How do you calculate rework firing load time?

Divide rework pieces by the firing clearance rate to get base time, then multiply by one plus the allowance. For 1,400 pieces at 18 per minute with a 12% allowance: 1,400 / 18 = 77.78 min, x 1.12 = 87.11 minutes.

Why add a sorting and kiln-change allowance?

Rework rarely arrives as a clean full load. Time goes to sorting odd pieces, setting them, and switching the kiln to the right rework curve. The 12% allowance turns 77.78 base minutes into a realistic 87.11 minutes.

What is a typical clearance rate for rework firing?

It depends on kiln type and ware size, but a value like 18 pieces per minute reflects a fast roller-hearth pass for small tile. Large sanitaryware fixtures clear far slower, so use a rate measured on your own kiln.

Should rework be batched or fired as it comes?

Batching usually lowers the allowance because you change the kiln once for many pieces. Firing rework piecemeal raises the effective allowance well above 12% because each small lot triggers its own setup and change.

How does rework firing time affect prime capacity?

Every rework minute is a minute the kiln is not firing prime ware. The 87.11 minutes here is direct capacity you must either schedule into a gap or accept as lost prime throughput, which is why reducing first-pass defects is so valuable.

What if my rework needs more than one firing curve?

Split the batch by curve and run the calculator once per group, then sum. A single blended rate hides the extra kiln-change time between incompatible curves.

Ceramic, Tile & Sanitaryware Manufacturing calculator

Rework Firing Load Time Calculator

Rework Firing Load Time estimates the kiln minutes needed to refire rework tiles or fixtures, including the realistic overhead of sorting them and switching the kiln to a rework cycle. Refiring for reglaze, redecoration, or color correction competes for the same kiln capacity as prime production, so planners need to know exactly how much firing window each rework batch consumes. Firing schedulers and production planners use this to slot rework without starving the main line. The allowance factor keeps the estimate honest by accounting for the time lost handling odd lots and changing kiln settings.

What this calculator does

Estimate added kiln or handling time required to refire rework tiles, reglazed ware, or repaired sanitaryware pieces.
a kiln team is deciding whether a rework load can fit into the available firing schedule
It calculates the base kiln time to clear a rework batch at a given firing rate, then inflates it by a sorting and kiln-change allowance.

Formula used

Base rework kiln time = rework pieces to refire ÷ rework firing clearance rate
Required rework firing load time = base rework kiln time × rework sorting and kiln-change allowance factor

Inputs explained

Rework tiles or fixtures to refire:
Rework firing clearance rate:
Rework sorting and kiln-change allowance:

How to use the result

Use it when scheduling rework firings, sizing spare kiln windows, or deciding whether to batch rework or run it as it arrives.
It assumes a steady clearance rate; if the rework mix needs different firing curves, a single rate and one allowance will understate the true schedule impact.

Current U.S. benchmarks

Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate rework firing load time? Divide rework pieces by the firing clearance rate to get base time, then multiply by one plus the allowance. For 1,400 pieces at 18 per minute with a 12% allowance: 1,400 / 18 = 77.78 min, x 1.12 = 87.11 minutes.
Why add a sorting and kiln-change allowance? Rework rarely arrives as a clean full load. Time goes to sorting odd pieces, setting them, and switching the kiln to the right rework curve. The 12% allowance turns 77.78 base minutes into a realistic 87.11 minutes.
What is a typical clearance rate for rework firing? It depends on kiln type and ware size, but a value like 18 pieces per minute reflects a fast roller-hearth pass for small tile. Large sanitaryware fixtures clear far slower, so use a rate measured on your own kiln.
Should rework be batched or fired as it comes? Batching usually lowers the allowance because you change the kiln once for many pieces. Firing rework piecemeal raises the effective allowance well above 12% because each small lot triggers its own setup and change.
How does rework firing time affect prime capacity? Every rework minute is a minute the kiln is not firing prime ware. The 87.11 minutes here is direct capacity you must either schedule into a gap or accept as lost prime throughput, which is why reducing first-pass defects is so valuable.

Last reviewed 2026-05-12.