Pre-made corners are factory-made elements that replace the on-site miters in a molding install. The corners are made from the same profile as the molding, in the same material, with the same finish, and they ship ready to install.
The labor savings are the main reason to use pre-made corners. A typical room has four outside corners in the crown and four in the baseboard. Each miter is a measurement, a cut, a dry-fit, and often a re-cut. With pre-made corners, the miters become simple butt joints, and the install is much faster.
The material savings are a secondary benefit. A mitered corner produces a triangular offcut from each piece of molding, and the offcuts are usually waste. Pre-made corners are made from the same material as the molding, but the factory uses the material efficiently — there's less waste, and the cost of the pre-made corner is often comparable to the cost of the molding material that would have been wasted in the miters.
The accuracy benefit is the third reason. A factory-made corner is more accurate than an on-site miter, because the corner is made on a calibrated miter saw or a pre-formed tool. The joint between the pre-made corner and the straight run is tight and clean, and the finished install looks more professional.
For sourcing, pre-made corners are a stock product at most factories that sell crown molding and baseboard. The corners are sold in pairs (two outside corners for one room, or one inside corner and one outside corner), with the profile matched to a specific molding profile. The lead time is short because the corners are made from stock material.
A practical install note: pre-made corners require the wall corner to be close to 90 degrees. If the wall corner is significantly out of square (more than 2 or 3 degrees), the pre-made corner won't fit cleanly, and the install will require shimming or a different approach. The walls should be checked before the corners are ordered.
A practical note on measuring for pre-made corners. The factory needs the leg length on each side of the corner. The measurement is taken from the corner to the point where the straight run will start. The factory makes the corner to those dimensions, with a small tolerance for fitting. The straight runs are then cut to fit between the corners.
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Frequently Asked Questions
Q: What is polyurethane (PU) decorative material?
A: Polyurethane (PU) decorative material is a high-density closed-cell polymer molded into architectural profiles such as cornices, ceiling medallions, wall panels, columns, and skirting boards. It replicates the appearance of plaster, carved wood, or stone at one-quarter the weight, is fully waterproof, impact-resistant, and arrives factory-primed for paint.
Q: How does PU compare with plaster and wood mouldings?
A: PU is lighter than plaster (no scaffolding required), impact-resistant during transport, and immune to cracking. Compared with wood, PU does not warp, split, or attract termites, and it tolerates moisture in bathrooms and kitchens. The trade-off: PU cannot be refinished the way solid wood can, but its lifespan is 20–30+ years with minimal maintenance.
Q: How do you cut and finish PU mouldings?
A: Cut PU mouldings with a fine-tooth miter saw (40+ teeth for a 10-inch blade) to avoid chipping the molded edge. Sand the cut edge with 220-grit, then apply two coats of interior latex paint. Mitre joints at corners, fill seams with lightweight spackle, sand smooth, and finish with one final top coat.
Q: Is PU moulding safe for indoor air quality?
A: Yes. Premium PU mouldings are manufactured without formaldehyde, asbestos, or VOCs. They meet EN 13501-1 Class E fire classification as a minimum, with Class B fire-retardant versions available for commercial projects. The factory-applied water-based primer further reduces off-gassing once installed.