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Question DetailsAsked on 1/27/2017

What is the best material (and how do i protect it) for a high moisture/humidity outdoor porch?

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Good brandname (not cheap import) stainless steel, weathering steel (ASTM 588/606), or outdoor-rated aluminum - factory coated with anti-slip material if exposed to rain or icing conditions to make it non-slip - though these are also generally the highest-priced option. Followed by high-durability stone or sealed concrete. All of those should last at least closer to 100 years than 50, though concrete needs resealing (with a slip-resistant product like from Dow) every few years to keep it from spalling in outdoor environments.


If a situation where icemelt will have to be used (front porch for instance) then except for high-grade (not cheap import) stainless, or a very frsot-resistant granite or such, the above wouldnot be recommended.


Then - for around 40-60 year life likely, a ground-contact natural gas-carried treatment copper pressure treated wood, with the incisions for better penetration. 0.4 or 0.5 #/CF chemical retention is needed for long-life in exposed wet/damp conditions, so if you don't like that look that is out (image here - I realize this is from England, but that is where I found photos showing it clearly -


http://www.timberincising.co.uk/advan...


A non-incised ground-contact rated treated wood might last 20-30 years in an off-the-ground location. I recommend definitely NOT using the brown Wolmanized treatment (I have seen it rot in less than a year), and not the 0.10 - 0.25 #/CF landscape timbers.


Either type of treated timber should be cleaned and retreated with an end-cut treatment copper nathenate or similar copper-based treatment solution every 10-20 years depending on weathering severity and whether incised or not (unincised needs the more frequent treatment because it does not penetrate so well).


Creosoted timber will also last that long but except for underframe supports no one is in contact with, sticky and messy, and also illegal for that use in many states.


After that, probably exotic hardwoods like ipe and ironwood and oily teak and tigerwood and such - can run from 20-25 to 50 or more years depending on wood type and exposure conditions.


Then heart red cedar and heart redwood with similar overall life but commonly has enough defects in the wood that at least a few pieces may last only 10-20 years - and both give nasty splinters that fester up (as does treated wood), so if a deck kids will play on or people will sit on be prepared for a few festering splinter injuries over the years.


Next probably (and I hate to even say it) the plastic imitation woods like Trex - which they claim will last 40-50 years or more, but I have never seen an installation where it did not start splitting or fuzzing up and radically bleaching out or irregularly start turning color within a very few years - so I recommend shying away from that type of product. Ditto to plastic decking panels - generally the ultraviolet in sunlight turns their color in a few years, they warp in exposed hot sunlight, are subject to cracking especially in cold winter climates.


Next - normal deck softwood (a good cedar or western Douglas Fir o similar rot-resistant wodds preferred) double treated with a deep penetrating oil-based stain-sealer and retreated typically every 2-5 years depending on exposure. A penetrating one, not the surficial "coating" types, not the heavy-body "truck body liner" types like Rhino, not heavy paint, and not silicone sealers like Thompsons, because with those all I have ever seen is either 6-12 month recoating being needed to keep the wood sealed and the finish not peeling, or with the heavy-body products mass peeling of the coating and rot underneath because of the way it lets in water through pinholes and cracks, which then rots the wood because it cannot evaporate out the way it came in.


Basically speaking, on organic materials, a high-solids coating or finish is not good because it retains moisture in the wood, preventing it from drying out, so you get rot. The only type of treatments that work well are ones that are poison to molds and rot like copper azeole or copper napthenate/napthelate and similar chemical treatments, or to a less effectiveness low-solids penetrating oil-based stain/sealers. (Note the copper treatments come only in a fairly british green or brown, though it is possible to mix those two or color them for other colors in the darker side of the spectrum).


Number one way to protect it - a good roof or awning overhang to limit wetting to the occasional blowing rain/snow (or better yet add screening with fabric storm rollups), and removing any snow before it can melt and saturate the wood.


And of course have proper ground clearance so it does not get damp or insect attacked from below.


If you browse the web, in blogs and manufacturer websites (realizing each is touting its own products), at home improvement sites like This Old House and Hometime, and maybe with a DIY book like from the Black and Decker series, you can get a good idea of what has worked and not worked so well for different people.


You can also see a lot of previous questions with answers and info on some specific products and types, and problems with solid-type coatings on wood, in the Home > Decks and Porches link in Browse Projects, at lower left.

Answered 1 year ago by LCD




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