Timber treatment explained

Dip treated vs tanalised timber

Both treatments help protect timber, but they work in very different ways. Dip treatment coats the surface with preservative, while pressure treatment drives preservative into the timber under controlled vacuum and pressure. That difference matters when you are choosing how much long-term protection and ongoing maintenance you want from your shed.

All Beast Sheds frameworks are pressure treated, whichever shed range you choose.

The difference at a glance

The easiest way to think about it is depth of protection. Dip treatment is primarily a surface treatment. Tanalising is an industrial pressure-treatment process designed to give the preservative much deeper and longer-lasting protection within the timber.

Dip treated timber

Timber is immersed in or coated with a water-based preservative so the treatment is concentrated around the surface. It gives useful initial protection against fungal growth while keeping the cost of the shed down.

Good-value treatment for our Standard shed cladding.
Provides initial surface protection while the shed is manufactured, delivered and installed.
Needs a suitable exterior timber treatment after installation for ongoing weather protection.
The finish can then be maintained in accordance with the treatment manufacturer's instructions.
A good choice if you are happy to apply and maintain your own exterior finish.

Important: Dip treatment should not be treated as a permanent exterior finish. Once the shed is installed, apply a suitable exterior wood treatment promptly, allowing for the timber condition and the coating manufacturer's instructions.

Tanalised / pressure-treated timber

Pressure-treated timber is placed in a treatment vessel where vacuum and pressure are used to impregnate the wood with preservative. The treatment is therefore not simply sitting on the surface.

Long-term protection against fungal decay and wood-destroying insects when treated for the intended use.
Much less dependent on a regularly re-applied preservative coating for rot protection.
Particularly useful where future access for re-treatment may be awkward.
Can still be painted, stained or finished for appearance once sufficiently dry.
Used throughout our Tanalised and Beast ranges, and in the framework of every Beast Sheds shed.

Pressure treated does not mean waterproof. The preservative protects against biological decay; the timber can still absorb and release moisture, weather in colour and move naturally as conditions change.

What does that mean for our shed ranges?

The treatment choice is only part of the specification. Cladding thickness and framework size also increase as you move through the ranges, so it is worth comparing the whole construction rather than treatment alone.

Feature	Standard	Tanalised	Beast
Cladding treatment	Dip treated Lowest initial cost	Pressure treated Lower maintenance	Pressure treated Heavy duty
Cladding	16mm timber, planed to approximately 12mm finished thickness, with our rebated shiplap profile.	16mm timber, planed to approximately 12mm finished thickness, with our rebated shiplap profile.	25mm timber, planed to approximately 20mm finished thickness, with our heavier rebated shiplap profile.
Framework	Pressure-treated 38 x 50mm timber.	Pressure-treated 38 x 50mm timber.	Pressure-treated 3" x 2" planed timber framework.
Floor protection	Pressure-treated timber floor.	Pressure-treated timber floor.	Pressure-treated heavy-duty timber floor construction.
Ongoing treatment	The dip-treated cladding needs an appropriate exterior timber treatment after installation and future maintenance.	Pressure treatment provides the preservative protection; an exterior finish can still be used for colour or additional surface weather resistance.	As with the Tanalised range, pressure treatment protects against decay while optional finishes can be used for appearance and added weather resistance.
Rot protection	Initial preservative protection to the dip-treated cladding, followed by the exterior treatment you apply and maintain.	Includes our 10-year rot-resistant guarantee, subject to the applicable guarantee terms.	Includes our 10-year rot-resistant guarantee, subject to the applicable guarantee terms.

One point that is easy to miss: choosing a Standard shed does not mean the whole building is only dip treated. The structural framework is pressure treated on every range, and the shed floor is pressure treated too. On a Standard shed it is primarily the exterior cladding where the treatment choice differs.

How pressure treatment works

Tanalising is carried out before the shed is built. The exact treatment cycle is controlled according to the timber and its intended use, but the principle is straightforward:

Timber enters the treatment vessel

The timber is loaded into a sealed industrial treatment chamber.

A vacuum is applied

Air is removed from the vessel and from accessible spaces within the timber structure.

Preservative is applied under pressure

Controlled pressure forces the water-based preservative into the timber rather than simply coating its surface.

The cycle is completed

Excess solution is removed and the timber is allowed to drain and dry before it is used in the building.

Diagram explaining the pressure-treatment process used for tanalised timber — The pressure-treatment process drives preservative into the timber under controlled conditions.

Graph illustrating the long-term performance of pressure-treated timber — Long-term testing illustrates why properly specified pressure treatment is used where extended protection against timber decay is important.

What pressure treatment does — and what it doesn't

There are a few common misconceptions around treated timber. Knowing the difference between preservative protection and normal timber weathering makes it easier to look after your shed correctly.

It protects against decay

Properly specified pressure treatment gives long-term protection against fungal decay and wood-destroying insects by getting preservative into the timber rather than relying only on a surface coat.

It does not make timber waterproof

Treated wood is still wood. It absorbs and releases moisture, and a suitable water-repellent or decorative coating can be used if you want extra surface weather protection.

Colour change is normal

Pressure-treated timber can change colour as it weathers outdoors. That visual weathering does not, by itself, mean that the preservative protection has stopped working.

Natural movement is still normal

Knots, grain variation, small surface checks and movement as moisture levels change are normal characteristics of natural timber and are separate from rot protection.

You can still paint or stain it

Pressure-treated timber can be painted, stained or finished once it has dried sufficiently for the chosen product. Always follow the coating manufacturer's preparation and moisture guidance.

Take care if you modify treated timber

If pressure-treated timber is cut or drilled after treatment, exposed end grain may need an appropriate brush-on end-grain preservative to maintain protection. Follow the preservative manufacturer's instructions.

Looking after each treatment

Good maintenance is mostly about keeping water moving away from the shed and inspecting the timber before small issues become bigger ones.

For dip-treated cladding

Apply a suitable exterior wood treatment after installation rather than relying on the factory dip as the long-term finish. Re-treat according to the product you use and the exposure of the shed. Pay particular attention to surfaces that receive the most sun and driving rain.

For pressure-treated timber

You do not need to keep repainting pressure-treated timber simply to preserve the pressure treatment. You can, however, add a suitable stain, paint or water-repellent coating for appearance and enhanced surface weather resistance once the timber is sufficiently dry.

For every timber shed

Keep the base well drained, don't allow soil or wet leaves to build up against the lower walls, maintain airflow beneath the floor and check the roof after severe weather. No preservative treatment is a substitute for good siting, drainage and basic maintenance.

So which should you choose?

Choose Standard if keeping the initial price down is important and you are happy to apply and maintain an exterior treatment on the cladding. Choose Tanalised if you want the same general cladding thickness with pressure treatment throughout the timber and less reliance on future preservative re-treatment. Choose Beast when you want pressure treatment combined with substantially heavier cladding and framework for demanding storage, workshop or office use.

Compare cladding & framework Read the flooring guide Explore the full shed guide

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All planed timber sizes are nominal (approximate) due to the planing process. Wood is a natural material and is therefore susceptible to changes in the environment.

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