Internal Door Fitting Instructions

Installing an Internal Door

When trimming a door to fit, 6mm can be removed from each edge of the door to a maximum reduction of 12mm in both height and width, as any reductions must be evenly removed from each side of the door. For example, to trim your door by 8mm in width, you will need to remove 4mm off each side.
This ultimately excludes Fire Doors, Bi-Fold doors and rebated door pairs.

Three hinges should always be used to hang doors, particularly on glazed, heavyweight and fire doors, or wherever there is a large difference in temperature or humidity such as in bathrooms. As for latches and locks, they should not be fitted adjacent to door mid-rails where the joint may be compromised. As well, all hardware screw holes should be pre-drilled to prevent the splitting of timber.

Paint ‘N’ Peel is a glass protection film and should not be removed until the painting or staining of the door has been completed. Some glass styles are smoother and more obscure on one side than the other, so always remember to check the obscure glazed faces of multiple doors are oriented in the same direction, for example, if you are installing 2 glazed doors side by side.

For Bi-Fold doors, they are supplied with a track and folding hardware and should not be trimmed. As for fire doors, they have individual fitting guidelines, so the installer must refer to the Global Assessment Report referenced on the front of the fire door label.
Rebated Door Pairs are supplied with separate instructions for fitting/trimming.

Finishing an Internal Door

Bare timber doors will require a light sanding prior to finishing, and always take care when finishing glazed doors so you can ensure that the finish does not go on the glass. Secondary protection is always important – such as using masking tape when necessary, even on Paint ‘N’ Peel protected doors.

All timber surfaces should be fully finished. When applying the finish, pay particular attention when sealing the timber end grain on the tops and bottoms of the doors, and always ensure that all lock, latch, and hinge cut-outs are also fully treated. Refer to the finish manufacturer’s instructions for number of coats to be applied.

Failure to treat all the timber surfaces may lead to an excessive change in moisture content, which will ultimately cause the timber to shrink or swell, possibly causing splits and deformation.

White Moulded and White Primed doors require a topcoat after fitting and are only suitable for painting. All edges and cut outs should be treated before the final fitting.

Factory finished doors will require any bare timber areas caused by trimming and hardware fitting, to be adequately treated before final fitting.

Summary and Do’s and Don’ts


  • Use a good quality paint, stain, or varnish
  • Apply to all faces and edges
  • Apply the same number of coats equally to the face, edges, lock and hinge cut-outs
  • Apply at least 1 coat of finish as soon as possible after unpacking the door
  • Check that the final manufacturers’ product is suitable for veneered / engineered doors


  • Use thin penetrating seals, such as oils, wax, dyes, or hard, brittle finishes
  • Use thinned/mixed paints or stains
  • Mix incompatible products, e.g paint on one door face and stain on the opposite face

26th May 2022 Emily Green

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