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4x2 Treated Timber C24

4x2 treated timber, or 100x50 treated timber, is one of the cornerstone materials of the construction industry. Quality C24 graded timber which has been shortened to the requisite length and pressure laced with chemicals to prevent both fungal and insect attack. We supply good quality 50x100 timber, which comes various lengths in 2.4m, 3m, 3.6m, 4.2m, 4.8m and 6m lengths which can then be cut to the required length for any given project.

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What size is 4x2 timber in mm?

The most common way to express this size of treated timber is in inches (4x2). However, in metric, it is 47mm x 100mm or 50mm x 100mm. The 47mm and 50mm are largely interchangeable due to the miniscule difference between them and we sell 47mmx50mm as this size just allows for a neater finish to the wood. Either of these metric sizes is referred to as 4x2. 

What is 4x2 C24 wood used for?

There are a huge number of different uses for 4by2 timber as it is an extremely adaptable structural building material, suitable for both indoor and outdoor use. This is thanks in large part to the protective treatment of the timber, and its C24 grading, 47x100 treated timber can be used in many different applications such as flooring, roofing and walling.

Treated 4x2 is often used in the framing of outdoor decking, as 4x2 timber decking joists for the rest of the decking to be attached to. The C24 4x2 treated timber sold on this website is ideal for use as decking joists as it is able to bear heavier loads than ungraded timber or that which is graded to a lower level such as C16.


With its structural C24 grade 100x50 timber can be used as carcassing timber in floor joists, or as timber framing that is an integral part of the structure of a building. It can also be used in roofing applications, as rafters or as. joists in a loft floor.


Garden furniture and other outdoor projects are another excellent use for 4 x 2 timber, because it has the in-built advantage of being sealed already against fungi and insects.

Tell me the difference between treated timber and sawn timber?

Sawn timber is wood that has been cut to the required dimensions but hasn't yet been pressure treated and kiln dried. Pressure treating provides many benefits, making the timber weather proof and protecting it from the elements.


The pressure treatment process that gives treated timber these resistant properties usually includes copper and organic co-biocides to repel both insects and moisture. This confers a high degree of protection against both of these potential problems. Treated timber can also be called tanalised timber, named after the preservative (tanalith E) that is used in the treatment process. After the treatment is applied, the timber lengths kiln dried in an oven.

Many people will tell you that it is very important to use good quality treated timber for your construction projects because most of the timber used in building is located in places that are not easy to get to. This means we usually have no way of knowing if parts of the structure are under attack from insects or dampness, thereby weakening it.

This could obviously cause longer term difficulties, depending where on the building the untreated timber was located. It is preferable to take the steps that we can in the beginning, in order to prevent potential problems from occurring.

Frequently asked questions about 4x2 timber

Can I paint 4x2 treated timber?

It is possible but slightly difficult to paint treated timber as it comes with its own complications due to the pressure treatment and chemicals that are involved in this. It is important to remember that it really isn’t a good idea to begin painting treated timber too soon after you have bought it. 

This slightly strange sounding advice is because when shipped, most 100mmx50mm timber is still “wet” and needs time for the chemicals permeating the wood to settle and dry. At this point, the wood is noticeably heavy and will still feel damp to the touch.

If primer or paint is added to it at this point, there is every likelihood that it will be rejected by the water based chemicals that are still working their way through the wood. It is important to permit the timber to dry out fully before attempting to add paint or primer. This can be a lengthy process and may even take up to a few weeks depending on where the wood is stored. If there is too much heat and direct sunlight, this can cause the treated timber to warp instead of dry out. Damp conditions can also prolong the drying out period. 

How easy is it to cut 4x2 treated timber to my preferred size?

It is fairly easy to cut treated timber to the size needed for what you’re doing, though this should only be undertaken with the requisite power tools. A respirator should be worn as there will be tiny airborne pieces of wood, which may be soaked with the chemicals used in the pressure treating process. Eye protection is also highly recommended.


It is important to heed the necessary safety precautions before proceeding to cut the treated timber as it cuts a little more like a wet wood. Some extra care must therefore be taken to ensure the blade doesn’t slip while cutting. 


Although it is a little more difficult than cutting sawn timber, it is still reasonably easy to cut cheap 4x2 timber into the sizes that are needed for your project. As long as care is taken, it can be accomplished fairly easily. This material is considered adaptable for a reason and if it was very difficult, it wouldn’t be used in so many different projects.

How much does 4x2 sawn treated timber cost?

Sawn carcassing timber is a very common and therefore fairly inexpensive building material. 100x50 treated timber prices are prone to fluctuation, depending on seasonal demand. We will provide you with a very competitive price if you wish to buy 4x2 timber through Materials Market.

Is 47x100 treated timber environmentally sustainable?

All of the timber lengths sold by Materials Market are Forest Stewardship Council (FSC) or Programme for the Endorsement of Forest Certification (PEFC) certified, which is a certification to show that the timber has been responsibly sourced.