PC21
PC21 hardener for 2K PU coatings
Aromatic (isocyanate) hardener with fairly high reactivity and fast drying. Second component for 2K PU primers and matt PU lacquers. There is no official t-color.ru page and it is not on the 2025–2026 catalogue hardener chart; the dealer text is word-for-word the same as for PC20.
- Part B for 2K PU primers (incl. white PPS50277, where the owner lists it as an alternative to PC20)
- Part B for matt PU lacquers
Ask about PC21
Answers are based on the PC21 data and the products it mixes with.
Mixing matrix
- S50Thinner% by weight: 10–20 % of part Aworkshop
thinning the PPS50277 + PC21 mix
Don't thin the hardener itself — thinner goes into the mix per the base product's sheet. On a 1.5 mm tip run 20 % S50 and accept lower build.
- % by weight: per host product %recommended
any other host
S80 slows evaporation but doesn't change cure time.
| Role | Material | % by weight | % by volume | When |
|---|---|---|---|---|
| Thinner | S50 | 10–20 % of part Aworkshop | — | thinning the PPS50277 + PC21 mixDon't thin the hardener itself — thinner goes into the mix per the base product's sheet. On a 1.5 mm tip run 20 % S50 and accept lower build. |
| Thinner | S50 / S80 | per host product %recommended | — | any other hostS80 slows evaporation but doesn't change cure time. |
Percentages are per 100 parts of component A.
Characteristics
- Chemistry
- aromatic isocyanatedealer
- Solids
- 28 ± 1 %dealer
- Reactivity
- fairly high reactivity and drying speeddealer
- Lightfastness
- Lightfastness of PU coatings depends on the hardener's isocyanate: aliphatic hardeners are more lightfast than cheap aromatic onesofficial
- Moisture sensitivity
- Isocyanate hardeners are moisture-sensitiveofficial
- Yellowing rank
- expected similar to PC20: low end of Technocolor's yellowing-resistance scale (PC72 → PC10 → PC20 → … → AC40)recommended
Application
HVLP
- Nozzle
- 1.8–2 mmworkshop
- Pressure · air
- per host product (HVLP: ~2.0–2.2 bar at the inlet with trigger pulled, ≤0.7 bar at the cap)recommended
- Spray viscosity
- per host; adjust with the host's thinner, never with extra hardenerrecommended
- Consumption
- 120–150 g/m²workshop
The hardener is never applied on its own. Mix by weight on scales, stir, let it stand 5–10 min, strain; stay inside pot life (PPS50277: 3–4 h).
Process and compatibility
- Temperature and humidity
- work at 18–25 °C, RH below ~70 %recommended
- Don'ts
- Don't leave the can open — air moisture ruins it (goes cloudy, thickens, gels).
- Don't mix it with water-borne products.
- Don't add it by eye or above the host's ratio.
- Don't use it in white/pale topcoats or gloss systems where non-yellowing matters — use hardeners higher on the catalogue's yellowing-resistance scale (PC60, PC210/AC200 for gloss, AC40/AC41 for acrylics) as the host's sheet specifies.
- Never pour leftover mix back into the hardener can.
Storage
- Conditions
- tightly closed, out of direct sun and weatherdealer
- Storage temperature
- +5…+25 °C, dryrecommended
- After opening
- reseal immediately; if cloudy, skinned or gelled — discardrecommended
- Packaging
- 0.5,2.5,12.5,25 Ldealer
Safety: Wear overalls and respiratory, eye and hand protection. Keep out of reach of children. Dispose of waste at an approved site, not into the environment. Contains isocyanates: when spraying use an A2P3 carbon respirator or air-fed mask and good extraction; anyone sensitised to isocyanates must not use it.
Mixed into
Sources
Value tags: “official”, “dealer”, “catalog”, “schedule” are Technocolor data; “workshop” is from our own datasheets; “recommended” is our engineering estimate (hover to see the reasoning).
- dealer product page: properties, use, storage/safety note, solids 28 ± 1 %, pack sizes 0.5/2.5/12.5/25 L, per-litre prices by pack (re-checked 2026-10-05)
- PC20 dealer page — identical text and solids, used for comparison
- dealer hardener listing: PC21 from 508 ₽/L (= 25 L pack price per litre)
- aromatic vs aliphatic hardener lightfastness
- isocyanates: water-sensitive, partly volatile
Not covered by the sources
- No official t-color.ru page; not on the 2025–2026 catalogue hardener chart or in any official finishing schedule
- No TDS found (local PDFs none; dealer searches on t-colormarket.ru/woodonline.ru turned up only the t-colormarket page; web search budget exhausted)
- How PC21 differs from PC20 is not stated anywhere (dealer text identical)
- Viscosity, density, NCO %, flash point of the hardener
- Ratio by volume for any host (PPS50277 given by weight only)
- Which official products allow PC21 (only the owner's PPS50277 datasheet names it)
- Shelf life (unopened/opened) and storage temperature limits
- Schedules mention a hardener 'C61' (otdelka-izdelii-iz-ppu-pu, otdelka-stoleshnits) — unknown whether related to PC21