Alcohol Used as Wet Water
A glue mixture is often used to attach scenery material to the layout or module. This glue mixture is usually some dilution of white glue with water. Unfortunately, water has a surface tension that tends to cause the water to form isolated drops rather then flow evenly into the scenery.
Wet water is often used to help break this surface tension. It is water mixed with a drop or two of dish soap. The soap assists in lowering the surface tension and moistening the scenery. This allows the glue mixture to flow more freely and form a bond with all of the material. However, this method is still not ideal. Often the wet water will only lower the surface tension, and not completely eliminate it. The problem of scenery material pulling together on a water drop will still occasionally occur, and the soap can make tiny bubbles itself.
Rubbing alcohol is an effective alternative to wet water that eliminates the problems. It has almost no surface tension so it flows readily into the ballast and other scenery material ready to accept the glue mixture without disrupting the shape or distribution of the scenery material. Bottles of Isopropanol Alcohol at 70% solution work great and can be purchased at major drug stores for about 30 or 40 cents a bottle. I use it at full strength.
The alcohol dries faster so you are ready for second and third coats much faster. I have used rubbing alcohol with a great deal of success. The material is firmly attached to the layout or module without the disruption and redistribution caused by surface tension. Be sure, however, to provide plenty of ventilation.