Replies

1. 
   SteveSchoene | Jan 24, 2011 11:01am | #1

   Your expert wants to sell you lumber.  If used for an exterior it will soon pick up moisture to nearly the local air-dried level.  Just as the cumaru or ipe will do, though bringing it down from 18% to reach that level.  I can't imagine why kiln drying the mahogany would hurt it's longevity.

    I do suspect that ipe would be more durable in the long run than the mahogany.  Not so sure about the cumaru.   And, for sure you could sell the mahogany for enough to pay for the ipe and a bit more.  The mahogany would be of great value in furniture applications, but only one of the satisfactory woods for an exterior deck. 

   Choosing a varnish like Waterlox would be a very high maintenance choice, needing annual freshing and every few years stripping and starting over.  Shifting to a marine spar varnish  would extend the interval between needed maintenance.  Besides, a varnishing deck could become a skating rink every time it got wet. 

   If I were doing it I would choose ipe and leave it unfinished to turn a very attractive silver grey.  Needed maintenance would just be an annual scrubbing.  If you must try to preserve the finished color, on ipe I would recommend Messmer's UV.  This will work well in shade, but still require renewal and maintenance in areas that get lots of sun. 

2. 
   Artex | Jan 24, 2011 05:00pm | #2

   Moisture

   David, moisture content within any wood species will change depending on the ambient moisture present on a specific geographical area. Wood will absorb or release moisture as needed to reach a balance between its moisture content and the surrounding moisture, this is known as emc or equilibrium moisture content and yes it will change with seasonal variations. Your 8% kiln dried wood or 18% air dried will adjust its moisture content as needed to reach its emc. This is the reason wood needs to sit for a little while on the place where it will be worked. Anything else sounds like plain ole salesman bull. For the intended use, IMHO if you want to keep it looking nice the best you can do is go ahead with a high quality marine varnish, expect 2 or 3 years at best before recoating.   

3. 
   hammer1 | Jan 24, 2011 05:31pm | #3

   Perhaps well intentioned but misinformed advice. 18% moisture content lumber is going to shrink and posibly warp, not something you want on rails, etc. You have the Honduran in hand, use it and enjoy it. It will shrink and swell like any other wood exposed outdoors but it won't shrink much smaller than it is now. I would not recommend using a film forming finish like spar varnish. A clear deck finish won't split open, chip, crack and discolor and recoating won't require intensive labor to prepare like a varnish. This site has great info and a lot of products specifically designed for mahogany and what you are doing. Check out their tips section and contact for advice on specific products.

   http://www.opwdecks.com/

1. 
   dvk2651 | Jan 24, 2011 08:39pm | #4

   moisture in mahogany

   artex, hammer1 and steve s. -- thank you guys! i really appreciate the feedback, and the forums. it's good to back on track with my original plan. will likely finish with sikkens cytol, so i can have an easier, even if more frequent, refinishing process. -- warm regards, david

1. 
   SteveSchoene | Jan 25, 2011 07:47am | #5

   I'm not so sure that Cetol is an easier refinishing process.  It's pretty durable, but I've seen it (in marine context) where some parts were peeling, and other parts were so tenaciously attached, and darkened, that it was a bear to strip. 

2. 
   acornw | Jan 25, 2011 12:42pm | #6

   No Barrier Coats

   Any barrier finish like Spar varnish, Sikkens Cetol, Epiphanes, or epoxy will have two major drawbacks:

   --It will be slippery as the deck of a boat when wet and be a danger to those who walk it.

   --The finish will crack  and peel and be a nightmare to maintain, even for the 'maintainence obsessives' among us.

   The Sikkens Cetol will fare the best, but will still fail early and dramatically. It is designed to fade away with weathering, and will require frequent recoats, then building up to a slippery, crackable and peelable surface.  I have seen barrier coats on several decks and all have regretted it. The owners were desparate to 'protect their investment' or 'feed the wood' or some similar sentiment.

   There is no miracle finish for exterior woodowork.  All exterior woodwork should be finished with the idea of future finish maintenance and removal. To ignore this reality is to suffer. Once the wood is finished with a barier coat, it is an ongoing struggle, until one gets the chemical strippers and is done with it.

   The finish should be a twice annual coating of Penofin or similar penetrating oil. This is easy to do, looks great and is a flat finish so it will not be slippery and will not peel.  It does not shine or glare, but will darken the wood.  Mahogany will bleach to a natural Maple color in the sun (depending upon exposure - Phoenix vs British Columbia), so be prepared for that. This occurs at the surface and does not go deep, but expect it to happen and know that is what the wood does, and all is fine.

   Mahogany will also look and weather just fine if nothing is applied.  Be sure to use stainless or non- ferrous fasteners (ferrites react with tannins in the wood and cause a black stain).  Please, no nails!  Design the deck so the wood can move with seasonal variations in EMC, and you will be fine.  The better work is fabricated in a shop so real joinery can be used, then back-primed before install.

   Dave S    Acorn Woodworks