Deep Terracotta in a Bar: Base Choice, Undercoat, and Adhesion on Gloss Alkyd
A bar renovation calls for one accent wall behind the taps, 14 ft tall by 22 ft wide, to be recoated in a deep terracotta red - 100% acrylic, eggshell - from a national fan deck. The existing finish is a dark forest-green semi-gloss alkyd about eight years old over gypsum board; it is sound but slick. The supplier is out of the deep tint base, so the clerk tints a light base, adding 10 fl oz of colorant per gallon, near the maximum the dispenser allows. The painter wipes the wall with a liquid deglosser, lets it flash, and applies two coats in one day with a 3/8 in nap roller cover. Under the worklights the wall reads muddy brown instead of red, lap lines are visible, and masking tape left overnight pulls the new paint down to the green when removed the next morning. The designer arrives in the morning with the client; the wall is lit by 3000 K LED track heads at night and by a south-facing window by day.
1. Explain every reason the wall reads muddy brown instead of the specified terracotta.
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Four factors are stacking up:
- Wrong tint base. A deep red needs a deep or ultra-deep base, which carries pigment load with less binder and allows the colorant to develop correctly. Forcing 10 fl oz of colorant into a light base pushes the colorant toward the dispenser limit, so the pigment never reads true and film properties (hide, adhesion, block resistance) fall off.
- No primer over dark green. A deep red is a relatively translucent color; two coats over a dark forest green will let the green pull the red toward brown. The fix is a primer tinted toward the topcoat - a gray or a red-shaded primer - so two topcoats can actually achieve the color.
- Sheen change. Going from semi-gloss to eggshell alters how the surface reflects light and reads to the eye, especially on a tall wall where light falls off.
- Metamerism. A fan deck chip viewed in the store under one light does not match the same color under 3000 K LED versus daylight from the south window. This is a spectral difference, not a mistake by the painter - and it is why the color must be approved on a dried job-site mockup under both lighting conditions.
Lap lines come from rolling into a flashed-over edge, which also creates a visible sheen difference on a tall wall.
2. Write the corrective plan, including the mockup and documentation you will require before the wall is recoated.
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1. Get the right product. Have the wall mixed from the deep base with the correct manufacturer formula; record the formula, batch, and store. Do not accept more colorant than the base allows.
2. Mockup before production. On the same gypsum/alkyd substrate, apply primer and two topcoats to a 2 ft × 2 ft panel. Let it dry fully - deep colors shift as they cure - then view it under the 3000 K track heads and in daylight with the client and designer present. Get sign-off in writing on the mockup, including sheen.
3. Correct substrate prep. Sand the old alkyd with 80–100 grit to dull the gloss and give profile, then clean and rinse; a deglosser wipe alone is not a substitute for abrasion on a hard, cured alkyd.
4. Prime. Apply a primer tinted toward the red to kill the green undercoat.
5. Apply. Two finish coats, cutting in and then rolling full wall-height passes to keep a wet edge; keep one batch and box pails to avoid lot-to-lot variation; back-roll for uniform texture.
6. Document. Attach the mockup photo, formula, batch numbers, and sign-off to the job file.
3. The tape test pulls paint to the green. Diagnose the adhesion failure and state how you verify the repair before recoating the full wall.
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The failure is at the interface between the new acrylic and the old alkyd, not within the substrate. The only prep was a liquid deglosser wiped on and allowed to flash: that removes surface contaminants but does not create mechanical profile on a slick, fully cured semi-gloss alkyd, and any residue left behind becomes a bond breaker. Over-tinting compounds the problem, because excess colorant in a light base reduces the cured film's cohesion and adhesion.
Repair: strip the failed area back to sound coating, sand to dull the gloss and open the surface, then clean and rinse with a TSP substitute and let it dry. Apply a bonding primer specified for hard, glossy alkyd - or an appropriate primer after proper sanding - then the tinted primer and two finish coats.
Verify before going wide: apply the full system to a 2 ft × 2 ft test patch in a representative area, cure it per the data sheet, then do a cross-hatch/tape pull at the edges and in the field. Also check adhesion over a caulk joint and at a corner. Only when the patch passes do you commit the wall. If it fails, the answer is removal of the old alkyd, not another primer on top.