Before you apply a stain or paint to a wood surface, you need to make sure the surface is free and clear of dirt, dust, fibers, grease, mildew and moisture. When a surface is not clean, paints will have trouble sticking to the wood and stains will have a difficult time penetrating into the wood and this will likely cause premature peeling. Not only will forgoing this step cause painting to peel quicker, most of the unclean blemishes will show through your stain or varnish- thus resulting in a waste of your time and money!
As for the exterior of your home, although it may look clean to the eye, there is likely dust, chalking and mildew present. If you decide not to power wash beforehand, not only will your new paint not stay for very long, but your old paint will still be underneath. Pressure washing will not only remove the dirt and grime, but it can also remove old, chipped paint that may cause discrepancies in you new paint job. In short, forgoing the pressure washing step will likely cause a lot of injustice to your new paint job!
Here is the important part! Knowing the difference between pressure washing and soft washing.
Regular pressure washing uses high pressurized water to remove all sorts of build-up from the surface it comes into contact with, which if done correctly, it can prepare the right surfaces for refinishing. However if it is not done at the right pressure, pressure washing can damage your surfaces; for example, if you use too much pressure on your fence or deck it could leave gouges in the wood- this is where soft washing comes in.
Soft washing is a low-pressure approach, combined with safe, eco-friendly chemicals that remove unwanted elements from your surfaces such as your deck, fence, roof and siding. Soft washing is not only just as effective as regular pressure washing, but it also maintains your finishes longer- without the risk of damage.
Both pressure washing and soft washing can be effectively used to prepare your surfaces for painting or staining depending the surface. An experienced professional would be able to determine which chemical combination and approach to take to achieve the desired result without damaging your surface.