Surface Welding Symbol – How To Read And Apply Metal Buildup Specs
A surface welding symbol indicates that metal should be deposited onto a base part to build up dimensions or provide a wear-resistant coating. It is represented by two side-by-side half-circles placed on the reference line, typically specifying the thickness of the weld deposit to the left of the symbol.
This symbol is essential for hardfacing or restoring worn parts, ensuring the welder knows exactly how much material to add without joining two separate pieces together.
Staring at a complex welding blueprint can feel like trying to decipher an ancient language. You might be comfortable with fillet welds or groove welds, but then you see those two little “humps” sitting on the reference line. When you encounter a surface welding symbol on a technical drawing, it is a signal that the job isn’t about joining two parts, but rather enhancing one.
I promise that by the end of this guide, you will feel confident identifying this symbol and knowing exactly what to do when it appears on your workbench. We are going to break down the anatomy of the symbol, explain the dimensions involved, and look at the real-world workshop scenarios where this technique is a lifesaver.
We will cover everything from hardfacing a tractor bucket to restoring a worn-down shaft in your garage. Understanding these specifications is a major step in moving from a hobbyist to a truly proficient metalworker who can handle any professional-grade project that comes through the door.
Understanding the Exact Requirements of a Surface Welding Symbol
In the world of AWS (American Welding Society) standards, most symbols tell you how to stick two pieces of metal together. The surface welding symbol is the exception to that rule because it focuses on a single surface. It consists of two side-by-side semicircles that resemble the letter “C” turned on its side, resting on the reference line.
This symbol indicates that a layer of weld metal needs to be applied to the surface of the base metal. This process is often called “surfacing” or “cladding.” Unlike a fillet weld that fills a corner, this weld sits on top of a flat or curved face to change its properties or physical size.
When you see this on a print, the arrow will point directly to the surface that needs the treatment. Because you are only working on one side of a single piece of metal, the symbol is almost always placed on the arrow side of the reference line. You rarely see it on the “other side” because that would imply welding through the part.
The Purpose of Surfacing in the Workshop
Why would we spend time and expensive rod or wire just to “paint” metal onto a surface? There are two primary reasons: restoration and protection. If a part has worn down over years of friction, surfacing allows us to build it back up to its original factory dimensions.
The second reason is hardfacing. This is where we apply a layer of very hard, wear-resistant alloy over a softer, tougher base metal. It is a cost-effective way to make tools like plow shares, excavator teeth, or even custom shop jigs last ten times longer than they would otherwise.
In some specialized cases, we use surfacing for “buttering.” This is when we apply a layer of compatible metal to a surface before joining it to a different type of metal. It acts as a metallurgical bridge that prevents cracking during the final assembly weld.
Anatomy of the Surfacing Specification
To read a surface welding symbol correctly, you have to look at the numbers surrounding those two semicircles. The most important number is usually located to the left of the symbol. This number indicates the minimum thickness of the weld deposit that you need to achieve.
If the print says “1/8” to the left of the humps, you need to ensure that after you have cleaned up the weld, you have at least an eighth of an inch of new material. If no size is specified, it usually means you should follow the general notes on the drawing or build it up to the original finished dimension.
The symbol can also include information about the extent of the welding. If the entire surface needs to be covered, the symbol might stand alone. However, if only a specific area needs buildup, the drawing will use dimension lines to show the exact boundaries of the weld zone.
Arrow Placement and Direction
The arrow of the welding symbol points to the specific surface where the buildup is required. If the buildup needs to follow a specific direction—perhaps for better wear resistance or grain structure—that direction will be noted in the tail of the symbol. You might see a note like “Parallel to long axis.”
In most DIY and repair scenarios, the direction is less critical than the coverage. However, in industrial applications, the “lay” of the weld beads can affect how material slides over the surface. Always check the tail for these specific instructions before you strike your first arc.
If the surfacing is intended to cover multiple layers, the symbol might be stacked or have a note indicating the number of passes. This is common in heavy equipment repair where a single pass isn’t enough to reach the required thickness for the repair.
How to Execute a Surface Weld in Your Shop
Once you have identified the surface welding symbol and know your thickness requirements, it is time to prep the metal. Surfacing requires a very clean base. Any rust, oil, or old paint will get trapped under the buildup, leading to porosity and eventual peeling or “spalling” of the new layer.
Start by using a 4.5-inch angle grinder with a flap disc or a wire wheel to get the metal down to a bright, shiny finish. If you are hardfacing, you might even need to preheat the base metal to prevent the hard, brittle weld metal from cracking as it cools down too quickly.
When you start welding, use a technique called “stringer beads” or a slight weave. You want each bead to overlap the previous one by about 50%. This ensures a flat, uniform surface rather than a series of disconnected ridges that are hard to grind down later.
Choosing the Right Consumables
The material you use depends entirely on the goal of the surfacing. If you are just building up a worn-out hinge pin hole, a standard E7018 stick electrode or ER70S-6 MIG wire will work perfectly. These match the strength of mild steel and are easy to machine afterward.
For hardfacing, you need specialized rods like “Stoody” or similar brands. these contain high amounts of chromium or carbides. Be aware that hardface weld metal is often non-machinable. This means you can’t use a drill or a lathe on it; you can only shape it with a grinder.
If you are a DIYer working on a lawnmower deck or a garden tool, a simple “wear-resistant” rod can be a great investment. It prevents the thin steel from wearing through in high-abrasion areas. Always wear a respirator when using these specialty rods, as they can produce hazardous fumes.
Common Challenges and Pro Tips for Success
One of the biggest mistakes when following a surface welding symbol is over-welding. It is tempting to put down a massive amount of metal “just to be safe.” However, too much heat can warp the base metal, especially on thinner plates or shafts.
To avoid warping, use a “staggered” welding pattern. Weld a small section, move to a different area, and let the first section cool. This manages the heat-affected zone (HAZ) and keeps your part straight. If you are working on a shaft, rotate it constantly to keep the heat input symmetrical.
Another tip is to always check your height with a depth gauge or a straight edge. It is much easier to add another pass while the metal is still warm than it is to realize you are 1/16th of an inch short after the part has cooled and you’ve already put your gear away.
Managing Slag and Cleanup
If you are using Stick (SMAW) or Flux-Core (FCAW) for surfacing, slag management is vital. Because you are overlapping beads, slag can easily get trapped in the “valleys” between the beads. This creates slag inclusions, which are weak spots in your buildup.
Use a chipping hammer and a stiff wire brush between every single pass. I often keep a needle scaler handy for larger surfacing jobs; it makes quick work of removing slag from the tight crevices between weld beads. Cleanliness is the difference between a repair that lasts years and one that fails in weeks.
Once the welding is done, you may need to grind the surface flat. If the part needs to be a specific size, leave yourself about 1/32 of an inch of “extra” weld metal to grind away. This allows you to reach a perfectly smooth finish without dipping below the required dimension.
Essential Tools for Surface Welding Projects
To properly follow a surface welding symbol, you need more than just a welder. You need the tools to measure and prep the work. Here is a quick list of what I keep in my shop for these specific tasks:
- Angle Grinder: Essential for both prep work and finishing. I prefer a 4.5-inch model for maneuverability.
- Caliper or Depth Gauge: To verify that you have met the thickness requirements specified on the print.
- Wire Brush/Needle Scaler: For removing slag between overlapping beads to ensure a solid buildup.
- Preheat Torch: A simple propane or oxy-acetylene torch to take the chill off thick sections or high-carbon steels.
- Temperature Crayons (Tempilstik): To ensure you’ve reached the correct preheat temperature for hardfacing materials.
Having these tools ready prevents “project creep” where you have to stop every ten minutes to find something. Surfacing is a rhythmic process; once you get into the flow of laying beads, you want to keep going until the layer is complete.
Safety Considerations for Surfacing Operations
Surfacing often involves long periods of “arc-on” time compared to simple tacking or joining. This means your equipment—and your body—will get much hotter. Ensure your welding gloves are in good condition and that you are wearing a leather welding apron to protect against the sustained heat radiation.
Ventilation is also critical. Many hardfacing electrodes contain manganese or chromium. Breathing these fumes is dangerous. Always use a fume extractor or work in a very well-ventilated area with a P100 respirator under your welding hood.
Finally, be mindful of the “fire watch.” Because surfacing puts a lot of heat into a part, that part will stay hot for a very long time. Never leave a freshly surfaced part near flammable materials, and stay in your shop for at least 30 minutes after the job is done to ensure nothing is smoldering.
Frequently Asked Questions About Surface Welding Symbols
What does a surface welding symbol look like?
The symbol looks like two side-by-side semicircles or “humps” that sit on top of the reference line. The flat side of the semicircles rests on the line, and the curves point upward (if on the arrow side). It is distinct from the single-hump “back” or “backing” weld symbol.
Where is the thickness of the weld shown?
The required thickness of the weld deposit is placed to the immediate left of the surfacing symbol. If the drawing requires a 1/4-inch buildup, the number “1/4” will be written right next to those two semicircles on the reference line.
Can a surface welding symbol be used for pipes?
Yes, it is very common on pipes and shafts. When used on a cylindrical part, the symbol indicates that the entire circumference of the part should be built up unless a specific length or area is otherwise noted on the drawing.
Is surfacing the same as “cladding”?
In many contexts, yes. Cladding is a type of surfacing where a layer of different metal (like stainless steel) is applied over a base metal (like carbon steel) to provide corrosion resistance. The surfacing symbol is used to specify this on technical prints.
Do I need to grind a surface weld?
That depends on the instructions. If the symbol is accompanied by a contour symbol (a flat line above the humps) and a finish mark (like “G” for grinding), then you must grind it. If no finish mark is present, the weld can often be left in its “as-welded” state.
Final Thoughts on Mastering the Surface Weld
Mastering the surface welding symbol is a rite of passage for any serious DIYer or metalworker. It moves you beyond simply “fixing” things and into the realm of “improving” them. Whether you are saving a piece of expensive equipment from the scrap heap or making a custom tool more durable, surfacing is a powerful skill to have in your pocket.
Remember to always read the left side of the symbol for your thickness, check the tail for specific material or direction notes, and keep your work area clean. Take your time with the overlapping beads, and don’t be afraid to use your grinder to clean up the edges for a professional look.
Now that you know what those “double humps” mean, you can approach your next project with the confidence of a pro. Grab some scrap plate, practice your bead overlaps, and see just how much material you can accurately add to a surface. Happy welding, and stay safe in the shop!
