Grade 10 woodwork Wood Processes and Products – Surface preparation Notes

1. Explain the reasons for finishing a wood product.
2. Select materials and tools for surface preparation.
3. Prepare a wood surface to receive clear varnish.
4. Appreciate the importance of preparing wood surfaces before finishing.
5. Understand the concept of surface preparation.

What is Surface Preparation?

Surface preparation means getting the wood ready so a finish (paint, stain or clear varnish) will stick well and look good. Good preparation gives an even colour, smooth feel, strong adhesion and longer life for the finish.

Why finish and prepare a wood product?

• Protects wood from moisture, weather, insects and wear (longer life).
• Improves appearance — brings out grain and gives a smooth, even surface.
• Makes cleaning and maintenance easier.
• Helps the finish bond correctly — prevents peeling, flaking or blotching.
• Seals knots and reduces movement (swelling/shrinking) when varnished correctly.

Materials and tools for surface preparation

Choose tools and materials that are commonly available in Kenya: local timber yards and hardware shops usually stock these.

PPE and safety: dust mask or respirator, safety goggles, gloves, good ventilation, and no open flames near solvents.

Step-by-step: Prepare wood surface for clear varnish

1. Inspect the wood: check for cracks, knots, unevenness, old finishes or glue residue.
2. Clean the surface: remove dirt, grease and oil with a cloth dampened with denatured alcohol or turpentine; allow to dry.
3. Remove old finish (if any): use a scraper, sandpaper or chemical stripper. Work with care and follow safety instructions.
4. Level and flatten: plane or sand rough high spots. Start with coarse grit (e.g., 80–120) only where needed.
5. Progressive sanding: sand across the grain starting coarse → medium → fine (e.g., 120 → 180 → 220). Finish with 320 grit just before varnish for a very smooth surface.
6. Fill defects: use a suitable wood filler for holes or gaps. Let it dry fully, then sand flush with fine grit.
7. Remove dust: wipe with a tack cloth or slightly damp lint-free cloth to remove all dust. Compressed air can help in joints.
8. Apply sanding sealer (optional): for open-grained woods (e.g., some local softwoods), sealers reduce blotching and improve varnish build. Lightly sand after sealer cures.
9. Final tack: wipe with tack cloth immediately before varnish to ensure a dust-free surface.
10. Apply first coat of clear varnish: follow manufacturer instructions for brush type and drying times. After drying, very lightly sand with 320–400 grit between coats and remove dust before the next coat.

Tip: Always sand with the grain to avoid visible scratches. Test finish on a scrap piece of the same wood first.

Importance of preparing surfaces

• Prevents finish failure (peeling, flaking or uneven gloss).
• Produces a smooth feel which is important for furniture and doors.
• Ensures the clear varnish shows the true colour and grain of the wood.
• Helps conserve local timber by extending product life (good for households and small carpentry businesses in Kenya).

Suggested learning experiences (practical & classroom)

• Demonstration: Teacher demonstrates sanding sequence and filler application on a scrap pine board. Learners note steps and safety points.
• Group practical: In groups of 3–4, learners prepare a small board (e.g., 200 x 100 mm) of local timber (pine/eucalyptus/mahogany). Tasks: clean, sand, fill defects, seal and apply at least one coat of clear varnish.
• Compare results: Each group displays an unprepared board and their finished board. Class discusses differences in appearance and toughness.
• Field visit / guest talk: Visit a local carpenter or invite a craftsperson to show professional surface preparation techniques used in Kenyan workshops.
• Safety practice: Run a short session on correct PPE use, handling solvents, and safe disposal of oily rags (important: rags soaked in oil/varnish can self-ignite if bunched).
• Assessment tasks: Practical test — prepare and varnish a sample board to specified standard; short quiz on selection of grits, tools and safety rules.
• Extension: Try different varnishes (water-based vs oil-based) on matched samples and record differences in drying time, sheen and ease of sanding.

Quick visual reminders

Short lesson plan (1 practical lesson — 90 minutes)

1. 10 min — Introduction: explain outcomes and safety.
2. 15 min — Teacher demo: sanding sequence and use of filler.
3. 50 min — Practical: learners work in groups to prepare and varnish sample.
4. 10 min — Clean up and safety checks.
5. 5 min — Show & tell and short reflection.