Greetings,
I built a bench last August and finished it with Wipe-On Poly (my finishing approach is to find whatever I have in the shop that should do the trick and use it - what could go wrong)? Well, now a year later the “stretchers” below the bench surface have turned a dark color. The bench has been outside its entire life and I would have thought any issues would show up on the surface but that is still looking good. Pictures attached - the first after it was built, then more recent shots.
Any idea what I did wrong? I’ve been asked to build one for our daughter and I’d like to get it better right this time.
your bench is a nice piece of work…
is the top solid or open???
sistered wood will hold moisture… open construction allows for water lets…
you did nothing wrong…
your stretcher oxidized and that piece of wood is probably tannin rich which isn’t helping matters…
the process started w/ too much moisture getting into the wood and it never really dried out…
it wasn’t completely sealed which is about impossible w/ outdoor furniture… one day one it’s sealed and a couple of months later it isn’t… UV, rain and temperature swings conspire against you…
it could also be an indication of mold or bacteria present… they thrive in damp conditions…
rot is the next step and it will only get worse…
you could salvage the stretcher w/ a lot of work but I’d just change it out…
for outdoor furniture I like oil base un-pigmented exterior house paint base w/ UV inhibitors… it dries clear…
test it for clarity before you leave the store… latex is your 2nd choice…
TIP…
sand your wood to #80 or #100 grit max…
apply your finish/sealer cut 10% by volume… let it soak in…
apply a 2nd coat full strength when recommended by the mfg. …
now you lightly sand to the smoothness you desire… if you start to remove the base coating you are sanding too aggressively… reapply another coat and carry on…
you are now happy w/ the smoothness, apply a finish coat…
prefinish your pieces before assembly w/ paying special attention to end grain w/ extra coatings of finish…
Sanding…
The objective of sanding wood is to remove mill marks… The most efficient method of doing this is to begin sanding with a coarse enough grit of sandpaper to cut through and remove the problems quickly, then sand out the coarse-grit scratches with finer and finer grits until you reach the smoothness you want…
too fine of sanding closes the pores of the wood and then the sealers/finishes won’t penetrate or soak into the wood…
Note…
hand sand…
power sanders can make thing go south quite easily…
I can’t see the top, but if it has slots so the rain can run through the stretcher is in the shade,and wet it will grow fungus plus accumulate all the dirt in the air,surprising how much there is, and will take on a darker color.
If it is stored under the eves so it doesn’t get direct rain, then it might be alright. Some simple covers can be made out of a plastic material too to cover when not in use.
Herb
When I make something for outside I like to use an oil base stain, it puts some oil back in the wood. After it soaks in good and wipe off the excess ,the grain usually shows through. Then every year or so give it another coat . it will look good for ever.
What ever you do ,don’t use old used motor oil, it will always be “Sticky” LOL
Herb
Thanks for all of the help - attached a better picture of the bench - yes, the top has slots. The seat and legs are made from 1"x3" cedar, the stretchers are 1"x2" cedar. The work is part of Steve Ramsey’s Weekend Woodworker program which my wife got me as a Christmas present almost two years ago. I’ve completed the first three projects - not exactly moving to the head of the class.
I should mention that I also waited until I completed the project to apply the finish - which means I never got into the 3/4" space between the seat pieces very well. I’m thinking this time of applying the finish before assembly.
very good plan…
is the bench exposed to rain??? wood will adsorb moisture from humid air…
size the end grain a 25% solution and give them all they will take…
the wood being cedar - I’m leaning to mold… hard to tell for absolute from a picture…
by the pics I was thinking pine but now I believe it’s eastern white…
cedars inherently a high MC wood…
if that stretcher is red cedar it’s doing what red cedar naturally does,
it changes color over time due to chemical reactions. This process happens very quickly when it is exposed to sunlight. If you are using Cedar for the exterior application then after about 2 weeks. The color will rapidly change from red to gray.
so gray is natural… black is mold…
the down side to cedar is that it requires maintenance due to it being a softwood… Cedar needs regular maintenance if you are using cedar for an external purpose, then it needs maintenance every year…
some questions come to mind…
are all of these pictures taken outdoors???..
are you sure all of your wood is cedar???..
are the last pictures relatively new/latest ???..
could you date the pictures and their location as in inside or outside???..
is your patio well sheltered and walled??? what side of the house is on???..
The wood used was supposed to be Western Red Cedar - I got the unusual dimension (1"x3") from Dunn. The pictures showing the bench on a deck are from August of last year just as the project was finished (and all of the pictures were taken outside). The deck is uncovered, and faces south. The bench is exposed to all the elements, light, rain, etc.
as white as your wood looks I thought it was pine…
w/ Dunn being a better and reliable supplier, I now think your WRC is sap wood… this explains the mold…
to get a leg up on mold ,
make sure your MC is low before you start your finishing… single digit is best…
if you suspect mold is present - wash the wood w/ hydrogen peroxide 1st to kill the mold/fungus…
Tip…
instead of a butt join on the leg return use a rebated rabbet…
very strong and stable…
