How to paint shiplap so the gaps, knots and seams look right

Real shiplap boards or MDF panels?

Shiplap is a wall of boards whose edges overlap, leaving a small, even gap between the faces. Real shiplap is solid wood, often pine. It's also sold as MDF, a panel of wood fibers glued together and milled to look like boards.

Check a cut end, a leftover piece or the edge beside an outlet. Wood shows grain and growth rings; MDF is the same brown fiber all the way through.

The table is our editorial summary of the sources below, not a measurement. The Composite Panel Association's bulletin on MDF trim, the same material as MDF shiplap, says the surface is flat, smooth and free of knots and grain, that most of it comes pre-primed, and that water-based primers can raise its fibers with any significant contact with water. Our post on painting MDF cabinets covers the same material on doors.

The Board, Gap, Bleed, Move check for painting shiplap

Most painting shiplap guides start with the roller. We start with four questions, because each one changes the order of work. It's our editorial framework, not a lab standard.

• Board: real wood or MDF? It decides the primer and how hard you can sand.
• Gap: how will paint reach the back of the reveal without pooling in it?
• Bleed: are there knots, sap or old stain that could come through a light color?
• Move: will the boards shrink in winter and show a stripe of bare wood at the overlap?

Move is the one nobody plans for. The USDA's Wood Handbook says indoor heating in northern winters can drop the moisture in interior wood to around 4 percent, against roughly 8 to 10 percent in air-conditioned rooms. Wood shrinks as it dries, so an overlap that looked painted in July can show a pale line in January. MDF moves too: the panel association says it changes size with humidity, like solid wood.

How to paint shiplap gaps by brush, roller or sprayer

Paint the gaps first, then the faces. A roller bridges the reveal, so rolling first leaves bare edges and ridges of paint that you end up chasing with a brush.

What a nickel gap is

A nickel gap is shiplap hung with an even reveal about as wide as a nickel is thick. It's the look, not a flaw, so paint has to coat the back of the gap without filling it.

With a brush and roller

1. Work paint into one gap at a time with a lightly loaded angled brush, along the full length of the board.
2. Brush out any paint gathering on the lower lip of the gap before it can run.
3. Roll the faces of the next two or three boards while those gaps are still wet, so the marks blend.
4. Finish each board end to end with light strokes in one direction.

For the faces, see what nap roller to use.

With a sprayer

Wagner SprayTech, a sprayer maker, does the gaps first on a narrow spray setting with two passes, one angled up and one angled down, so nothing is left bare. It sprays lengthwise to avoid pooling and drips in the gaps, then switches to a wide pattern for the faces. Its first step is masking and covering the floor, windows, fixtures and furniture, because overspray travels.

Putting up new boards? Paint the edges and the overlap before they go on the wall. That's the Move question answered in advance.

Knots and tannin bleed on pine shiplap

Real pine shiplap has knots, and knots bleed. The Wood Handbook says knots of almost all species contain enough oils and resins to discolor light-colored paint, and that extractives in wood discolor finishes most in humid rooms such as bathrooms and kitchens.

The handbook's answer is a stain-blocking primer. Knots can be sealed with shellac or a knot sealer and then the whole board primed, it says, and modern high-quality stain-blocking primers usually work without any special knot treatment. Our post on the best primer for cabinets compares the primer types side by side, and the same types apply to boards.

Sap is a different problem

Sticky amber beads are pitch, and primer won't hold them back. The handbook is blunt: coatings will not stop pitch bleed. Once the pitch has hardened, scrape off what you can and sand to bare wood before priming.

If color comes through after the paint is on, another coat of the same paint won't stop it, the handbook says. Apply a stain-blocking primer, then the topcoat again.

Should you caulk shiplap?

Not the gaps between boards. The reveal is the look, and the boards move with the seasons, so a bead of caulk in every gap is asking to crack. Caulk where shiplap meets something else: inside corners, door and window casings, the baseboard and the ceiling line.

The Wood Handbook says fillers should be flexible when cured, to move with the wood as its moisture changes. Fill nail holes before the topcoat, as the panel association's bulletin advises, and see our guide to caulking baseboards for technique.

Best sheen for painting shiplap

Satin is a good default for shiplap walls, with semi-gloss where a wall gets wet or wiped often. Dunn-Edwards says higher gloss improves scrub, stain and moisture resistance but tends to highlight defects, and the Wood Handbook adds that gloss accentuates planer marks, raised grain and joints in the wood. Shiplap is all joints. For MDF, the panel association's bulletin recommends satin or semi-gloss.

Dunn-Edwards also notes that a color looks brighter and richer in a higher gloss, which flatters a deep charcoal wall and every dent in it. See paint sheens explained for the full range.

Painting shiplap that's already stained or painted

Stained or clear-finished boards need what any glossy wood needs: clean, scuff sand and prime. Over stain or knotty wood, use a stain-blocking primer, since the old stain and the wood under it can both come through a light color.

Boards that are already painted need less, if the paint is sound. Test before you commit. The Wood Handbook's check is to paint a small, out-of-the-way spot, let it dry at least overnight, then firmly press an adhesive bandage on and snap it off. If the new paint comes off, the old surface needs more cleaning or priming. If both coats come off, the old paint isn't holding to the wood and has to be removed.

Going from dark to light takes more coats; see painting over dark paint.

When to stop and call a professional

• Stop before sanding or scraping old painted boards if your home was built before 1978 and you don't know what's in the paint.
• Call a pro when the tape test pulls both coats off, since that old paint has to be removed first.
• Fix the moisture first when boards are damp, swollen or musty, especially on an outside wall or in a basement.
• Wear real dust protection to cut or sand MDF. The panel association calls for at least a NIOSH-approved half-mask respirator with a HEPA filter, side-shielded safety glasses, long sleeves and gloves.

The first one matters in older houses. EPA says about three quarters of U.S. homes built before 1978 still contain some lead-based paint, and that any renovation, repair or painting work in a pre-1978 home that has it can easily create dangerous lead dust. Tell any painter the age of the house. Our post on painting older Madison homes covers the rest.

How we paint shiplap at GK Painting

Shiplap walls are part of our interior painting for homes and businesses. Small holes are fixed and primed first, and the furniture stays covered the whole time. George quotes every job himself, so ask him how he'd handle the gaps and knots on your boards.

Interior painting is priced by the square footage of the space, with paint included. We use premium paint from Sherwin-Williams and Behr, or a brand you already like, and the written quote is built around the paint you pick. The written quote is the price, no extra charge if the job takes longer than expected.

If a problem comes from the quality of our work, like a finish that peels or didn't bond, we come back and make it right. We're based in Waunakee and work across Madison and Dane County. Read about our interior painting, see what clients say, or ask for a free estimate.