What type of primer is best for sealing knots in wood?

The best primer for sealing knots in wood is a shellac-based primer. Shellac is particularly effective at penetrating the wood and sealing off knots, which can contain sap and resin that may bleed through the paint over time. This type of primer dries quickly and adheres well to a variety of surfaces, making it ideal for woodwork that can present challenges, such as knots.

When knots in wood are left unsealed, they can cause discoloration of the paint applied over them, leading to unsightly spots and uneven finishes. The shellac-based primers form a barrier that prevents these substances from bleeding through, ensuring a more uniform and lasting paint job. Additionally, shellac-based primers are known for their excellent stain-blocking properties, which is crucial when working with natural materials like wood.

In contrast, water-based and latex-based primers may not provide the same level of sealing capability for knots and can allow some bleed-through, particularly in cases of more resinous woods. Oil-based primers can be effective as well but may take longer to dry and clean up compared to shellac. Thus, for the specific task of sealing knots in wood, shellac-based primers are superior due to their sealing properties and rapid drying time.