Some of these chemicals are effective against a range of organisms. Others are very specific and protect wood from only one type of organism. No single chemical will protect wood from all degrading organisms. Terms often used interchangeably with preservative include pesticide, fungicide, insecticide, and mildewcide. These chemicals are all preservatives but they protect wood from specific organisms.
Fungicides protect wood from wood-degrading fungi.
Many fungicides will also protect wood against mildew. In turn, mildewcides can sometimes provide protection against decay fungi, but they are most effective against mildew and similar staining fungi. The chemicals used to formulate WRPs are generally fungicides and impart resistance to both mildew and decay fungi. Penetrating finishes were traditionally formulated using organic solvents as carriers for the binder and water repellent. The organic solvents facilitated the absorption of these components, thus giving a penetrating finish.