PVC flat bar: sizes, uses and fitting

One of the simplest profiles in the whole PVC accessory range, and the one that most often rescues a finish: the PVC flat bar. A flat strip of rigid plastic 2.5 mm thick, available in ten widths from 20 to 150 mm, it can hide a fitting gap, cover uneven plaster or close an edge nobody planned for, all in a matter of minutes. In this guide we show how the widths differ, when to choose the version with a seal, and how to fit the trim so it stays put for years.

Flat bar, flat trim, plastic strip - the same profile

Let us start with the names, because this is where most confusion arises when ordering. The flat PVC trim goes by several terms on the market, depending on the trade the enquiry comes from:

• PVC flat bar - the name used in factories and workshops,
• flat plastic strip - the everyday term, commonest among private customers,
• flat masking trim - from the point of view of the job, that is covering gaps,
• thin plastic strip or flat PVC profile - descriptively, by thickness and section.

Behind every one of these terms is the same product: an extruded strip of rigid PVC with a rectangular section, no chambers and no shaped edges. The simplicity is an asset, because it lets the trim fit situations where a more elaborate profile would simply be too big.

Specification of the PVC flat bar

Feature	Detail
Material	rigid PVC, moisture- and UV-resistant
Thickness	2,5 mm
Widths (without seal)	20, 30, 40, 50, 60, 70, 80, 100, 120, 150 mm
Widths (with seal)	20, 30, 40, 50, 60 mm from stock, 70 and 90 mm by arrangement
Length	6 m without seal, 5 m with seal
Finish	white or foil wrapped
Fixing	adhesive tape or construction adhesive

The 2.5 mm thickness defines the character of this profile. The trim is thin enough not to catch the eye once fitted and not to create a noticeable step, yet stiff enough to hold a straight line along its whole length and not to ripple as it is pressed home.

Ten widths and what they are all for

Choosing the width comes down to one rule: the trim must cover the gap with room to spare on both sides, without needlessly encroaching on the glass or the wall. Below are the typical uses of each size.

Width	Typical use
20-30 mm	small details, frame-to-reveal junction, covering narrow cracks and joints
40-50 mm	the range most often chosen on windows: covering foam and the fitting gap
60-70 mm	wider gaps, uneven reveals, making good after replacing joinery
80-100 mm	large areas of missing plaster, finishing at doors and gates, casings
120-150 mm	cladding, panels, covering services, workshop and exhibition work

In practice it is best to measure the gap at several points around the opening, not just one. Reveals are rarely perfectly true, and the top sometimes needs a wider trim than the sill. If the difference is large, pick the width that suits the widest point.

Versions with and without a seal

The flat bar without a seal is the basic version: a plain PVC strip, cut and bonded straight to the substrate. It suits anywhere both surfaces are true and the trim beds down over its whole face.

The version with a seal has a soft lip along one edge that lays over the frame when pressed and closes the joint line. It is the answer where the substrate is slightly uneven, or where the trim meets a smooth window profile and you want no visible gap. The seal is colour-matched to the foil, so the finish stays coherent. The price for that comfort is a shorter length: 5 m instead of 6 m.

Where flat PVC trims are used

Although the profile was created with windows and doors in mind, its uses quickly went beyond them:

• Finishing windows and doors - covering fitting foam, the gap between frame and masonry, and small defects in the plaster.
• Reveal detailing - closing the edge of plasterboard or plaster at the window, without filling and painting.
• Window boards - covering the sill-to-wall junction, where cracks always appear first.
• Covering services - wider flat bars conceal cables run along a wall or in the corner of a room.
• Furniture and fit-outs - edging panels, spacer strips, display elements.

PVC absorbs no water and does not distort as humidity changes, so the trim works just as well on a facade, in a bathroom or in a utility room. That is usually its advantage over timber or MDF equivalents.

Flat bar, angle profile or hollow-chamber trim

The three commonest finishing profiles solve three different problems, and it pays to tell them apart before ordering:

Profile	When to choose it
PVC flat bar	when covering a flat surface or a gap lying in one plane
PVC angle profile	when the gap runs in a corner and two planes must be covered at once
Hollow-chamber trim	when the gap is wide and the profile should also stiffen and insulate the junction

A full rundown of finishing profile types with the rules for choosing between them is in the guide to PVC finishing trims for windows.

Colours and foil wraps

The white version covers most orders, because it matches standard PVC windows. For coloured and wood-effect joinery we wrap the flat bars in foils from established makers: Renolit, Hornschuch, Cova and LG. The most ordered shades are golden oak, walnut and anthracite - the same ones that dominate in windows.

A well-chosen wrap means the trim stops reading as a separate part and reads as part of the frame. That is the whole point of a finish: the less it catches the eye, the better the job.

Fitting step by step

1. Prepare the substrate. The surface must be dry, clean and degreased. Grease and dust are the commonest reason a trim comes away after a few weeks.
2. Check the temperature. The tape’s adhesive only bonds properly above freezing, so the work is not done in frost.
3. Cut the profile. Cut square on straight runs and at 45 degrees in the corners. Leave expansion gaps at the ends, because PVC moves with temperature.
4. Bond it gradually. Peel the tape’s backing as you press, ten or twenty centimetres at a time, rather than stripping it all off. Run the trim along the line with a steady movement.
5. Press home and check. Run your hand along the whole length, paying attention to the ends and corners. Make any corrections straight away, before the adhesive sets.

From 100 mm wide upwards it is worth adding spots of construction adhesive along the centre line of the trim. Tape alone copes on a true substrate, but on plaster of varying texture a wider profile moves more.

Cutting to size and trade orders

As standard we ship flat bars in 6 m lengths and the sealed versions in 5 m lengths. For joiners, fitting teams and manufacturers we also cut profiles to a set length, which reduces waste and speeds up work on site. On repeat jobs that has a real effect on cost.

Frequently asked questions

Is a PVC flat bar the same as a flat trim? Yes. They are two names for the same profile. Flat bar is heard more in the workshop, flat trim more in retail.

Which width for finishing a window? Usually 40 or 50 mm. Measure the gap and add a few millimetres on each side so the trim laps securely onto the frame and the reveal.

Is the trim suitable for outdoor use? Yes. Rigid PVC resists moisture and UV, so the profile works indoors and on the facade alike.

Can it be fitted without drilling? Yes, adhesive tape is standard. No drilling or plugs are needed; what matters is a clean, degreased substrate.

Do expansion gaps have to be left? Definitely. PVC expands and contracts with temperature, and a trim pressed hard against both ends can bow in time. A few millimetres of play at the ends solves it.

Can a flat bar be painted? It can, though usually there is no need. Rather than painting, order the profile ready wrapped in foil of the colour you want - the factory finish lasts longer.

In summary

With the PVC flat bar the whole difficulty comes down to two decisions: the right width, and the choice between the sealed and unsealed version. The rest is careful fitting on a clean substrate with expansion gaps left. Ten widths from 20 to 150 mm cover practically every situation, from a narrow crack beside the frame to covering services.

As a manufacturer of trims and PVC accessories since 1994 we will help you choose the width, version and wrap colour for your job, and on larger orders we cut the profiles to size. Write to us and we will prepare a quote and ship anywhere in Poland.