Which uPVC trim do I need? Angle, bead and quadrant sizes

How do I measure the gap before I choose a trim?

Measure the widest point of the gap, not the average. Run a tape along the full length of the joint and write down the biggest reading.

Old walls and old frames move, so a joint that is 4mm at one end is often 15mm at the other. Then apply the bearing rule. A trim has to land at least 5mm on solid material each side of the gap. Take the leg size of the trim, subtract 10mm, and that is the widest gap it will cover and still look deliberate. The leg is the flat face of the trim, the part that sits against the wall or the board.

Rigid angle or flexi angle, what is the difference?

Rigid angle is a fixed 90 degree corner. Flexi angle is hinged down its spine and opens or closes to suit a corner that is not square.

Use rigid angle on new work, on flat boards, and anywhere you have checked the corner with a square and found it true. Use flexi angle on old brickwork, on splayed reveals, and on any corner that changes angle as it goes up. Rigid angle is stiffer and holds a straighter line over a long run, which matters on anything above about 2m.

Which trim covers which gap?

Trim leg minus 10mm is the widest gap it will cover. The table is the stock range and what each size will hide.

Figures are the leg size minus 10mm of bearing, so read them as a maximum, not a target.

Trim	Sizes stocked	Widest gap it covers	Typical use
Rigid angle	25×25, 40×40, 50×50, 60×40, 100x100mm	15mm to 90mm	External corners on flat, true boards
Hollow angle	100x80mm	70mm to 90mm	Wide corner returns and boxing in
Flexi angle	12.5×12.5, 25×25, 50x50mm	2.5mm to 40mm	Corners that are not 90 degrees
Quadrant	12mm, 19mm	2mm to 9mm	Internal angles, panel and bath edges
D bead	28mm	18mm	Panel edges and window boards
Fillet bead	20mm, 28mm	10mm to 18mm	External joints that must shed water
Block bead	15×13, 25×20, 30x25mm	5mm to 20mm	Window frame into a brick reveal
Architrave	45mm, 65mm, 95mm	35mm to 85mm	Door and window reveals

D bead, fillet bead or block bead, which goes where?

Block bead against a window frame, D bead over a board edge, fillet bead anywhere water has to run off.

Block bead is L-shaped with a rebate, so it sits tight to the frame and covers the gap back into the reveal. D bead is half round with a flat back, used to finish the edge of a panel or a window board where there is no reveal to fix into. Fillet bead has a right angle leg and a sloped face, so rain runs off it instead of sitting on it. Externally, fillet bead is usually the right answer.

Do I need architrave or quadrant?

Architrave for wide gaps around reveals, quadrant for small gaps in internal angles.

Architrave at 95mm covers an 85mm gap, which handles most reveals where plaster has been hacked back. Quadrant is a quarter round and is an edge finish, not a gap filler. The 12mm covers about 2mm and the 19mm covers about 9mm. If you are trying to hide more than 20mm in an internal angle, quadrant is the wrong trim, use a rigid angle or architrave.

How do I fix trim without wrecking the frame?

Use adhesive and sealant, not nails, on anything that touches a window or door frame. A nail through a frame face punctures the chamber and lets water into it.

Clean both surfaces with PVCu solvent cleaner first, because grab adhesive will not hold on dust, old sealant or mould. Double sided foam tape holds the trim in place while the adhesive grabs, which saves propping it for an hour. Seal the top edge with a low modulus silicone and leave the bottom edge open, so any water that does get behind can drain out. Into timber, colour head stainless pins are fine.

How many lengths do I order?

Beads, quadrant and architrave come in 5m lengths, so measure each run and round up. Add 5 to 10 per cent for mitres and mistakes.

Mitres cost more length than people expect: every 45 degree cut on 95mm architrave loses 95mm. Buy one spare length on any job with more than four corners. Five metre trim does not travel well by parcel carrier, so most people take collection from us at Heysham Road or wait for the van. If the reveal is splayed, or the gap changes along the run, ring us with the measurements before you order.