Gang: I painted metal Bower kit with last of my Floquil stash yet the paint is not durable and is removed with handling. Would coating with and matte acrylic or dullcote help? Thanks
Use a proper etching primer.
Did you clean off the boiler and lightly sand the surface for ‘tooth’? Die castings may have a parting agent, which is just as good at ensuring ‘parting’ between the casting and a layer of paint…
In my opinion, acrylic will bond no better to an unprimed metal surface, and Dullcote is basically talcum powder in clear lacquer and needs a good paint film to bond onto.
I’ve used auto primer and Shellac in the past. I baked the piece with auto primer in a small oven. Both worked. Vallejo primer for acrylics is not as good.
Simon
Thank you Simon. Never thought of auto primer but great idea. I used Tamiya primer then covered that with Floquil. I was thinking clear coat on top of the Floquil would add a level of protection. Thanks for your kind response.
I washed boiler shell with soap and water, then painted it with acetic acid (10%) for several minutes, then rinsed and dried. Did not think about light sanding which is a good idea. Another poster suggested baking on auto primer FIRST, which is probably a good solution, albeit to late for me! Thanks for your kind response. Andy
That seems to me to have been reasonable prep for the metal shell. I assume that by ‘soap’ you mean a ‘dish soap’ that is actually a detergent, like Dawn, and not a hand soap.
You’re already using a stronger pickling solution than this thread recommended:
One reason in the past we have recommended comparatively gentle ‘picklants’ has been to avoid damage or dissolution of solder joints on preassembled detail, as on brass locomotives. That probably wasn’t the case for your shell.
Sanding would remove any ‘skin’ on the casting and raise some tooth, and you could address any flash at the same time, but you might also lose detail. I suspect that good old ‘quad-ought’ steel wool (0000) might tend to burnish the surface as much as ‘key’ it for mechanical adhesion. Probably the “best” solution would be some kind of media blasting – there are ‘kits’ that use an airbrush-size compressor for small pieces that would work with at least some of the ‘right’ media for Zamak prep. That raises a directionless matte finish that ought to hold primer well.
I am a ‘fan’ of baking the primer in the oven. I suspect you could use the pecan trick to avoid potential danger from fumes: preheat the oven to 250 to 275 F, then turn it off and put the parts inside. By the time the oven cools to a safe removal temperature, the “curing” should be good without any element heating. But don’t do this if you have a gas oven with standing pilots!
Little toaster ovens may be a course less expensive (to both wallet and marriage) but they do not have the thermal mass needed for pecanery. That implies that you let the self-etching primer dry its full recommended interval before baking it – and that you set the oven up in a well-ventilated space like a garage, or on an rextension cord outside a door.
This project is a lot more complicated than it seems when started, 2 years and a hurricane ago. I have learned much and will remember your tips when working with zamac castings. Cheers.
In an unrelated vein: when you start assembling the valve gear, following their instructions, use small pieces of paper between the rods as you mushroom the rivets down firmly. When you pull the paper out the joints will work freely without excess lateral play.