Primer problem

This topic has 10 replies, 7 voices, and was last updated 20 June 2014 at 14:32 by Russell Eberhardt.

Viewing 11 posts - 1 through 11 (of 11 total)

Author

Posts
18 June 2014 at 22:09 #7203
GaryM
Participant
@garym
Advert

18 June 2014 at 22:09 #155690
GaryM
Participant
@garym
I'm usually too cautious. "Measure three times and cut the following week" could be my motto. However, the other day after doing some final fettling of the S50 base casting that I'm building, I degreased it and gave it a coat of red oxide primer. That bit was OK, the mistake came when I got the flywheel I'd prepared the previous week and painted that, forgetting I hadn't degreased it. Therefore the finish is glossy and very slightly soft compared to the matt and sound finish on the base.

Should I give it another coat of primer or try and remove it with paint stripper or rub it back to metal?

Thanks

Gary
18 June 2014 at 22:17 #155691
stevetee
Participant
@stevetee
A mate of mine who is a better engineer than I will ever be made the observation "90% of paint problems are to do with adhesion." I suspect he is probably right, if the item hasn't been de-greased then you will struggle to get the paint to adhere to the base material, due indeed to the thin layer of oil. Try wire brushing the paint, if it comes off in sheets you will need to redo it sooner or later, so why not now. If the brush glides over the finish, as it probably would on the matt item ….. you are OK.
18 June 2014 at 22:46 #155693
stan pearson 1
Participant
@stanpearson1
Hi Gary

Go to your car paint supplier and buy 5lts of gun wash its like celli thinners and will cost about £10 that will wash it off without marking it and if you can afford it buy some self etching primer spray a thin coat and leave for 24hrs to etch. Don't mess with red oxide.

Regards

stan
18 June 2014 at 23:22 #155694
GaryM
Participant
@garym
Thanks for the replies guys.

Looks like you are both suggesting getting the primer off. I think I knew that was probably the correct course of action. So I'll have a go at that with cellulose thinners and/or abrasives. I didn't want to spray it because I've zero experience of spray painting and masking the flywheel would have taken a while and probably not been that successful. Also, just to clarify, the castings have been machined, the engine tried on air and this is the final stage before final assembly.

Gary
18 June 2014 at 23:41 #155696
Oompa Lumpa
Participant
@oompalumpa34302
Stan is absolutely on the money with his advice. Red oxide primer is for road bridges.

(though £10 a gallon for gunwash….. I buy it in 25 litre – 5gal – containers for about that. I use LOTS)

graham.
19 June 2014 at 06:50 #155705
Tim Rowe 1
Participant
@timrowe1
SteveItee's mate is correct and the old adage that a good paint finish is at least 95% in the preparation. Red Oxide – "Off with its head"!
19 June 2014 at 19:24 #155761
duncan webster 1
Participant
@duncanwebster1
If it's oil based red oxide then caustic soda will shift it, cheaper than thinners and easier to dispose of. Wear rubber gloves, it's wicked on your skin
19 June 2014 at 22:32 #155775
stan pearson 1
Participant
@stanpearson1
Hi Graham

Yes your right it was antibloom thinners I bought as I spray all my locos in celli.

Stan
20 June 2014 at 10:19 #155806
GaryM
Participant
@garym
Thanks for the suggestions everyone, I'll take them on board, but what is so bad about red oxide primer? I try to find as much info as I can before asking questions. I have Chris Vine's excellent book "How (not) to paint a locomotive" and realise that acid etch primer is very useful, but due to it being a small casting and brush applied I thought red oxide would be OK in this instance. Top coat will be Humbrol enamel.

Gary
20 June 2014 at 14:32 #155832
Russell Eberhardt
Participant
@russelleberhardt48058
There's nothing wrong with red oxide primer for clean iron or steel I've used it on everything from models to vintage car chassis with no problems. Of course there is good and bad quality. The old "red lead" primer was a better rust preventer but the Elfin Safety boys have stopped that.

For brass, bronze, and aluminium you do need to use an etch primer or it won't stick.

Russell.
Author

Posts