Questions & Answers 

Need Help?

If you need any help with specification or visualising what your project will look like if you apply SiOO:X products you can make contact with Russwood, our Premier Specification Partner - ask on 01540 673 648         

If you wish to contact Sioo directly our detals are:



Sioo Wood Protection AB, Von Utfallsgatan 20, 415 05 Göteborg, SWEDEN
Tel +46 (0)31-42 42 62 • •

You may find answers to your questions in the Q&A list below:


How to prepare the surface before treatment

The best results are obtained by applying SiOO:X onto sawn surfaces. This is because the surface has been opened up by the saw blades and much better penetration of the SiOO:X fluid into the wood surface substrate occurs.  

The surface must be clean. New untreated timber can be coated with SiOO:X directly, but fresh planed surfaces MUST be sanded according to the instructions with no finer paper than 60 grit.

Older timber or timber which has been oiled, such as a patio or balcony or cladding facade and which has blackened, needs to be cleaned. You either need to wash with a pressure washer and  detergent or caustic soda. Rinse well. Alternatively, you can sand the whole patio or cladding surface.

On untreated wood that is well maintained, it is sufficient that you wash off with the SiOO:X Maintenance Wash. Wash and rinse well.

Weathering to silver-grey - water is the activating factor

After the application of all three treatment coats  (2 coats of Wood Protector + 1 coat of Surface Protector), and when dry, the surface needs to be in contact with water to activate the silicon to form a network of silica crystals. This crystallisation eventually makes the surface become a beautiful silver-grey colour and smooth and strong. This process is gradual and can take a number of months depending on the timber species and how much it rains for the effect to fully show.  Thereafter, the crystallisation continues to develop. Western Red Cedar developes quicker than Siberian Larch where there is a noticeable change after about six months.

SiOO:X mirrors what happens to timber as it weathers naturally but protects it and accelerates the development of a silver-grey lustre. This protected and gradual weathering process is sought by many customers. For those customers seeking the attributes that SiOO:X provides but requiring an immediate grey appearance, the light-grey or mid-grey pigmented products can be specified.

On treated wood which is sheltered such as under roof eaves or where rain water cannot reach, we recommend that you should rinse the surface with water several times.

If you want to accelerate the silica crystal formation, you can use a brush and work in the water.

In the early stage just after treatment and before silica crystals have had time to form the surface will look a yellowish brown initially. Be patient, wait and water


1. Do I need to cover adjacent surfaces when I want to coat with SiOO:X?

Glass, stone, aluminium and metal must be protected. If the treatment spills on these surfaces, wipe directly with a wet cloth (the tip is to have a bucket of water and cloth available). It is best to mask surfaces such as glass if possible.

Galvanized sheets are not damaged by SiOO:X Impregnation.

2. How do I apply SiOO:X?

On new projects the best option is to purchase timber which has been factory treated with SiOO:X. This gives certainty when the weather is unpredictable or in cold winter conditions. Factory treatment by SiOO:X approved coaters ensures excellent quality control.

By hand the easiest and best way is to use a broad brush on a shaft. Apply abundantly and  distribute well. Brush away excess fluid.

3. It has rained before the Surface Protector was applied. What do I do?

SiOO:X Premium Wood Protection tolerates some light showers but it can leach out if it rains lightly over about 45 minutes or there is more than about 5 mm of rain. In this case apply another full coat of SiOO:X Premium Wood Protector.

With less rain after the second application of SiOO:X Premium Wood Protector, supplement with a light coat of more SiOO:X Premium Wood Protector.

For longer periods of rain re-treat fully with the SiOO:X Premium Wood Protector.

As soon as the SiOO:X Premium Surface Protector has dried (about 45-60 minutes), it does not matter if it rains.

4. Can SiOO:X be used on newly laid, pressure treated wood?

Yes, but wait until the treated wood has dried, which takes a maximum of two months. The surface should look dried out and feel dry when you iron over it with your hand.

5. Can SiOO:X be used on all types of wood?

Yes, on most natural timber and on many engineered timber brands. On some of the very dense hardwoods it can be preferable to let the timber weather for anything up to a year to allow the surface to open up. This will allow the SiOO:X treatment to penetrate  better.

6. Some of my project is covered. How do I get this just as grey as the rest of the structure?

Parts that are covered or which cannot be exposed to rain will take some more time before they  cure to the same shade of grey. They will get there.

These parts can be soaked with water and rubbed in with a  brush to speed the crystallisation. Repeat several times.

Weathering time to see noticeable change in colour depends on temperature and timber species. With engineered timber species such as ThermoWood it takes 6 to 8 weeks for the parts that are exposed to rain to begin to change colour but longer with the natural timbers such as cedar and larch.

7. Why Is the surface speckled and mottled after I have applied SiOO:X?

Our product requires that it is exposed to rain and moisture to activate the silicon in the liquid.

The silica networks which form are what make the surface a beautiful velvety grey over time. The activation takes place over a period of about 4-8 weeks depending on the weather and continues. During this period any surface speckling will disappear.

8. The wood surface is really nice but it grows a little green in the corner where there is shade. On the cladding, there are some little black spots. How do I remove and why does this occur?

SiOO:X Impregnation forms a protective and dirt-repellent layer in the wood surface. When it is wet and dirt falls on the surface, a little green or black algae can grow on the surface. Black dots are usually dirt which can be brushed off. There is usually much less of this on SiOO:X treated wood. The wood is protected from algae penetration.

It should be understood that green algae and black algae can grow on almost anything, even metal and stone. When you use the SiOO:X Maintenance Wash, the algae very easily washes off the surface with a brush and hose. Avoid using a pressure washer. If you wash very heavily, we recommend that you re-coat with SiOO:X Premium Surface Protector to reseal the surface. In severe cases of algae formation, stronger agents should be used to remove it. The SiOO:X Premium Wood Protector itself has a strong cleaning action and can be applied to remove severe cases of algae and staining. Rub/apply the SiOO:X Premium Wood Protector onto the affected area and leave to soak. Wipe away any sediment and leave to dry. Apply a coat of SiOO:X Premium Surface Protector to the cleaned area. See cleaning of extractives and black/grey spot

Very occasionally, freshly treated wood can develop grey spots locally under the SiOO:X envelope in conditions where there is high localised humidity and little air flow. This is due to discolouring fungi metabolising residual starch in the sapwood and is not harmful although it can, close up, look a little unsightly for a while. It is not induced by the treatment. The grey spots will disappear when the starch depletes and as the curing of the treatment developes. 

Sapwood should be avoided on exterior surfaces. Where sapwood does exist on exposed exterior surfaces a coat of a commercial clear biocide is recommended to be applied to the wood and allowed to thoroughly dry before the SiOO:X is applied. See the Product Information Sheet for more details. Properly specifying high quality timber from reputable timber companies who offer comprehensive profile design and product detailing will minimise the risk of timber containing sapwood being supplied for use on exterior surfaces.

In the case of surface damage, particularly with vulnerable surfaces, apply more SiOO:X Premium Wood Protector followed by the SiOO:X Premium Surface Protector.

9. I have a pool on the wooden deck, can I still use SiOO:X?

Yes, SiOO:X is non-toxic and entirely environmentally friendly.

10. How long does the treatment last?

Up to 10 years for horizontal surfaces and up to 15 years for vertical surfaces.

11. What do I do if there is an injury to the wood?

For light surface damage apply the SiOO:X Premium Surface Protector locally. Where the integrity of the surface has been breached apply both the SiOO:X Premium Wood Protector and the SiOO:X Premium Surface Protector locally. The surface will evenly grey again after a few months.

12. What do I do when the treatment reaches the end of its lifecycle?

Clean and re-apply the full treatment.

13. When it rains the surface looks wet. Why is this?

The SiOO:X system leaves the wood open for diffusion and it can breathe unlike with film coatings. The SiOO:X Surface Protector seals the SiOO:X Wood Protector into the surface substrate and provides water repellency. When it rains there is some water ingress and the surface looks wet but the wood cells are protected. As the atmosphere dries the SiOO:X system rapidly diffuses, repels, moisture from the wood and produces a dry surface remarkably quickly.   

14. What are the most important factors for achieving long project life?

Good design detailing is crucial; for instance with cladding avoiding ground contact, achieving a design which sheds water at eaves level and ensures adequate airflow behind the cladding, orientating the cladding vertically as against horizontally. With decking ensure positive falls to shed water off the surface; avoid ground contact and allow for good airflow around the supporting structure. The selection of good quality durable timber ensuring that there is no sapwood on exterior surfaces is vital. Good preparation of the timber surface is very important; sawn surfaces give the best penetration of the SiOO:X treatment and are to be preferred, otherwise sanding is needed with a 60 grit paper. Treating the timber to professional standards in the right environmental conditions is essential using factory treatment where possible. A very important factor is to treat end grain including any end grain exposed during site construction. In service maintenance is a key factor, keeping the timber surfaces clean and removing dirt and any surface fungi that forms at an early stage.