To understand why and how MDF splits, it's helpful to consider the characteristics of the material.

Medium Density Fibreboard is made of closely packed fibres from hardwood and softwood. These wood fibres are compressed and glued together to create a smooth and dense material which can be painted or covered with veneers. 

When you screw into the MDF sheet, the screw tears the fibre and wedges into the material. The fibres are tiny and loose, so they do not have much strength to hold the board together. If you use a large screw, this can often lead to splitting as a result.

Choose the right screws

To keep the chance of splitting as low as possible, it's essential to opt for a screw with a small diameter and preferably a straight rather than a tapered screw. This will reduce the amount of tearing it causes to the fibres. Long and thin screws are preferable for use with MDF. You might use MDF screws instead of standard wood screws, fully threaded screws, type A or AB sheet-metal screws, or Twin Fast screws to join your boards. 

Clamp the sides of the sheet

Clamping the sides of the sheet of MDF makes it very hard for the material to split. You can use a handscrew clamp to do this. 

Make a pilot hole

The best way to avoid splitting is by using a pilot hole. Pre-drilling a hole in the board means less tearing of fibres, reducing the chance of splits. It's essential to use a very sharp drill, such as a brad point drill, to pre-drill the pilot hole. You will need a drill bit with a diameter just slightly smaller than the root of the screw and drill the hole a little deeper than the screw's length. If you drill slightly deeper than necessary, this ensures that the MDF doesn't split if you accidentally screw in too far. 

To make sure you get the size of the pilot hole right, it can be helpful to practise on a scrap piece of material first.

Use a countersink bit

A good trick is to use a countersink bit for the head of the screw to rest in. This prevents the screw head from forcing the fibres apart and causing a split. Plus, it looks nice and neat in your MDF panel.

Or use epoxy for more strength

After drilling your pilot hole, you might drop a small amount of epoxy into the hole before screwing. This helps secure the screw to the board for strong joints with less risk of splitting. 

Avoid screwing near the edge

Another tip is to avoid driving your screws into MDF too close to its edges where the fibres are weaker. This way, even if the sheet splits a little, it won't end up cracking to the edge of the board. We recommend avoiding screwing within 75mm of the edge of your MDF. 

Don't tighten your screws too much

Over-tightening your screws can sometimes lead to breakages. MDF is less robust than natural timber due to its use of wood fibres. Take care to tighten your screws firmly but not too much. 

If you're still not succeeding with your screws and MDF, consider trying another tactic for your joints. You can use wood glue for joining MDF sheets in some cases. Another technique some woodworkers use is glueing solid wood corner blocks to the MDF sheet and screwing them into this wood instead for strong joints without the risk of splitting. 

While MDF is one of the best and most versatile materials to work with, there's one thing to keep in mind when using these panels for your projects. Due to the fibres of wood used in the construction of MDF, cutting or drilling the sheets can result in large amounts of dust. Make sure to wear protective equipment, including a mask, to avoid breathing in these potentially hazardous particles. 

Alternatively, you can order your panels cut to size. Here at Cworkshop, we offer a cutting service to allow everyone, from woodworking professionals to DIY enthusiasts, to get the perfect sizes every time. Whether you're using the boards as carcasses for furniture, wall panelling, for your cabinet doors, or any other project, we can quickly and efficiently provide you with the exact.