The coupon came out looking like a caterpillar. Thick in the middle, crowned way past spec, with two spots where the bead had rolled down over the solidified metal below it and a ragged toe on the left side that a grinding wheel would never fully forgive. My instructor flipped it over, handed it back, and said the sentence I still hear when I set up a vertical joint: “You let it get too hot, and you moved too fast when you should have paused and too slow when you should have moved.”
That is vertical-up flux core welding in one sentence, and it is the position that separates people who can weld from people who can make production. Gravity is now an opponent instead of an ally. The pool hangs on the arc and the freezing slag, every parameter has to work together in real time, and there is no such thing as settings you can dial in once and forget. The good news is that the physics is well understood, the parameter ranges are well published, and the difference between a caterpillar and a stacked, slag-peeling, glass-shaped weave is almost always a couple of volts and a bit of patience.
Short Answer: Vertical-up flux core welding generally runs 17 to 26 volts and 90 to 300 inches per minute of wire, depending on material thickness and wire diameter — usually one to two volts lower than the same joint welded flat, with wire feed speed nudged slightly up to keep arc stability. travel speed stays slow enough that the pool freezes ahead of gravity, gun angle is a 5 to 15 degree drag with the work angle close to perpendicular on grooves and around 45 degrees on fillets, and everything is validated with a test bead before the real joint gets touched.
This guide walks through the whole setup: why the position matters, what each machine setting actually does to the puddle, a practical settings chart you can start from, consumable choice, technique, gas, troubleshooting a defect list, test-weld procedure, and the safety gear specific to welding uphill. If you are completely new to the process itself, start with what is flux core welding and come back — this article assumes you know what a wire feeder does.
Flux core arc welding, FCAW, feeds a tubular wire — a hollow tube of steel filled with mineral flux — through a gun and into an arc. The flux does three jobs at once: it releases shielding gas as it burns, it forms a slag that covers and protects the hot metal, and it adds alloys that improve the deposited weld’s characteristics. There are two broad families: self-shielded wire (FCAW-S) that carries everything it needs inside the tube, and gas-shielded or dual-shield wire (FCAW-G) that needs an external cylinder in addition to its core. Both can be welded vertical up, and both behave differently when you do.
Vertical up simply means the weld progresses from the bottom of the joint toward the top. AWS position numbering calls the fillet version 3F and the groove version 3G; the horizontal cousin is 2F/2G, and flat is 1F/1G. The reason to fight gravity at all comes down to penetration and soundness: welding uphill lets the arc dig into the root and lets each pass support the next, producing deep, interlocked fusion in thick material. It also keeps the heat-affected zone tighter than a heavy flat pass would on an already-assembled structure.
The trade-off is speed and difficulty. You cannot drag a fat bead up a wall as fast as you can run one across the floor, and the pool wants to sag every fraction of a second you leave it unattended. Vertical-up FCAW is slower per inch than flat, and it demands more attention per inch than flat. What you get back is a joint that carries load, passes inspection, and can be welded in place when the plate is already bolted, welded, or bolted into a frame that will not turn over for you.
Quick Note: Position is a qualified variable, not a personal preference. If the WPS for the job says flat, welding it vertical up without a procedure change is a reject waiting to happen, no matter how good the bead looks.
The industries that lean hardest on vertical-up welding are the ones where the joint cannot be moved to the table:
| Industry | Where vertical-up FCAW shows up |
|---|---|
| Construction | Structural column and beam connections, bridge members, gusset plates |
| Shipbuilding | Hull seams and bulkhead fabrication, often vertical-down for speed on thin plate but vertical-up for root passes and heavier sections |
| Oil and gas | Branch connections, structural steel on platforms, heavy wall piping supports |
| Heavy equipment and manufacturing | Frames, buckets, chassis, and weldments too large to rotate |
| Automotive and motorsport | Roll cages, suspension mounts, and repairs in the installed position |
| Maintenance and repair | Everything from worn equipment buckets to structural damage you cannot take apart |
Advantages over other options: deep penetration in a single root pass; high deposition compared with stick in the same position; the slag blanket of flux core buys you a little pool-holding time that bare-wire MIG does not; self-shielded wire works in wind where gas-shielded processes fail; and the deposit rate lets a competent welder build a vertical joint faster than stick with less operator fatigue from rod changes.
The challenges, honestly: gravity never stops working; slag can hide a bad profile under a pretty one; heat input climbs fast if your travel speed drops; and the position exposes the welder’s face and chest to falling spatter in a way flat welding does not. It is also the position where new welders discover that their machine’s settings chart was written for flat and nothing else. Related reading: is flux core welding strong covers what the finished metal can actually carry.
Every vertical-up problem traces back to one of three numbers, or to what your hands are doing between them: voltage, wire feed speed, and the heat input that results. Learn to read them and the position stops being mysterious.
Voltage controls arc length, which controls the shape and width of the puddle. Too much voltage and the arc gets long, the bead goes flat and wide, spatter picks up, and the toes wash out into undercut. Too little voltage and the arc gets short and aggressive, the bead stands up in a narrow ridge with poor tie-in at the toes, and the slag locks into the corners where the metal never fused.
For vertical up specifically, start one to two volts below what the same joint takes flat. The lower voltage shortens the arc, tightens the pool, and gives the slag something to grab before gravity does. As a working example: a 3/16 inch fillet with 0.035 inch dual-shield wire that runs happily at 23 volts flat often belongs at 21 to 22 volts pointing up.
Wire feed speed sets amperage. The machine is a constant-voltage power source; you set voltage, the feeder sets current, and current is what melts base metal. On most FCAW machines there is a useful practical pairing — roughly every 25 ipm of wire feed corresponds to around 25 to 30 amps of output on common wire sizes — which is why parameter charts pair the two together.
Here is the vertical-up wrinkle that catches people out. Lowering voltage without touching feed speed changes the balance toward a colder, stiffer pool — which is what you want uphill — but if you drop feed speed too as well, you double-shift into an underpowered arc that cannot fuse. When you take voltage down one or two volts for position, leave wire feed where the flat setting put it, or nudge it slightly up to compensate. The pool should freeze quickly, but the arc should not sound weak.
Pro Tip: Think of voltage as the pool’s width and wetness, and wire feed as the pool’s mass and heat. Vertical up wants a smaller, wetter-on-the-toes, lighter pool moving continuously — not a heavy one sitting still.
Heat input is what the joint actually receives, and it is the number that decides grain structure, toughness, distortion, and whether your bead sags. The formula welders actually use:
Quick Note: Heat input (kJ/mm) = (amps × volts × 60) ÷ (25.4 × travel speed in ipm × 1000). Run 180 amps at 22 volts moving 10 inches per minute and you are at about 0.94 kJ/mm — a normal structural range. Drop to 6 inches per minute without changing anything else and you are near 1.6 kJ/mm, which is where grain coarsening and sagging start showing up.
| Condition | What excess or missing heat does |
|---|---|
| Heat input too high | Sagging and roping on vertical passes, coarse grain in the heat-affected zone, reduced toughness, distortion, wider HAZ, burn-through on roots and thin sections |
| Heat input too low | Lack of fusion, cold laps, poor wetting at the toes, hard brittle structures in the HAZ, slag trapped against unfused metal |
| Heat input controlled | Consistent bead profile, clean tie-in, predictable mechanical properties, inspection-passing profiles |
Travel speed is your real-time heat input control. Voltage and feed set the machine; your hand decides how long each square millimeter sits under the arc. On vertical up, that means the corrective move for a pool that is getting too big is almost never “turn the machine down” — it is “move,” or better yet, pause less at each weave step. Turning the machine down fixes nothing and costs fusion.
Charts vary by wire manufacturer, and your machine’s own manual deserves the first and last word. But the ranges below reflect typical published values for self-shielded and dual-shield FCAW in vertical up, and they are a legitimate starting point for dialing in on scrap before the actual joint:
| Material thickness | Wire diameter | Volts | Wire feed (ipm) | Approx. amps |
|---|---|---|---|---|
| 16–18 ga (1.2–1.5 mm) | 0.030″ | 16–18 | 60–95 | 50–80 |
| 14–10 ga (1.9–3 mm) | 0.030″ / 0.035″ | 17–19 | 90–135 | 75–115 |
| 1/8–3/16″ (3–5 mm) | 0.035″ | 19–21 | 130–185 | 110–155 |
| 1/4–5/16″ (6–8 mm) | 0.035″ / 0.045″ | 21–24 | 175–235 | 150–205 |
| 3/8–1/2″ (9–12 mm) | 0.045″ | 23–26 | 215–285 | 190–250 |
| 5/8″ and heavier | 0.045″ / 1/16″ | 25–28 | 260–330 | 230–285 |
How to use it, in order:
Pro Tip: For broader parameter reference across processes, the site’s flux core amperage chart and flux core wire speed and voltage chart give flat-position baselines you can subtract one to two volts from for uphill work.
Self-shielded wire deserves one caveat. Gasless flux core typically wants a longer stick-out — around 1 to 1.5 inches — and slightly higher voltage for a given thickness than dual-shield, because the shielding gas has to form inside the arc zone from the flux alone. The arc also sounds rougher and spatters more. If you are running a small 120-volt machine with gasless wire, stay inside the thinner rows of the chart and accept that heavier plate in vertical up will take multiple passes; crank the machine to its limit and you will get a hot, saggy, under-fused mess instead of one good pass. More on that machine class in best flux core welder for beginners.
Not all flux core wires are built for uphill work, and choosing wrong makes the position feel twice as hard as it should. The classification stamps on the spool tell you almost everything you need.
Under the AWS A5.20 specification for carbon steel flux-cored electrodes, three designations come up constantly in vertical work:
The “-1” in E71T-1 is the position digit: 1 means all-position capability. A stamp of E71T-14 or similar indicates a flat-and-horizontal-only wire — that spool will fight you uphill no matter what the machine is set to. Same reading logic applies to stick electrode stamps; the basics are covered in welding rod numbers explained and the general options in flux core wire types.
Wire diameter follows thickness and current: 0.030 inch for light plate and lower-amperage machines, 0.035 inch as the all-rounder from roughly 3/16 to 1/2 inch, and 0.045 inch when deposition and current go up on heavy structural work. The site’s 0.030 versus 0.035 flux core wire comparison walks through the trade-offs in detail. A quick sanity rule: the heavier the plate, the larger the wire, because larger wire carries more current without melting back — and more current means faster travel at equal penetration, which means less heat input per inch. On vertical work, that is always the direction you want to be trending.
Four filters decide the spool:
Consumable storage matters more than people expect. Flux core picks up moisture from humid air, and wet wire burns with extra porosity and erratic arc behavior. Keep spools sealed until use, store them off the floor in a dry cabinet, and if a coil has sat in a damp shop for a year, do not discover its condition on the production joint. Ovens and storage discipline for stick electrodes are covered in homemade welding rod oven; the same principle applies to tubular wire, just with less urgency.
Quick Note: Dual-shield wire (FCAW-G) needs gas; the name is not marketing. Welding it “flux core only” because the cylinder is empty produces a porous, contaminated weld that looks fine until the inspector’s grinder finds it.
Pro Tip: Before committing to a new consumable on a critical joint, run a vertical-up test bead on the same material and thickness. Every wire has its own sweet spot even within its published range, and dual-shield versus self-shield arcs feel completely different — the process background is in what is dual shield welding.
Settings only work if the hardware delivers them consistently, and vertical up exposes weak equipment faster than any other position. Four pieces matter.
Power source. A constant-voltage machine with enough headroom for the current you need. Inverter-based welders hold arc characteristics tighter than old transformer-rectifier units, which shows up directly in puddle consistency on a long vertical pass. Duty cycle matters more here than on flat work: vertical passes take longer per inch, so a machine rated 100 amps at 60 percent duty will overheat sooner than you expect if you are burning 180. If you are shopping, the class of machine that handles this work is covered in beginner flux core welders — pick one with a real voltage range, not a coarse low/mid/high switch, because vertical work lives in the fine adjustments.
Wire feeder. Smooth, constant, adjustable. A feeder that hiccups under a slight cable bend will stutter the arc halfway up a critical joint, and the restart is where defects hide. Check drive roll tension: too tight and the wire slips or shaves, too loose and it slips under load. The rolls must match wire diameter — grooves sized for 0.045 running 0.035 will feed erratically. Details on roll selection are in drive rolls for flux core wire.
Gun and liner. Vertical work puts the gun in an awkward orientation for minutes at a time. A gun that is comfortable flat becomes a wrist problem uphill. Look for a comfortable trigger reach, a barrel that does not obstruct your view of the contact tip, and a liner and liner-to-feed-tube alignment clean enough that the wire feeds without surging. Typical contact tip recess for flux core is 1/4 to 3/8 inch; a longer stick-out for self-shielded work sometimes means running a slightly deeper recess to keep the arc stable. Replace tips on wear rather than on failure — an hour-glass bore tip feeds crooked and drags the arc with it.
Cable management. The feeder should sit close to the joint with a gentle service loop, not across the shop. On vertical work the cable hangs and pulls on the gun; an awkward cable angle translates straight into gun-angle drift halfway through the pass.
Quick Note: Maintenance is a settings issue. A contaminated liner, worn tip, or kinked liner consumes one or two volts of your carefully chosen setting before the arc ever reaches the plate — and then you compensate for the machine’s problem with the wrong numbers.
Vertical-up rewards preparation because once the pass starts, both hands are committed. Run this sequence on every job:
That last point deserves emphasis because it is where vertical welds fail inspection. Slag trapped between passes is the single most common defect in uphill work, and it is a planning failure, not an execution failure. Every pass must leave a profile the next pass can tie into, and every surface must be chipped, wire-wheeled, and visually checked before the next bead goes on. The full defect playbook is later in this article, and flux core welding troubleshooting covers the broader process-specific issues.
If the machine is the physics, your hands are the steering. Three variables: travel angle, work angle, and travel speed — plus whatever weave pattern you choose to tie them together.
Travel angle (the drag or push angle relative to the joint) for vertical-up is a 5 to 15 degree drag: gun handle below the barrel, wire being pulled up the joint. Dragging lets the arc point slightly into the frozen edge of the pool below you, which supports the incoming metal and keeps the force of the arc digging at the root instead of blowing the pool sideways. Push angles on vertical-up almost always produce a tall, narrow, poorly tied bead with slag stuck in the corners.
Work angle depends on joint geometry, not preference:
| Joint | Work angle | Notes |
|---|---|---|
| Butt or groove, vertical | About 90°, square to the plate | Favor each side slightly when stacking a multi-pass cap so both toes tie in evenly |
| Fillet (T-joint), vertical | About 45°, bisecting the corner | Roll slightly toward the heavier plate when thicknesses are unequal |
| Lap joint, vertical | Roughly 60–70° | Aim at the top edge of the lower plate; too much toward the upper sheet causes undercut there |
| Outside corner | About 45° | Watch the thin edge for burn-through; consider slightly lower voltage |
Angles drift as fatigue sets in, which is the quiet enemy of long vertical passes. A support — a forearm brace against the structure, a finger on the gun barrel for reference, a magnetic torch holder for the tack phase — buys consistency that willpower cannot.
Travel speed on vertical-up should be slow enough that the pool stays small and freezes behind each movement, and fast enough that the arc never dwells long enough to let the pool grow past the joint’s throat. As a physical cue: you should be able to see the leading edge of the pool solidify as you move. If the pool looks like it is chasing you downhill, you are either too hot or too slow.
The rhythm most successful vertical welders settle into is a series of controlled pauses — dwell briefly at each side of the weave to let the toes wet in, then move across the center quickly so the middle stays low. Typical pause is half a second to a second per side; typical weave width caps out around 3/16 to 1/4 inch (5 to 6 mm). Wider than that and the center of the bead gets too hot, sags, and the grain structure in the middle coarsens. Stringer beads — no weave at all, just a straight stack — are often the better answer for root and fill passes because they keep heat input low and minimize pooling.
Pro Tip: Watch the pool, not the wire. The wire tip is a reference, but the pool’s leading edge tells you everything: size, wetness, freeze rate, and whether gravity is starting to win. New welders stare at the arc flash; experienced ones read the puddle’s edge.
Technique generalizes across processes, so the position skills built here transfer to vertical stick and vertical MIG as well; the site’s broader vertical welding techniques and FCAW techniques guides go deeper on the handwork itself, and push or pull with flux core covers the drag logic in more detail.
Self-shielded wire carries its own protection — nothing to set, nothing to leak, nothing to blow away in a moderate breeze. Dual-shield wire needs external gas, and the shielding around a vertical pool matters more than it does flat, because the pool’s surface is exposed at an angle to the atmosphere the whole time it is molten.
Gas-related defects follow a recognizable pattern. Porosity concentrated near the start of the weld points at shielding not established yet — purge the gun line before striking. Porosity along the whole length means flow too low, a leak, or wind. Porosity on only one side of the bead usually means the gun was angled so the shield lagged behind the pool — fix the travel angle, not the gas bottle. Symptom-by-symptom diagnosis continues in the troubleshooting table below.
Quick Note: A flow rate that reads correct at the regulator can still be wrong at the gun if the hose is long, coiled, or leaking at a fitting. Check flow with the trigger open, at the nozzle, on the joint — not at the cylinder.
Real vertical joints are rarely one bead. Heavy plate means layers, and the pass strategy you plan before striking is just as consequential as the machine settings — because every subsequent pass reheats, tempers, and sometimes undermines the one below it.
The root pass carries the joint. Run it as a tight stringer, 1/8 to 3/16 inch wide, with the slowest deliberate travel you can hold consistently. The root has the least tolerance for sagging because there is nothing below it to catch a fall, and it has the highest consequence for defects because a lack of root fusion is invisible from the surface and shows up on ultrasonic examination. If the fit-up has an open root gap, bridge it with a slight side-to-side motion at the very bottom of the joint rather than a wide weave — the goal is two tied toes and a thin, fully penetrated center, not fill.
Fill passes build thickness. Alternate slight weave widths so each pass overlaps the toes of the one below without burying them under a valley. Keep every fill bead convex to slightly flat; a concave fill pass guarantees a trapped slag line for the person welding above you. Watch interpass temperature as layers accumulate — the plate around the joint is storing heat from every previous pass, and the pool you are welding now is sitting on preheated steel. Typical structural practice caps interpass temperature around 600°F (315°C), and the preheat and interpass requirements for structural work come from the governing code, generally AWS D1.1 for structural steel. If the plate feels too hot to keep a hand near, it probably is — stop, let it cool, and record the delay rather than rushing the cap.
The cap is where appearance and profile discipline show. A narrow zigzag or crescent weave up to about 1/4 inch wide, equal pauses at both toes, consistent step-over of roughly half a bead width per cycle. Two capped passes side by side should read as parallel ridges of even height; if one is taller, your work angle drifted toward that side. Where the cap must terminate mid-plate — a typical situation on a long vertical seam — feather the end into a taper, chip the crater, and overlap it by about an inch when you restart so the joint line never shows a dense spot.
| Pass | Technique | Width | Priority |
|---|---|---|---|
| Root | Stringer, minimal weave, bridge only if gapped | 1/8–3/16″ | Penetration and tie-in, zero sag |
| Fill | Stringers or narrow weave, alternate position | Up to 3/16″ | Fusion to previous layer, convex profile |
| Cap | Crescent or zigzag weave with toe pauses | Up to 1/4″ | Even profile, clean toes, no undercut |
Quick Note: Reheat changes settings. A fill pass on plate already at 400°F will run hotter than the same pass on cold steel — travel a little faster on later passes rather than adjusting the machine down mid-job and losing fusion on the toes.
Two practical habits keep multi-pass vertical work inspection-friendly: chip and wheel between every single pass regardless of how good it looks, and grind the toe of any pass with visible hesitation marks before covering it. Both take under a minute. Both prevent the only two defects that routinely reject vertical flux core welds — trapped slag and lack of fusion at a covered surface.
Every defect has a signature. Match what you see to the cause before touching a knob.
| What you see | Most likely cause | Fix |
|---|---|---|
| Slag inclusions between passes | Unremoved slag, overstretched weave bridging over slag, profile too concave | Chip and wire-wheel every pass; keep beads convex; narrow the weave; do not cap a pass you have not cleaned |
| Porosity, scattered | Contaminated surface, wet wire, poor shielding, wrong gas | Clean joint, check flow at gun, confirm gas type, replace damp spool |
| Porosity, wormholes | Excessive travel angle, too much stick-out, gas turbulence | Reduce drag angle toward 5–10°, shorten stick-out, lower flow if over 45 CFH |
| Undercut at the toes | Voltage too high, dwell too short at toes, travel too fast | Drop a volt, pause at each toe, slow slightly |
| Cold lap / lack of fusion | Too cold overall, travel too fast, weave too wide | Wire feed up 10–15 ipm, narrow weave, verify preheat on thick plate |
| Tall, narrow, roping bead | Voltage too low, travel too slow, pool over-massive | Add a volt, move, keep bead width under 1/4″ |
| Sagging or flat, washed-out bead | Too hot, dwell too long, travel too slow | Drop a volt, speed up, shorten center of weave |
| Heavy spatter | Voltage high, long stick-out, wet or rusty wire, bad liner | Trim voltage, reset stick-out, replace wire/liner/tip |
| Burn-through on root | Too much heat for thickness, root gap too wide | Lower feed and volts, bridge technique, verify fit-up tolerance |
| Arc wandering / stubbing | Contaminated tip, bad liner, wrong polarity, voltage too low | Replace tip, check liner, confirm polarity, add voltage |
The two entries worth memorizing are the first two. Slag inclusion and porosity account for the overwhelming majority of rejected vertical flux core welds, and both are preventable by discipline rather than talent: clean the pass, protect the pool, verify the consumable. If you are chasing a defect through three different settings changes and the root cause was never the settings, you are doing expensive archaeology. Flux core welding troubleshooting expands on process-level faults like feeding problems and polarity errors, and reducing spatter in flux core handles the messy-arc case in full.
Quick Note: Change one variable per test bead. Adjust voltage and feed together and you will never know which change fixed the profile — or whether they cancelled each other out.
Professional shops treat the test weld as part of the job, not as an optional confidence builder, and the reason is arithmetic: a five-minute test bead on scrap costs almost nothing, while a rejected vertical weld on a structural member costs a grind-out, a re-weld, a re-inspect, and a conversation. Both Lincoln Electric and Miller publish parameter resources for their wires, and both are written by people who tested those wires in position — use them as your starting row, then confirm on your own material.
Make the test in the same position, on the same thickness, with the same stick-out and gas as the real joint. Then evaluate in this order, because order matters:
When the test bead tells you something is wrong, work down this list rather than guessing:
| Observation | First move | Second move | Never do this |
|---|---|---|---|
| No side fusion / cold toes | Wire feed +10–15 ipm | Slow travel slightly | Raise voltage only (widens arc, doesn’t add current) |
| Bead too tall / crowned | Voltage +1 V | Speed up the cross-weave | Drop feed speed (loses fusion) |
| Bead too flat / washed | Voltage −1 V | Speed up travel | Drop feed speed first |
| Undercut at toes | Pause longer at toes | Voltage −1 V | Speed up to “outrun” it |
| Sagging pool | Speed up travel | Voltage −1 V | Add feed (makes pool heavier) |
| Spatter excessive | Check stick-out and surface | Voltage −1 V | Raise voltage |
| Porosity | Check gas flow at gun + cleanliness | Check wire and polarity | Change volts (it almost never is volts) |
| Erratic arc / stubbing | Replace tip, check liner | Confirm polarity | Power through it |
When the bead passes all five checks, write the numbers on a card and tape it to the machine: wire brand and size, gas and flow, volts, ipm, stick-out, travel speed, position, material. That card becomes the shop’s institutional memory, and it is worth more than any settings chart printed in a manual because it was generated on your equipment with your consumables. Over time these cards accumulate into a genuine procedure library — which is exactly what a formal weld procedure specification looks like before someone stamps it.
Pro Tip: Re-test after any consumable change. A new spool of the “same” wire from a different batch, or a different manufacturer’s take on E71T-1, can shift the sweet spot by a volt. Treat wire like a new machine until proven otherwise.
Quick Note: If your first three test beads all fail the same way, stop adjusting and inspect the equipment. Three consistent failures point at a mechanical or polarity problem, not a settings problem.
Most people who struggle with this position are making one of about six errors, and all of them are fixable in an afternoon:
The site’s flux core welding mistakes list covers the process-wide versions of these, and every one of them gets worse in the vertical position because the position removes your margin. Flat welding forgives a sloppy parameter set; vertical welding reports it immediately in the form of a bead that will not behave.
Quick Note: If a joint feels like it is fighting you, it usually is. The fix is almost always a stop, a clean, a test bead, and a fresh start — not a heroic completion of a pass that went bad at inch three.
Vertical up is a choice, and comparing it against the realistic alternatives clarifies when to use it:
| Option | Strengths | Weaknesses | Best for |
|---|---|---|---|
| Vertical up FCAW | Deep penetration, high deposition, all-position capability, works outdoors (self-shielded) | Slow, demanding technique, slag management required | Structural roots and fills on heavy plate |
| Vertical down FCAW/MIG | Fast, minimal heat input, light penetration | Shallow fusion, unsuitable for heavy roots | Thin sheet, shipbuilding-style fabrication, cover passes |
| Vertical up stick (SMAW) | Simple equipment, excellent root control with 7018/6011, weather-proof | Lower deposition, rod changes, more fatigue | Pipe, field repairs, positions where a feeder cannot reach |
| Vertical up MIG (GMAW) | Clean, fast, easy arc, no slag | Gas-dependent outdoors, more heat input for equal fill, no slag support for the pool | Controlled-shop fabrication, thinner material |
| Horizontal FCAW | Fastest flux core position, easiest pool control | Only works when the joint is horizontal | Whenever the work can be turned — always preferred over vertical if possible |
The honest hierarchy: if the piece can be turned flat, turn it. If it can be welded horizontal, weld it horizontal. Vertical up earns its place when the structure is already in its final position and the joint has to carry load. That constraint is why structural steel, shipbuilding, and heavy repair dominate the position’s user list.
Process comparisons matter when a shop is deciding what to standardize on. Flux core versus stick is largely a deposition-and-mobility question — see stick versus flux core — while flux core versus MIG comes down to wind, penetration, and slag tolerance: flux core versus MIG lays out the trade. And if you are deciding whether to move from horizontal work into vertical, the companion settings guide at horizontal flux core welding settings shows exactly what changes when the joint rotates 90 degrees — usually a volt or two and a different relationship with gravity. The general process baseline sits at flux core welding settings.
Pro Tip: Vertical down with flux core gets proposed by well-meaning people regularly. On anything structural, it is the wrong answer: the arc blows forward faster than the pool can wet, penetration is shallow, and the code will not accept it for roots that matter. Save vertical down for thin sheet and cover work where penetration was never the goal.
Vertical-up flux core has two safety characteristics distinct from flat welding: spatter and molten slag fall downward, toward the welder’s face, neck, and chest, and the position often puts the welder’s head at or below the joint — which is exactly the wrong place to be in a shower of hot metal.
| Item | Why it matters vertical-up |
|---|---|
| Auto-darkening helmet with reliable shade range | Spatter exposure is continuous and from below; a helmet that fails darkening leaves you flash-burned mid-pass |
| FR welding jacket or leathers, collar closed | Slag bounces off the joint and drops straight down your front; short sleeves and open collars take the hit |
| Gauntlet-style welding gloves | Falling spatter lands on wrists and glove cuffs; loose or thin gloves also lose dexterity needed for fine pool control |
| Closed, leather, dielectric-soled boots | Molten slag falls to the floor and stays hot; also guards against shocks from stray current |
| Hearing protection | FCAW arc noise plus grinding in an enclosed structure adds up over a shift |
| Half-mask respirator or PAPR when extraction is not feasible | Fume exposure rises when your face sits in the plume path; see the fume section below |
Helmet selection gets its own emphasis because the position makes lens performance load-bearing: you cannot flinch away from a bad view when both hands are committed to a pool. The options across budgets are covered in best welding helmets for flux core and best welding respirator for the respiratory side. General shop discipline — pre-work equipment checks, fire watch, ventilation, and housekeeping — is the foundation, laid out in welding safety tips.
Flux core generates more fume than short-circuit MIG — the flux burning off is part of the shielding and slag chemistry, and some of it becomes visible smoke. When you weld uphill, that plume rises directly into your breathing zone before the shop’s general ventilation can move it. Controls, in order of preference:
The regulatory floor for ventilation during welding is set by OSHA’s welding, cutting, and brazing standard — which requires ventilation sufficient to keep contaminants below exposure limits and specifies when local exhaust is mandatory — codified at 1910.252 in the eCFR with plain-language guidance on OSHA’s welding portal. The health endpoints behind those rules — manganese, zinc oxide, iron oxides, and the rest of the flux core fume recipe — are tracked by CDC/NIOSH’s welding program. Fume composition and long-term effects get their own treatment at are welding fumes toxic.
Quick Note: Galvanized and painted base metal make everything worse — zinc oxide plumes are immediate metal fume fever material, and coatings containing cadmium are genuinely dangerous. Burn through coatings only with extraction running and know what the coating is before you strike.
Pro Tip: On vertical passes your helmet sits in the plume. Even with a PAPR, position yourself slightly to one side of the joint’s vertical line rather than directly beneath it — you will see the pool just as well and inhale considerably less.
What is vertical up flux core welding?
It is FCAW — tubular flux-filled wire — welded with the arc progressing from the bottom of the joint upward. The position gives deep, sound penetration on heavy material because each pass supports the next, and it is standard practice in structural steel, shipbuilding, and heavy repair wherever the joint cannot be reoriented. AWS position numbering calls it 3F on fillets and 3G in grooves. The flux’s slag blanket helps hold the pool against gravity, which is one of the reasons flux core handles uphill better than bare-wire MIG.
What are good starting settings for vertical up FCAW?
As a baseline, take your flat-position settings for the joint and subtract one to two volts while keeping wire feed the same or slightly higher. For concrete ranges: a 1/8 to 3/16 inch joint on 0.035 inch wire commonly starts around 19 to 21 volts at 130 to 185 ipm; a 1/4 to 5/16 inch joint starts around 21 to 24 volts at 175 to 235 ipm; heavier plate climbs to 23 to 28 volts and 215 to 330 ipm depending on wire size. Always confirm on a test bead — machine and wire-brand variation is real, and the full reasoning sits in the settings chart section above.
Why does my vertical bead keep sagging or rolling over?
Almost always one of two things: too much heat input, or dwelling too long in one spot. Fix it by speeding up your travel first, then dropping a volt if the pool still moves. Do not reduce wire feed to fix sag — that removes current and fusion while leaving the pool just as hot relative to its mass, and you end up with a sagging bead that also lacks fusion. A third possibility on root passes is an oversized gap or excessive fill in a single pass; split it into two.
Push or pull on vertical up?
Drag — a 5 to 15 degree pull angle, gun handle low, wire pointing slightly up into the joint. Dragging directs arc force into the frozen pool edge below you and gives the incoming metal something to fuse against. Pushing uphill produces a tall, narrow, poorly tied bead with slag stuck in the corners. The reasoning in depth is at push or pull with flux core.
How do I stop slag inclusions between passes?
Clean every pass completely — chip, wire-wheel, visually inspect — before laying the next one. Keep each bead profile slightly convex so the following pass can tie both toes without bridging across a valley. Narrow your weave so the center never sinks below the toes. And never cap a pass you have not looked at: slag inclusions are almost always found at the start of the next pass, not where the first pass was laid.
What gas should I use for vertical up flux core?
It depends on the wire. Self-shielded wire (FCAW-S) uses no external gas at all and is the right answer outdoors or in wind. Gas-shielded and dual-shield wires (FCAW-G) take either 100 percent CO2 or a 75/25 argon-CO2 mix — CO2 for penetration, 75/25 for a calmer pool that many welders find easier to control uphill. Flow for FCAW-G commonly sits higher than MIG settings, roughly 30 to 45 CFH at the gun per the wire’s data sheet, always verified at the nozzle with the trigger open.
Can beginners learn vertical up with flux core?
Yes, and flux core is arguably the most approachable process for it because the slag supports the pool and the parameter ranges tolerate some error. Start on fillet joints at the thinner end of the chart, use stringer beads rather than weaves, and practice stops and restarts deliberately — they are the skill that takes longest to develop. If you are still choosing a first machine, beginner flux core welders covers the class of equipment that makes this learnable, and the fundamentals of the process itself are in what is flux core welding.
Vertical-up flux core welding is not a mystery, it is a set of relationships. Voltage shapes the pool; wire feed sets the heat and mass; travel speed decides how much of both the joint actually receives. Run a volt or two under your flat settings, keep wire feed where it was or slightly higher, drag at 5 to 15 degrees, hold your work angle to the joint geometry, keep passes narrow, pause at the toes, clean between passes, and test on scrap before every adjustment. That is the entire recipe, repeated with discipline until it becomes muscle memory.
The position earns its reputation because gravity never gives you a break and because defects hide better under slag than under bare arc. But it also earns its place in every structural shop on earth: deep, sound, load-bearing welds in joints that cannot be moved to the table. Shops that do this work well share the same habits — parameter cards taped to machines, test beads before production, wire wheels between every pass, and a supervisor who will stop a pass that has gone bad instead of finishing it for the schedule.
Start with the chart, trust the test bead over your memory, adjust one variable at a time, and read the pool instead of the arc. Do that consistently and the caterpillar beads turn into stacked, uniform, slag-peeling welds that pass inspection the first time — which is the whole point of spending extra seconds per inch in a position that fights you the entire way up.