Technical How to Hide a Visible Cast Iron Weld Repair

Obviously you can't grind or sand it - that would make it smooth.

One technique I saw was to smash up some carbide into small chunks. Spread they close together on the bench and pick them up with duct tape. Hold them over the smooth area and begin tapping he tape with a small hammer. The resulting irregular indentations come very close to an "as-cast" surface when painted.

I was also thinking a needle descaler would leave a mottled surface but I'm concerned it might be destructive since it is a thin section ~3/16 inches.

Sit there for a long time and dimple it with a pick hammer with a rounded point.

I have also seen using a die grinder with a carbide burr where you let it bounce around and let it gently cut dings out of the surface. In this case, you try to let the die grinder bounce around.

Anyone have any other Trade Secrets they'd like to reveal?

ANOTHER RELATED PROBLEM: how to make the new shiny surface match the unpainted as-cast? I know Evap-O-Rust will turn steel (and probably cast iron) dark gray.

 

A photo of the offending repair may ***ist. JW
Edit; the pic above has since been added.

 

I know this isn't exactly the same thing,but it may work here for you as well:
When I'm trying to disguise aluminum parts (heads,intakes,etc.) as cast iron,I contour any sharp machined edges or surfaces with a carbide bit til they look similar to a cast part,then,as you say,I carefully use a pneumatic needle scaler to add texture to the surface.
I also use a small ball peen hammer that has had a few random size "g****s" of mig weld applied to the face,and gently tap the surface for a more irregular surface texture.You can also use punches of various sizes,the pick end of a welding chipping hammer,etc.
To get the surface to quickly oxidize to hide things even more,sandblast the area of possible,then mist that fresh,white metal after blasting with some salt water out of a spray bottle,and leave it for a few days.If it's a part you can leave outside for a week or two,that works ok too,then just wipe the entire part with Gibbs or WD-40 to prevent the oxidation from going any further.
Even if you just spray freshly blasted steel with Gibbs it seems to give kind of a dark colour to it.

Hope some of this was helpful.

Scott


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Thanks Scott!

I like the MIG spall on the hammer face and the weathering chemicals.

While a it of a cheat, "dimpling" high-build primer would be so easy but I really don't want to go that route.

Also debating whether to Glyptal the inside surfaces too.

 

Use a needle descaler to make it almost impossible to pick

 

Needle gun. You can control how hard you hit it.

 

Just paint it. HRP

 

The needle scaler approach was shown to me about 40 years ago.
The old guy that rebuilt the wood products machinery where I worked had to repair old broken castings that were no longer being made. If it was a hidden part he usually didn't get that fussy but on parts that were visible he'd make them look like new.
I've tried it a few times, definately takes a practiced hand. The bigger the needle the better and he showed me how to use only half of the needles in the holder especially when trying to replicate an original texture of the casting.

 

All of those ideas mentioned will work for sure. I would still smooth out the weld first with a high speed die grinder or Emory cartridge. If you are going to paint the head you can spray a couple of heavy coats and after a few minutes take a small co**** nap house paint roller ad dap the area to match the casting .


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I think it's a recommended step in repairing cast iron to "peen" the weld to reduce stress. I expect that the added bonus of hiding the weld is incidental.

 

Yea you only hide it if you are planning on tricking someone into thinking it is a virgin.

By the way cast when welded properly gets the **** peened out of it while it is still cooling. I like to use a needle chipper but a chip hammer will do in a pinch.

 

Another vote for the needle gun.
Cheap at Harbor Freight & works well

 

Is this a show car? Just paint it who will care?

 

Grind to shape and use some of the grindings in the paint.

 

This one.

 

This worked for me on an aluminum intake:
1) Blend the surface with the surrounding area with a die grinder or Dremel.
2) Put a piece of course sandpaper (rough side against the metal) where you want to roughen the surface.
3) Pound on it with the flat face of a ball peen hammer.

 

Some good ideas here..

 

Grind it then sandblast.

 

If you want it to be perfect, level it with a grinder or die grinder, then have it shot blasted. That's how the factory finished it.

 

Descaler or needle gun