Wood that is used to construct boat docks, decks, handrails, picnic
tables or any other horizontal outdoor surface is subjected to the absolute
harshest weathering conditions. Unprotected wood absorbs enormous amounts
of ultraviolet (UV) radiation from the sun. UV rays can actually blast
apart the lightning that bonds wood fibers together. Rain water and snow
melt can pond or pool on flat boards. This water can easily be absorbed
by the wood causing it to swell. When the sun or wind dries the wood,
it shrinks. The shrinkage forces cause cracking, twisting and warping.
Conventional pressure treatment chemicals will inhibit rotting but will
not stop these other destructive and unattractive phenomena. New wood
needs to be sealed immediately. Water and sunlight begin to destroy it
as soon as it is exposed to these elements.
Cleaning a wood surface prior to sealing is very important. The cleaning
will remove any dirt, tree sap, algae or mildew. It will also remove the
decaying wood fibers destroyed by the UV rays. All of these things prevent
the wood sealer from adhering or penetrating into the wood. Do not use
chlorine bleach (sodium hypochlorite) to clean your wood! It is a very
strong oxidizer that will remove the natural color from your wood. In
addition, it is toxic to any vegetation surrounding your wood surfaces.
A better cleaner is sodium percarbonate or oxygen bleach. This product
will not remove the natural colors from the wood nor will it harm vegetation.
Sodium percarbonate should not be used to clean redwood. It can actually
darken the wood. Use oxalic acid instead. I have cleaned cedar with
oxygen bleach without darkening it. You may want to experiment yourself.
If you feel it darkens the cedar, then use oxalic acid to complete the
cleaning job.
When selecting a sealer, try to choose one that is a penetrating water
repellent. Look for ones that are formulated using synthetic oils and
resins. Some are available that are water based. You can - in some cases
- clean and seal your deck the same day! Choose a sealant that is heavily
pigmented if possible. The pigments in sealants do a great job of reflecting
and absorbing harmful UV rays. Some sealants that you can purchase contain
natural oils like linseed oil and tung oil. Both of these oils can do
a great job of protecting wood, however the manufacturers often have
to add mildewcides and fungicides to the sealants. The natural oils
are actually food for mildew and algae! That is why many decks turn
black or green in just a matter of 6 - 9 months.
Avoid using sealers that are film forming sealants. Beware of products
that contain acrylic resins, varnish resins or alkyd resins. Look on
the label for these ingredients. These products do not readily soak
into the wood. They leave a film that will eventually peel. If the film
peels unevenly from your wood surfaces, it will become a maintenance
nightmare. You will have to strip your wood in the future to add additional
sealants.
Be sure to follow the instructions on all cleaning and sealant products.
Hot, sunny, windy days can be the worst time to apply certain products.
Some synthetic sealers will last up to 3 years if you apply them according
to instructions. I have a synthetic sealer on my front porch that is
2 years old. It looks practically new. There is no sign of mildew or
algae growth whatsoever.
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Newsletter:
3 February 2012 to 10 February 2012 - Krugersdorp, Gauteng, South Africa
