Waterborne acrylic and urethane-acrylic topcoats

Overview

This entry covers single-component waterborne clear coats whose resin is acrylic or a urethane/acrylic blend. The USDA Wood Handbook lists acrylic among the clear film finishes. General Finishes (GF) publishes comparable specification tables for its range, which lets us compare them on the maker's own scales: all of the products below are listed as 21-day-cure films, with VOC from under 125 to under 250 g/L. These are manufacturer tests and ratings, not independent ones. Brush-on consumer products sold as water-based polyurethane are covered in Water-based polyurethane.

Pros

• Low VOC. GF lists Exterior 450 at under 125 g/L, High Performance at under 175 g/L, Pro Series under 200 g/L and Enduro Clear Poly under 250 g/L, against a federal 450 g/L limit for varnishes (40 CFR 59).
• Water cleanup; GF recommends distilled water for thinning at 5 to 10%.
• Quick recoat: 30+ minutes to touch and 1 to 2 hours to recoat for the GF lines.
• A range of sheens from flat to gloss on GF's data (Pro Series is flat, satin and semi-gloss).
• GF rates High durability for High Performance, Enduro Clear Poly and Exterior 450.

Cons

• Scales are the maker's: for example GF lists Koenig hardness 30 for Exterior 450 against 100 for Enduro Clear Poly, but Taber wear is the other way round (95.3 mg against 35.7 mg), so no single number ranks them. Read the sheet for your use.
• Enduro-Var II is listed as a water-based oil-modified urethane that dries amber with a Medium durability rating, so not all GF waterborne coats stay water-clear.
• Not a rubbing-out finish like lacquer; for harder, more chemical-resistant film see Catalyzed polyurethane (2K).
• Do not use steel wool on water-based finishes (GF).
• 21 days is a long full cure; light use at 7 to 10 days on the High Performance sheet.

Suitability

Chosen for pale interior work where clarity matters, such as Hard maple, Soft maple, European ash and Eastern white pine; spray lines suit cabinet shops, while High Performance suits brush or roll work. Exterior 450 is the only one of these that GF lists for exterior use; the others are interior only. See Outdoor finishing for how exterior clear coats fare (Wood Handbook: about 10 years at best).

Coats and application

GF: sand raw wood no finer than 220; thin with distilled water 5 to 10%; spray wet films of 3 to 5 mils with a 1.1 to 1.3 mm HVLP tip (Spraying with HVLP); finish-sand between coats with a 220-320 foam pad; a coat is dry when it powders under 220-320 sanding. High Performance, Exterior 450 and Enduro-Var II go on by brush, roller or spray; Enduro Clear Poly is spray only. Number of coats is 2 to 3 (3 for Enduro Clear Poly). Seal needs vary: see Sanding sealer (and vinyl sealer).

Compatibility

• Oil-based over water-based: GF says let the water-based dry 24+ hours. Water-based over oil-based: 72+ hours.
• Do not use these over linseed or Danish oil finishes (GF).
• Do not clear-coat over white or light paints; GF warns of yellowing.
• On pre-finished or sealed surfaces: scuff clean, wipe with 50:50 denatured alcohol and water, sand lightly with 220-320, and test adhesion (GF).
• GF says do not use steel wool.

Care and repair

Clean with a damp cloth and avoid commercial cleaners during the cure. Scuff-sand and recoat to repair, testing a scrap first. For rubbing out, check the maker's sheet first (Rubbing out a finish).

Safety and environment

Water cleanup does not remove the need for ventilation when spraying; GF's pre-cat sheet says to wear a mask and work in a ventilated space. Check the label of each product for Prop 65 and ingredient notes. No food-contact claim is made here; see Food-safe finishes.

Related

• Water-based polyurethane: consumer brush-on versions
• Water-based lacquer: GF pre-cat lacquer
• Catalyzed polyurethane (2K): two-part waterborne
• Spraying with HVLP, Outdoor finishing