Bonnet painting order of operations?

[saabguy (Lester)]

Good Morning all!

So disassembly is mostly complete and re-assembly looms. I would like some input on epoxy prime / Sikaflex / painting.

I feel confident putting on the epoxy primer but I plan to have a shop put on the final coat of color/clear and I would also like to have the body painted as one piece at one time.

So far what I see is:

Epoxy prime bonnet and all bits
Take to shop to have them paint underside of bonnet and all bits
Sikaflex and bolt together
Take to shop to do exterior paint

Or is there a better way? Any and all comments appreciated.

Lester

[tbob (bob trimpe)]

Not sure where you are with reassembly, but of course subframe needs to be installed prior. Otherwise, Your order looks good to me.

There will be much agonizing and tweaking to get a good bonnet fit, so its best to have it unpainted when fitting.

FWIW I painted my bonnet six months after I painted the tub and had no issues with color match. If I had it to do again i would use your plan.

[Nickolas (Nick Saltarelli)]

@saabguy

Take to shop to have them paint underside of bonnet and all bits
Take to shop to do exterior paint

I’m not clear on what you’re saying, Lester, but assuming you’ll shoot epoxy primer and colour onto the underside of the bonnet yourself and will leave the exterior painting to the shop?

I can only share the approach I took. I applied Sikaflex over bare steel as was done in the factory but there will be no problem applying it over epoxy given attention to either the approx. one week maximum epoxy cure window and/or scuffing prior to application. I do not think it’s a good idea to apply Sikaflex over finished colour as you’d be adding another variable to the bonding equation. When it comes to primer, paint and adhesives bonding is everything.

I dismantled the bonnet after the Sikaflex set up, epoxy primed the inner bonnet shell, diaphragms and ducts and reassembled, leaving off the bonnet belly pan to allow access for painting the headlamp and nose areas. Epoxy over fasteners. Final colour the next step - originally all the fasteners - pozidrive screws, nuts, bolts, lock washers and oval washers - holding the bonnet together were painted. At the same time I shot the belly pan inside and out before waiting a couple of days to colour sand and compound and mount it back onto the bonnet. When I shot the outside of the car entire the belly pan was masked off at the break line. Makes for a better job and much less work later on. I did the same with the underside of the boot while the monocoque was still on the rotisserie, for the same reason.

It is not a good idea to do the exterior paint on the bonnet ahead of the main paint job. If you want to achieve a smooth flow across the bonnet middle section and wings onto the skuttle you need to prep the bonnet to blend into the monocoque, doors and bootlid. Ideally when you are doing the final paint job the inside of the bonnet, the engine compartment, the bonnet belly pan, the boot underside and inside, the cockpit, the inner doors will be in final colour. None of these areas requires much in the way of paint prep - you can shoot colour directly over epoxy - but the same can’t be said for the exterior of the car. If you want a show quality paint job it will require many hours of paint prep. I didn’t keep close track of how long the entire paint job took from bare steel to final colour sanding and buffing but a good estimate would be 160 hours.

Final paint will not hide any shortcomings in prep. It will enhance them. Even the slightest variation in elevation and contour will manifest itself. That’s why you need to have the body assembled for prep.

This is the stage of my resto after having completed the bonnet reassembly:

The exterior of the monocoque is already in high solids primer and has already undergone paint prep. The next job is to prep the bonnet and make it flow into the rest of the car. Mask off and epoxy prime:

followed by a couple of heavy wet coats of high solids primer

the next day dry sanding with a dead flat long block just until the epoxy starts to poke through, highlighting low areas

followed by a thin skim of polyester putty over low areas (maximum 1/10", but 1/16" is a good tolerance to shoot for when you’re doing the bodywork).

This is wet sanded to bring everything to the same level with a smooth transition with the skuttle

Epoxy touchup of exposed steel

A couple of final wet coats of high solids primer

Final dry blocking

Remove doors and bootlid, shoot boot and bonnet shut channels

shoot final colour over entire car

Shooting final colour all at once and with the car essentially assembled avoids slight colour variation from differences in ambient humidity from shooting days or weeks apart and minimises exposure to paint chipping while putting things back together. Since the bonnet belly pan and boot underside are low profile, shadowed and separated from the rest of the car by chrome any slight shade variation from painting days before will not be detectable.

[64etype (Eric)]

Lester,

As mentioned here and in the other thread, bonding to finish paint isn’t a good idea, so you’d want to either mask off the epoxied flange areas on both the bonnet and the brackets prior to finish paint, or sand off the finish paint prior to bonding. Neither is a very good option.

Here’s what I did…

Epoxy primed the ducts, headlight panels and bracketry.

Masked the bonding surfaces on the bracketry.

Finish painted the ducts (inside and out), the headlite panels, and the mounting bracketry.

Epoxy primed the underside of the three bonnet sections and the chin section.

Finish painted the interface surfaces of the bonnet (a little over spray onto the outside surface was sanded back by the body shop/painter.

Assembled the sheet metal shell.

Attached the empty shell to the tub/frame and adjusted it to fit. (R & R Twice )

Removed shell, flipped over, and trial fit ducting, headlight panels and radiator rock guard with flanges bolted in place.

Masked along the edges of the flanges and along outer edges of the ducting (to define the area that would be difficult to reach with the ducts installed).

Removed the ducting/bracket assemblies/headlight panels and separated the brackets from the sheet metal.

Lightly sanded the epoxy on the bonding surfaces (bonnet and the brackets).

Bonded the brackets to the bonnet. Pulled the masking tape when the Sikaflex was beginning to set.

Color painted the underside of the fenders and center section that would be masked by the installed ducting.

Installed the ducting, headlite panels and stone guard to check for fit.

Removed and rebounded one flange because I didn’t like the alighnment. (A real chore).

Installed the assembled bonnet to the tub/front frame assembly one last time.

Removed and placed on the bonnet dolly.

Masked the ducts and areas of fenders that were finish painted.

Finish painted the underside of the center section to include the visible edge of the Sikaflex.

Took the bonnet to the painter on it’s own dolly where they did finish body work and painted…separate from the body. Climate controlled paint booth. Doors and boot lid were also painted separately. Zero issues with paint match (OP Gunmetal). That said, my painter is a magician.

Prior to wet sand…

Bonnet dolly

[saabguy (Lester)]

Thanks guys,

I think that I am saying the same thing. A question comes to mind though, when you “Attached the empty shell to the tub/frame and adjusted it to fit” what did you adjust? the mounting pivots with shims or something else?

And what was wrong with the one flange? Something that you didn’t do earlier or did it move while setting?

Thanks and keep those answers coming. I have to get the compressor working again before I do anything.

[64etype (Eric)]

I first adjusted/shimmed the mounting pivots. Then I had trouble getting the curvature at the aft end to match the cowl area on the tub. (The bonnet was off the car when I purchased it, so don’t know how well it fit before I took it apart). I also worked with the gap of the horizontal close “seam” behind the wheel on one side.

I eventually elongated the holes in the corner brackets very slightly to allow the aft, bottom of the fenders to move inward. Wrapped a long cargo strap around it and squeezed…then tightened the brackets. Mating flanges might have been bent very slightly…who knows. Depends on how precisely you want it to fit.

I probably had the masking tape slightly skewed before I bonded the flange. It was at the rear of the duct. I could get it on, but it wasn’t perfect.

Are you using single stage or base/clear paint? Greatly simplified things by painting the underside myself.

[saabguy (Lester)]

That seems to be the ideal way to do things, Epoxy-prime the underside and related bits, paint what will be hidden and bits EXCEPT for the flanges, Sikaflex bits then paint what can be seen. Thanks all.

[MichaelPMoore]

[quote=“saabguy, post:1, topic:355837”]
Or is there a better way? Any and all comments appreciated.

Lester

Lester, I think your plan will work just fine.
I initially fitted the center section and wings (no interior parts) and made sure the bonnet fit was "shimmable ".
I disassembled everything and had all parts finish painted on both sides. The rest of the body was painted about the same time bonnet-less.
I am pretty sure I called Sikaflex and discussed bonding to the finished surface. I do not recall sanding the finished paint in the bond area. When I began assembly on the car, I assembled the fenders and the center section .Each day for several days, I bonded one piece of bracketry to the bonnet attached to the part. It turns out that every part uses something else not bonded for support. I assembled in small steps and as finished bonding one part at a time, I spent a good bit of time cleaning up the Sikaflex. I ended up with black joint lines on a ODM paint job, but I could easily brush paint those joint lines I suppose.

Mike Moore 63 OTS

[vlad11]

Nick, excellent visual guide - and apparently superb result.

Did you paint right there in the garage?
That is my plan…

Your thoughts on single stage vs base/clearcoat?

Vlad
67 Series I roadster

[Nickolas (Nick Saltarelli)]

Yes, Vlad, in the garage. Paint prep is the key to a satisfactory result. I think I logged about 160 hours from bare metal to final polishing.

Single stage urethane is the best option for a home paint job because the colour sanding step takes out any dust that has settled on the paint while it sets up, at the same time flattening the orange peel. It’s an option only with solid colours, though, not metallics or pearlescents. Three wet coats followed by progressive wet sanding starting with 800 and ending with 2500 grit then buffing with ultrafine machine compound first with a wool pad and finishing with a foam pad - spritz a little water on the pads before buffing to prevent burning the paint.

I highly recommend HVLP equipment for home painting. A three stage turbine setup is perfect for primer application - almost zero overspray so there is no need to tent off the area and mid-high 90 percentile material efficiency - in addition to lower cost there’s very little cleanup and air contamination wafting to your next door neighbour. Another great advantage of turbine equipment is the air delivered to atomise the primer and paint is warm, dry and oil free. Turbine droplet sizes are much more even than what standard LVHP equipment can deliver but they’re also larger, so not ideal for the finish coats. I used my turbine to apply the colour and flattening the orange peel was manageable but laborious. Turbine guns are also bleeders - air is continuously expelled out the nozzle, even when the trigger is closed - so there’s a greater propensity to move dust around when the gun’s not pointed directly at the car. The final coats are best applied with a good compressor driven HVLP conversion gun - this is what I will use next paint job. Droplet size is smaller, so the finish goes on smoother, but transfer efficiency drops to the high 80s - low 90s (vs mid 70s for LVHP guns) and you will need an air dryer and oil extractor between the compressor and the gun, and you will need a sufficiently large compressor to deliver the CFM needed - my DeVillbiss Gti requires 11 CFM minimum.

If you’re going metallic or pearlescent you’re pretty much confined to base/clear for a home paint job and still pull off a show quality result. That’s because you’re still going to need to colour sand and buff out the clearcoat. Base/clear paint applications are not as durable or repairable as single stage urethane and introduce a secondary risk of delamination.

Last point in this long answer is material quality. I use PPG products but there are other top brands. Expensive, but when all that work is factored into the cost/benefit equation it makes no sense to scrimp on the finish.

[vlad11]

@Nickolas

DeVillbiss Gti requires 11 CFM minimum

NIck, thank you for a most erudite answer. “Three stage turbine”… something else to learn!

I am the second owner of this puppy, which has 20k original miles, on salty Michigan streets. It was BRG, but badly rusted, so I had to weld in new rocker panels and other parts. With so much destruction, I decided to change to Opalescent Maroon [year-correct for 67] - which is metallic… So I guess I have to go base/clear per your discussion [no way around it, eh?]. I already sprayed the frame and door jambs with single stage, but assume it will be possible to blend in a two-stage finish for the outside?

BTW, my first two resto projects I did in lacquer, in the permissive 70’s! What a forgiving medium it was!

[64etype (Eric)]

I used the R-M/Glasurit Diamont line of paint (base/clear). I found it easy to use when spraying the frame, interior, and underside of the bonnet. The painter who did the exterior loved the stuff. R-M was the only company I could find at the time that had a paint code/mix for OP Gunmetal. Of course Glasurit was the original supplier back in the day.

[Nickolas (Nick Saltarelli)]

@vlad11

I guess I have to go base/clear per your discussion [no way around it, eh?]. I already sprayed the frame and door jambs with single stage, but assume it will be possible to blend in a two-stage finish for the outside?

You can’t colour sand metallics or pearlescents, doing so cuts through flake particles and presents shadows on the finish. The answer goes to your expectations, Vlad. A good, practiced car painter can achieve a show finish with metallic or pearlescent single stage under closely controlled spraybooth conditions but he’d need to tent off, illuminate and ventilate a home garage to achieve the same result. Amateurs like you and me, not a chance. However, if you were to apply a couple of wet coats, wait a week and colour sand the pearlescent to kill the orange peel, dry, clean and shoot a wet mist coat you just might pull it off.

You won’t notice any difference between the two finishes. Actually a very good strategy if you’re going with a base/clear exterior finish.

I did two show quality lacquer paint jobs years ago, the first with lead-based DuPont acrylic then several years later with the new lead-free stuff. That second paint job crazed after ten years. Lacquer ain’t what it used to be.

Glasurit also an excellent line of products, per Eric.

[saabguy (Lester)]

Now I have trial fitted everything and it looks good, good fit to body, good shut lines.

Here are my goals:

1. Make sure that fasteners are painted as per original

2. Make sure that there is Epoxy primer EVERYWHERE

Next thing is to epoxy prime everything disassembled to insure that all flange surfaces and panel flanges have epoxy on them.

Then reassemble to get bonded flange positions, mask now epoxy primed center section and wings and bond in flanges.

… and here is my concern…

The fasteners have not been primed at this point.

Do I spray another coat of epoxy primer to the visible parts to insure fastener coverage and then apply the color leaving the hidden parts in epoxy primer only
or
Do I disassemble, apply the color to all the parts, assemble, then apply another coat of color to cover fasteners
or
Do I disassemble , apply color to all of the hidden parts (Area in front of diaphragms but behind headlights) , then reassemble to apply color to the visible parts and fasteners ?

How do I, or do I, need to prime / treat the fasteners before painting? I will be using primarily original fasteners.

I keep thinking that I am overlooking some obvious step but it’s just not coming to me.

All ideas entertained.

[64etype (Eric)]

I epoxy primed and color painted all fasteners prior to reassembly. Touched up those that were marred by tools.

[Ole-XKE1974 (Ole Würtz)]

My bonnet sections were etch primed inside/out and all joining faces were painted in the car color before assembly. Bonnet assembled and the whole lot painted after spending endless hours fitting and adjusting the bonnet to the car for correct gaps.
After the car returned from paint I used a cavity wax on all joints, welds and cavities. Only have had to touch the diaphragms since and they have new un-painted bolts and screws. But that’s where I will be accessing when a new bulb needs fitting, so I’m OK with that.
Cheers … Ole

[vlad11]

My approach has been to do what the factory probably did. When I disassembled mine, the “invisible” parts were primed with red. Then apparently the bonnet was assembled, and painted. It seems that the fasteners, and inner faces of flanges, only got paint, no primer. In the wheel wells, the undercoating was applied directly to primer, without paint. Photo evidence on request.
Vlad
67 OTS, #1E15615

[saabguy (Lester)]

Please tell me more about undercoating. Pictures are always a plus.

[saabguy (Lester)]

Wow. I can see priming them or otherwise treating them but I would mess up final color a LOT getting it all together. That is serious dedication!

[MichaelPMoore]

@Nickolas

I can only share the approach I took. I

Great work Nickolas, beautiful car. I did things little differently. I completely assembled the outer panels of the bonnet on the car and got it aligned. The bonnet panels (center, wings and valence) were all finish painted on the interior. There were no bonded brackets anywhere when I assembled the “shell”. Once it was aligned, latches installed and could be closed and latched I began installing the brackets one at a time. I found every stiffener in the bonnet could be mounted without a bracket. I would mount a stiffener each day, put Sikaflex on the faying surface and install it with nuts and bolts. In many cases, I reshaped the brackets for a better fit. I always chose installing a bonded bracket late in the day, glued it down, cleaned up the surplus and latched the bonnet for the night. I felt I had more control that way even thought took a while. I had called Sika about bonding on top of the finish paint and they were ok with that 12 years ago, The concern is if the bond from Sika to the paint is weaker than the bond of the paint to the steel. I had planned to go back and paint the black bond lines (OD maroon car), but I ended up leaving it with black bondlines. Your approach will certainly result in a nicer and more concours look under the bonnet. Great job! Mike Moore