Two drums, two different failure modes. The A-side is ISO, which reacts with any moisture it meets, including the air in a half-empty drum. The B-side is the resin blend, which separates when it sits and loses its catalysts to heat and age. Both are cheap to protect and expensive to lose.
The numbers from the data sheets
| Thermoseal HFO (closed cell) | Thermoseal 500 (open cell) | |
|---|---|---|
| Storage temperature, both drums | 50 to 75°F | 50 to 80°F |
| Shelf life, A-side (ISO), unopened | 1 year | 1 year |
| Shelf life, B-side (resin), unopened | 180 days | 180 days |
| Drum temperature before spraying | warm gradually to 77°F, do not recirculate | recirculate at 77 to 90°F |
Shelf life assumes the drum stayed inside the storage range the whole time. A B-side that spent August in a trailer at 110°F does not get its 180 days.
The A-side: keep water out
ISO reacts with water. Humid air, condensation from a cold night, a splash from a hose: each one makes carbon dioxide and solid urea crystals inside the drum. The signs are pressure when you crack the bung, a skin or crust at the top, crystals on the fitting, sludge at the bottom. A drum with crystals is finished. Do not try to spray through it, and do not pour it into another drum.
- Keep the bung and the vent fittings closed tight whenever a hose is not in it, between sets and overnight.
- Never add anything to an A drum, and never warm it with water.
- Bring a cold A drum up slowly in a warm room or with a drum blanket. From a 25°F trailer plan on the better part of a day; a full drum warms from the outside in.
- Use the oldest A first. Write the date you received it on the drum.
The B-side: keep it cool and mixed
The resin blend holds the catalysts, surfactants, fire retardants and the blowing agent. Heat ages it: the catalyst load drops, the foam rises slower and cures softer. Sitting lets it settle: the heavy parts go to the bottom and the first sets off the drum run off recipe.
- Keep B drums out of the sun and out of a closed trailer in summer. 75°F is the ceiling for the HFO resin.
- Roll or stir a B drum that has sat more than a few days before you draw from it.
- Watch the 180 days. A weekly crew never gets near it; a crew that buys a pallet in spring for the whole year does.
- Thermoseal HFO B-side is not recirculated through the rig: the blowing agent is pressure-sensitive. Warm it to 77°F and spray.
Storage that works on a real lot
- Upright, capped, on a pallet, inside a conditioned space. A heated corner of the shop beats the best trailer.
- Drums on the truck overnight in winter are cold drums at 7 am. Load from the warm shop in the morning or run a drum heater overnight.
- Do not stack B on A. A leaking B drum on top of an open A fitting is a ruined A drum.
- Keep the A-side and B-side clearly marked and the hoses color-coded. A cross-contaminated drum is a cross-contaminated pump.
Signs a drum is bad
| Drum | What you see | What it means |
|---|---|---|
| A-side | Crystals, crust, sludge, pressure at the bung | Moisture got in. Replace the drum. |
| A-side | Very dark, thick, slow to pump | Old or overheated. Check the date and the storage. |
| B-side | Separated layers that do not re-mix with rolling | Past its life or frozen. Replace. |
| B-side | Foam rises slowly and stays soft at the right temperatures | Catalyst has faded. Check age and heat exposure. |
| Either | Swollen drum | Pressure from reaction or heat. Do not open indoors; move it out and call the branch. |
A half set that is capped tight, kept at 60 to 75°F and used within a couple of weeks sprays fine. That is how the leftover from the set-count math gets used on the next job.