The Spray Painting Thread

[GeneSPIDA]

Also polyester spray bog i wouldnt recommend as over time it goes to hard and develops "crows feet" cracking in the paint.

This is why I'm still debating it, and one of those things where different sources have different views

If it's sprayed, not too thick, and sanded back properly before covering with the urethane 2-pak primer to "lock everything in", is this still likely to be a problem?

I have noticed that it is exempt from the PPG lifetime warranty because of "so many variables that can affect it's performance". Which is why I'm a bit reluctant.

My experienced repairer/restorer also recommended not to use it, when I said I was thinking about it. So, not sure I want to go against his experience too much.

[turbocaldina]

it does apply to polyester bog only if its applied to thick. I have had car com over from the states with an awesome body and paint only to find a crack in the paint and finding out that the bog is an inch thick. If you were going to use spray polyester i would only use it on repaired areas and not all over the car.

[GeneSPIDA]

Yeah, that car from the states doesn't sound like it was repaired very well then, if the bog was an inch thick.

Any use of bog/filler shouldn't be that thick.

["Z" UTE]

If you are reconstructing parts of a car in bog, due to lack of metal fab skills, use fibreglass reinforced bog, it will stand up better than the other body fillers. Generally if your filler is thicker than 2-3 mm there are serious problems with the repair. A skim coat can be applied over a panel to give a uniformly flat surface.

Any spray filler will shrink back, as will laquer paint, if it is applied too wet. Put simply, the surface will dry due to the contact with the surrounding air, the underlying paint remains wet, and when it finally dries, it will pull, or shrink back. Cracks and crowsfeet are a sure sign that the spray filler/primer or topcoat were applied too wet.

When spraying high fill, I would rather apply 2 to 3 medium coats in lieu of a single heavy wet coat.

cheers Chuck.

[turbocaldina]

spraying to wet doent cause shrink back, its when the prep work under the primer is to coarse, say the bog is only finished off with p80 grit and then the primer doesnt have time to properly cure before sanding and painting over. when priming always let the coats flash off before applying the next coat, if you dont you will get pin holes where the coats on top have dried to much and the solvent from the coats underneath are still trying to escape. cracks and crows feet are from to much paint being on the panel.
some brands of paint you cant apply to wet as they "pin hole" to easy, then others you can put really heavy coats on and get no pin holes.
Ask the supplier as they have the best knowledge of there product and how to apply it.

Des

[Z2TT]

hi

I have seen many micro cracks mostly in plastic bits, bumpers. On my Celsior it doesn't seem like the rear bumper has ever been repainted, but it still has these very fine micro cracks (like a web) when i look close.

Is this because of a badly prepped bar at the factory? as in didn't use adhesion/flex agent primer beneath?, or whether you use or don't use adhesion premoter (plastic primer), will the plastic shrink eventually years down. Or does it depend on the basecoat you use? i.e some paints flexible and some not as much as others?

I wouldn't think the whole bumper flexes that much, especially the more solid parts but it has cracks all over, so I'm wondering how come plastic parts always get cracks like this and metal doesn't?

Thanks.

[pac]

simply the bumper has been bumped and paint has minimal flex, Flexaid needs to be added when painting to prevent the cracking

[takai]

FYI, this is that engine bay with the 1.7mm nozzle:


Quite glossy off the gun IRL, yellow cast is from the 1000w of halogen lights which are off to the left.

["Z" UTE]

Takai, the 1.7mm nozzl is a does everything size, just takes a guy who has used a spray gun before to use it right. Test panels are worth their weight in beer cans. Looks quite good.

The trick on these colder days is to use a fast hardener with your 2pac, or fast thinner with acrylic.


cheers Chuck.

[o_man_ra23]

Just bought a new Transtar LVLP gun with 1.3mm nozzle. Hopefully that should lay the bright orange down better than the old workquip did.

[twentyEight]

Just bought a new Transtar LVLP gun with 1.3mm nozzle. Hopefully that should lay the bright orange down better than the old workquip did.

LVLP? For painting a car, or a bumper bar?

An HVLP gun is what you should have bought IMO, but the Transtar LVLP has no air control, only Spread (Fan) and Paint Flow controls which may make it about as good as the Workquip. The seals maybe a bit more reliable though.

[Z2TT]

Yeah pac thing is this is the factory paint, so I take it they added flexing agent to the paint and still there's cracks all round, not just in random places like where its been bumped.

Takai - I might buy some 1.4 and 2.0mm nozzles from the manufacturer if the paint store doesn't have ones to suit, Want me to buy you a set too?, $15 Posted to your door or so.

[takai]

Nah, ive got a pretty good feel of the 1.7mm and can use that well

[o_man_ra23]

Actually the Transtar does have air control. It will take a while to paint as the coats will be quite thin, so lots will be required, but that was how the car was going to be painted anyway to try and maximise the mica effect. The workquip will be fine with it's 1.8mm nozzle for the primer.

[kremsra28]

my 2 cents worth as i am a painter is that soda blasting is a good source of paint stripping, and that after its soda blasted use only epoxy primer as its the best for sticking to bare metal, we use it on cement trucks that have had the chassis blasted. All so polyester spray bog i wouldnt recommend as over time it goes to hard and develops "crows feet" cracking in the paint.

i have read in heaps of tech books and watched many hrs of american hotrod and the other 1 with chip foose and they all use spray poly (but the yanks do weird things!!) in a few of them they even cover whole cars in bog and then spray poly!!

in all the tech books i have read they all say that its a very stable product as when it cures it wont move, cant shrink or anything (when its used properly), i guess that there is always the 1 time that some dickhead misuses it and whinges about it that makes ppl say "maybe its not real good after all), i have used it on a few of my jobs and the only problem i had with crows feet were from where i had a small patch where i thought i might have rubbed thru the primer to the poly, instead of spraying a little bit of primer 'incase', i just ignoerd it (being under the pump and it was late at night) i just cleaned up and painted, it cracked up around 3 weeks later and i had to redo the whole panel, the rest of the car in which i used poly, there was never an issue, that was around 7yrs ago and its still all fine.

krem