A single soft patch on a hand-poured project is a nuisance; the same defect showing up unpredictably across an automated dispensing line is a production problem with a root cause hiding somewhere in the metering, mixing, or dispensing hardware — not in operator technique.

Q: Our parts show random soft patches even though the dispenser settings haven’t changed — where do we look first?

Start with the static mixer, not the metering pump. A worn or partially clogged mixing element can pass a perfectly correct resin-to-hardener ratio through the system while still delivering streaks of unmixed material at the nozzle tip, because the ratio and the mixing quality are controlled by two different pieces of hardware. Pull the mixer and inspect the internal elements for wear rounding or a partial blockage before assuming the metering pump has drifted.

Q: How do we tell a ratio problem from a mixing problem without sending samples to a lab?

A simple shot-weight check answers this quickly. Dispense several individual shots of Part A and Part B separately into tared cups and weigh them; if the ratio is outside the formulation’s tolerance — commonly held to within about 2% by weight on a volumetric metering system — the fault is upstream in the pump or ratio valve. If the shot weights check out but soft spots persist, the fault is almost certainly incomplete mixing downstream of the metering stage, not a chemistry problem at all.

Q: What acceptance window should the ratio actually be held to?

Most industrial two-part epoxies specify a ratio tolerance in their technical data sheet, and it’s tighter than most operators assume — a formulation nominally mixed at 100:35 by weight often has no more than 2-3% tolerance before excess unreacted resin or hardener starts showing up as tack. Incure recommends verifying that tolerance against the specific grade’s data sheet rather than relying on a generic industry rule of thumb, since cure chemistry and stoichiometric sensitivity vary meaningfully between formulations.

Q: Can ambient temperature alone explain a soft spot if the ratio and mixing both check out?

Yes, and it’s worth ruling out before pulling the dispensing hardware apart further. An exothermic cure reaction slows measurably below a formulation’s minimum cure temperature, and a work cell positioned near a loading-dock door, an HVAC vent, or an uninsulated exterior wall can run several degrees cooler than the rest of the floor. An infrared thermometer scan of the work cell surface — not just the ambient air reading from a wall thermostat — often reveals a localized cold zone that a general facility temperature log would miss entirely.

If a batch keeps showing intermittent soft spots after ratio and mixing both check out clean, Email Us with your shot-weight data and cell temperature log — a second set of eyes on the numbers often catches a pattern that’s hard to see from inside the process.

Q: A soft spot showed up in one specific work cell but nowhere else on the line — what does that usually mean?

Isolate the variable to that cell specifically: check the dispensing head’s mixer age against your preventive-maintenance schedule, confirm the cell’s resin and hardener reservoirs are drawing from the same lot as neighboring cells, and verify the cell’s local temperature against the rest of the floor. A defect confined to one cell almost always traces back to equipment condition or a localized environmental factor rather than the resin formulation itself, since the same lot is presumably feeding multiple cells without the same failure.

Q: Once we’ve isolated a soft batch, what’s the right way to log it so this doesn’t recur?

Record the cell ID, shift, resin and hardener lot numbers, shot-weight verification result, and cell temperature at the time the defect was found — not just “soft spot, reworked.” A defect log built this way turns an isolated incident into a searchable pattern; if the same cell ID or the same hardener lot number keeps appearing across multiple soft-spot reports over several weeks, that’s the signal to schedule mixer replacement or investigate a supplier lot rather than continuing to treat each incident as independent. This kind of traceability matters just as much for catching a slow equipment drift as it does for any single acute failure, and it turns troubleshooting from guesswork into a data review.

Correcting an Isolated Soft Spot Once Found

A confirmed soft spot needs full removal rather than an attempt to reheat and restart the reaction — a stalled cure generally will not resume once the reactive window has passed. Scrape and solvent-wipe the uncured material back to sound, hard epoxy, lightly abrade the surrounding perimeter to create a mechanical key, and recoat with a freshly verified batch rather than assuming the same conditions that caused the original defect have changed on their own.

Incure’s technical support team works through this same ratio-mixing-temperature diagnostic sequence with production customers regularly, since the order matters — checking mixer condition before assuming a ratio drift saves a line from an unnecessary pump recalibration. For related process guidance, see how CTE mismatch causes adhesive bond failure, a different but related thermal-cycling failure mode worth ruling out on any bonded assembly, and how physical damage during cure is handled differently in our guide to footprints and imprints in soft epoxy. For heavy-duty repair applications where cure consistency is safety-critical, UV glue versus epoxy for heavy-duty repairs covers a related chemistry comparison.

If soft spots are recurring across your production line despite a clean ratio and mixing check, Contact Our Team to review your dispensing equipment maintenance schedule and batch documentation practices.

Visit www.incurelab.com for more information.