Mold in Southern Yellow Pine

[AliciaS]

I’m not sure if this question is appropriate but I see mold and stain as very closely related. 

So here’s my mold question:
What levels do you set your inline moisture meter at for a southern yellow pine to avoid mold in the summer season?

[admin]

This is a great point. We will expand this forum to include mold and stain issues.

[TimothyD]

Hi Neissa,
You don't really "set your inline moisture meter" to any particular value.  You can assign markers to fire sprayers or tipple gates to maker or drop out wet lumber, etc...  But, you can't set your moisture meter to achieve any particular drying average. I think what you meant to ask was "what is the target mean MC one strives for to prevent mold in SYP in the summer season?"  If so, I think that is, as they say, "the million dollar question"

Drying is of course a trade of over-drying and under-drying as there are costs, both real and opportunistic in both directions and mold growth cost is of course weighed in the upper direction of under-drying (or having too high an average MC).  I can tell you that if you target an average MC of 10% then there will be no mold growth (or perhaps a little on some few boards in the upper tail of the distribution), however, the overdrying costs of degrade, etc... will far outweigh that achievement of no mold.  So, there is a balancing act from a business analytics approach.

Wagner spent years of research and development with multiple mills and with Mike Milota to produce analysis tools we call "Sweet Spot Technology"  We were recently awarded a patent for these tools as they use inputs from the mills on business data and our inline moisture measurement systems data to actually determine the optimum drying target for every particular product and kiln.  Kilns usually have slightly different variance to their drying distribution and this can affect the optimum mc target from kiln to kiln.  Our tools will also track and adjust optimum drying targets with seasonal and lumber diet changes as well as alert kiln operators to system performance degradation resulting from potential mechanical issues in a kiln or from other issues.

Probably a lot more than you were seeking, but I wanted to make clear the importance of taking in all variables aside from just potential mold growth in determining a target MC.

[PhilM]

Hi Neissa,

I agree with what Tim Duncan had to say but will add my thoughts below.

Molds are fungi, but they are not decay fungi.  Molds can be an early warning sign of moisture problems in the wood.  Mold fungi attack the readily utilizable material such as starches and sugars and mostly affect the appearance and permeability of the wood.  Most molds occur at or near the surface of the wood and are usually shallow enough to come off with planing.

Most sources indicate that a wood moisture content of at least 20% is required for mold fungus to grow on wood.  Some have reported, however, that molds can occur even as low as 18% MC.

In my opinion, lumber manufacturers use their inline moisture meters to insure that their kiln dried dimension lumber meets the grade specifications for moisture content.  (That is, the meter, as Tim points out, can set an upper limit to operate a tipple or spray wet lumber.)  For lumber represented as KD 19 that means the moisture content should not exceed 19%.   Pine lumber dried to meet the KD 19 specification and is at or below 19% MC should not readily mold.

If the pine lumber was high temperature dried to meet the KD 19 requirement it’s surface should be well below the moisture content at which mold will develop.  Of course lumber can pick up moisture, even after it has been kiln dried, if placed in a humid environment, and it is possible for the wood moisture content to gain enough moisture to reach 19% if exposed to air which has a relative humidity of about 85% or above (or if it is placed in the rain).  Hence mold can occur in kiln dried lumber if it is stored in excessively humid conditions long enough.

 I invite southern yellow pine producers to contact me to discuss their mold issues.

[MichaelM]

You have to be a lot more careful in the summer.  I can't give you an absolute value, but if you might set the drop out at 23% in the winter (leaving in some pieces over 19%) you might need to set it at 21% in the summer (leaving fewer wets so the number of potential sites for mold is reduced).  When you do this you are really pushing the edge for the occurance of mold and for passing SPIB inspections and any reinspections.

If you do not drop out, then you have to adjust your drying times if you want to have a similar effect.

Keep in mind that any piece over 18 or 19% is a potential site for mold and by the time the pieces get to 25 or 30% mold on that piece and the ones surrounding it in the package is likely.

Mike M.

[MichaelM]

There is another forum thread with good info, you might look at that.  Mold comes in lots of different colors, depending on what's in your region so the orange color is probably not the issue.  If it is on lumber planed at 15%, then at some point that board was above 15% after planning (for example condensation within a package) or perhaps the board was adjacent to a wet board in the unit and the surface was wet enough for mold to grow.