Wood is hygroscopic. So wherever there is a change in relative humidity (RH) the wood will change in moisture content (MC). When this happens, the wood will either expand (RH and MC go up) or contract (RH and MC go down). Changes in MC lag changes in RH. It typically takes 48 to 72 hours for Stikwood to reach what is called equilibrium moisture content (EMC). That is the MC where the material is neither gaining or losing moisture at a given RH. So we are interested in the average RH over this period.
That being said Stikwood performs well in average relative humidity between 30% and 65% at typical room temperatures. In properly functioning residential bathrooms you will see RH that is higher than this for short periods. This will bump the average RH up a few points but not significantly over the EMC lag time. So if the bathroom RH is normalizing after wet events like showers then there should be no issues using Stikwood. On the other hand if the bathroom has a moisture issue that prevents the RH from normalizing after showers etc. then it is not recommended that stikwood be installed. This type of issue is usually related to poor ventilation and or water leaks that soak into the floors and walls.
When installing stikwood into areas with rapid RH fluctuations like bathrooms there are two moisture considerations to take into account.
First is the average relative humidity of the space it is installed in. This needs to be between 30% and 65%. The product needs to acclimate (store) in these conditions for at least 72 hours prior to installation.
Second is the moisture content of the surface stikwood is being attached to. Although the adhesive is very moisture resistant once adhered (we have weathered wood stikwood installed on our outdoor patio) it must be installed in dry conditions. The surface you are installing to must be dry. That is have a moisture content less than 8%. To put that into perspective freshly painted drywall can have a MC of 20% and take a few weeks to get below 8% depending on conditions.
All this may seem complicated but applies to the installation of any wood or fiber product. We have many successful stikwood installs as well as a few failures due to impossible site conditions. If in doubt you may want to test a small area with the material to see how it will react to the your real world conditions.