24 replies to this topic

[Fondmetal]

Whilst I always knew paint would add some weight to a aero part of a car, I didnt realise it was as much. Today I weight two identical parts, one painted and one non painted. There was some 300 grams difference.





I think my car has something like 5 or 6 layers of paint on it, I would ideally like to remove all of it from the tub as well as the aero parts.

Any suggestions on an easy way of removing it?

Edited by Fondmetal, 27 February 2011 - 18:07.

[Canuck]

Even more remarkable than the weight gain is the percentage gain - it's almost doubled the weight of the part.

[Fondmetal]

Yeah tell me about it, as soon as I find a way to remove the paint I will take it back to carbon. If anyone knows and easy way to strip off the paint that would be great.

[desmo]

http://forums.autosp...howtopic=135378

[Bloggsworth]

Lead paint? I would estimate a square metre of spray paint to weigh about 50gms sq. metre given a thickness of less than 0.05mm thick, just how many coats of what did you put on? A square metre of ABS 0.1mm thick only weighs 106gms - there's something wrong with your scales...

Edited by Bloggsworth, 27 February 2011 - 22:44.

[Fondmetal]

Lead paint? I would estimate a square metre of spray paint to weigh about 50gms sq. metre given a thickness of less than 0.05mm thick, just how many coats of what did you put on? A square metre of ABS 0.1mm thick only weighs 106gms - there's something wrong with your scales...

Maybe but its all relative.. will take it to my local post office and get it weighed on their scales, will be a bit more detailed.

Soda blasting seems good, any idea on costs?

[Engineguy]

I was at the Gannasi Ganassi Gannassi Target Racing shop a year ago, and expressed surprise at how often they strip and repaint their indy cars. They just sand the paint off with orbital sanders. I asked the engineer showing me around if they worry about the sanding having an effect on the strength, by sanding into fibers. He just shrugged his shoulders like it'd never occured to him and said, "I guess they're just careful."
Perhaps the epoxy sands so much harder than paint/primer that you don't damage he composite?

[Magoo]

Well-cured epoxy resin is pretty damn hard -- you'll scratch it up with a DA and 80 grit but you won't blow straight through it while the paint will come off more quickly. I mean relatively hard, of course, compared to paint, primer, and polyester filler. Like when you are finish sanding epoxy with with 320 or 400 -- requires some elbow grease. Paint stripping is not difficult but it does require some work and time... which is how stuff ends up with four or five complete paint jobs on top of each other.

It is possible, sort of, to calculate the weight of the finish by referring to the solids content of the material on its MSDS or product data sheet. If the paint weighs say 8 lbs per gallon and is say 50 percent solids, it should weigh 4 lbs per applied gallon, so if you know your cover rate and area, minus overspray and material removed in color sanding, you have a figure of arguable utility. You can figure one to two mils of material thickness per coat of material applied via spray. And there is not just paint in typical finish , of course, but direct-to-surface primer-sealer, primer-surfacers and glazing, primer-sealer, and then colorcoat and clearcoat if two-stage is used. A conventional automotive paint job will be 5 to 8 mils anyway if it needs to look good close up. If you just need basic color and coverage, one to two mils of single-stage color can do it. The lighter the color the more colorcoats required, with yellows and oranges being the most translucent. Yellow will always need four coats minimum over light gray primer to look like anything. Wrap is light, allegedly, but never looks good close up. Passenger airliners are typically finished with two coats total, primer-sealer and color, total thickness just over two mils. The practice there is to paint 2x and then strip and start over. The paint on a 747 weighs 550 lbs, or so I've been told.

[Tony Matthews]

The lighter the color the more colorcoats required, with yellows and oranges being the most translucent. Yellow will always need four coats minimum over light gray primer to look like anything. Wrap is light, allegedly, but never looks good close up.

I had a friend complain once that he'd had to put about ten coats of yellow emulsion on a wall before it looked OK and the dark original colour didn't show. I told him one coat of white and two of yellow would have done it. I believe , in the crazee world that is F1 that most painted carbon is stripped and re-painted on a very frequent basis, using water-based paints. I had a chat with a paint sprayer at Williams some years ago, but stupidly didn't ask how they stripped the old finish off

Edited by Tony Matthews, 28 February 2011 - 09:49.

[Magoo]

I had a friend complain once that he'd had to put about ten coats of yellow emulsion on a wall before it looked OK and the dark original colour didn't show. I told him one coat of white and two of yellow would have done it.

Absolutely. Also, sealer is usually cheaper than paint. Materials are so expensive these days.

[Fondmetal]

Maybe I will just take the whole car back to carbon and vinyl wrap it.

[mariner]

I seem to recall an article in Racecar Engineering ( I think) that explained a very high tech and expensive ( of course) film that McLaren use to apply the complex artwork on their cars.

I would imagine that paint weight would be big issue for F1 given what ehy will spend to increase the ballast amount.

[Tony Matthews]

I seem to recall an article in Racecar Engineering ( I think) that explained a very high tech and expensive ( of course) film that McLaren use to apply the complex artwork on their cars.

I would imagine that paint weight would be big issue for F1 given what ehy will spend to increase the ballast amount.

Yes, I was going to mention film, or decals, but don't know enough to make a pertinant point. I know, I know, doesn't normally stop me... I think some of the paint schemes, paticularly McLaren at various times, have been sufficiently tricksy as to make spraying/airbrushing probably too demanding or time-consuming. Just a guess. I have in my posession two small samples of white and rich blue 'sticky-backed plastic' that exactly match the paints used on the Williams FW21, given to me as colour reference. This was, I believe, used to make some of the swoopy shapes and applied to the base paint scheme. Got some Penske Pennzoil 'go-faster' stripes too, I've just remembered!

[PhilG]

I remember that the original paint chosen for the Jaguar F1 was rejected cos it was too heavy.

The paint guys spent more time stripping than painting, always back to carbon , but the finish was superb.

[Tony Matthews]

I haven't checked on the year - might have been 1987 - I tipped up at a workshop to photograph a new Champcar. The previous evening, the tub had been sprayed in team colours, a departure from the normal practice of shipping the cars in carbon, and I think requested by the team to save time. As there were concerns about dust gathering on the paint over night, clingfilm was draped over the fresh paint. When I arrived there was a scene of panic, as the cling film had clung, bonding to the paint.

[SWB]

As I understand it the carbon is OK with UV light, but the glues used to bond the carbon aren't so stable. So if there are any glued joins in the stucture, perhaps like a tub, it needs painting or at least a UV resistant clearcoat. Just what I heard.

Steve

[Tony Matthews]

Right - some info! Carbon cloth is liable to damage from UV, but iit isn't a rapid process. Secondly, F1 cars are normally stripped and painted every couple of weeks, in which time the paint does not harden fully, so it is removed with - ready? - a scalpel! That is what I have been told, it is scalpeled off, by which I assume a blade is meant, rather than an impliment used by a surgeon. The paint removed recently from a Penske PC26 weighed 30 kilos...

[Canuck]

30 kilos?!?! Wow.

[Fat Boy]

The paint removed recently from a Penske PC26 weighed 30 kilos...

Were there a couple gallon cans in the seat? I _guarantee_ Penske did not race a car with 30 Kg of paint on it.


FWIW, I think we saved about 5 pounds on a DP car by going the 'wrap' route. It looks like hell close up, but it's fine on track and on TV. The wrap weighed about 12 pounds, if memory serves.

[Tony Matthews]

Were there a couple gallon cans in the seat? I _guarantee_ Penske did not race a car with 30 Kg of paint on it.


FWIW, I think we saved about 5 pounds on a DP car by going the 'wrap' route. It looks like hell close up, but it's fine on track and on TV. The wrap weighed about 12 pounds, if memory serves.

Well, I was very surprised at the figure, but it is what I ws told. This is a PC26 in private hands, and looking stunning in four coats of white and Rocket Red. Perhaps, if it was a show chassis, it had been re-painted without stripping - I didn't get the chance to query it.

[Magoo]

30 kg is pretty amazing. Figure 4 kg per gallon, 66 percent solids, and then a gallon per finish (which is more like a Cadillac than an Indy car in surface area) to be well on the fat side, and the car would still have the equivalent of a dozen paint jobs on it. High-build poly primer-surfacer (yon liquid bondo) weighs about 50 percent more than paint, but still.

[gtsmunro]

When we prep an aircraft for refinishing (F/A18 Hornets for example) all the carbon fibre surfaces are sanded down to primer to minimise damage to the composite. Once you sand through the primer, you risk sanding off the composites gel or clear coats. The surface becomes compromised and weakened plus it releases mirco particles of carbon fibre into the atmosphere which is as bad, if not worse, than fibreglass towards your health. The corsest sanding paper we use is 150 grit, mainly on heavy area's that have multiple coats. These days advances in technology is allowing workshops to move rapidly toward media blasting using grade 5 plastic media for example. Media Blasting strips the paint and primer right down to the composite with out any damage leaving a totally clean skin surface. The advantage here is the smaller components such as TEF (trailing edge flaps),or aluminium panels such as Door 68's (engine covers) can be done in a booth together. I would imagine that race teams would be using this process already as it's the quickest, cleanest, most efficient way to thouroghly remove the finish without compromising the integrity of the carbon fibre. It's also far easier to prep for paint and lessens the risk of old paint and primers 'blowing up' or reacting with new primers and paints, plus a blasting booth takes up the same space as a paint booth. Easily fit a full race car let alone components. Using a scalple to remove paint would scratch up and cut the surface compromising the integritiy of the carbon fibre.
The average weight of paint on a larger aircraft is around 1 ton, so the removal of the old finish helps substantially with weight reduction which is critical to the aircrafts overall performance. F1 would be the same.
Refinishing the carbon fibre I would imagine F1 teams would be using either 'wraps' (entire car is one big sticker) or one coat of high solid primer and two of top coats. In 1977 Holden painted their A9X race shells in very thin coats of primer and white to reduce weight.

Edited by gtsmunro, 22 March 2011 - 23:06.

[Tony Matthews]

Very interesting. Do you use water-based paint on aircraft? I suppose that is a general trend. I think some of the F1 schemes must involve wraps, in part if not complete. However, wraps must suffer damage/abrasion too, so how are they replaced - just peeled off?

[gtsmunro]

No, we're moving head first into the eighties by using hi solids.......
Water based paint is one of those things that everyone agrees is fantastic, but nobody wants to use!!! I think the problem is the thought that water getting trapped (under rivets etc) and potentially creating corrosion. It is being used in the States and Europe.
Wraps would be a peel off and replace item. Most times they can be heated and they peel right off. You'd probably try solvent removal if that failed (soaking the area with Methyl Ethyl Keytone (MEK Thinners). Prepsol damages the substrate). You can sand them off if they dont come off but that'd be rare.

Edited by gtsmunro, 23 March 2011 - 10:21.

[RDV]

Something wrong in the weights, didn't think it could go that high in this type of part. Had introduced electrophoresis in the 90s to paint carbon parts and had very good weight savings...easy as the team livery was single colour, with minimal film for the sponsor stuff...if one remembers correctly full livery ended up at 9kgs for a F1, not much bondo as we had very good mould preparation and the carbon was impeccable...filler is a killer...