Puddle Weld Symbol Explained: What It Means, How to Read It, and When to Use It

Table of Contents

Introduction to the Puddle Weld Symbol

If you’ve ever flipped through a steel deck drawing and spotted a small circle or rectangle floating over a joist, you’ve seen what crews call a “puddle weld.” The term gets passed around job sites so naturally that most people assume it’s official AWS terminology. It isn’t — and understanding what the drawing is really calling for is the difference between a connection that passes inspection and one that gets flagged.

What a Puddle Weld Actually Is

In plain language, a puddle weld is a weld made through a hole in one piece of metal to fuse it to the piece beneath — usually an arc spot weld or plug weld attaching steel deck to beams, joists, and angle members. The welder punches or pre-drills a hole, or the deck comes with one, then fills it with weld metal so the deck fuses to the support below.

In practice, “puddle weld” is a field word, not a spec word — it simply describes the molten puddle sitting in a hole. When an engineer puts a symbol on a drawing, they use the standardized language of the American Welding Society.

Why It’s a Nonstandard Term

Here’s where the confusion starts. AWS A3.0, Standard Welding Terms and Definitions, explicitly recognizes “puddle weld” as a nonstandard term — a colloquialism for an arc spot weld or a plug weld. It’s tolerated, but it isn’t the defined term, and it doesn’t appear as a defined weld symbol name in AWS A2.4:2020, Standard Symbols for Welding, Brazing, Nondestructive Examination, and Thermal Cutting, the authoritative standard for welding symbols.

Quick Note: When a spec says “puddle weld,” read it as either an arc spot weld or a plug weld and confirm which one with the symbol, detail, and weld size callouts. The ANSI/AWS A2.4 symbol — not the spoken term — is the contract document.

The A2.4:2020 symbol set gives you the real vocabulary: spot, plug, and slot weld symbols, plus the field weld flag showing whether the connection is made in the shop or on site. Puddle welds on steel deck are almost always field welds, which is why misreading the symbol gets expensive fast.

Arc Spot Weld, Plug Weld, or Something Else?

The distinction matters because each weld type has its own geometry, procedure, and acceptance criteria:

Arc spot weld (flow drill or through-hole): Weld metal is deposited through a hole (or onto a single surface) to join two overlapping pieces. On steel deck, this is the classic “button” weld.
Plug weld: A hole in one member is filled with weld metal to fuse it to the underlying member — closely related, and the two terms are often used interchangeably in the field.
Seam weld: A continuous or intermittent weld along a joint, sometimes called out on deck drawings alongside puddle welds.

References like STRUCTURE magazine’s primer on arc spot welding for steel deck show how these connections are detailed, sized, and inspected — and how the symbol on the drawing drives all of it.

Why Reading the Symbol Correctly Matters

Steel deck connections carry load. A missing puddle weld, a weld in the wrong location, or an undersized button can compromise diaphragm action — the deck’s ability to transfer lateral loads to the frame. Inspectors check these welds against AWS D1.3, Structural Welding Code — Sheet Steel, which governs the thinner materials deck is made from.

Misreading a symbol also signals a bigger skill gap. If you’re still building fluency, our complete welding practice guide and guide to good and bad MIG welds build the visual judgment inspection demands — a puddle weld with excessive undercut or poor fusion looks wrong to a trained eye, symbol or not.

What This Article Covers

We’ll break down the AWS symbol basics behind puddle welds, compare puddle vs. plug vs. spot weld side by side, walk through symbols on real deck drawings, and cover applications, procedures, inspection, common mistakes, and shop-floor tips. By the end, you’ll translate what the field calls a “puddle weld” into the exact weld the engineer specified — no guesswork.

Short note: Terminology confusion isn’t unique to puddle welds — overlapping welding and overlap defects are routinely mixed up in conversation too. Learning the standard vocabulary early saves rework later.

Understanding AWS Welding Symbol Basics

Before anyone can read a puddle weld symbol on a steel deck drawing, they need to speak the underlying language. That language is defined by AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination — the document that governs how welds are called out on drawings across North America and beyond.

Weld Symbol vs. Welding Symbol: The Distinction That Trips People Up

A2.4 draws an important line between two similar-sounding terms. A weld symbol is the glyph itself — the arc, circle, or rectangle — indicating the weld type, such as a fillet, plug, slot, or puddle (arc spot) weld. A welding symbol is the entire assembly: arrow, reference line, weld symbol(s), dimensions, tail, and supplementary symbols.

In practice, a single welding symbol carries far more than the shape at its center. It tells the welder what weld to make, on which side of the joint, how big it is, and — when the tail is used — how to make it. Think of the weld symbol as a word, the welding symbol as the full sentence.

The Reference Line and the Arrow

Every welding symbol starts with a horizontal reference line and an arrow pointing to the joint. The arrow is directional: it identifies where the weld goes, while symbols along the line describe what goes there.

This is where the arrow side / other side convention comes in — the single most useful habit when reading drawings:

Arrow side — the side of the joint the arrow points to. Symbols below the reference line apply to the arrow side.
Other side — the side opposite the arrow. Symbols above the reference line apply to the other side.

A symbol below the line, above it, or both — position decides placement. On a deck drawing, a puddle weld symbol under the reference line belongs on the side the arrow touches; flip it above and you’re welding the opposite face.

Quick Note: If the arrow points at a sheet of deck and the puddle weld symbol sits below the reference line, weld from the side the arrow touches. Getting arrow side and other side backwards is one of the most common blueprint-reading errors on the job.

Dimensions, Extent, and Supplementary Symbols

Around the weld symbol, A2.4 places the numbers that matter: weld size or diameter, pitch (spacing), and quantity. For intermittent or spaced welds, extent notation tells the welder where the pattern starts and stops. Supplementary symbols — the field-weld flag, the weld-all-around circle, and finish symbols — add context without clutter.

For puddle welds, you’ll usually see a required diameter and a pitch or “each location” count rather than a length. To see how those settings translate to the arc, our guide to how to use a wire welder walks through the GMAW fundamentals deck welders rely on.

The Tail: Process, Procedure, and Notes

At the far end of the reference line, a fork-shaped tail may appear. Inside it, the drafter can specify the process (like “ARC” or “FCAW”), a reference to the applicable WPS, or a brief note. Per A2.4 §6.12, the tail may be omitted when no such information is needed — so its absence is normal, not an omission. When present, it may point to a procedure governing everything from polarity to preheat.

A tail calling out a process sends you to that procedure’s requirements — our breakdowns of polarity for flux core welding and TIG welding polarity show how much detail sits behind a short designation.

Why the Basics Matter for Puddle Welds

Puddle welds (arc spot welds in AWS terminology) live inside this same framework — they aren’t a separate system. The symbol tells you type, location, size, and extent using the same reference line mechanics as every other weld. Master the arrow side/other side rule, read the tail, and check supplementary symbols, and a steel deck drawing becomes straightforward. Building these skills from scratch? welding practice fundamentals and an understanding of AWS A30 welding terms and definitions give you the vocabulary that makes A2.4 symbols click.

Note: The 2020 revision of A2.4 introduced notable symbol changes, so pre- and post-2020 drawings can look different. ANSI has a useful summary of the AWS A2.4:2020 symbol changes worth reviewing if you work with mixed-vintage drawings.

Puddle Weld vs Plug Weld vs Spot Weld: Key Differences

If you have spent time around steel deck drawings, you have seen “puddle weld” written in a note while the symbol on the detail looks like something else entirely. These three terms get traded back and forth on jobsites, but they are not interchangeable. Each describes a different joint preparation, a different symbol under AWS A2.4, and a different acceptance standard.

What Each Joint Actually Does

A plug weld fills a hole. One member is punched or drilled, and weld metal fills that cavity until it fuses to the member below, creating a solid plug. A spot weld fuses two overlapping sheets at a single small point: resistance spot welding squeezes and heats the sheets from both sides, while an arc spot weld uses an arc to form the same localized nugget. A puddle weld, in field language, is the arc spot weld used to attach steel deck to beams and joists — the arc burns through the thin deck and pools on the structural member underneath, as covered in this arc spot welding primer from STRUCTURE magazine.

Quick Note: “Puddle weld” is a trade term, not an AWS term. Under AWS A2.4, the joint you are welding is symbolized as an arc spot weld — though older drawings sometimes still label it a plug weld.

The Symbols: Rectangle vs Circle

On the drawing, the difference is simple once you know where to look:

Plug weld — a rectangle on the reference line. Per AWS A2.4 §9, the callout carries the hole diameter, depth of fill, spacing, and number of welds. A rectangle with no hole diameter leaves the fabricator guessing.
Spot weld — a plain circle on the reference line. Several processes can produce one, so AWS A2.4 §11.1.3 requires a process designation in the tail, such as RSW for resistance spot welding — a convention laid out in this spot weld symbol reference.
Puddle weld — the circle, not the rectangle. No hole is punched in the deck, so a rectangle would be wrong. Deck drawings call for the arc spot weld symbol, usually with a note giving weld size and required number per location.

Placement matters too. A resistance spot weld symbol sits centered on the reference line with no side significance, because the joint is symmetrical. An arc spot weld symbol sits above or below the line, and that position indicates which member the weld is made from. The full welding symbol chart shows both conventions side by side.

Short Note: If the detail shows a circle but the callout lists hole diameter and depth of fill, stop and clarify with the engineer. Mixing the two conventions is a fast way to fabricate the wrong joint.

Hole Preparation Is the Real Difference

The symbol follows the physics. A plug weld requires a hole in one member — that cavity sets the weld’s size and load capacity, which is why diameter and fill depth are spelled out. An arc spot or puddle weld melts through the top sheet instead; punching thousands of holes through every panel would slow erection and weaken the deck for no benefit. That difference drives the work: plug welds need clean, correctly sized holes, often opened with a spot weld cutter bit, while puddle welds need disciplined welding practice — steady arc length and heat input so the arc punches through without blowing a crater.

Choosing the Right Callout

Use the rectangle when a hole exists and its dimensions control the joint. Use the circle — with the process in the tail — when the weld is a localized point made by an arc or by resistance. When a note says “puddle weld,” read it as an arc spot weld unless the detail shows a prepared hole. Getting this right at the drawing stage keeps polarity for flux core welding and wire welder settings matched to the process, prevents field arguments, and gives inspectors a clear standard to measure against — the difference between a sound weld and one you would reject on sight.

How to Read the Puddle Weld Symbol on Blueprints

For most welders, the hardest part of reading a blueprint isn’t seeing the symbol, but knowing what each piece tells you. When a puddle weld is specified for steel decking or sheet steel, it will almost always be called out using the arc spot weld symbol from the AWS A2.4:2020 standard. Learning to break this symbol down piece by piece helps you avoid costly errors and meet the exact requirements of your job.

The Basic Shape: Location Determines Side

The puddle weld is represented by a plain circle. This is the same base shape used for arc spot welds, and its placement on the reference line tells you which side of the joint it belongs to. If the circle sits below the reference line, the weld is made on the arrow side. If it sits above the line, the weld is made on the other side. This rule is outlined in AWS A2.4 §11.1.3, and it is the first thing to check before striking an arc.

If blueprint reading still feels shaky, it pays to brush up on the fundamentals first. Resources like our Welding Practice: The Complete Guide to Building Real Welding Skills can help solidify these skills before you tackle large structural drawings.

Quick Note: The circle alone does not mean “puddle weld” by name, but rather “arc spot weld”. The tail of the symbol is what specifies the process, such as GMAW, which is what most shops mean when they say “puddle weld” on metal decking.

Dimensions: Size, Pitch, and Quantity

With the location known, the next step is reading the numbers around the circle. These dimensions control the strength and spacing of your welds. For arc spot welds, the rules were updated in AWS A2.4:2020, so always read to current standards.

Weld size (diameter): Placed to the left of the circle. This is the diameter of the fused weld nugget, not the hole size.
Pitch: Placed to the right of the circle, representing center-to-center spacing between welds.
Number of spots: If only a set number of welds is required, the quantity appears in parentheses above or below the symbol, depending on the side.

On a typical steel deck callout, you might see “0.50” left and “12” right of a circle below the line. That means a 1/2″ diameter arc spot every 12 inches on the arrow side. If a strength value is required instead of a diameter, that information goes in the tail as a note, not to the left of the symbol.

The Tail: Process, Equipment, and Notes

The tail is where the “how” is specified. For puddle welds this matters, since the process must be called out for arc spot welds. Common entries include GMAW, FCAW, or GTAW, and each ties directly to your equipment. When running GMAW with a wire welder, for instance, the tail may reference the specific process to use.

The tail can also hold references to procedures, filler, or strength requirements. Shops running automated processes such as robotic submerged arc welding will see these notes clearly laid out. Keeping consumables in check, like your contact tips for GMAW, is just as important as reading the symbol correctly.

Short Note: Never assume the process. If the tail is blank for an arc spot, refer to the job specifications or the applicable code, such as AWS D1.3 for sheet steel.

Putting It All Together

To read a puddle weld callout with confidence, use this order: check side (above or below the line), read size left, read pitch right, check quantity in parentheses, then read the tail for the process and notes. For visual references, the Clause 5 spot weld chart is an excellent supplement to the AWS standard.

With practice, this becomes second nature. Whether you work in a small shop or a large-scale welding facility, taking the time to read these details correctly ensures your welds are safe, compliant, and built to last.

Applications: Steel Deck, Metal Decking, and Structural Framing

Most real-world uses of the “puddle weld symbol” appear on steel erection job sites. The most common application for an arc spot weld (also called a puddle weld) is attaching metal deck to its supporting framing — beams, joists, and trusses. That connection lets the deck act as a diaphragm, transferring lateral loads across the structure.

Unlike a true resistance spot weld, the arc spot weld uses an electric arc to melt through the thin sheet steel of the deck and fuse it to the heavier structural steel below. The result is a round, fused puddle, typically around 5/8 to 3/4 inch in diameter depending on the job specification. That is why the puddle weld symbol is so prevalent in metal decking layouts: it denotes a fast, economical, code-compliant way to secure the deck.

Quick Note: The puddle weld is not meant to replace full structural fillet welds for heavy load transfers. Its purpose is to secure the deck and enable diaphragm action, not to develop the full strength of the supporting member.

The Arc Spot Weld Process for Steel Deck

For welders working with metal decking, the arc spot weld is straightforward but still demands precision. Before striking an arc, proper welding practice and a safe environment — such as those outlined in welding facilities planning — are crucial. With that in mind, the process typically follows these steps:

Fit-up and positioning: The steel deck is placed over the supporting beam, joist, or truss with the correct bearing and side lap specified by the deck manufacturer.
Surface preparation: Heavy mill scale, paint, or debris is removed from the weld zone to prevent porosity or lack of fusion.
Arc initiation: Using a shielded metal arc (SMAW) setup, the welder strikes an arc and holds the electrode long enough to burn through the deck sheet, melting both the deck and the top flange below.
Puddle formation: As the metal melts, a puddle forms. The welder manipulates the electrode so the fused metal solidifies into a round weld at the specified visible diameter.
Inspection readiness: After cooling, the weld is visually checked for size, fusion, and visible defects before moving on.

To refine technique with other processes, resources such as how to use a wire welder help — though SMAW remains common for field decking because of its portability.

Electrode Types, Codes, and Specifications

Compliance with the correct governing code is one of the most important factors here. Arc spot welding of steel deck and sheet steel falls under AWS D1.3 (Structural Welding Code – Sheet Steel), not AWS D1.1. That distinction matters: prequalification allowances and acceptance criteria differ greatly between the two.

There is no single universal electrode for every job. In steel deck applications, common practice uses E6022 type electrodes, but the specific rod always depends on job specifications, base metal, and the approved Welding Procedure Specification (WPS). Since many arc spot welds for sheet steel are not prequalified under AWS D1.3, a WPS and Procedure Qualification Record (PQR) may be required.

Note: Always defer to the structural drawings, the deck manufacturer’s requirements, and the Engineer of Record before selecting an electrode. These override general recommendations in every case.

For clarity among inspectors and fabricators, this table breaks down the key parameters of the most common field application:

Parameter	Typical Value/Reference
Governing Code	AWS D1.3 (Structural Welding Code – Sheet Steel)
Common Process	SMAW Arc Spot Weld (Puddle Weld)
Visible Diameter	~5/8 – 3/4 inch (commonly 3/4 inch)
Electrode Types	E6022 type electrodes (per job specs)
Documentation	WPS/PQR may be required (not always prequalified)

From securing steel deck to beams, joists, and trusses, the puddle weld symbol represents one of the most time-tested connections in structural framing. By following AWS A3.0 terminology and AWS D1.3 requirements, fabricators and welders keep these connections safe and efficient for years to come.

Welding Procedures, Quality, and Inspection

Ensuring that a puddle weld symbol on a drawing translates into a sound joint requires disciplined procedures, qualified personnel, and consistent inspection. For arc spot welds used on steel deck and similar applications, quality is governed by process control, welder qualification, and acceptance criteria aligned with industry standards. This section outlines key considerations for welding procedures, quality assurance, and inspection practices.

Welding Procedures and Qualification (WPS/PQR)

A Welding Procedure Specification (WPS) documents how welding will be performed, while a Procedure Qualification Record (PQR) provides test data demonstrating that the procedure produces acceptable results. For arc spot welds, qualification requirements are not always prequalified and typically follow AWS D1.3. Contractors are responsible for developing and qualifying procedures as needed.

When specifying or executing work governed by the AWS A2.4 standard for welding symbols, it is critical that the WPS matches the symbol intent. Key parameters include base metals, thickness, electrode/wire type, shielding (if any), current/polarity, travel speed, and arc time. For operators working with semi-automatic processes, understanding polarity for flux core welding and related process choices helps ensure consistent energy input.

Quick Note: Research and industry guidance indicate proper arc spot welds typically require 3–6 seconds of arc time. Quality varies with equipment, settings, and technique.

Proper procedure development also considers the work environment. Setting up effective welding facilities supports consistent results and safe operations.

Welder Qualification

Welders must be qualified to perform the process and joint type used. Qualification tests confirm that the individual can produce sound welds under the qualified procedure. Records should be maintained and available for inspection. Training and practice are essential: welding practice builds the muscle memory and control needed for consistent puddle formation.

Safety is integral to qualification and production. Proper protective eyewear for welding protects the welder and supports quality by allowing clear observation of the puddle.

Visual Inspection and Acceptance Criteria

Visual inspection is the primary method for evaluating arc spot welds. Inspectors check for proper diameter, fusion, penetration into the supporting member, and puddle engagement around the perimeter. Common concerns include burn-through and cold lap. Acceptance criteria are typically defined by project specifications and referenced codes such as AWS D1.3.

Key visual indicators of quality include a uniform, well-formed puddle that fully engages the supporting steel, adequate diameter relative to the symbol, and no visible cracks or porosity. Inspectors should also verify that the weld does not exhibit overlap welding defects or other discontinuities. For reference on identifying sound welds, see good and bad MIG welds.

Arc Time, Technique, and Process Control

Consistent arc time is critical for puddle welds. As noted, industry guidance points to 3–6 seconds per weld depending on material thickness, equipment, and technique. Too short an arc time can result in insufficient fusion; too long can cause burn-through or excessive heat input. Maintaining proper contact tip condition and equipment setup is essential—refer to contact tip welding best practices.

Operators should follow documented procedures and monitor parameters continuously. For those using wire processes, understanding equipment operation is important: how to use a wire welder covers setup fundamentals. Process choices may vary, but the goal is consistent energy delivery to form a proper puddle.

Quality Assurance and Common Defects

A robust quality program includes procedure control, welder qualification, inspection, and documentation. Common defects to watch for include lack of fusion, cold lap, burn-through, porosity, and undersized welds. Addressing these requires root-cause analysis and corrective action, such as adjusting parameters or technique.

Short Note: For projects governed by AWS standards, inspectors should reference the latest AWS A2.4 and related code documents for symbol interpretation and acceptance. Clause 5’s weld symbol chart is also a useful quick reference.

Ultimately, achieving quality with puddle welds hinges on aligning the symbol, procedure, and inspection. Proper fusion and perimeter engagement are non-negotiable for structural integrity, particularly in steel deck applications where these welds transfer loads.

Common Mistakes When Reading or Specifying Puddle Weld Symbols

Most puddle weld problems start on the drawing, not at the torch. A symbol that looks obvious to the detailer can be read three ways in the field — and by the time an inspector catches it, the deck is attached.

1. Confusing the Plug Weld Rectangle with the Spot/Puddle Circle

This is the single most common mix-up. A plug weld symbol is a rectangle, implying a pre-punched or pre-drilled hole in one member that you fill with weld metal. A spot weld symbol is a circle, and for arc spot (puddle) welds on steel deck there is typically no hole — the arc burns through the top sheet into the support below.

Read a rectangle as a circle and you’ll wait for holes that were never drilled; read a circle as a rectangle and you’ll try to fill a hole that isn’t there. For a side-by-side breakdown, see our guide to spot weld cutter bits and spot weld basics, and the Clause5 spot weld symbol reference.

2. Leaving the Process Out of the Tail

Writing “puddle weld” tells the fabricator little about how to make it. AWS A2.4 requires the welding process in the symbol’s tail for spot welds — RSW for resistance spot welding, GTAW for an arc spot weld made with a portable arc gun, and GMAW for a semiautomatic arc spot. Omit it and the shop guesses, producing inconsistent nuggets and failed quality checks. The ANSI overview of changes in AWS A2.4-2020 explains how tails and process designations are handled, and the full document is available through the ANSI webstore listing for AWS A2.4.

Quick Note: If the tail says GTAW, the operator is using an arc spot gun with a tungsten electrode — polarity and arc stability directly affect penetration, so review TIG welding polarity: DCEN, DCEP, and AC explained before striking an arc. If the tail says GMAW, wire feed consistency and contact condition matter just as much; see contact tip welding: selection, maintenance, wear, and troubleshooting.

3. Mixing Up Arrow Side and Other Side

Side significance depends on the weld type. Resistance spot welds (RSW) are drawn as a circle centered on the reference line — no side significance. Arc spot and puddle welds differ: arrow-side means weld from the near face; other-side, from the far face. AWS A2.4 spells this out. Reverse it and you weld from the top instead of underneath — a guaranteed inspection rejection.

4. Using the Wrong Code

AWS D1.1 and AWS D1.3 are not interchangeable. D1.1 covers structural steel in general, while AWS D1.3 is the Structural Welding Code — Sheet Steel, governing the thinner materials and spot/seam criteria deck assemblies fall under. Pulling acceptance criteria from the wrong code sends inspectors chasing discontinuities the applicable standard never intended to flag — or overlooking ones it does. Teams shifting between sheet and structural work should keep welding practice fundamentals fresh.

5. Wrong Diameter, Pitch, or Quantity

The required weld size — diameter for puddle and plug welds, weld-spot size for RSW — plus pitch (center-to-center spacing) and quantity must appear in or near the symbol. Omitting pitch is common when a detailer assumes “as required,” but inspectors don’t assume. Confirm the notation order against a welding symbol chart and cross-check it with STRUCTURE magazine’s primer on arc spot welding steel deck.

Short Note: Dimension lines put diameter before pitch, separated by a space — for example, ¾ 2 reads “¾-inch diameter weld at 2-inch pitch.” Reverse the order and you’ve just called for 2-inch welds spaced ¾ inch apart, which will burn through the deck.

A Five-Point Self-Check Before Release

Shape: circle for spot/puddle, rectangle for plug — does the symbol match the intent?
Tail: is the process (RSW, GTAW, or GMAW) stated?
Side: is the symbol on the correct side relative to where the welder actually stands?
Code: is D1.1 or D1.3 cited correctly for the material?
Dimensions: are diameter, pitch, and quantity all present and in the right order?

Catch those five before the drawing leaves the office and you’ll eliminate most puddle weld rework before it starts. For a visual gut-check, compare finished welds against good and bad MIG welds.

Practical Tips for Fabricators and Welders

Reading a puddle weld symbol correctly is one thing. Turning it into a sound, code-compliant weld on the shop floor is another. These tips come from the kinds of details that trip up even experienced crews, and they’ll save you rework, failed inspections, and awkward phone calls to the engineer.

Verify Which Standard the Drawing References

Before you strike an arc, confirm whether the drawing follows AWS A2.4 or ISO 2553. The two systems look similar but handle placement differently. Under AWS A2.4, the side of the joint is determined by the symbol’s position relative to the reference line—above the line means the arrow side, below means the other side. ISO 2553 flips some of that logic and adds its own conventions, so a symbol read with the wrong rulebook can end up on the wrong face entirely. When in doubt, check the drawing’s general notes or title block for the governing standard.

Quick Note: A symbol that “looks right” isn’t proof. If the drawing cites AWS A2.4 but your crew is trained on ISO 2553, pause and verify placement before welding.

Confirm the Governing Code

For steel deck and metal decking, arc spot welds (the formal name for what most people call puddle welds) are usually governed by AWS D1.3, Structural Welding Code—Sheet Steel. That code sets minimum effective weld sizes, spacing limits, and quality criteria that a general drawing note won’t repeat. Always review the project specifications for electrode type and diameter, required spacing, and inspection requirements—D1.3 compliance often depends on details buried in the spec, not the symbol itself.

Check the WPS Before You Start

Every puddle weld should trace back to a qualified Welding Procedure Specification. The WPS tells you the process, filler metal, amperage, and travel technique—the variables a symbol can’t capture. If you’re running semi-automatic GMAW, basics like wire feed, gun angle, and consumable condition matter as much as the symbol. Our guide to contact tip selection and maintenance is a good reminder that small equipment details drive weld quality. For flux-cored work, polarity choices are just as critical—see our breakdown of DCEN vs DCEP for flux core before you dial in settings.

Make Sure the Symbol Has Every Element

A complete puddle weld callout includes several parts. Missing one is a common reason for rejected submittals.

Circle symbol on the reference line—identifies an arc spot (puddle) weld.
Size to the left of the symbol—the required weld diameter.
Spacing to the right if the welds are intermittent—pitch and count.
Process in the tail—for example, GMAW or FCAW.
Correct placement—arrow side or other side per the governing standard.

If any element is vague, ask before welding. Good and bad MIG weld quality often traces back to ambiguous instructions interpreted differently by two shifts.

Coordinate With the Engineer

Field conditions rarely match the drawing. Warped deck, misaligned framing, or gaps beyond tolerance all affect whether a puddle weld meets code. A quick RFI to the engineer is cheaper than cutting out failed welds. Document any deviation in writing—inspectors want to see that the decision was deliberate, not improvised.

Safety and Field Best Practices

Arc spot welding on decking throws sparks and molten metal downward and outward, so protect yourself and anyone below. Wear proper eye protection—our guide on welding eyewear covers lens shades for the process. Keep a fire watch when welding over combustible material, and never weld over trapped moisture or sealant without checking the spec. Don’t overlook setup either: a well-planned welding facility layout reduces hazards before they start. In the field, verify your ground path, keep leads and connections sound, and re-check fit-up before each pass. Consistent technique from a qualified practice routine is what keeps puddle welds reliable job after job.

Short Note: Keep a marked-up set of drawings on the deck showing every puddle weld location. It makes inspection faster and catches missed welds before the deck gets covered.

Comparisons and Industry Context

The puddle weld symbol doesn’t exist in a vacuum. It sits inside a larger family of spot-type welds, and understanding where it fits helps you avoid one of the most common mix-ups on the shop floor: confusing resistance spot welding (RSW) with arc spot welding. They may share a name, but they are different processes, and their symbols carry different meaning.

Resistance Spot Welding vs. Arc Spot Welding

Resistance spot welding joins overlapping sheets using pressure plus electrical current — no filler metal, no arc. The current passes through copper electrodes that clamp the metal together, and the heat generated by resistance fuses the sheets at a single point. Because there’s no arc and no filler, the process lives mostly in high-volume manufacturing: automotive bodies, appliance panels, and similar thin-sheet work.

Arc spot welding, by contrast, uses an arc process with filler metal to melt through an outer layer into the base plate below. This is the process behind what deckers call a puddle weld.

Those technical differences show up directly in the symbol:

RSW symbol: centered on the reference line, with no side significance — there’s no arrow-side vs. other-side distinction because the weld inherently joins two stacked sheets.
Arc spot symbol: placed above or below the reference line, carrying side significance just like a fillet or groove weld.

That side-significance rule is the single biggest source of confusion. If a detailer uses the resistance spot symbol but the fabricator interprets it as an arc spot callout, the wrong process gets bid, the wrong equipment gets set up, and inspections fail. You can read more about how process choices ripple through equipment and settings in our guide to polarity for flux core welding: DCEN vs DCEP.

Quick Note: The AWS A2.4:2020 standard is the governing reference for these symbol conventions. When in doubt, it decides the argument.

Why “Puddle Weld” Persists in the Decking Trade

Walk onto a metal decking crew and you’ll hear “puddle weld” all day long. The term is deeply rooted in that trade — it describes the little molten pool that forms and collapses as the arc burns through the deck sheet into the structural member below. It’s vivid, practical, and has been used for decades.

But engineering drawings are shifting. Increasingly, they call the same joint an arc spot weld and annotate it with the proper spot weld symbol per AWS A2.4. This isn’t nitpicking — it’s precision. As STRUCTURE magazine notes, arc spot welds on steel deck are a well-defined structural connection with their own quality and inspection expectations.

The terminology gap is real, and it creates friction between four parties:

Engineers who specify by standard symbol and code language.
Detailers who translate intent into fabrication drawings.
Fabricators who bid and build to those drawings.
Inspectors who verify against the specified standard.

When the decking crew says “puddle” and the drawing says “arc spot,” a translator is needed. A shared vocabulary — and a shared understanding of the symbol — is what prevents a misinterpreted callout from becoming a structural problem. Strong welding practice starts with reading the drawing correctly before the first arc is struck.

Where This Fits in the Wider Welding World

Spot-type welds are just one branch of a broad family. Compare them with the automation driving heavy fabrication, like robotic submerged arc welding, or with the precision of a dedicated handheld process such as a permanent jewelry welder. Different process, different symbol, different inspection criteria — but the same underlying logic: the symbol you draw communicates exactly what you mean, to anyone who can read it.

Note: Terminology drift is normal in a trade that spans decades. What matters is that the standard remains the shared reference point. Learn the symbols, respect the side-significance rules, and you’ll bridge the gap between the decking lingo and the engineering sheet every time.

Conclusion and Key Takeaways

If you take one thing away from this guide, let it be this: there is no such thing as a standalone “puddle weld symbol” in the official AWS system. The term is shop-floor shorthand — useful in conversation, but nowhere near precise enough for a drawing that a fabricator, welder, and inspector all have to interpret the same way. What people call a puddle weld is almost always an arc spot weld or, in specific situations, a plug weld, and each one has its own defined symbol in AWS A2.4:2020.

The practical translation is simple. When the joint is an arc spot weld — the classic steel-deck attachment where an arc melts through the top sheet into the base — the correct symbol is the spot weld symbol, a circle, with the welding process called out in the tail. When the joint involves a hole or slot filled with weld, you use the plug weld symbol, a rectangle. Getting that distinction right is the difference between a clean drawing and a costly RFI.

Read Every Symbol Against the Governing Standard

Symbols don’t live in a vacuum. Always read them against the controlling document for the job. For steel deck and metal decking attachments, AWS A2.4 handles the symbol convention while AWS D1.3 governs workmanship, qualification, and inspection. Reading one without the other is how misinterpretations creep in. The same discipline applies across every process you run — whether you’re dialing in polarity on a TIG setup or setting up a production robotic submerged arc cell, the paperwork and the weld itself have to agree.

Quick Note: The 2020 edition of AWS A2.4 tightened and clarified symbol conventions, including the use of the spot weld symbol for arc spot welds. If your shop still references an older edition, confirm which revision the contract actually cites before you build to it.

Clear Drawings Prevent Expensive Errors

Most puddle weld problems aren’t welding problems at all — they’re communication problems. A drawing that says “puddle weld” and nothing else forces the welder to guess the process, the size, and the spacing. That guess becomes an inspection finding, a rework ticket, or worse, a structural connection that doesn’t meet the engineer’s intent. Three habits eliminate almost all of it:

Name the process in the tail. Specify SMAW, FCAW, GMAW, or whatever the design assumes, so nobody defaults to the wrong electrode or gas.
Include size and spacing. Weld diameter and pitch aren’t optional details — they define the connection’s capacity.
Use standard terminology. Say “arc spot weld” and show the correct symbol instead of relying on slang that means different things to different trades.

Those three rules matter far beyond deck work. The same precision that keeps a spot weld callout honest is what keeps any weld spec defensible — the kind of discipline covered in our complete guide to building real welding skills.

Train the Eye, Then Trust the Document

Experienced welders develop instinct for what a joint “should” look like, and that instinct is valuable. But on structural work, instinct takes a back seat to the governing code and the approved drawing. When a symbol looks ambiguous, stop and ask. A five-minute question to the engineer beats a rejected connection every time. Keep the relevant standard within reach, verify the symbol against AWS A2.4, and confirm the workmanship criteria in the applicable code.

Note: Want to strengthen the fundamentals that make symbol-reading second nature? Browse more guidance in our beginner’s guide to using a wire welder and our breakdown of good versus bad MIG welds.

The Bottom Line

Puddle weld is a nickname, not a specification. The moment that nickname hits a blueprint, it should convert into the precise language of AWS A2.4: a spot weld symbol with a process designation for arc spot welds, or a plug weld symbol when a hole or slot is filled. Pair that symbol with the governing code — D1.3 for steel deck — and you close the gap between what the engineer intended and what the welder builds. Clarity isn’t bureaucracy; it’s the cheapest quality control you’ll ever run.

Frequently Asked Questions

Is there an official ‘puddle weld symbol’ in AWS A2.4?

No. AWS A2.4:2020 does not define a puddle weld symbol. ‘Puddle weld’ is a nonstandard field term. Depending on the joint, it corresponds to either an arc spot weld (represented by the spot weld symbol – a circle) or a plug weld (represented by a rectangle).

What symbol is used for a puddle weld on blueprints?

Most commonly, puddle welds on steel deck are shown as arc spot welds using the spot weld symbol (a plain circle) on the reference line. The process (e.g., GMAW) must be specified in the tail per AWS A2.4 §11.1.3. Arrow/other side placement indicates which side is welded.

How is a plug weld symbol different from a spot weld symbol?

The plug weld symbol is a rectangle, while the spot weld symbol is a circle. Plug welds typically fill a pre-punched hole in one member; arc spot welds (puddle welds) melt through the top sheet without requiring a pre-punched hole. Dimensions and placement rules also differ per AWS A2.4.

Does AWS D1.1 or D1.3 govern puddle welds for metal deck?

For attaching steel deck to structural framing, AWS D1.3 (Structural Welding Code – Sheet Steel) typically governs arc spot welds (puddle welds). AWS D1.1 covers structural steel welding but arc spot welding of sheet steel is addressed in D1.3.

Where do size and spacing go on a spot weld symbol?

Per AWS A2.4:2020, the spot weld size (diameter) goes to the left of the circle symbol. Pitch (center-to-center spacing) goes to the right. The number of spots appears in parentheses above or below the symbol. Process designation is required in the tail.

Can puddle welds be intermittent like fillet welds?

Yes. When multiple arc spot welds (puddle welds) are required at regular spacing, the spot weld symbol shows pitch to the right of the symbol (e.g., 3 in. diameter spots at 12 in. pitch) and may include the total number in parentheses.

Why is process designation required in the tail for spot welds?

Because spot welds can be made by different processes (RSW, GTAW, GMAW, etc.) with different requirements. The process affects symbol placement (RSW has no side significance; arc spot does) and inspection. AWS A2.4 §11.1.3 requires process reference in the tail.

What’s the difference between arrow side and other side for arc spot welds?

Arrow side means the weld is made on the side the arrow points to; other side means made on the opposite side. For arc spot welds, symbol placement (below = arrow side, above = other side) indicates which member the weld is made from, per AWS A2.4.