essence--how do I prep the rusty metal before the first primer.
    Answer: Lots of work removing the surface rust (sandblasting, sanding grinding), followed by a 2 part metal conditioner process (phosphoric acid).

    Here is PPG's tech sheet for 2 part metal conditioning. It pretty much lays out the steps very clearly.

    Now everyone is not going to do this lengthy and messy procedure, because it is a lot of work, even though not very costly in materials. This is, however, the closest process to the factory phosphate treatment.
    PPG states that if using wash (self etch) primer, that pretreatment with DX579 etc. is not necessary.
    Now if I remove as much rust as I can by sanding, sandblasting, or grinding, I still have rust in the pits and crevices of the steel. A self etching primer can chemically convert a good amount of this rust in pits. Epoxy primer will cover the rust in those pits, but it will do nothing chemically to control or stop it.

    2) All epoxy primers and etch primers are not alike. Before you decide on a primer or primer system, learn about the products and how they work and protect the surface. Most of the failures in any primer or primer system are due to lack of experience and knowledge with products.

    There are basically 2 kinds of etch primer.

    Vinyl wash primer: very little build (fill) and it is slightly more aggressive, acid wise because it has only a vinyl resin as the film. This etch primer should be coated with either a primer sealer or primer surfacer (filling primer) before a topcoat/paint is applied usually with a wet on wet system after the etch primer has flashed for 1/2 to 2 hours. In industrial/fleet applications this is usually applied to sandblasted steel or aluminum then sealed with a primer sealer and painted. For restorations it is usually applied to bare sandblasted steel or aluminum and primed with a filler primer so it can be blocked sanded or leveled before painting. This type of etch primer should not be used over body filler.

    Mild etching primer: this has some build or fill but is less agressive acidwise because of the solids or filler in the primer. This can be painted over with some single stage paints without other primers (check the tech info for the brand). It is usually applied to sandblasted steel or aluminum and can be coated with primer surfacer (filling primer) or sealer wet on wet after about 30 minutes up to 72 hours (or longer) with some brands. This type of etch primer is OK over body filler.

    Most companies use the same activator/reducer (actually more of a reducer) for both etch primers, which is a solvent blend with about 5% phosphoric acid. In a 1:1 mix ratio, that leaves 2 1/2 % phosphoric acid in the primer mix. The acid in the primer mix is minimal and continues to neutralize by converting with iron oxide and some of the solids in the primer (mild etch primer). If you spray on more coats than recommended without proper dry/flash time between coats, you could trap solvents containing some acid, in the film build. With proper technique, conditions and dry time, the acid should not be an issue for problems later.

    Automotive panels new from the factory have a phosphate coating on the bare steel. When you sandblast or sand the metal on a car you usually remove all or some of this coating. You can replace this factory corrosion protection (phosphating) with a 2 part metal prep acid wash which is messy and time consuming. Although not quite as good, using an etch primer on old sandblasted or sanded steel panels is the closest you can get to replacing the phosphate coating. If you use the metal prep and converting system to phosphate coat panels, you should NOT use an etch primer. Several automotive refinish companies require using an etch primer when repairing new car finishes in order for the paint and repair to be warrantied at the body shop.

    My favorite system for sandblasted rusty old car bodies is, sand the sandblasted steel with 80# DA--clean with wax and grease remover-- 1 or 2 medium wet coats of mild etch primer---and after the proper flash time--- followed by 2 coats of compatible hibuild urethane 2K primer. That system has been holding up for me. I'm not against good epoxy primers (and I DO mean the good ones), but I like the idea of converting the hidden rust left in the pores of the sandblasted steel to iron phosphate. If you have removed ALL the rust from the steel, you probably don't need an etch primer.
    If you are skeptical about the etch primer film before doing filler work, grind it off before applying filler, the "etch" has already taken place. I still believe, as most filler companies state, apply filler over properly prepared and clean bare steel.

    Polyester based primers (featherfill-morton eliminator-etc) usually cannot be applied over etch primers, because the acid will slow down the catalyst (MEKP) in the polyester primer and cause the cure to be longer. I did read in the new Evercoat Easy Sand tech sheet, for that brand of polyester primer surfacer, it can be applied over etch primer but it extends the cure time of the primer.

    AS always, read the tech info. Most of these companies have good information available on the web or at their local distributor's store, and you can always email or 1-800 a question to their tech dept.

    As with all good priming systems (epoxy-etch-urethane-polyester-etc) , if you read the tech info,it always says: "The bare steel should be clean of grease, oil, and dirt and free from rust."

    Epoxy primers are not all the same.
    One of my biggest pet peeves is the term "epoxy". There are so many different epoxy primers and coatings with different characteristics for prep, handling, spraying, coverage, film build, solids content, cure time, recoat window, etc. EPOXY is not spelled M A G I C! They are not all created equal. There are some real good epoxy primers, and a lot more mediocre to poor ones that do not have very good corrosion protection. I have not found any epoxy primers in the automotive refinish area that are waterproof. There are very few coatings for automotive refinish that have any very long term moisture resistance. The same goes for other types like etch primers, urethanes, and polyester primers. Most all primers or primer systems need to be protected by a paint or topcoat finish. If you read some tech sheets and compare information you can find a good system to fill your needs.

    One thing you probably will find in the tech sheets for most primers, is that removing rust by sanding sand blasting or metal conditioner (phosphating) is usually reccommended before priming
    You really need to research products to educate yourself and see which product will work for you.
    Let's look at film build for some PPG epoxies.

    PPG DPLF (LF means lead free) epoxy primer sealer yields about .5 to .75 mil per coat, which is pretty thin and does not produce much corrosion protection.

    PPG Shopline JP375 epoxy primer shows film build at 1.0 mils.

    There are others that have film build around 1.5 to 2+ mils per coat. Most of these can and should be coated with high build urethane primers for filling and sanding and of course adding to the corrosion protection "layer" system.

    Most of this info is on the internet and this post is the tip of the iceberg.

    BuiltFerComfort and john worden like this.
  18. indyjps
    Joined: Feb 21, 2007
    Posts: 3,576


    Last edited: Apr 3, 2016
  19. Porttownsend119
    Joined: Nov 19, 2012
    Posts: 35


    indyjps, they're fairly shallow. Possibly. As much as 1/16th in the darkest spots in the pic. i'm at a little bit of bare metal in a few other spots. nothing bigger than a half dollar. I'm a newbie, so I've never used high build...I bought some feather fill surfacer/sealer to use next. Perhaps you're right...go over it with high build and block again. May be just the ticket.

    Thanks to everyone else for the info. I love this community. BTW, just shot my firewall and door jams with Full Base IF over 600 grit sanded epoxy primer and it came out perfect. Couldn't be more happy with my first paint job!
    ImageUploadedByH.A.M.B.1459903628.559788.jpg ImageUploadedByH.A.M.B.1459903642.543287.jpg [/ATTACH]

    Attached Files:

  20. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 1,014


    I'm a big fan of the cheap marhyde brand 2K, been using it for almost two decades, killer build, drys quick, sand's BooBie's, lil spritz of lacquer prime for guide.. I worked at a Hi end vette shop for 16yrs. On/off We use to do a few metal cars as well, the owner stopped using fether fill because he had some issues, then went to a product called Sandy, Works mint on glass, But stopped using it on metal, can't recall at the moment why, but I think it had to do with adhesion if I'm not mistaken, definitely check out the 2K, it's an Amazing product.. IMO.. Paint looks good!
  21. overspray
    Joined: Jan 14, 2003
    Posts: 1,228


    For small low spots or dents, a product like Evercoat's Metal glaze is very nice and easy to work with. Click on the videos tab for some more good info on fillers, primers, and other products. Make sure to sand the powdered guide coat (low) area before adding a filler or primer. The powdered guide coat could decrease the adhesion of any product used on top of it.

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