How to Trim Internal Doors
When buying new internal doors, it can sometimes be difficult to find an exact size match for your opening. Even if your door is only a few millimetres off, this is still enough to cause issues such as sticking.
If the door is too small for your frame opening, you can simply pack out the frame with additional pieces of timber. This will effectively reduce the size of your frame opening and ensure there are no gaps when fitting your door.
Alternatively, if the door is too big for your frame opening, you will need to trim down the size of the door until it fits. While this may seem daunting, it’s fairly common for doors to need trimming, and it can be done easily with a bit of know-how.
To help you do it, we have put together a step-by-step guide on how to safely and easily trim your door to a professional standard.
Table of contents
Recommended door trimming tools
Door trimming guidelines
Before you start trimming, it is important to be aware of the trimming guidelines for your door, which is how much you can take off before damaging its stability. The guidelines will vary depending on the type and brand of the door, as we’ve outlined below.
Deanta Internal Oak Fully Finished Seville 7P Door
Engineered timber doors
An engineered timber door is constructed in four parts: the core, the lippings, the front and back faces, and the solid veneer. The lippings are the solid edges that border the bottom and both sides of the door, protecting the particleboard core inside.
The lippings are usually around 12mm thick, and we recommend trimming a maximum of 8mm from each side. This means you can safely reduce the door by a maximum of 16mm. If more is trimmed, the door’s warranty will be voided, and the veneer may be ruined.
If you are looking to cut more, Deanta doors are specially manufactured with extra thick 18mm solid wood veneers, allowing up to 16mm to be taken from each side. This increases the total that can be safely reduced to a maximum of 32mm.
White moulded & primed doors
White moulded and primed doors are constructed differently from timber doors. Because of this, they can only be reduced by 6mm on each side. Any more than this, and the door will become unstable.
Fire doors
We recommend never altering the size of a fire door, as this could affect its fire rating and may mean it does not meet fire safety regulations. If you require a custom-size fire door, please contact us, and we will inquire with our suppliers to see if one can be made to suit your needs.
Recommended door trimming tools
Once you have decided on how much you need to trim, the next step is to make sure you have everything you need to trim your door. Our recommended tools are as follows:
- Finetooth Blade Circular Saw, or Planer
- Guide/Rule (Plywood)
- Tape Measure
- Pencil
- Clamps
- Stanley Knife
- Masking Tape
- A workbench with enough surface area and strength to hold the size & weight of your door
It is important that you use a finetooth blade rather than a rough-cut blade, such as a handsaw or chainsaw, as this won’t leave a smooth finish, making the door more likely to stick.
Door trimming instructions
Step 1- Give yourself a guide
With your door secured to the workbench, take a tape measure and mark out the required thickness at either end. Be sure to even out the thickness on both sides of the door.
Step 2- Trim the door
Once you’re sure you’ve accurately marked where you want to cut, you can start trimming down your door. The technique you’ll need will depend on whether you’re using a planer or a saw.
Using a planer
Set the provided guide in place against the plywood and begin. Starting at the left side, gradually plane down the lipping to the centre of the door and then again from the right.
Carrying out this technique will effectively reduce the risk of the veneer splintering. For the best result, move the plane in the same direction as the wood grain, as this will give a smoother finish.
Using a saw
Trimming using a saw is much quicker than with a planer but requires more attention to the cut. Splintering is a big factor when using a saw, caused by the blade teeth exiting the timber as you cut. Making sure you have already created your score line in the veneer will help to avoid this.
Starting from whichever side feels most comfortable, run the circular saw through the door, using the plywood guide to keep in a straight line. In one single motion, you will reach the end of the cut.
Step 3- Finish the door
After the cut, there are only a few things left to do before the door is ready to hang. Using a fine 140-grit sandpaper, sand along the newly cut side, rounding off any sharp edges and possible splinters.
The cut will also have left an exposed area on the door, which will need to be repainted or restained to protect it from bowing, warping, and splitting when exposed to humidity and temperature changes throughout the year. Once the paint or stain has dried, your door will be ready to hang.
Need to cut more?
If you’re looking to trim more than the recommended maximum from your door, you have the option to do so.
Remove the lipping with a precise cut and then cut down the door as needed. The lipping must then be re-attached to the door using a wood adhesive to ensure its protection.
As this is a much more technical job, we would recommend leaving it to a professional joiner.
Internal doors at Leader Online
If you’re looking to update your internal doors, we have a huge variety to choose from. Take a look at our fantastic range of internal oak doors or our exclusive Liberty collection, and bring a new look to your home right now.
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