Red oak is rather porous - but it now seems to be a common replacement wood; the common wood of choice offered in bed wood kits and commonly used on our trucks. I suspect that it is more of a supply issue - meaning readily available... Cut a short piece of red oak and blow through the end grain and you will see that it is porous enough to feel the air come through the other end ...the same action applies with water; put one end in water and in a few minutes you will see the other end discolor from water wicking through the opposite end- the grain or long pores called tyloses enable moisture and water transfer into the wood and do not resist water movement. I’m not saying that red oak is a poor choice, but rather, if there are other choices then consider other wood species and compare.
If white oak is available - consider it over red oak; it is the same wood used in cask and ship construction too. the closed grain white oak has very short tyloses that inhibit water and moisture transfer.
If you have the choice, quarter sawn wood - will minimize expansion and cupping across the width. Quarter sawn boards do tend to be available in narrow widths - but wider widths can be found..if a larger diameter tree is quarter sawn and milled. If wood is flat or plain sawn it will tend to "cup" especially if one face is subjected to more moisture or temperature extremes than the other side or face.
Quarter sawn red or white oak has the added benefit of showing a rather spectacular wood grain effect (rays).
Tight grained soft wood is a good choice such as Douglas fir or old growth southern yellow pine. Red pine? - knot (pun) the best choice - it tends to decay. Finding old growth species such as these is a challenge and best searched from websites that salvage old buildings or web search for logs and a mill that reclaim logs from the bottom of lakes and rivers and lost during transport down those waterways back in the day.
Plantation grown softwoods have wide growth rings because they grow fast in open sunlit lands - rapid annual growth produces wood that is less dimensionally stable; great for production and satisfying shareholders - but not great for use in finish applications. For 2x material...its good enough. For furniture and better truck beds, if you are discerning - not so good. Cedars are strong, light, and some species more dense and less prone to gouging and scratching than others, and some species are more decay resistant than others. Trees harvested in far northern areas may grow slower and have the desirable tighter grain. Flat sawn, relatively wet and fresh plantation grown wood will be less stable, and will tend to twist, cup and warp. Yet, bolted down to the frame and bed cross members…these things can be minimized. Again, if you can, - ask for quarter sawn fir higher grade pine...it will help minimize any of these issues. Hardwood and softwood species each have their pros and cons and each species has regional wood property variations that occur within each sub species.
So... all of this is good information - but in the end - does it really matter? I mean, if its a work truck and subject to use and abuse - ya may not need to pay close attention to these details; or if protected by a steel sheet, tonneau cover or cap - it will be fine. But for a person putting valuable time and money into a truck they are proud to own and show - then this information may be valuable. And, there is a case to be made for the amount of time and cost put into a bed wood floor: ...why go through all of the trouble of building a wood floor bed to have it sit outside and use wood that is susceptible to absorbing water only to have to replace it again ...do it right (where you can) the first time and spend less time later fixing it. As we have seen - with periodic maintenance, protection from the elements, and finishes, wood bed floors can last decades...careful wood selection can only help.
If you want to learn more about wood properties and choose woods for decay resistance - search the web for the USDA Forest Service, Forest Products Laboratory in Madison, Wisconsin. I suspect they can provide a list of wood species and their properties, decay resistance, density, and overall use or recommendations. They may have a Wood Technology section on their site - or give them a call. Or, if you have specific questions - PM me - I can get the same information for you too.
Last edited by tom moore; 03/17/2022 11:54 PM.
