How to Read Date Codes and Rotate Shelf Stock

Why this matters

Some of what rides in a van is quietly expiring. A can of solvent cement that has started to gel makes a joint that holds for a pressure test and lets go a month later. A tube of sealant past its life stays tacky for a week. A smoke alarm that sat on a shelf for four years arrives at the customer's ceiling with less than six years of its ten-year life left, and nobody told them. None of these look wrong in the bin. The only defense is to know which items age, read the date the manufacturer printed, and use the oldest first.

Which parts actually have a shelf life

Not everything ages, and treating every item as perishable wastes a shop's attention. The items that do, and what aging does to each:

• Solvent cements and primers (PVC, CPVC, ABS). The solvent evaporates through the cap over time and the cement thickens. Past its life, or once it turns jelly-like and will not flow off the dauber, it no longer softens the pipe surface enough to fuse. The manufacturer states the shelf life on the can or its data sheet; read it rather than assume one.
• Sealants, caulks, adhesives and two-part epoxies. Moisture-cure products (most silicones and many hybrids) start curing in the tube once moisture gets past the nozzle or the seal. An expired tube may extrude normally and never fully cure.
• One-component foam cans and some fire-stop products. These carry a printed expiration because the propellant and the chemistry degrade.
• Batteries. Alkaline and lithium primary cells carry a "use by" or manufacture date. Lead-acid batteries self-discharge on the shelf and are damaged if left discharged, so they need a recharge schedule, not just a date check.
• Electrolytic capacitors. In HVAC this means start capacitors, which are aluminum electrolytic. Run capacitors are metallized film and age far more slowly on a shelf. An electrolytic that sits unpowered for years can show increased leakage when first energized; the capacitor maker's data sheet states a storage period and what to do after it.
• Rubber and elastomer goods. O-rings, gaskets, washers, hoses and diaphragms harden and crack with heat, sunlight and ozone. Electric motors and battery chargers produce ozone, which is why a bin of O-rings next to a compressor ages faster than the same bin in a closet. ISO 2230 gives storage guidance and shelf-life periods by rubber type.
• Life-limited safety devices. Smoke alarms are to be replaced 10 years from the date of manufacture under NFPA 72, as adopted by your jurisdiction, and carbon monoxide alarms at the life the manufacturer states. The clock starts at the factory, not at your install, so shelf time comes straight off the customer's service life.

Metal fittings, wire, fasteners, copper and most electrical devices do not belong on this list. Keep it short so it gets done.

The steps

1. Make the shelf-life list for your own stock

Walk the shop shelves and each van once and write down every item that falls into the groups above, by part number or description. A typical small plumbing or handyman van carries ten to twenty such lines; an HVAC van adds capacitors and refrigeration sealants.

Why first: you cannot rotate what you have not identified, and a generic "check dates on everything" instruction is ignored by the second week. What breaks if skipped: the sweep in step 5 turns into a random glance, and the expensive misses (cement, alarms) are the ones nobody thinks of as perishable.

2. Decode the date on each item and write it in plain words

Manufacturers print dates in several formats, and the format is rarely labeled. Read the code once, at receiving, and write the real date on the item or bin in a form anybody can read: "USE BY 2028-03" or "MADE 2026-05".

WHAT IS PRINTED        HOW TO READ IT
EXP 03/28              expires March 2028
MFD 2026-05-14         made 14 May 2026
25073                  Julian: year 25, day 073
                       -> made 14 March 2025
2511 (on a capacitor)  year 25, week 11, OR
                       week 25 of 2011: ask maker
3Q24 (seal packet)     cured 3rd quarter 2024
LOT B4471              a lot, NOT a date

The Julian line is worth checking by hand once: January has 31 days and February 28 in 2025, so day 59 is the last of February and day 73 is 14 days later, 14 March. A four-digit week code is genuinely ambiguous between year-week and week-year; the maker's data sheet or the distributor resolves it, and a date that would be in the future under one reading settles it the other way. A lot code tells you nothing about age on its own, but it is the number a recall notice will name, so leave it legible (see related: How to Check a Part Against the Recall Databases).

Why: the person picking from the bin at seven in the morning will not decode a Julian date. What breaks if skipped: a tech reads "2511" as November 2025, or reads a lot number as a date, and keeps an item that should have gone.

3. Sticker anything that carries no date

Some items, especially loose rubber goods, bulk washers and repackaged kits, have no printed date. Put a received-date sticker on the bag or bin when it arrives: "REC'D 2026-06". It is not a manufacture date, so treat it as the latest the item could have been made.

Why: a received date is the only age evidence you will ever have for that item, and it costs seconds at the door. What breaks if skipped: undated stock never leaves the bin, because nobody can prove it is old.

4. Arrange every bin first-in, first-out

First-in, first-out (FIFO) means the oldest unit is the one picked next. In practice: new stock goes in at the back or bottom of the bin, picking happens from the front or top. On a van, where bins are shallow, put the older unit in a small "use first" tray in front of the bin.

Why: rotation only works if the default grab is the right one. A tech in a hurry takes what is in front. What breaks if skipped: new stock is loaded in front of old, the old unit migrates to the back and expires there, and the shop pays twice for the same line.

5. Run a monthly sweep against a window, not against the expiration

Once a month, someone with the list walks the shop and each van. Anything within 60 days of its use-by date moves to the "use first" tray and onto the next jobs that need it. Anything past its date comes out. Sixty days is a common starting point for a shop that turns these items every few weeks; a shop that uses a line slowly should widen it to 90.

Batteries get their own check at the same sweep: lead-acid units are recharged per the manufacturer's storage instructions, following your battery-handling procedure for ventilation and eye protection (see related: How to Charge and Handle Lead-Acid Batteries Safely).

Why a window: an item found on its expiration day is already a loss. An item found two months out is a scheduling decision. What breaks if skipped: the shop discovers expired stock at the job, which is the most expensive place to find it.

6. Test the marginal item before you trust it

Inside the window, or where a date is unreadable, test before use. Cement should flow freely off the dauber and wet the pipe; if it strings, gels or skins over in the can, it is done, and it is not thinned back to life with primer or thinner. Sealant gets a small test bead on scrap at the start of the day; if it has not skinned in the time the tube states, the tube is out. Open solvent cement only with ventilation and away from flame or a running pilot, since its vapor is flammable and an irritant to breathe; the product's SDS names the respiratory and glove protection.

Why: a date is a manufacturer's conservative estimate under good storage. A hot van shortens it, a cool shop can extend it, and the test is what tells you which happened. What breaks if skipped: you either throw away good stock on a date alone or install bad stock on a date alone.

7. Dispose of expired items by what they are, and record the loss

Expired cement, primer, foam and adhesives go out by the disposal instructions in section 13 of the product's SDS and your local business-waste rules, not loose in the van trash. Expired lithium and lead-acid batteries go to a recycler, with terminals taped on lithium cells. Expired smoke alarms go back to the manufacturer's take-back or local rules, since some contain a small radioactive source. Log what was scrapped and how many units.

Why log it: the scrap list shows which lines you overstock. What breaks if skipped: the shop keeps reordering the same quantity of a slow item and keeps throwing a third of it away.

Worked example: one van, one sweep

A handyman and light-plumbing van is swept for the first time. On the list: 6 smoke alarms, 3 cans of PVC cement, 4 tubes of silicone, 2 start capacitors and an O-ring assortment.

• Smoke alarms. Two are marked made 2026-02, four are marked made 2022-03. The sweep happens in October 2026. A 2022-03 alarm installed today reaches its 10-year replacement date in March 2032, which leaves 5 years and 5 months of service; a 2026-02 alarm installed today lasts to February 2036, 9 years and 4 months. The four older alarms are not expired, but each one installed hands a customer a device with roughly half its life gone. The shop decides to install them only where the customer is told the replacement date, writes that date on the alarm and on the invoice, and stops buying more than a month's worth at a time.
• Cement. One can is past its printed date. It still looks liquid. Test: it strings off the dauber and leaves a skin in the can. Out, by the SDS disposal section. The other two are in date and flow freely.
• Silicone. Four tubes, no printed date anyone can read. Received-date stickers say 2025-11 on two and 2026-08 on the other two. The two older tubes get a test bead: one skins in the stated time, one is still wet the next morning. One tube out.
• Start capacitors. Both carry "2511". The distributor confirms the maker uses year-week, so week 11 of 2025. In date, used first on the next two compressor calls.
• O-rings. The assortment box rode in the cab next to a battery charger. Several rings in the most-used sizes have surface cracks when bent double. The box is replaced and the new one moves away from the charger.

Tally: of 5 lines checked, 3 lost stock (cement 1 of 3 cans, silicone 1 of 4 tubes, O-rings the whole box), 1 was reclassified rather than scrapped (alarms, 4 of 6 now sold with a stated replacement date), and 1 was clean (capacitors).

What changes the answer. A shop in a hot climate whose vans sit in sun all day should treat the printed date as optimistic for cement, sealant and rubber, and widen the sweep window. A shop that installs alarms in volume should stop treating them as stock at all and order them per job, because every month on the shelf is a month taken off the customer.

How to verify you got this right

After three monthly sweeps, two things should be true. The scrap log should shrink, because the "use first" tray is moving items out before they expire. And nobody on the crew should be able to point to a bin where the oldest unit is behind the newest. If the log is not shrinking, the window is too narrow or the order quantities are too large; if old units keep turning up at the back, the loading habit from step 4 has not taken, and it is a crew conversation, not a list problem.

References

• NFPA 72, National Fire Alarm and Signaling Code, in the edition your jurisdiction has adopted (smoke alarm replacement at 10 years from manufacture).
• ISO 2230, Rubber products, guidelines for storage.
• Manufacturer data sheets and SDS for each shelf-life product (stated shelf life, storage temperature, section 13 disposal).
• See related: Climate and Storage Considerations for Sensitive Inventory
• See related: How to Charge and Handle Lead-Acid Batteries Safely