Tips on using medium density fibreboard on external projects

MDF (Medium Destiny Fibreboard) is now one of the most commonly used composite boards on the market and it’s easy to see why.

Most important of all is it’s relatively inexpensive. You can usually purchase MDF boards at the fraction of the cost of real wood such as plywood and by and large, it is just as good, if not better at certain applications. With it’s composite construction, made up of tiny wood chips, fibres and resin, it offers a strong and adaptable solution to many building projects needs.

When cut, it tends to leave a relatively smooth edge unlike some timber boards that split and splinter, and the overall finish achieved when edged or painted can be of a particularly high standard. It’s dense, heavy and durable under most conditions.

However, most MDF’s are not great in damp or wet conditions and if put under a lot of strain, can split or crack if put under too much stress. MDF also does not tend to take nails or screws as well as real wood boards, due the fibres not being able to thread as well. That said, it still offers an excellent, cost-effective way of producing great looking finishes for a number of items such as furniture, shelving, laminate flooring, mouldings and doors. In most instances, every home in the country will have MDF somewhere or other.

Where can I use MDF effectively?

MDF is ideally suited to dry, internal environments only. Standard MDF tends to absorb rather than repel moisture, so if there is water near by, watch out! It won’t take long for the boards to soak up any damp nearby and that’s when the resin in the MDF starts to break up and deteriorate. If this happens, the boards will have been compromised and will most certainly need replacing.

There are however, certain types of MDF which are adapted to cope better under damp conditions. Both Veneered Fibreboard and Moisture Resistant Fibreboard are both designed to deal with moisture far better than Standard MDF.

Veneered Fibreboard

As the name states, this type of MDF is veneered with a thin layer of wood such as ash, cedar, cherry, oak, maple, pine or walnut to name a few. By veneering the MDF, it dramatically improves the aesthetic appeal of the board but also its water resistant properties. By choosing a strong wood as the veneer, this will inevitably improve is ability to resist water when used outdoors on all veneered facing sides.

Remember however, that if any edges are cut and exposed, these need to be veneered or protected to prevent water from penetrating and damaging the boards.

Moisture Resistant Fibreboard

Unlike Standard MDF, MR MDF does not use urea-formaldehyde based resin and instead uses a moisture resistant phenol-formaldehyde glue instead. Due to this type of resin being more expensive, MR MDF invariably comes with a higher price tag. But if you’re in need of an MDF that can deal with the wet, this the most suitable option to go with.

Extra Tips

Even if your MDF is veneered or uses moisture resistant phenol-formaldehyde resins, its is still advisable to paint or seal the MDF to improve its water resistant qualities. Where the MDF is unfinished or has exposed edges, a water sealant or paint will give you an extra insurance policy against water damage if you intend to use the boards where water is ever present.

Some MDF boards may not take a waterborne polyurethane based paint so well on first application which is perfectly normal. If binding does not occur, try applying a seal with a shellac first, then apply the sealant polyurethane once dry.

Know It’s Limitations

Remember, MDF was never designed to be used is extremely wet conditions. Even if you choose to use a veneered or water-proofed MDF, they are only suited to environments with a modest level of damp. If the area you intend to use the boards is consistently wet, perhaps you should consider using another material that can cope with such applications better.