DX579 vs. Wash Primer

[RexWorks]

On a steel surface, with areas of sanded primer and areas of bare metal should a metal prep such as PPG DX579 be used or should the whole thing be sprayed with wash primer?
The finish system will consist of DPLF sealer, K36 primer and Concept topcoat.
Thanks,
Rex Perry

[dauer]

Hi Rex,


You can go either way the DX579 will be just an adhesion promoter while etching primer will keep rust from spreading should that area ever get chipped down to bare metal you do not how ever have to spray your entire surface with etching primer as it will not do you any good on areas that are not bare metal...Good luck with your project..

Dave

[James Kirk]

Rex,
I thought PPG quit producing K36.

Kirk

[RexWorks]

Dave and Kirk,

Thanks for the response.

I think that I will treat the bare areas with the DX579 conditioner. I already have some to play with.

I guess I have not heard that the K36 has been discontinued. The K38 high build may be a better choice anyway.

I just don't want the whole mess to fall off after the first bump.

Thanks again,

Rex

[tombsycles]

Living far away from ready sources of new products, I still rely on old stock products that will cleanly wash any impurities off the surface with a hand wash prior to any sprayed etching primer.
(Mine still says "Rinshed Mason" on the packaging)
Many I know layed vinyl wash on in heavy-wet coats after washing (etching), as well as zinc chromate in heavy-wet coats in it's time.
Both were meant to be dusted on a clean surface to allow adhesion for surfacing primers, not replace them.
A good water-diluted acid wash on smooth, clean metal will promote the adhesion of laquer based or catylized filling primers of today.
It's supposed to look streaky when it dries up after dry-wiping.
I have forgotten what the acid wash product number in RM and Ditzler (PPG) is, but I'm sure PPG and Dupont still sell it. They may not stock it, but Dupont still sells two colors of Duco Nitocelluous Laquer, and don't stock that either.
Wear industrial strength rubber gloves. Wear safety glasses.
Wear a respirator, not just a dust mask.
All this stuff is real bad for you.
I had to say it.
What I can't understand is why these new filling products are so unforgiving as to final sanding grit. We used to be able to sand a complete with 180-220, and three coats of enamel produced a mirror finish. Maybe it's the paint.
Now the primer is thick, not the paint.
Today's Basecoat-clearcoat systems don't allow a finish sanding under 600 grit if the sand scratches aren't supposed to appear a month later. A wet sand and a buff later, they still come back a year later.
Ho-hum.... :)

[ogorir]

the process we have used for the last 15 years in my dads shop w/ no issues apart from PPGs muck-ups is this:

strip to bare w/ aircraft remover methelyne chloride stripper
metal prep with DX579 and scotch brite
sand with 80 grit DA changing paper often for good tooth.
spray w/ DP50 and DP402 catalyst
let sit for a week so solvents completely flash
spray with 4-5 coats K36/k201
wait a week, block w/ 150
reapply if necessary
block to 400, make sure there are no 'rogue' scratches
spray w/ K36 w/ DCC added for sealer
sand w/ 600
base/clear(DBC/global 8150 right now. we still miss 2020 around here)
wait a week
wetsand to 1500
wait atleast overnight
rub w/ 5973 on fine wool
rub w/ 5991(discontinued) on fine waffle

that procedure has been tweaked to reduce scratch shrinkage.

and w/ regards to 'we did it this way in the past and got a mirror finish.' I've never seen a repair or respray that didnt shrink at least a little over time, regardless of finish system (enamel, lacquer, poly).


I'd also like to point out that DX579 is NOT an adhesion promoter. it's a surface prep. you still need to sand it afterwards. it doesn't etch the surface enough for non-etching primer to stick to it. but, if you have something sitting around in bare metal, you should DX579 it as it will prevent it from rusting (at least in michigan) for 6 months, if not longer. It's also a great way to neutralize/clean off a chemically stripped part.

anyway, take what you will from it (and I just realized that this is from 3 1/2 years ago, so... for the record, K36 is still not discontinued)