1. What are Volume Solids?
Volume solids of a paint are the percentage of the wet paint volume that remains as solid film on the surface after drying or curing.
It includes the volume of pigments, extenders and binder solids, and excludes the volume of solvents, water and other volatile components that evaporate.
Volume solids (%) = (Volume of non-volatile components ÷ Total wet paint volume) × 100
- High volume solids → thicker film per coat, higher build.
- Low volume solids → thin film, more coats needed for same DFT.
2. Why Volume Solids Are Important
- Dry film thickness (DFT): directly linked to how much solid material stays on the surface.
- Coverage (m²/L): determines how many square metres can be coated to a given DFT from 1 litre.
- Cost per m²: high volume solids generally give lower cost per specified DFT.
- VOC & regulations: higher volume solids usually mean lower solvent content and lower VOC.
3. Relationship Between Wet Film and Dry Film
For a given paint, volume solids link the wet film thickness (WFT) and dry film thickness (DFT).
DFT = WFT × (Volume solids ÷ 100)
Rearranged to get WFT required for a target DFT:
WFT = DFT ÷ (Volume solids ÷ 100)
Example (ideal, no losses):
- Volume solids = 50 %
- Target DFT = 50 µm
- Required WFT = 50 ÷ 0.50 = 100 µm
4. Coverage from Volume Solids and DFT
Theoretical coverage in m² per litre at a given DFT can be approximated by:
Coverage (m²/L) ≈ (Volume solids (%) × 10) ÷ DFT (µm)
Example:
- Volume solids = 45 %
- Specified DFT = 30 µm
- Coverage ≈ (45 × 10) ÷ 30 = 450 ÷ 30 = 15 m²/L (theoretical)
Practical coverage will be lower due to losses (overspray, absorption, roughness, application method).
5. Typical Volume Solids Ranges
- Conventional solvent-based enamels: 35–55 %
- Water-based architectural emulsions: 35–50 %
- High build epoxies / PU: 55–80 %
- Very high solids & 100 % solids systems: >80 % up to 100 %
6. Formulator’s Checklist
- Calculate true volume of all pigments, extenders and binder solids using densities.
- Exclude all volatile components (solvents, water, reactive diluents that evaporate).
- Use volume solids to design coating systems that meet specified DFT with minimum coats.
- Combine volume solids with PVC and CPVC to balance hiding, durability and cost.