Plastic packers are used to level, align, and space components during installation before fixings are tightened. Common uses include fitting door and window frames so they sit plumb and square in an opening, supporting glazing units to prevent seal failure, levelling kitchen units and worktops, and correcting minor height differences under flooring battens. They can be stacked to achieve the exact thickness needed and trimmed back once the component is secured.
Plastic Packers and Shims for Levelling and Alignment
Packers, sometimes called shims, are small plastic spacers placed between a surface and the component being fixed to achieve a level, plumb, or correctly spaced result before tightening. They are a practical solution anywhere precise alignment matters. MacBlair stocks plastic packers as part of its broader fixings range, making them easy to pick up alongside other fixings for the same job.
Common applications include:
- Window and door frame installation, to align frames in openings and maintain even reveals
- Glazing, to support glass units correctly and prevent seal failure over time
- Levelling cabinets, worktops, and fitted units
- Flooring and battens, where small height corrections are needed across a surface
Plastic is the go-to material for most packing jobs. Unlike timber offcuts or cardboard, plastic packers will not swell, rot, or degrade over time, and they are manufactured to consistent thicknesses so there is no guesswork involved. They can also be stacked to reach the exact depth needed. If a door frame is out of plumb, or a window unit is not sitting square, the right packer thickness corrects the problem without rework. For jobs requiring frame and hammer fixings, packers are often the first step before any fixing goes in.
Packers are often bought alongside wall plugs and wood screws when fitting frames or units. Order online from MacBlair for delivery across Northern Ireland, or visit the store to collect.
Packers FAQ's
In most trade and DIY contexts, the terms are used interchangeably. Both refer to thin pieces of material placed between two surfaces to fill a gap or correct alignment. Shims tend to be wedge-shaped and are often used for gradual adjustments, while packers are typically flat and come in specific, consistent thicknesses. For window and door installation in the UK, plastic flat packers are the most widely used option.
Yes. Once a frame or unit is fixed and level, plastic packers stay in place to continue supporting the load. They do not rot, swell, or degrade like timber or cardboard alternatives, which makes them a far more reliable long-term option. After fixing, any excess packer material that protrudes beyond the frame can be trimmed back neatly before sealing or plastering.
Measure the gap between the frame or component and the wall or surface it needs to sit against. Packers are available in various thicknesses and can be stacked to build up to the exact depth required. Many packs contain a mixed selection of sizes, which is useful when gaps vary slightly across an opening. Use a spirit level throughout installation to check the frame is plumb and level as you go.
Yes. Purpose-made plastic glazing packers are specifically suited to supporting double-glazed units within window frames. They distribute the weight of the glass correctly and keep the unit from sitting in any water that collects at the base of the frame, which helps protect the unit's seals over time. Using the correct packers during glazing installation reduces the risk of premature seal failure and internal condensation between panes.