Sunday, December 16, 2012

Cold Frame/Greenhouse - Protecting the Wood

It may not seem like progress, because the incipient mini-greenhouse (I still don’t have a good name for this thing) is now dis-assembled and the components are on sawhorses.  But it is.  The first post described the rudimentary assembly of the greenhouse frame.  The next day I saw that some changes were needed.   From the last post, this is the rough frame.

First the depth of the structure was reduced to 27 inches from 30 inches.  It was actually easy enough to do that.  First the diagonals were removed, then each end was reduced in turn, keeping the basic frame intact while I cut down the cedar 1 x 8 bandboard and the crosspieces of the bottom support frame.  Once that was changed  I held up the diagonals in their new position.  The smaller size looks and feels more “right”, whatever that is. 
Then I took apart the entire unit, leaving only the temporary bottom frame, which I will use again when it is put back together.  This is where using screws as fasteners really shines – all I had to do was back them out with a cordless drill.

I put all the wood on sawhorses for staining (why do they call it staining, it actually makes the wood look better?).  This included the carsiding for the back and bottom, so it was a lot of wood.  I set two 10 foot metal fence posts on sawhorses to hold all that lumber, and stained the wood on another set of sawhorses. 
Which brings me to the topic of protecting outdoor structures.  Most of my years working as a carpenter I put on the outside woodwork on high end homes – the siding, overhangs, dormer details, etc.  So I formulated a few simple rules for protecting wood exposed to the weather.   Here they are:

1.      Stain the wood BEFORE assembly.  That means putting it on sawhorses and staining the wood.  When the wood shrinks on exposure to weather it will not reveal an unstained area if all the wood has been stained.  If the pieces have already been cut to size then stain the end grains also. 

2.      Use a staining brush and roller pan, not a paint brush.  You won’t believe how much faster the job goes with this tool, and the stiff short bristles really work the stain into the wood fibers. 
3.      Stain both sides of any dimensional lumber.  That’s right, both sides.  A stained surface will absorb and release moisture at a different rate than an unstained surface.  Staining both sides makes the wood more stable and reduces the likelihood of cupping and splitting. 

4.      Once together the structure can get a second coat of stain.  This will go on much faster than the first coat. 

This is where the mini-greenhouse stands right now - on sawhorses.  I wanted to get some work done on it today but my lower back said no way.  Just as well, chair bound there was time to come up with a design solution for the sides.  Next post it gets put together and I’ll go into some detail on the design concept.  

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