What's inside
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Why filler shows through paint
Wood filler can look smooth before painting and still leave a visible patch afterward. The usual causes are a raised edge, a shallow dip, sanding scratches, or filler that absorbs primer differently from the surrounding wood. Paint hides color differences better than stain, but it does not level the surface. A coat of paint can make a ridge or hollow easier to see, especially in raking light.
The goal is not to sand the filler as aggressively as possible. It is to bring it flush with the wood without cutting a depression into the surrounding surface, then prime the patch so it takes paint evenly.
Choose filler that suits the repair
For small nail holes and shallow dents in interior trim or furniture, premixed water-based wood filler is inexpensive and easy to sand. It is a good choice when the repair will be painted and does not need to move much. For deeper holes, use a product rated for thicker repairs, or fill in layers; a thick mass of ordinary filler can shrink, crack, or take a long time to dry.
Two-part epoxy filler is tougher and usually shrinks less, which helps on damaged edges or larger repairs. It costs more, has a limited working time, and can be harder to sand. For a routine painted nail hole, that extra durability is rarely worth the expense. Check the label for maximum fill depth, drying time, and whether the product is suitable for interior use.
Compare paintable wood fillers by intended repair depth and drying time, not just package size.
Tools and sanding grit
A small sanding block gives more control than holding a folded sheet of sandpaper, particularly on flat trim. Use a flexible sanding sponge for profiles and corners. A random-orbit sander can remove filler too quickly on a small patch and round over nearby edges, so save it for broad, flat surfaces where it is easy to keep moving.
| Surface or task | Starting grit | Finishing grit | Trade-off |
|---|---|---|---|
| Small filler patch on trim | 120–150 | 180–220 | Hand sanding is slower but gives better control. |
| Broad flat panel | 120–150 | 180 | A sander is efficient, but can dish the patch if held in one spot. |
| Softwood with a shallow repair | 150 | 180–220 | Finer grit reduces scratches but will not correct a proud patch quickly. |
These are practical ranges, not rules: follow the filler maker’s instructions if they specify a grit. For most paint-grade repairs, 120 or 150 grit is enough to level the filler, followed by 180 or 220 to refine the surface. Starting very fine, such as 320 grit, may polish the surface without removing a noticeable ridge.
Sand the patch without creating a hollow
Let the filler dry fully before sanding. A surface that feels dry may still be soft underneath, especially in a deep hole or in cool, humid conditions. If sandpaper clogs, the filler rolls into crumbs, or the patch smears, stop and give it more time. Clogged paper also makes it tempting to press harder, which can gouge the wood.
With a sanding block, use light, even strokes that extend a little beyond the patch. Check the repair often by running fingertips across it from several directions. You should feel no lip at the edge. Keep the block flat and avoid concentrating pressure on the center; that is how a flush repair turns into a shallow bowl.
If the filler sits high, start with 120- or 150-grit paper. Once it is close to flush, switch to 180 grit, then 220 if the surrounding surface is smooth enough to benefit. Do not try to sand away a deep low spot: add another thin layer of filler, let it dry, and sand again. A second application is usually cleaner than over-sanding a wide area of wood.
A hand sanding block and assorted-grit paper are enough for most small repairs; a sanding sponge is more useful when the trim is curved or profiled.
Remove dust, then prime
Vacuum the patch and surrounding area, then wipe with a clean, dry cloth. Dust left in the repair can make primer rough or weaken adhesion. Avoid soaking water-based filler just before painting; a damp wipe can soften it or raise the grain in nearby wood. If you use a tack cloth, choose one suitable for the coating system and use light pressure so it does not leave residue.
Prime the filled area before applying finish paint. Filler and bare wood may absorb paint at different rates, leaving a dull or patchy spot even when the surface is level. A brush-on primer works for a few small holes; a small can of interior primer suitable for wood is more practical for repeated repairs or a larger panel. Follow the label for recoating time, then lightly sand raised fibers or dust nibs with 220 grit and remove the dust before painting.
Check the repair before painting
Inspect the surface from the side under a bright light. Raking light makes ridges and dips easier to spot than looking straight at the patch. Run a fingertip across the edge again, and check that sanding scratches are no coarser than those on the surrounding wood. If the primer reveals a low spot or an obvious edge, let it dry, apply a small amount of filler, and repeat the process.
Do not keep sanding just because the repair looks different in color. Primer will cover color variation; it will not hide a physical defect. The cheaper water-based filler and a sanding block are fine for ordinary paint-grade nail holes. Spend more time—or choose a tougher filler—when the damage is deep, on an exposed edge, or likely to take knocks.
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