Mill Scale inside of smoker

[Gaddywb]

I’m beginning my first smoker build. It will be very similar to a vertical smoker. Is it necessary to remove all of the mill scale from the inside (or outside) of the cook chamber? This seems to be the most time consuming and expensive part of the build. This is the first panel I’m working on. It is 3 feet x 2 feet. I’m about halfway done after 3 hours and 4 strip discs. I used a grinder wheel for some of it but seems to be damaging the steel. Thanks for any advice.

 

[Coreymacc]

That looks like cold rolled steel so your not really seeing millscale. Hot rolled sheet looks black and it has a millscale on it, that almost looks white, like its been blasted. Does anything flake flake off? You could probably use a wire wheel on a grinder to buff the metal clean. Using a grinding disc will take for ever.

Corey

 

[Gaddywb]

That looks like cold rolled steel so your not really seeing millscale. Hot rolled sheet looks black and it has a millscale on it, that almost looks white, like its been blasted. Does anything flake flake off? You could probably use a wire wheel on a grinder to buff the metal clean. Using a grinding disc will take for ever.

Corey

Thank you for the reply. I’m pretty sure it was hot rolled, but I guess I could be wrong. I don’t have anything flaking, it I would call it a dark gray color. The wire wheel seems to take even longer to get to the shiny metal. I don’t plan on painting, but seasoning the outside with boiled linseed oil and the inside with vegetable oil. Here is another picture. The piece of the left is the same in the original and on top of unworked metal from the same piece. The piece on the right I covered in white vinegar for about 7 hours. Wiped it off and a lot of black definitely came off.

 

[DougE]

If it does indeed have mill scale on the surface, a flap disc on an angle grinder will make short work of it.

 

[Gaddywb]

I thought so. I can assure you, nothing seems to make short work of this. Is it necessary to remove?

 

[SmokinEdge]

If it does indeed have mill scale on the surface, a flap disc on an angle grinder will make short work of it.

Flap disc it once over and be done, I agree.

 

[Gaddywb]

Flap disc it once over and be done, I agree.

Is it necessary to remove? And if I use a flap disc do I need to go all the way down to the really shiny part (for lack of a better term). This is something I didn’t completely anticipate for in my build plan. It looks to take a considerable amount of time and money with an angle grinder. If it needs to go to the shiny part, I’ll probably go with an overnight white vinegar soak.

 

[DougE]

These things eat through mill scale like it ain't even there.

 

[SmokinEdge]

Is it necessary to remove? And if I use a flap disc do I need to go all the way down to the really shiny part (for lack of a better term). This is something I didn’t completely anticipate for in my build plan. It looks to take a considerable amount of time and money with an angle grinder. If it needs to go to the shiny part, I’ll probably go with an overnight white vinegar soak.

All depends on what you want for a finished product. If it’s scale it must come off, if it’s just discoloration then if you leave it will always be there. just common sense type thing.

 

[Gaddywb]

All depends on what you want for a finished product. If it’s scale it must come off, if it’s just discoloration then if you leave it will always be there. just common sense type thing.

Thanks for the help. I’ll give the brand of flap discs posted above a shot. As far as discoloration goes, if I coat it in boiled linseed oil, it will give it a dark color anyways from what I understand. So if I go all out to remove it to a nice sheen just to add the oil, is that just a waste of time? Also, for the inside, that won’t really be seen anyways and will get dark anyways from cooks.

Sorry if the are basic questions. I thought I had it all planned out but now I’m feeling lost and don’t want to ruin anything.

 

[DougE]

Paint won't stick to mill scale and I expect your seasoning will flake off similarly. I usually get my flap discs from Harbor Freight and those are cheaper than the one I posted but work well. I just posted that one since it was handy.

 

[Gaddywb]

Paint won't stick to mill scale and I expect your seasoning will flake off similarly. I usually get my flap discs from Harbor Freight and those are cheaper than the one I posted but work well. I just posted that one since it was handy.

Oh I thought it was a specific brand. I’ve tried flap discs already. I used a DeWalt brand and another I can’t remember off the top of my head. I’ll give them a try again though. Do you think the vinegar method is worth it? It seemed to do alright and if I left it over night it might have done even better l.

 

[Fueling Around]

I suspect hot rolled, especially from the vinegar spray results.
Is this plate 1/4" and thicker or sheet under 1/4"?
Plate is almost always hot rolled. Sheet can be either, but under 3/16" it is often cold roll or formed. Cold formed often has an oily feel from residual machine oils used to reduce oxidation.
Either needs a cleaning prep to remove scale or oils. You just need to clean the surface. You do not need to polish the surface.

 

[Jonok]

I suspect hot rolled, especially from the vinegar spray results.
Is this plate 1/4" and thicker or sheet under 1/4"?
Plate is almost always hot rolled. Sheet can be either, but under 3/16" it is often cold roll or formed. Cold formed often has an oily feel from residual machine oils used to reduce oxidation.
Either needs a cleaning prep to remove scale or oils. You just need to clean the surface. You do not need to polish the surface.

With a good respirator (important!) and a big enough compressor, 50 lbs of fine mortar sand and a $75 sand blaster from harbor freight will take off whatever you need taken off. (A hood or good goggles makes it a lot more pleasant) remember the respirator though, because silicosis sucks…

 

[Gaddywb]

I suspect hot rolled, especially from the vinegar spray results.
Is this plate 1/4" and thicker or sheet under 1/4"?
Plate is almost always hot rolled. Sheet can be either, but under 3/16" it is often cold roll or formed. Cold formed often has an oily feel from residual machine oils used to reduce oxidation.
Either needs a cleaning prep to remove scale or oils. You just need to clean the surface. You do not need to polish the surface.

Thanks for the reply. This is 3/16”. I looked at the website of business I bought from. They offer cold or hot rolled sheet, but neither go as thick as 3/16”. 3/16” is the thinnest plate they sell, and they don’t give a choice of hot or cold rolled, but they don’t specify which it is. If I hit it with a wire cup brush, it will give it a little shine, but it won’t be bright silver. What would you clean it with, just a wire brush or some sort of cleaning solution/water? I’m going for a dark metal look when I finish it with the boiled linseed oil.

 

[Fueling Around]

Muriatic Acid is the best descaler.
BE WARNED!!! Working with Muriatic Acid is not a task to approach casually.
Muriatic Acid is actually Hydrochloric Acid in 10-40% strengths.
IT IS TOXIC IF NOT HANDLED SAFELY!!!

 

[Gaddywb]

I suspect hot rolled, especially from the vinegar spray results.
Is this plate 1/4" and thicker or sheet under 1/4"?
Plate is almost always hot rolled. Sheet can be either, but under 3/16" it is often cold roll or formed. Cold formed often has an oily feel from residual machine oils used to reduce oxidation.
Either needs a cleaning prep to remove scale or oils. You just need to clean the surface. You do not need to polish the surface.

I took a flap disc to the piece that I soaked it vinegar. It came off very easy compared to what I was previously dealing with. Here’s a picture. Do you think it is worthwhile to do this to all the metal if I’m seasoning with oil?

 

[DougE]

If it makes it easier, do it that way but you need to get the mill scale off. Paint will not stick to it so I don't think oil seasoning will either.

 

[Gaddywb]

If it makes it easier, do it that way but you need to get the mill scale off. Paint will not stick to it so I don't think oil seasoning will either.

Thanks. That is what I’m going to do. It took about 10-15 minutes with a flap disc to do twice as much as what I did in 3 hours with no vinegar. I don’t think I’m brave enough to try the muriatic acid.

 

[DougE]

I just disc it off, but phosphoric acid may work as well. Ace hardware carries a product called ospho which works for converting rust and also for etching bare metal to accept paint. It isn't caustic like muriatic acid is. You can put it in a spray bottle and spray the sheets down a time or three and flap disc.