Body Filler and Skim Coat for My Hood

[MARTINSR]

Originally Posted by nsb29

I wouldn’t leave the lacquer but just because lacquer thiner will take it off don’t mean much when it will remove ppg DP90 epoxy its $500 a gallon lol

I haven't tried DP90 in years but generally any 2k product is going to be resiliant to lacquer thinner where it would take a LOT more to even get any color on the rag. Where as lacquer primer will WIPE off with a rag soaked with lacquer thinner.

And certainly a urethane like a clear LAUGHS at lacquer thinner. I rub off "paint transfers" all the time with thinner with ZERO damage to the clear.

So let's make this perfectly clear, the epoxy primer is recommended by MANY auto manufacturers to be applied over bare metal prior to bonding, to bare metal prior to installing a urethane set window that IS part of the "Structure" of the cars safety, to bare aluminum to apply filler over it, epoxy primer is NO EVEN CLOSE to lacquer primer which WILL wipe off with a thinner soaked rag.

I am not attacking your point on this as there is truth to it that lacquer thinner will soften some epoxy primers. But I just wanted to make clear to anyone else reading this that there is a BIG difference between lacquer primers and epoxy primers.

Brian

[nsb29]

Lacquer doesn’t just soften it it washes it off just as easily as lacquer I no longer use it but yes always use epoxy on bare metal

[MARTINSR]

Originally Posted by nsb29

Lacquer doesn’t just soften it it washes it off just as easily as lacquer I no longer use it but yes always use epoxy on bare metal

WOW, all that tells me is DP90 is CRAP for epoxy primer! WOW!

I just did a scrub test on SPI epoxy primer after reading this post of yours. I RUBBED IT as hard as I could with Lacquer thinner, enamel reducer and urethane reducer. NOTHING not even a tiny hit of a softening or color transfer to the rag.

No kidding, I wouldn't use DP90 on a friggin picture frame!

Now, I also have to think, (I find it hard to believe it's as crap as you describe) are you mixing it right or are you not keeping it warm enough for what the PDS says is a cure time? Is the hardener too old, was the lid left off during storage? I have to believe something was done wrong to hear that you can wipe it off with thinner. No kidding, that is PURE CRAP if it does that.

If you want SPI go to https://www.southernpolyurethanes.com/ where you can buy a gallon of primer, and a gallon of hardener (mixed 1-1 of course) is under $200 delivered to your door. I just ordered a gallon of gray and a quart of black with the hardeners yesterday. They will be on my porch in a few days.

Brian

[nsb29]

I use spi all of ppg epoxy primers can be washed off I used it for a long time with no problems but my point was someone said the fact that lacquer wasn’t good because you could wash it off that you could wipe the expensive stuff off to my biggest problem was the price and the fact that you can’t wipe it down if you have to

[nsb29]

I like spi black you don’t have to top coat it on frames inner fenders and it’s tough

[MARTINSR]

Originally Posted by nsb29

I like spi black you don’t have to top coat it on frames inner fenders and it’s tough

Yep, that is what I am doing. That blows me away that the PPG can be washed off, wow.

Brian

[nsb29]

Didn’t mean to hijack your thread

[MARTINSR]

We didn't hijack anything, it's GOOD information for him!

Brian

[sick472]

I appreciate the paint lessons, truly I do, but I went to my local Bumper to Bumper who services the down town autobody shops and was shocked at the prices for the recommended items. I just don’t have it in my budget to drop several hundred dollars on chemicals for this hood. It’s the last piece to be prepped for paint (besides the final wet sanding).

[sick472]

At any rate, I have stiffened up the hood supports with good results which reduced a lot of the low spots. For those interested, here is what I did. I bit unorthodox, but it is working for me so far.

I put 3/16” x ¾” bar stock at the side supports, drilled and tapped for #10-32 screws every 5 inches with matching holes in the support. The bar stock gives the screws something to push on and the aluminum flats (about 0.060" thick by 5 or 6" wide) protect the under side of the hood from the screws and evens out the pressure. The center support was made from ½” x 1” x 1/8” thick channel, drilled and tapped for the same screws.

[sick472]

I will be applying widow urethane tube caulk through the holes (Red Arrows) in the braces to create supports about every 5 inches along ALL the supports, front, back, sides and center, and the jack screws will be removed. Then the final sanding and filling will be performed.

[sick472]

SIDE NOTE: I measured the widest rear width of the hood to be 71-1/2” before the addition of the supports and jack screws. Once the hood was “jacked” the 71-1/2” dimension remained, meaning the hood kept its form…thank goodness!

The results are show below…the Green Stripes represent what used to be low areas that are now flat. I can see no light between the hood and a straight edge. I still have some low spots (Red Circles) to deal with. These areas are associated with the dings that have been hammered out. These areas will require some filler, but minimal, I hope.

[sick472]

I will be layering in some lacquer fill primer in the low spots to help, but some fill may be necessary. I’ll do some research regarding the type of filler to apply over the lacquer primer if the layers of primer will not do the trick.

My next step will be to long block sand a misted black guide coat to really show the the low areas and go from there. At least now the areas to be filled are greatly reduced and the ole' fiber strand filler that I have been using can be applied, if nothing else seems suitable for laqcuer primer, and some heavy filler primer should finsih it off. Time to research that "suitable filler".

More later...

[MARTINSR]

I have to say, your method here is WAY, WAY out of the "auto body world" but creative and I hope it works out for you. On the window urethane, don't glue the hood to the braces with that urethane. If you do, later down the road you WILL have some serious "ghost lines" as it will get hard and not let the skin move at all and it needs to. So the skin WILL move some with the flexing of the hood and NOT move right at the urethane, you can imagine what this will do, not good. It would be akin to welding it there, not good.

On the primer, a quart of SPI with a quart of hardener would be less than $100 mailed to your door (free shipping) so you may want to think about that.

You can do all the research you want on the filler, but just regular old filler, any type, Rage Gold, 3m Platinum or cheap stuff like Nexera 2820 (about half the cost of the others and DAMN GOOD stuff) is going to do the job. Anyone who throws something out there like fiberglass reinforced or something like that is dreaming, just regular filler. And that Nexera blew my mind how good it worked for the money.

Brian

[sick472]

Just for clarity, I will be injecting the urethane through the holes in the support pieces with the hopes of creating standoffs like the ones pictured below - not full length long beads. Some of the gaps to be filled with the standoffs will be about 3/4" tall (along the back brace) while the front brace is about 3/16" gap. The large gaps may require the standoffs to be built up in stages so that I do not end up with overly large urethane pads. I'm shooting for 1" diameter urethane pads.

Would you still be concerned?

I guess I could put aluminum pads down against the hood panel prior to the urethane application. This would act like the long aluminum strips and allow for some slippage between the hood supports/urethane standoffs and the hood panel.

[MARTINSR]

Originally Posted by sick472

Just for clarity, I will be injecting the urethane through the holes in the support pieces with the hopes of creating standoffs like the ones pictured below - not full length long beads. Some of the gaps to be filled with the standoffs will be about 3/4" tall (along the back brace) while the front brace is about 3/16" gap. The large gaps may require the standoffs to be built up in stages so that I do not end up with overly large urethane pads. I'm shooting for 1" diameter urethane pads.

Would you still be concerned?

I guess I could put aluminum pads down against the hood panel prior to the urethane application. This would act like the long aluminum strips and allow for some slippage between the hood supports/urethane standoffs and the hood panel.

YES I would be.

That was my point, if you put that urethane there, it's literally like putting a weld. And when things move which they WILL it won't move right at that "weld", get my point? You WILL have at the very least a "ghost" line there, at the very least, and very likely with as much as a hood flexes, and twists, you will have much more.

If you will notice in that photo you posted, it's simply a "foam" that flexes a little.

Brian

[MARTINSR]

The urethane may be slightly "flexible" when fully cure, I mean slightly, it is basically a weld.

Let me put it this way, it makes the glass part of the "structure" on a unibody car. The manufacturers guidelines for it are over epoxy primer or factory e-coat and to NEVER apply it over new paint. This is for a structure that is, you wouldn't have to worry about that here, but I just want to make it clear, that stuff cures to pretty hard, the foam is a whole different thing.

On door skins what I do is cut foam off the skin when I remove it and then put a tad bit of urethane on the foam when I put the new skin on. That way the foam is still there doing it's job and the urethane is simply holding it to the skin.

Knowing the crazy depths to where this industry is going, I am probably going to be sued for a million dollars because I didn't put new manufacturer authorized flexible foam.

Brian

[72HuggerK20]

Originally Posted by sick472

I appreciate the paint lessons, truly I do, but I went to my local Bumper to Bumper who services the down town autobody shops and was shocked at the prices for the recommended items. I just don’t have it in my budget to drop several hundred dollars on chemicals for this hood. It’s the last piece to be prepped for paint (besides the final wet sanding).

As with anything, you have three qualities in every autobody product. Cheap, easy to use, and good. Pick two.

With some things, I will get pretty much the cheapest available product from the local autobody store's value line. I painted a tractor one time with "Autobody Master" Epoxy primer, used Evercoat "Lite Weight" filler, ABM urethane primer-surfacer, then thinned out more of the epoxy primer as a sealer, shot Omni basecoat over it, and cleared it with Autobody Master "Shop Clear." This stuff was ultra-cheap for autobody products. Under $75 a gallon for the epoxy primer with catalyst, about the same for the urethane primer, $25 a gallon for the filler, $100 a gallon for the Omni basecoat, and $40 a gallon for the clear and catalyst. I was very, very surprised how well everything actually worked. It's been holding up incredibly well, too. Again, not saying that going off-label and mixing brands is the best idea, but in some cases, it does work. Especially if you have a tight budget.

[sick472]

So, I have guide coated and dry block sanded the hood with a 16” durablock and pretty happy with the results. I wish I had a guide-coat sanded “before” photo, but I don’t because I just did not do any pre-sanding at all. The supports with screw are still in place along with wood shims along the front and back. I will be putting another 2 heavy coats of fill primer on and applying the urethan standoffs before the next round of block sanding with hopes to eliminate most of the low spots. A few will certainly need body filler. I have chosen to go with Evercoat Lite Weight because of the low cost and it’s got to be easier to sand than the fiber strand putty that I have been using.

Just and update to the progress and I am not saying, at this point, that this is the best method…just the path I’m taking.

And...Thank you all very much for your participation up to this point!

The darker gray areasa are low spots with the exception of the lines directly above the oem supports (there is steel or self-etch primer showing there). The ones on the front are from welding up rust and the GMC letter holes. The top/sides have made most of the improvements, but the areas along the center ridge have been greatly reduced from being about 1/16" low to barely visible with straight edge.

[MARTINSR]

Looks like it's going well, a few coats of polyester primer and you would be there!

Brian

[MP&C]

Sorry I'm late to the party, but thought I'd add a few comments that may or may not have already been covered....






This is textbook media blast damage, especially noted by the lack of damage under the support rails and sunken panel elsewhere. Excessive air pressure, and/or too large of media, is just like thousands of hammer heads beating on the metal. 99.9% of the time the panel is going to move TOWARD the source of what caused the damage, ie: the stream of media pounding on the sheet metal from underneath. That side is being planished/stretched, the other side is not, so the panel naturally gravitates to the source.

It doesn't take much stretch at all for the waves you see above to occur, and doesn't really take all that much time or effort in fixing it. The tricky part here is fixing it properly, and fixing it for good. These hoods are infamous for flopping in the breeze, even without adding media blasting in the mix. IMO the last thing needed here is to settle on "flat" as shown in your recent repairs, as "flat" seldom stays that way. I would attempt to get an ever so slight amount of crown, more specifically, CONSISTENT crown across the panel to provide support and eliminate the flopping for good. These hoods remind me of the Biederman hood we made, they are prone to developing low areas/flopping in the wide expanse of flat area. When we made the replacement hood, even though it may appear as flat (note the light reflection lines) there is indeed a slight amount of crown to help give the panel support throughout it's lifespan:



https://www.youtube.com/watch?v=KTXzEPYzPxE



I don't think filler will effect a permanent repair, but I could be wrong. I would also suggest putting the panel in some direct sunlight before you get too much farther along, and re-evaluate the "flat" areas to insure this bit of natural heat/stretch doesn't return the dreaded low areas. You may have sprayed some primer, but it is still a cheap fix before the finish coat(s) go on.

My preference to this repair would be to use a shrinking tip on a dent puller. Heating with a torch is IMO too aggressive for the novice (I include myself) to not get away from you. I prefer the slow, methodical approach in most processes, that allow you to sneak up on the fix rather than speeding past the exit ramp. With the hood on a stand upside down, and the slight bit of pressure applied by the weight of the dent puller (ie: NO other pressure required) as soon as the heat is applied to the shrinking tip you can visibly watch the panel move in the correct direction to remove the low. I feel shrinking this sheet metal is the only way to make this a permanent repair. Excess sheet metal is always looking for somewhere to go, especially with these hoods. Sometimes it takes driving down the road (wind forces applied) to see it.

[MARTINSR]

I hear you Robert, but I think he "tricked" it to flat with the spacers he made. If nothing else I would love to see it in person and see how it works out for him.

I think at this point, with his skills, there is no way I would use the dent puller shrinking tip. It would likely end up "shrinking" it by pushing the metal down at the tip making a little dent, at least that is how I have found it to work in a large area like this.

Don't get me wrong, I think you are right to correctly repair it is of course the best way to do it. He has found a "bestest" way. LOL

Brian