2K PU sealer additives must be selected without disturbing the polyol–isocyanate reaction, pot life, sanding, or topcoat adhesion. For a solvent-borne sealer, CHLUMIWE® 3071 is the wetting route, CHLUMIAG® 3467 is the compatibility/flow route, and CHLUMICRYL® DF-D912R is the solvent-side, varnish-compatible foam-control route when a grind stage exists. None should be added blindly to a mixed two-component pot.
Start with the first failed stage: substrate entry, Part A manufacture, mixed-pot stability, film flow, sanding, or recoating. A smooth fresh film can still fail through short pot life, soft cure, intercoat loss, trapped solvent, craters, or poor sandability.
2K PU sealer stage map
| Evidence | First controlled check | Product route if confirmed |
|---|---|---|
| Clean wood, veneer, or prepared substrate shows incomplete wetting or edge pullback | Verify moisture, sanding, dust, contamination, resin viscosity, and application | 3071 in Part A |
| Substrate wets but flow or resin/additive compatibility remains uneven | Remove optional surface additives and run a low-dose ladder | 3467 in a validated Part A stage |
| Filled or pigmented solvent sealer retains air from the grind | Standardize grind shear and foam-decay test | D912R at the abrasive/grind stage |
| Defect appears only after hardener addition | Audit mix ratio, induction, pot age, water contamination, film build, flash, and cure | Process/stoichiometry correction before additive escalation |
| Produit | Published fit | Supplier guidance | Critical boundary |
|---|---|---|---|
| CHLUMIWE® 3071 | Water, solvent, and UV; wetting/surface-tension reduction | 0.1–1.0% total formulation; grind, stir, or post-addition | Waterborne systems may show foam stabilization; test compatibility and pot life in 2K PU |
| CHLUMIAG® 3467 | Water, solvent, and UV; compatibility-prioritized surface control | 0.05–1.0% for solvent systems; direct or diluted addition | Published hydroxyl value is not proof of zero effect on NCO balance; verify stoichiometry and cure |
| CHLUMICRYL® DF-D912R | Solvent-based; 2% active; improved varnish compatibility, defoaming and anti-cratering | 0.1–0.25% total formulation; add to abrasive/grind | Do not assume a clear, no-grind sealer can use the same incorporation route |
Lock the 2K reaction conditions first
Record Part A resin, hydroxyl value, solvents, fillers, moisture, additives, Part B isocyanate type and NCO content, mix ratio by weight/volume, induction, temperature, humidity, pot life, application viscosity, film build, flash, and cure. Water, alcohol, amine, and hydroxyl-bearing materials may alter isocyanate demand or side reactions; evaluate the complete formulation rather than relying on an additive label.
Prequalify candidates in Part A when technically appropriate. Do not make unplanned post-additions to mixed material because every minute of pot age changes viscosity and film formation.
Use 3071 for a confirmed substrate-wetting problem
Screen 3071 when a clean, correctly sanded substrate still shows incomplete entry or retraction. Its public page covers solvent systems and gives 0.1–1.0% guidance. Start low, hold sanding and application constant, and compare wetting, craters, leveling, penetration/holdout, and edge coverage.
Measure mixed viscosity and pot life at the same time. Better initial wetting does not justify a dose that shortens working time, increases foam, or weakens sanding and topcoat adhesion.
Use 3467 only for compatibility and flow evidence
3467 is the compatibility-focused route after wetting and contamination are controlled. Its page allows solvent-system use and direct or diluted addition. It also reports a hydroxyl value and mentions polyurethane incorporation routes; this does not establish a universal reactive-leveling claim or guarantee that NCO/OH balance is unaffected.
Run a small Part A ladder, calculate the full reactive balance with current technical data, and compare pot life, cure, hardness development, sanding dust, gloss, intercoat adhesion, and resistance. The page says to avoid mixing with other additives, so evaluate it alone before rebuilding combinations.
Use D912R only for a verified grind-stage foam route
D912R is relevant when a solvent-based, filled or pigmented sealer entrains air during the abrasive/grind stage and varnish compatibility matters. The public page specifies 2% active content, 0.1–0.25% total-formula guidance, and addition to the abrasive material.
If the sealer is clear and has no grind, obtain a current supplier-approved incorporation method before trial. Do not convert a grind-stage instruction into a casual late addition. Track foam generation/decay, wet-film bubbles, pinholes, craters, clarity, gloss, and cure.
Why CHLUMIFE 3370 is not the default sealer route
CHLUMIFE® 3370 is presented publicly as a solvent/UV feel agent, supplied as a waxy solid with a melting point of at least 50°C. The page does not support the earlier “reactive leveling” positioning. A sealer normally prioritizes pore filling, sanding, intercoat adhesion, and topcoat acceptance; surface feel belongs to a later, separately qualified finish decision.
Build a controlled sealer experiment
- Fix substrate preparation. Hold species/veneer, moisture, sanding sequence, dust removal, and contamination.
- Fix Part A manufacture. Hold order, grind, shear, temperature, water content, aging, and filtration.
- Fix 2K mixing. Use calibrated mix ratio, induction, temperature, and defined pot-age application points.
- Fix application. Hold viscosity, film build, flash, airflow, cure, sanding time, and recoat window.
- Change one route. Compare a blank plus a short dosage ladder and repeat the winning candidate.
Measure cure, sanding, and recoat together
ASTM D5402 describes solvent-rub assessment for chemically curing coatings and warns that solvent resistance alone does not prove full cure. ASTM D3359 rates tape adhesion on suitable metallic substrates and notes limits for multicoat interpretation; use the substrate-appropriate customer method for wood or veneer. ASTM D823 helps control test-film thickness.
Also record pot-life viscosity, gel time, dry-to-sand, sanding powder/loading, pore fill, shrink-back, pinholes, craters, gloss, hardness development, topcoat wetting, intercoat failure location, water/chemical resistance, and appearance after aging.
Common 2K PU sealer errors
Calling 3467 a universal reactive additive
The public data does not justify that shortcut. Confirm current TDS, reactive balance, Part A stability, pot life, cure, and topcoat adhesion in the actual polyol/isocyanate system.
Adding defoamer to a mixed pot
D912R is documented for the abrasive/grind stage. A late mixed-pot addition changes both dispersion history and pot age and is not a valid equivalent.
Optimizing feel before sanding and recoat
A sealer that feels smooth but clogs paper, reduces intercoat adhesion, or rejects the topcoat fails its primary job.
Request a 2K PU sealer shortlist
Send the substrate, sanding and moisture, Part A resin/solvent/filler system, Part B isocyanate and mix ratio, water content, grind, current additives, pot-life profile, application, film build, flash/cure, sanding and topcoat window, plus defect photographs. Ask Longchang Chemical to compare 3071, 3467, or D912R.