FAQ - Wacker Chemie AG


SILRES® WH is usually diluted 1:4 to 1:9 with water for direct application to wood. SILRES® WH can also be added undiluted to waterborne stains in concentrations of up to 3%.

Yes. Using SILRES® WH provides long-lasting protection from water and water-related damages. That opens up the door to reductions in the use of biocides, especially fungicides. In the case of many biocides, it eliminates their use entirely.

Wood treated with SILRES® WH can in principle be painted, if some weathering of the impregnated substrate is allowed first. However, it is important to note that smooth wooden surfaces will absorb only some of the silicone – the rest remains on the surface. As a result, and especially in the case of highly concentrated wood preservatives, paint adhesion may be restricted and leveling impaired. For this reason, SILRES® WH should not be employed as a primer.

Yes, but the beading effect becomes visible best after it has been exposed to the elements for a while (approx. 2 weeks). Thanks to SILRES® WH, however, beading will then be visible for an unusually long time.

No. SILRES® WH does not prevent graying, because this is caused by UV radiation, which silicones are transparent to. SILRES® WH does, however, help make graying uniform.

SILRES® WH has been combined with different acrylic resins. So far we did not see any incompatibilities. As typical for combinations of organic resins with silicones the dry film appears hazy, but that has no impact on the product’s properties.

Pigmented wood coatings/wood stains can be modified with SILRES® WH (1–3% dosage level) without any problems – therefore no compatibility issues are expected.

Application trials on spruce have shown an approximate amount of 100 g/m2 of the diluted product (e.g., 1:9) to be sufficient. Of course, the precise amount best used depends strongly on the absorption capacity of the wood.

Basically yes – a dilution of 1:4 to 1:9 should be useful for the protection of construction timber. However, we have no certificates for SILRES® WH in this regard.

We have no figures on this. But with SILRES® WH being a water-based product, it is to be expected that high wood humidity will limit/reduce the penetration depth.

The penetration depth strongly depends on the type, density, and natural resin content of the wood. Also the penetration depth is strongly influenced by the method of application – grain-cut timber/fiber direction.

Whether or not the penetration depth is influenced in any way is unknown at this time.

We tested SILRES® WH as it is (not combined with other products). The focus of our trials was the durability during weathering. The outdoor weathering showed very good visual beading and low water absorption after 17 years of natural exposure (video clip, trial with Karsten tubes). Mainly though, we use a QUV-B chamber and observe the impact of weathering on the beading effect (the weathered wooden stripes on our demo-tool for the ECS have been weathered in a chamber).

To date we have used UV-B light with frequencies from 280 to 315 nm. The main frequency is 313 nm. Future tests will involve UV-A irradiation with frequencies of 315 to 380 nm and a main frequency of 340 nm.

SILRES® WH maintains the wood breathability on a high level, meaning shrinkage and expansion will not be completely prevented. However, since the silicone resin is flexible it will not flake off due to shrinkage or expansion. Also the silicone resin reduces the amount of moisture absorbed and therefore keeps shrinkage and expansion at a lower level. This has a positive influence on the cracking tendency.

We worked with both dilutions. The 1:9 dilution even shows slightly better results in terms of the visual beading effect. In the video regarding the wooden façade, the panels on the left are treated with a dilution of 1 part SILRES® WH to 9 parts water.

We tested for a change of appearance on spruce, oak, beech, and ash. With a 1:9 dilution there was no or only minimal influence on the appearance (slight darkening).

So far this has not been tested, but the reaction to fire will be examined in our labs. In this respect, it is important to note that silicone resins generally do have a high resistance to fire. They are, for instance, also used as binders in heat-resistant paints. The first positive feedback was given for the use of SILRES® WH in intumescent coating for wood.

SILRES® WH should only be used in water-based stains as it is an emulsion. We are, however, already working on solvent-based versions as well.

Yes, because SILRES® WH has outstanding durability and is not decomposed by weathering. This is why we regard it as a very good solution for replacing waxes.