Stripping Stains From Decks
Like most refinishing jobs, excellent PREPARATION of the wood
surface is the KEY to success. Prep right, and the deck will
turn out GREAT. Rush through prep, skip a step (or two) to save
money and/or time, and the deck won't look nearly as good.
Thorough cleaning of any deck or fence is essential to get good
results. If the wood was previously sealed, the common practice
is to strip off the old sealer. We do this to get back to the
actual wood. All sealers are designed to bond best to the wood
itself (rather than to bond to an aged layer of the old sealer).
By stripping off at least the "coating" portion of the old
sealer, we can eliminate most reasons for premature sealer
failure.
If the "coating" portion of the old sealer remains on the
surface, no part of the new sealer can penetrate down into the
wood. This results in a couple of situations that could lead to
premature failure of the new finish.
The first of these problems is a reduction of the permeability
of the overall sealer layers. Permeability refers to the ability
of the sealer to breathe. If we clog the surface with several
layers of sealer, each layer comes a little closer to closing
off the wood from breathing. In that case, the wood retains
humidity. This could lead to rot, as discovered in a recent
class-action lawsuit against a major manufacturer of sealers.
This could also lead to peeling and flaking, as the trapped
humidity tries to push its way up through the layers.
The second problem is bonding. As stated earlier, most sealers
are designed to bond to wood fibers to some degree. Many sealers
can also bond to themselves (such as a second coat). If we try
to apply one sealer over top of another brand (or type) of
sealer, there is no guarantee that the new sealer will bond to
the old sealer. If this occurs, the new sealer could flake and
peel off within months. Most sealer manufacturers are reluctant
to stand behind the performance of their product unless it is
applied to bare wood.
Further, sealers that are designed to penetrate, when forced to
dry on the surface without penetrating, will fail by design.
What I mean here is that a penetrant is not meant to stand up to
wear like a coating does, so when you force a penetrant to act
as a coating it fails. This happens when the penetrant can't
penetrate - and it dries on the surface.
There is at least one more reason to think about stripping every
time you run across a previously- sealed deck. The reason you
are being called in to do your magic is that the customer is
unhappy with the performance and/or looks of the current sealer.
Leaving that old sealer in place seriously limits how good you
can make the deck look with a new finish. If you leave old
stains, the new look won't be much better than the old look.
For all of these reasons, seasoned professionals always strip
decks that have old sealer on them. Exceptions are made if the
Deck Tech was the person who applied the previous sealer and he
or she knows exactly what the sealer is on the wood - AND the
sealer manufacturer says it's OK to recoat over an old layer.
How do you know if there is an existing sealer on the wood?
Believe me, it is not always obvious. Cheaper products contain
little or no UV protection, so a deck can look like a grayed-out
neglected deck within a year of being sealed with an inexpensive
product - particularly if it was a clear sealer. There are two
things professional Deck Techs do to find out if there is any
existing sealer that should be stripped off the wood. The first
is to inspect areas that get no sun. A hint of color on the
underside of a board is a sign of previous sealer. The second is
really the acid test for existing sealer and is called the
Splash Test. Sprinkle a little water from your fingertips on to
the dry wood on a vertical surface. If the droplets soak into
the wood right away, you don't need to strip. If they form
little droplets on the surface of the wood, then you have to
strip the wood.