water-based dye (CTH + CFH2 binder) under 2K solvent-borne polyurethane: thixotropic PU primer PTS50 ×2 + thixotropic PU lacquer PTL50 ×1, aromatic isocyanate hardener (legacy C50 → PC20/PC25)
Finishing beech chairs (PU)
- Substrate
- Solid beech — chairs (turned and profiled parts, vertical surfaces)
- Result
- Stained beech with visible grain and even, blotch-free colour; a clear thixotropic PU film with no sags, sheen set by the chosen PTL50 grade (10–90 gloss).
- 01
Sanding
Abrasive: K60, K80
Preparing raw beech for the dye. Coarse grit (60→80) opens the surface so the dye goes darker; finer grit gives a lighter tone (official wood-preparation page). De-dust before staining.
- 02
Staining (dye bath)
CTH 100 %CFH2 800 %WATER 1200 % (Thinner)
- Consumption
- 80–100official
Bath: 100 parts CTH concentrate (colour to sample) + 800 parts CFH2 binder + 1200 parts water. The binder evens out the colour on beech (less blotching on end grain and wild grain). Dip, let the excess drain, wipe off drips at the bottom of the legs.
Mix for this step
Mix calculator
gRatio 100 : 800.0 : 1,200.0
Component Weigh out CTHpart A 23.8 g CFH2base 190 g WATERThinner 286 g Total 500 g Covers roughly 6.25 m² at 80 g/m².
- 03
Drying
Drying: [object Object] °C, 30 min
The dye must be fully dry before the PU primer — the water stain raises the grain, which is cut back by the sanding of the primer coats.
- 04
Priming (coat 1)
PTS50 100 %C50 50 % (Hardener)S80 20 % (Thinner)
- Consumption
- 150official
PTS50 + 50 % hardener (C50 is a legacy code; use PC20 or PC25 today) + 20 % slow thinner S80. The thixotropic primer does not sag on legs and rails. S80 instead of the official S50: a slow thinner improves flow and prevents solvent popping during the 30–35 °C dry.
- 05
Drying
Drying: [object Object] °C, 2 h
Forced drying in a warm room until sandable.
- 06
Sanding
Abrasive: K120
K120 sanding mats: cut back the raised grain and nibs of primer coat 1 without cutting through the dye on edges. De-dust.
- 07
Priming (coat 2)
- 08
Drying
Drying: [object Object] °C, 2 h
- 09
Sanding
Abrasive: K120
K120 de-nib before the topcoat: a uniform matt surface for intercoat adhesion. De-dust.
- 10
Topcoat (lacquer)
- 11
Drying (final)
Drying: [object Object] °C, 2 h
After 2 h at 30–35 °C the chairs can be stacked/packed with spacers; testing and full service loads only after full drying.
Ask about this system
Answers are based on this finishing schedule and its products.
System characteristics
- Coats
- 1 dye + 2 primer + 1 lacquerofficial
- Wet application (g/m²)
- 80–100 (dye) + 150 + 150 (primer) + 150 (lacquer) = 530–550 g/m²official
- Solids · Primer part A
- 44 ± 1 (catalog 45)dealer
- Solids · Lacquer part A
- 44 ± 1 (catalog 46)dealer
- Solids · Hardener
- 28 ± 1 (PC20, as C50 equivalent)dealer
- Solids · Dye binder
- 41 ± 1 (CFH2)dealer
- Solids · Primer ready mix
- ≈ 34 %recommended
- Solids · Lacquer ready mix
- ≈ 32–33 %recommended
- Gloss
- set by the PTL50 grade — not stated in the schedule gloss units, 60°
- Thixotropy
- yes — primer and lacquer are both thixotropic: no runs on verticals, ideal for chairs; levels worse on large flat panelsofficial
- Viscosity · Primer part A
- 70 ± 5 s VZ-4, 20 °Cdealer
- Viscosity · Lacquer part A
- 80 ± 5 s VZ-4, 20 °Cdealer
- Viscosity · Spray
- ≈ 22–28 s (primer), 18–24 s (lacquer) DIN4/VZ-4recommended
- Pot life
- 4 h at 20 °C (primer and lacquer mixes)dealer
- Drying time · Touch dry
- primer 20 min, lacquer 30 min at 20 °Cdealer
- Drying time · Sandable or stackable
- 2 h at 30–35 °Cofficial
- Drying time · Full
- 8 h at 20 °Cdealer
- Drying time · Full hardness
- 5–7 days at 20 °Crecommended
- Adhesion
- good — mechanical key from K120 sanding between every coat; water dye with binder does not hinder PU adhesion once dryrecommended
- Hardness
- not published
- Elasticity
- primer: elastic, shrink-resistantcatalog
- Wear resistance
- moderate — furniture grade, not parquet graderecommended
- Chemical resistance
- not published
- Lightfastness
- aromatic hardener → the clear coat will amber over timecatalog
- Hiding power
- n/a — transparent systemrecommended
- Coats
- 4
- Coats detail · Dye
- 1
- Coats detail · Primer
- 2
- Coats detail · Lacquer
- 1
- Sanding operations
- 3
- Min cycle time (h)
- 6.5