The Unofficial Mamod and Other Steam Forum

flywheel61 · Posted: Tue May 13, 2008 9:27 am Post subject: VHT paint problems

I recently strpped and repainted my prewar SE3 becuase it had already been 'restored' by steam4fun with the Mt Vesuvius conflagration paint.

Imagine my supprise when after the first firing the fire box looked like this,

The base also was susceptible to a small amount of spillage from metho/s from the burner.

Both the bas and the firebox were allowed to dry overnight and subjected to the requiste, minimum one hour at 95 degrees Clecius in the oven.

I have since restripped the base and firebox again and the firebox is much better, but the base did the same thing.

Anyone got any ideas of how to fix/eliminate the problem so it doesn't happen again.

Cheers

Chris
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andysleigh · Posted: Tue May 13, 2008 9:31 am Post subject:

hmm. dont know realy.

i'v used bbq black and satin black, they seem to be fine.
not sure about the red
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Mamodman123 · Posted: Tue May 13, 2008 10:19 am Post subject:

Crank up the heat I imagine, I would personally bake it at around 200 for an hour or so (not straight away) whether the can says it or not

Not sure what you can do about the base though

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Stitch · Posted: Tue May 13, 2008 10:39 am Post subject:

I had a couple of bad experiences with VHT on a firebox, but none as bad as that. I worked out that mine were related (I think) to a bit of humidity in the air. I now only use on a very dry day.

Wallace · Posted: Tue May 13, 2008 10:48 am Post subject:

I've never seen VHT do that. What brand is it?

Is the base VHT too?

I guess we all have different methods for baking, and I vary mine from time to time, but whenever a VHT paint suggests baking via engine idling to cure it, (say 20mins), then I put the part in a cold oven. Turn the temp to 140degs cels, and bake it for 5mins longer, so 25mins in this example.

Could have also peeled if the metal was extremely smooth before painting?
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johnreid · Posted: Tue May 13, 2008 11:26 am Post subject:

I think that some paints are more sensitive to Alcohol than others, I would use a different brand of paint for the base.
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tmuir · Posted: Tue May 13, 2008 11:54 am Post subject:

Never seen that before.
I've used the VHT gloss black engine enamel on my SE3 and although the bit that sits in the direct flame has been slightly damaged the rest has held up well.
I used paint stripper followed by W&D and removed all paint and rust before respraying.
VHT brand paint has a minimum ambient air temperature (Think thats over 20C but could be 24C) for the paint to set properly which basically means I don't paint in winter.
I also cure at hotter temps than 95C, can't remember what temp I use but its what it says on the can.
If its not cured properly solvents can damage it.

Also if you used paint stripper make sure ALL of it has been washed off or it will stuff up the paint.

Hope that helps
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Les · Posted: Tue May 13, 2008 11:57 am Post subject:

I have only ever used BBQ paint on the firebox of my Wilson, didn't oven bake it, and I have never had a problem with it.

5600
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flywheel61 · Posted: Tue May 13, 2008 8:27 pm Post subject:

Thanks everyone, for the information.

I had a second go at both and the firebox is much better this time, but the same thing happened to the base,

. The temperature I baked both at is what is recommended on the can around 95 degrees Celcius. I don't have a problem with humidity - wish I had, as we are still in drought - Tony is probably right re the temperatures our daily maximum is only around 20-22 degrees Celcius, so I might have another go when the ambient temperature is higher towards summer.

You have to be very careful with using higher than recommended temperatures for colours as they can darken vey quickly, the first time I baked a base and mistook the recommended temperature (which was in degrees F) for Centigrade, the red base went the colour of dried blood,

Cheers

Chris
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Rob · Posted: Tue May 13, 2008 9:38 pm Post subject:

maybee putting a piece of brass or copper plate in the firebox for the burner to rest on would help? keeps it off the base...

xlchainsaw · Posted: Wed May 14, 2008 11:09 am Post subject:

this is a common problem

the reason its crinkling is the paint has been applied to thick. red paint in general needs to be applied in 5 coats with 24 hrs between them. if temperatures are low ..... after the second coat lightly sand the coat with fine sandpaper and then allow the sanded surface to dry 24hrs before repaint. this will apply for all coats after the second. if you dont do this then the paint will crinkle. black covers really well so light coats generally do thus the paint isnt as thick. this rule applies for all enamel vht or not! red as in our base colour,dark blues,dark greens are especially bad as one tends to apply the paint extra thick so as get a uniform colour.

hence it takes about 8 days to paint a red base with a little being done every day. of course if its a hot summer it wont take as long.

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flywheel61 · Posted: Wed May 14, 2008 8:26 pm Post subject:

Thanks for that Glenn, I forgot to metion that the red base paint only crinkled where the metho had spilled on it, under the the burner tank. It didn't happen anywhere else on the base.

Cheers

chris
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xlchainsaw · Posted: Thu May 15, 2008 12:36 am Post subject:

being a flat base it may have a slight buckle there so the paint may run a bit thicker at that spot.

probaly best to spray light coats and use a peice of wire through a hole as a hook and hang it up to dry.
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Cam · Posted: Thu May 15, 2008 9:09 am Post subject:

The exact same thing happened to me, so i re-stripped my MM1 and sanded and repainted. didnt heat or anything, the paint said heat from engine would be fine. To the point, the 2nd painting went fine no flaking or cracking of paint under the burner...Maybe and Australian Paint thing (im In SA btw)

flywheel61 · Posted: Thu May 15, 2008 8:39 pm Post subject:

Problem solved, thanks to Wallace's detective work. The base and the firebox were sand blasted. Apparently, if the metal requires longer sand blasting, due to say rust, the blasting can leave a layer of silicate on the surface. This is probably why the 'original' paint work came off so easily when stripper was applied.

When I redo the base, I' be using a fine grade W & D to ensure all the silicate had been removed.

It was also recommended that is use a primer - problem is that VHT no longer make a primer, they say it's un-neccessary with thier paint now. Will have to see if other brands like Septone are compatile or change to Septone paint as well.

Cheers

Chris
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