Brightening, and brightening, and brightening...

Brightening refers to the process of acid washing a deck prior to staining.  We use oxalic acid, although I know some people have used muriatic on redwood decks with success as well. The product we use is non toxic and biodegradable. It also contains a mildew removing component that sanitizes the deck of any fungal growth. 

We also brighten using deck brushes with a medium stiffness when the wood is dry to massage the solution into the grain of the wood. This helps produce the maximum desired effect and eliminates weak and uneven acid washing using a pressure washer to apply. We do this on all of our maintenance and restorations. 

Acid washing is especially important after sanding since there is a particular fungus that likes to grow on tiny bits of dust leftover after sanding.  This is also why we keep the deck as clean as possible throughout the process and never leave dust on a deck after it has gotten wet, or may be getting wet overnight. PH is important in terms of the reactivity of redwood and cedar with the pigments used in our deck stains, which are essentially metals. Acid washing makes the deck colors really "pop" as the name "brightening implies, as shown in these pictures:

Before brightening:

  After brightening:

We have also found that a second brightening is needed decks that had a lot of screw issues. or were left to weather for several days due to storms before staining.  The act of countersinking a screw can cause metal to flake away and get into the wood, which rusts and causes black bleeds along the grain of the redwood after the initial pressure wash/brightening. 

Screw bleeds after brightening and several rain showers:

Screw bleeds immediately after second brighten:

Hardwoods and brightening 

We do not use brightener on hardwood since the same ph issues in cedar and redwood are not present, and they are much more resistant to mold and other microbial growth. We do use a mildewcide/cleaner after sanding to eliminate microbes and deep clean the wood but have never had any issues with mold. 

Here is a job where we only pressure washed the greyed out ipe and then stained it with great results.  You will notice a slight darkening on the outer 2 deck boards due to increased weathering but overall very effective.