How the order quantities are calculated

Sealant volume (CP 606, FS-ONE MAX, CP 25WB+)

Joint cross-section × length × number of sides, then divide by the tube's net volume. Cartridges and sausages list fl oz — convert to in³ at 1.8047 in³/fl oz.

10.1 oz cartridge = 18.2 in³
20 oz sausage = 36.1 in³

So a 1″ joint × ½″ deep × 1 LF (12″) × 2 sides = 1 × 0.5 × 12 × 2 = 12 in³, which is about ⅓ of a sausage per LF, or 1 sausage every 3 LF. Real-world coverage drops because of joint irregularities, smearing, and waste — that's where the waste factor matters.

Spray coverage (CP 672 / CFS-SP WB)

Hilti publishes LF/gallon directly. From the Hilti Firestop Systems Guide for Specifiers:

½″ joint: ~153 LF/gal
1″ joint: ~122 LF/gal
1½″ joint: ~102 LF/gal
1¾″ joint: ~88 LF/gal
2″ joint: ~77 LF/gal
2½″ joint: ~61 LF/gal

This is for one-side coverage with proper overlap onto the wall and deck. Both sides = double it. A 5-gal pail of CP 672 on a 1″ joint covers roughly 610 LF one-side, or 305 LF both-side.

Deck plugs (CP 777)

Fluted metal deck has voids above the wall in every flute. CP 777 SPEED PLUGS are pre-formed mineral wool inserts sized to the deck profile, installed before the spray or sealant goes on. Plug count = (HOW LF × 12) / flute pitch.

1.5″ B-deck has a 6″ flute pitch → 2 plugs per LF of HOW.
2″ N-deck has an 8″ flute pitch → 1.5 plugs per LF.
3″ deep deck has a 12″ flute pitch → 1 plug per LF.

CP 777 ships 24 plugs per box, so a 500 LF run on B-deck = 1,000 plugs = ~42 boxes.

Mineral wool (Safing) backstop

The mineral wool packed into the joint behind the sealant is what holds the rating. Compressed 25-50% wider than the joint, full wall thickness deep. Volume:

MW volume (ft³) = LF × wall_thickness(ft) × joint_width(ft) × (1 + compression%)

Thermafiber Safing (8 pcf) ships in 33 board feet per bag (Thermafiber catalog), so divide ft³ × 12 by 33 to get bag count.

HOW vs BOW — what's different

Head-of-wall (HOW) sees the most movement (deflection from live load above) and the most variability (fluted deck conditions). It's the joint that gets all the attention — most listed systems are HW-D-XXXX (dynamic, deflection-rated) or HW-S-XXXX (static).

Bottom-of-wall (BOW) is the orphan joint. The W-L series UL listings cover this — typically a simpler sealant-only joint at the slab-to-track interface. No deck plugs needed. It's almost always smaller width than HOW and skipped on a lot of inspections (don't skip it).

Sausages vs cartridges — why pros run sausages

A 20 oz sausage gives you almost exactly 2× the material of a 10.1 oz cartridge but doesn't cost 2× — usually 1.3-1.5× the price. Sausages also load into the gun faster (no plastic case to deal with) and produce less jobsite waste. The only reason to run cartridges is a small punch list or a tight access spot where you need the slim cartridge gun nozzle.

FAQ

What's the difference between CP 606 and FS-ONE MAX? +

CP 606 is a flexible acrylic — paintable, smooth-finishing, lots of movement (up to ±33%). Used for joints. FS-ONE MAX is an intumescent — it swells when it hits heat and chokes off penetrations. Used for pipes, cables, ducts. Both can do joints in some UL listings, but the acrylic is the go-to for HOW/BOW.

When do I use spray instead of sealant? +

Spray (CP 672 / CFS-SP WB) is faster on long, repetitive runs — 500+ LF of HOW where you can mask once and spray straight through. Sealant is better for short runs, tight access, or where you need a tooled, clean finish line. Big projects with shaft walls and corridor partitions go spray every time.

Do I need deck plugs if the wall meets a flat slab? +

No — deck plugs only apply at fluted metal deck. Flat slab, flat soffit, or drywall ceiling above gives you a continuous bearing surface, so the sealant or spray just runs across it.

Mineral wool — what density? +

Most listed HOW systems specify 4 pcf for the wall-cavity backstop and 8 pcf (Safing) for the joint itself. Don't substitute — UL tested at those densities and the listings are density-specific.

Why is mineral wool compressed? +

Heat makes it expand, and the wall moves with thermal/seismic loads. Compression keeps it tight against the framing under all conditions. 25% is typical for HW-D systems; some go higher.

Does this account for shaft walls, control joints, or fire-rated penetrations? +

No — this is just HOW + BOW linear joints. Penetrations (pipes, cables, ducts) need their own UL CAJ or WL system numbers and a separate take-off. Control joints in CMU walls are also their own system (CJ series).

What about the curtain wall / spandrel joint? +

That's CW-D, totally different geometry and material (usually thermal blanket + mineral wool + sealant). Don't use this calc for perimeter fire containment — different math, different products.

How much waste should I really add? +

10% is a reasonable default for clean conditions and an experienced crew. 15-20% on cut-up floor plans, training crews, or when the deck condition is rough (rusty deck, paint flakes, debris in the flutes — all reduce sealant adhesion and increase rework).

Are the prices in the cost estimate accurate? +

They're distributor-list ballpark numbers. Your Hilti account, regional contractor pricing, and quantity discounts will all change them. Use the cost line to scope budgets, not to bid.