To choose a shadow gap profile for plasterboard, start with the surface (ceiling, wall or floor), the visible reveal width or height, and whether the junction should carry LED light. Then check the profile’s dimensioned drawing against your board build-up. Our product data lists visible dimensions rather than a compatible board thickness, so confirm the board layers with the drawing on the product page, or with us, before ordering.
The rest of this article explains how the profile meets the board, what the product data does and does not tell you, and the questions to settle before the profile goes on site.
How a shadow gap profile meets the board
A shadow gap profile is part of the board surface, not something applied to it afterwards. As described in our shadow gap guide, installation follows the same sequence for every family:
- The profile is fixed to the framing, substrate or board at the specified line and level, following the installation guide for that profile.
- The perforated flange is bedded in jointing compound, covered with reinforcing tape and skimmed flush with the board.
- The surface is finished and painted, and the profile edge keeps the shadow line straight.
So part of every profile sits behind or within the board, and only the reveal stays visible. That hidden part is why the build-up matters. The slim LPA126, with its 6 mm shadow line, is listed as plaster-in, flush with plasterboard. At the other end of the ceiling range, AST45 is ceiling-recessed and plaster-in, with a 45 mm visible width, a 42 mm visible height and a 68 mm profile height. The ceiling construction has to accommodate the full profile, not just the part you see.
What the product data tells you
Each profile page lists the dimensions that define the reveal. The type of dimension depends on the family:
| Family | Dimension listed | Range in the catalogue | Installation note in the data |
|---|---|---|---|
| Ceiling profiles | Width, shadow line or visible width | 6 mm to 45 mm | Plaster-in, creating a negative reveal between ceiling and wall |
| Wall concealed profiles | Height | 40, 60 and 91 mm | Installed behind plasterboard before finishing |
| Floor profiles | Height | 20 mm to 100 mm | Recessed at the foot of the wall, replacing the skirting board |
| Recessed curtain track | Recess depth | Approx. 80 mm for KA2 | Recessed into the plasterboard ceiling |
What the data does not list is a board thickness or number of board layers for each profile. Where a dimensioned drawing is on the product page, use it to check the profile against your section. Where it is not, ask us. We send drawings and installation guidance on request and aim to reply within one working day.
Choosing the profile step by step
1. Surface
Ceiling, wall and floor each have their own profile family. A wall-to-ceiling reveal uses a ceiling profile. A negative reveal, panel joint or flush door frame in a plasterboard wall uses a wall concealed profile. A wall-to-floor junction without skirting uses a floor profile.
2. Reveal size
The reveal size decides how strongly the shadow reads. A 6 mm line is a fine, almost graphic shadow. Wider reveals of 25 to 45 mm read as a deliberate architectural line, and every ceiling profile in that range has an LED channel. Choose the reveal from the drawing and the room, not from a photo of another project.
3. Light
If the junction should also give light, choose an LED-ready profile with an integrated LED channel and a matching clip-in diffuser. LPA126, for example, has no LED channel, while AST45 has one. LED-ready profiles also need driver and access positions planned before the boards go up.
4. Build-up
Compare the profile drawing with the actual construction: the framing, the number and type of board layers, and for recessed profiles the depth of the ceiling void. A recessed curtain track such as KA2, with its approximately 80 mm recess, is a good reminder that the void has to be checked, not assumed.
5. Length and finish
Profiles come in standard lengths of 2.5, 2.6 and 3.0 m, depending on the profile, and in the finishes listed on each product page. Plan joint positions on long runs before ordering.
Board build-up questions to settle before ordering
Before the order is placed, the drawing or the site should answer these questions for every junction:
- Board layers. Single or double layer at the junction, and the board type and thickness from the board manufacturer.
- Framing. What the profile is fixed to: metal or timber framing, a solid substrate, or the board itself, as the installation guide for that profile allows.
- Ceiling void. For recessed ceiling profiles and curtain tracks, whether the void is deep enough for the full profile height.
- Finished surface. Paint, skim or tile next to the reveal. Set out to the finished surface, not the bare board.
- Corners and ends. How internal corners, external corners and open ends of each run will be formed. Ask us for the installation guidance for the profile.
- Services. For LED profiles, cable routes, driver positions and access, agreed with the electrician.
Common mismatches
Most site problems with plasterboard shadow gaps come from a profile that was chosen before the build-up was fixed. The usual ones:
- The profile was chosen from a picture. The visible reveal looks right, but the hidden part does not fit the construction.
- The build-up changed late. A second board layer or a different framing system was added after the profile was ordered, and nobody checked the profile again.
- The set-out was taken from the bare board. The reveal ends up proud of or behind the finished surface.
- The LED profile has no plan for the driver. The light line is installed, but the driver ends up with no accessible position.
Each of these is cheaper to fix on the drawing than on site. Our article on specifying shadow gap profiles covers how to record the profile, build-up and set-out so the contractor orders the right thing.
Contractors and other trade buyers can request a free sample box. The profile sections in it can be held against the actual board build-up before a profile is committed to the drawings.
