Spray a 6 Panel Interior Door with a Fuji Q4 Gold HVLP and No Overspray on Adjacent Trim

Set the door flat before you touch the trigger

A vertical door invites sags on the panels and runs on the stiles. Lay the 6 panel slab horizontal across two trestles at around 850mm working height, packed on Bessey clamps or shim wedges so it sits dead level. The Fuji Q4 Gold atomises fine enough that a level surface holds 100 to 150 microns wet without moving, which vertical hanging cannot promise. Pull the hinges and handle set, and knock out the pins so nothing on the face interrupts a pass.

Grit choice off the shop decides how the film flows. Denib factory-primed MDF or a previously gloss-coated door with 240 grit on a random orbital, then wipe with a tack cloth and a slow methylated spirit wipe if the surface is oil-bound. On bare timber knots, spot the resin with a shellac-based knotting solution before any build coat goes down, because turbine heat will not lift resin that a solvent seal has already locked. Vacuum the trestle bay first. Dust that lands mid-pass shows as a nib you will feel through the topcoat, and no amount of flow additive hides it.

Overspray control starts at the room, not the gun

The adjacent architrave and skirting stay clean because the door leaves the frame entirely. Spraying in situ, with the slab still hung, is the single largest cause of trim contamination, and no masking tape edge survives a turbine cloud cleanly over a full session. Take the door to a dedicated bay: a garage, a stripped spare room, or a purpose-built spray tent such as the HomeRight Small Spray Shelter for narrower slabs.

Inside the bay, tent the walls with dust sheets and run a box fan low at floor level drawing air past the door toward an open window or extract point. The Q4 turbine already produces far less bounce-back than a 2 psi compressor gun, but fine solids still drift. Cross-ventilation pulls that drift away from the wet film so it does not resettle as a gritty haze on the panels you just laid.

If a section of frame genuinely cannot be avoided, mask it with a hard 3M blue tape line burnished down with a plastic applicator, then back the tape with masking film unrolled from a hand masker. Feather the gun trigger toward that edge so the atomised fan tapers off before it reaches the tape, instead of driving a full wet pattern straight at it.

Needle, aircap, and how thin the paint has to run

The Q4 Gold ships with a 1.3mm aircap set as the general-purpose fit, and that handles most water-based trim paints straight. For a self-levelling acrylic eggshell such as Little Greene Intelligent Eggshell or Tikkurila Helmi 30, the 1.3 gives a fine enough particle to avoid orange peel on the flat door frame panels. Drop to the 1.0mm set only for very thin sealers; step up to the 1.5mm for a heavier-bodied satinwood that will not push through the smaller orifice without over-thinning.

Viscosity is the variable that ruins more door finishes than technique. Water-based trim paint from the tin usually sits around 80 to 110 seconds through a Ford 4 cup, too thick for clean atomisation. Thin in 5 percent increments with clean water, or the manufacturer flow conditioner, and test through a Ford 4 or the Fuji-supplied viscosity cup until it drains in roughly 30 to 40 seconds as an unbroken stream. Each 5 percent thin also drops film build per coat, so plan on three thinner coats over two thick ones.

Set the fan pattern wide and the material flow low, then open flow gradually. A pattern test on scrap card at your intended 150mm to 200mm gun distance shows the fan shape. You want an even cigar with no heavy tails, tails meaning too much material or too close a stand-off.

The pass sequence on a 6 panel face

Work the recesses first. Hit the six sunken panel fields and their mouldings with a light banded coat, angling the gun 45 degrees into each corner so atomised paint reaches the shoulder of the moulding that a straight-on pass skips. Do not flood the recess; it is where sags collect. Then lay the horizontal rails, then the vertical stiles last, so the stiles carry the final visible grain-direction pass along their length.

Keep the gun perpendicular and moving parallel to the surface, not arcing off the wrist, which is what fans the film heavy in the middle and thin at the ends of a stroke. Overlap each pass by 50 percent. Trigger on just before the door edge and off just after, so no pass starts or stops mid-face where the build doubles into a ridge. On a standard 1981mm by 762mm slab that is roughly seven to nine overlapping stile-length strokes per full coat.

Between coats, respect the recoat window on the tin, usually two to four hours for water-based trim at 20C, longer in a cold garage. Denib with 320 grit or a grey Scotch-Brite pad between coats once each is hard, wipe with tack cloth, and shoot the next. Turn the slab and do the reverse face only once the first side is hard enough to rest on padded blocks without printing.

A worked build calculation

Take Little Greene Intelligent Eggshell rated near 12 square metres per litre at brush spread. A 6 panel door face plus edges runs close to 1.8 square metres both sides, so about 3.6 square metres total. Brushed, that is roughly 0.3 litres per coat. Sprayed with 10 to 15 percent thinning and typical HVLP transfer efficiency around 65 percent inside a tented bay, plan on 0.45 to 0.55 litres per coat to hit the same dry film across three coats. Buy a full litre and you have margin for the pattern tests and a touched edge.

Clean the Q4 before the paint sets

A turbine gun with dried acrylic in the fluid passage sprays spatter forever after. Flush the Q4 cup and needle with warm water within 20 minutes of the last coat, strip the aircap and soak it, and pull the needle to clear the tip. Run clean water through until the fan sprays clear on the test card.

The open question on any sprayed door is durability at the handle stile, where hands and cleaning cloths hit hardest, and whether a sprayed acrylic film there wears differently than the same paint laid by brush at higher build.