General Finishes Stain Blocker is a high-performance water-based primer formulated to prevent wood tannins, dyes, smoke, and other stubborn stains from bleeding through your finish. Designed for challenging projects—especially on woods like mahogany, pine, and cedar—it creates a strong, clean foundation that improves adhesion and enhances the clarity of your topcoat. Stain Blocker sands easily, dries fast, and delivers reliable protection against bleed-through, making it an excellent choice for furniture, cabinets, and refinishing work where a flawless final finish matters.