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Cleaning metal for painting

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tom_tom_go03/10/2020 15:17:57
7 forum posts

I have a 5" gauge loco that I have broken down to just the chassis and cylinders and would like to hear advice on how to clean before painting.

As the engine has been tested on steam a few times on my club track it is oily and greasy. White spirit is not cleaning the metal sufficiently as when I run my finger along the metal afterwards there is black dirt lingering.

I do own an air compressor with a cleaning gun so is there a detergent I can use to give the chassis a proper blast and scrub?

Thanks,

Tom

Roger Best03/10/2020 15:49:36
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369 forum posts
56 photos

Engine cleaner would be a good start, wash off as instructed, then a volatile solvent like meths or acetone to get rid of the wash, especially if its water.

White spirit leaves a little of its heavier elements behind, you might find that they will come off with meths and leave it clean.

As I found when working with printing ink, solvents just dilute dirt so you need to wipe it off and repeat endlessly, a detergent binds to dirt and is happy to be washed off.

Fowlers Fury03/10/2020 21:12:26
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404 forum posts
91 photos

Roger B's advice is fully endorsed !
I would suggest rubbing the surfaces all over with Swarfega, the "Orange" version is maybe better as it contains plastic microspheres - then flushing with hot water.
THE best preparation on those components which can withstand it - and when SWMBO is out for half a day - is to put them into the (empty) dishwasher. If the risk of detection is too great or you don't have a dishwasher, then boiling those parts with a couple of dishwasher tablets in an old pan will be nearly as effective. I suggest that because the big problem is old oil trapped in seams and especially under rivet heads. Unless that is effectively removed, you'll end up with "fish eyes" and streaks when repainting/spraying.

BTW - white spirits is an oil, OK for most oil-based enamel paints but not cellulose or some acrylics.

Graham Stoppani04/10/2020 08:28:46
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119 forum posts
26 photos

I have recently converted to using Ajax to prepare surfaces for painting. Not my idea but that of Dan Gelbart.

This is a link to his YouTube video on the subject and he mentions Ajax 11 minutes in but its worth watching the whole video. LINK

John Rutzen04/10/2020 08:34:21
348 forum posts
19 photos

I agree with Graham , surface activation is essential, especially if it's brass. A sand blast works very well too. Again that's all in the video. I have found that Screwfix No-nonsense zinc primer is very good if you bake it in the oven at 140 C for about 20 minutes for a base coat.

Speedy Builder504/10/2020 09:02:50
2590 forum posts
207 photos

The words and music from the book "How not to paint a locomotive" say that light grit blasting is the way to go. This means a total strip down. I have done this to my SPEEDY 5" chassis. I was able to buy an etch primer in aerosol can, and 2 part epoxy - also in aerosol, however you have to use the contents of the can within 24 hours, which was Ok as I wanted the insides of the chassis red silk finish and a few other bits followed by black semi mat on the outside of the chassis. All other painting will be done in 2 pack with a spray gun or air brush, mixing up just enough for the job in hand.

its too late now, but wheels do present an interesting problem to paint once mounted on their axles.

Tim Hammond04/10/2020 09:03:29
74 forum posts

I endorse Fowlers Fury's remarks about using very hot or boiling water to remove oily dirt. It's why we used hot water pressure washers (so-called steam cleaners) to prepare commercial vehicles for annual test. The way the hot water shifted the accumulated oily grime was remarkable, especially when used with a detergent. Another example - when I worked for the MoD as a vehicle fitter, many parts from the stores were heavily protected with a thick, waxy goo (probably Cosmoline) which was very tenacious and took ages to remove in the parts washer using paraffin. Far easier to lob the smaller parts into a pan of boiling water on the stove in the messroom and boil until all the goo was removed. It rose to the surface of the water and could be skimmed off. The parts when removed from the water were still very hot, of course, and dried off almost at once.

tom_tom_go04/10/2020 13:11:39
7 forum posts

Thank you for all your responses, very helpful.

Vic04/10/2020 13:41:29
3060 forum posts
8 photos

Dan Gelbart covered this, No solvents I think he said but I watched it some time ago. I don’t paint much stuff but realised years ago just how good sand blasting is.

**LINK**

duncan webster04/10/2020 16:44:59
3919 forum posts
61 photos

+1 for Fowler's Fury. I don't know what's in dishwasher fluid, but it completely removes oil and grease. Get it out as soon as it has finished the rinse and dry it or you will get light surface rusting

tom_tom_go04/10/2020 17:53:42
7 forum posts

Even if I could fit the chassis into the dishwasher my wife would tear me a new one if I tried!

Tim Stevens04/10/2020 18:00:16
avatar
1584 forum posts

Another factor you need to consider is the type of paint already on your model. Some paints and some solvents will attack existing layers, and the only remedy is to remove all the old paint and start from bare metal. But, you may be lucky and/or careful, so I recommend a trial on all the original colours with whatever you intend to put on next, before you get too deeply involved in the cleaning process. (Or you might have to do it again).

Cheers, Tim

duncan webster04/10/2020 18:12:00
3919 forum posts
61 photos
Posted by tom_tom_go on 04/10/2020 17:53:42:

Even if I could fit the chassis into the dishwasher my wife would tear me a new one if I tried!

OK so when you've got most of it off use caustic soda, hot and strong. Use mask and rubber gloves. Then rinse off in hot water so it dries quickly.

Fowlers Fury04/10/2020 22:34:34
avatar
404 forum posts
91 photos

Someone queried the consituents of dishwasher tablets. There are agents to "bleach", surfactants, and oxidisers e.g. sodium carbonate, sodium tripolyphosphate, sodium percarbonate and alcohol ethoxylates. Much of their oil removing properties are due to enzymes such as subtiliisins. However the enzymes need cool water, being deactivated in boiling water.

Despite Duncan's advised precautions, I would advise against using "hot & strong" caustic soda. It is very corrosive.
As before, it's safer to use either Orange Swarfega or a couple of dishwasher tablets in an old container big enough for the parts. Start with warm water to preserve the enzymes then if you can, boil the solution - if that's not possible then just steep in very hot water. At risk of repetition, if you don't get old oil out of seams, rivets etc, it can ruin your subsequent painting.

stevetee06/10/2020 00:11:45
144 forum posts
14 photos
Posted by Fowlers Fury on 03/10/2020 21:12:26:

Roger B's advice is fully endorsed !
I would suggest rubbing the surfaces all over with Swarfega, the "Orange" version is maybe better as it contains plastic microspheres - then flushing with hot water.
THE best preparation on those components which can withstand it - and when SWMBO is out for half a day - is to put them into the (empty) dishwasher. If the risk of detection is too great or you don't have a dishwasher, then boiling those parts with a couple of dishwasher tablets in an old pan will be nearly as effective. I suggest that because the big problem is old oil trapped in seams and especially under rivet heads. Unless that is effectively removed, you'll end up with "fish eyes" and streaks when repainting/spraying.

BTW - white spirits is an oil, OK for most oil-based enamel paints but not cellulose or some acrylics.

I have discovered at my cost that if one is to use the dishwasher for parts cleaning when the management is out, don't try and clean anything which has traces of paraffin on it. It leaves a lingering smell, which lingers long after the machine has finished, permeatjng the house , which ensures immediate detection of the offence, and causes domestic disharmony.

Speedy Builder507/10/2020 16:08:38
2590 forum posts
207 photos

I have just micro wire brushed the 5" wheels (mounted on their axles) and preparing for painting. The final process was to wash in acetone - the photo shows the muck that came off when the acetone was filtered and put back into a can!

filter paper.jpg

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