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Making mild steel look like cast iron

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Craig Brown 221/02/2021 17:02:37
51 forum posts
14 photos


Far from model making but im sure some knowledgeable people on here could advise. Long story short, I have restored a couple of these fireplaces for my house and unfortunately the mantel shelves have been lost to the sands of time and I would like to fabricate some out of mild steel. No problem there however the fireplaces are the bare, raw cast iron dark grey colour/finish and I would like to try and match this for the mantels if possible.

They will obviously be manufactured from mild steel, welded and ground/dressed etc. Just wondered if anyone could offer any advice on how to make them look like an original cast item. Painting is the last resort really, but will paint the mantels if necessary.

Thanks, Craig

Vic21/02/2021 17:06:39
3017 forum posts
8 photos

Sand blasting might provide a finish you like better?

Rik Shaw21/02/2021 17:11:30
1470 forum posts
398 photos

A bit of heavy duty sandblasting might do the trick if you can get it done locally.


Dave Halford21/02/2021 17:20:08
1890 forum posts
22 photos
Posted by Rik Shaw on 21/02/2021 17:11:30:

A bit of heavy duty sandblasting might do the trick if you can get it done locally.


Possibly with some steel shot mixed in

The Black finish may be Zebrite

gary21/02/2021 17:21:53
135 forum posts
31 photos

dont think you will ever get a good match craig, you could rub stove black onto the whole lot or make the mantle out of a nice piece of hardwood.

Neil Wyatt21/02/2021 17:27:12
18895 forum posts
734 photos
80 articles

The texture might be achieved through sand or bead blasting.

The black finish is not as-cast. It's probably a phosphorus dip, (like jenolite) which will turn surface rusting black and give a hard corrosion resistant phosphate finish.

You can simulate this on mild steel by allowing it to rust, wire brushing then treating with a phosphate rust treatment.

Another alternative is a fireplace 'black lead' like Zebrite (which is actually graphite based).


Neil Wyatt21/02/2021 17:29:32
18895 forum posts
734 photos
80 articles

Probably won't work unless you have a texture to 'hold' the finish.


noel shelley21/02/2021 18:19:38
1018 forum posts
19 photos

My lovely warm wood burner is cast door and steel body, all zebrited looks fine. As others have said sand blast and zebrite. I once saw a wonderful Oak Beam over a huge old fire place, the owner was a friend, and having let me admire it said touch it ! It was concrete grain and all. Very clever ! Noel.

Martin Kyte21/02/2021 18:25:47
2637 forum posts
46 photos

All of the above with the comment you could have a go with this stuff.


regards Martin

Pete.21/02/2021 18:34:52
764 forum posts
215 photos

You could try an air needle descaler with the rods rounded at the tips.

Stephen Millward21/02/2021 18:58:39
23 forum posts

Let it go rusty, then soak it citric acid - which should result in mild steel taking on a grey pitted appearance.

Pete.21/02/2021 19:37:10
764 forum posts
215 photos

To colour it after adding some texture, you could use cold blackening solution, on items too big to submerge, it actually works very well if brushed on in a flooding type of manner, you'd need to hold it over a plastic tray or something.

It would probably looks better as it ages also.

peter smith 521/02/2021 20:48:29
89 forum posts

To make a flat steel surface look as if it has been hand scraped use an electric sander - the type that is rectangular not round - with Emery or glass paper. I did the sides of my GHT bending rolls in the late 70’s and convinced everybody that I had hand scraped the effect.


Dave Wootton22/02/2021 09:22:21
230 forum posts
56 photos


As mentioned above steel shotblasting gives a good representation, At one time I worked for someone fabricating replica vintage/ veteran car parts and we had them blasted with steel shot ,it's quite hard to find places that used it, I found a marine company that did it as a favour and a donation to the tea fund. You must carefully mask any threads or bearing seats before blasting, It's a very convincing effect. Normal sandblasting didn't have as convincing an effect, but works for replicating forgings quite nicely.


I think theres a scrap water pump body somewhere ( see above re masking bearing seats and threads!) if I can find it i'll post a picture.

As an aside to give a cast finish on welded aluminium casting repairs, laying old fashioned sandpaper over the area and lightly tapping blends it in nicely, Technique beloved of naughty people who change crankcase numbers to make them into something more desirable, eg Triumph 6T into T120R. we were asked to do it all the time- but didn't.

Craig Brown 222/02/2021 10:09:54
51 forum posts
14 photos

Thanks all for the tips. I do know someone who does some agricultural sandblasting which might work to blend everything in and give it a bit of texture but that would obviously leave it a light grey.

I had thought of going down the route of submerging them in brine to let them go rusty in order to give them a bit of texture and then treat them to remove the rust. I do believe I have used a rust treatment before that turned the steel black as Neil described.

I do have a needle descaler which i might try out also for some texture.

Finally I could try polishing them with Zebrite and see how that comes out.

Thanks all for the ideas


Georgineer22/02/2021 14:06:34
525 forum posts
32 photos
Posted by Rik Shaw on 21/02/2021 17:11:30:

A bit of heavy duty sandblasting might do the trick if you can get it done locally.


Your local 'monumental mason' may be susceptible to a bit of persuasion. Ours is.

George B.

Nigel McBurney 122/02/2021 17:29:29
965 forum posts
3 photos

I knew a fellow stationary engine owner who set out to make a cover for the hot bulb of an 1890s Hornsby hot bulb oil engine,the original cast cover was long gone ,so he welded and fabricated a cover from 1/4 steel pate ,its box shaped about 8/10 inches cubed ,open sided with 3 flat pieces and one curved part. to get a cast iron effect on the steel he got a 3/8 twist drill bit broke off a piece off the sharp end,put in an electric drill and with drill running just let the drill bit rattle around on the steel,when it blunted ,a bit more was broken off the drill and the process restarted and he carried on until the cover looked like a casting,and he made a very good replica of an iron casting,he was very skilled and had lots of patience. I have found that when making replicas the welding has to be very good and then ground down to a smooth finish to hide all the welding marks,if not the welds will show through any grit or bead blast finish . Though thinking back to my childhood,the fires in all the bedrooms were all cast and had a fairly smooth finish,should you bite the bullet and go for the pattern /then casting route,ask the foundry to avoid any runner and riser marks on the top visible surface and not trim too closely with an angle grinder when the risers are cut off by the fettlers,they are usually on bonus pay. Another way to get a cast effect would be glue or bond a layer of very fine sand over the surface and then paint it with blackboard paint,or semi gloss black paint which I use on large engine flywheels.A matt or semi gloss does not sparkle on the spokes like black gloss paint does on 3 ft cast flywheels.

pgk pgk22/02/2021 19:26:52
2431 forum posts
293 photos

A salvage yard may have suitable mantles. . When we redecorated a large Sth London property and took down some boxing i found a beautiful marble and tiled fire surround lacking it's mantle. A few calls later and one chappy dropped by and later brought round a matching mantle from the same style of surround.

If the fire is going to be used I'd probablt shy away from an Iron mantle since I'm likely the first guy to grab hold to pull myself up and get burned.


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