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What is Wood Knotting?

Published in Wood Treatment 2 mins read

Wood knotting, specifically knotting, is a product used in painting and finishing timber to seal imperfections, particularly knots, and also treat certain types of wood like resinous and creosoted timber. Its primary purpose is to prevent bleeding – the unsightly seepage of resin or creosote through the applied paint film.

Applying knotting is a crucial step in preparing wood surfaces for painting, especially when dealing with knotty or naturally oily/tarry wood types.

Why Use Wood Knotting?

Knots in wood contain concentrated resin, which can react with paint and cause yellow or brown stains to appear on the surface over time, even after multiple coats of paint are applied. Similarly, resinous timber and creosoted wood contain substances that can bleed through paint.

The knotting agent creates a barrier or seal over these areas, effectively locking in the problematic substances and preventing them from migrating through the paint layer. This ensures a cleaner, more uniform, and longer-lasting finish.

How to Apply Knotting

Proper application is key to the effectiveness of knotting. Based on common practices and product instructions like the one provided, the process involves a few specific steps:

  • Preparation: Before applying knotting, the wood surface, particularly the areas around knots, should be sanded smooth. This creates a good base for the knotting to adhere to.
  • Application: Apply the knotting product liberally over the knots and the surrounding wood area.
  • Coverage for Specific Timber: For resinous and creosoted timber, the entire surface that will be painted should be sealed completely. This typically requires applying two coats of the knotting agent for thorough protection.
  • Handling After Application: Once knotting has been applied, do not sandpaper it. Sandpapering the knotting can break the seal it forms, reducing its effectiveness in preventing bleed-through.

Application Checklist

Here's a quick summary of the application steps:

  1. Sandpaper the surface smooth before applying knotting.
  2. Apply knotting liberally over knots and surrounding areas.
  3. Apply two coats to completely seal resinous and creosoted timber.
  4. Do not sandpaper the knotting once it has been applied.

By following these steps, the knotting creates a necessary seal, ensuring that the subsequent paint layers remain clean and unstained by natural wood resins or creosote.