Can wood dry too slowly?

[bkhunter]

I was talking to someone about drying wood too fast and all the problems that creates, when I started to wonder: Is it possible to dry wood too slowly, either in a kiln or air-dried? If it takes longer does that have any negative side effects? Is it different for hardwoods or softwoods? Help me out if you know!

[Ga_Boy]

Yes, you can dry to slowly.

You need adiquate air flow to remove the moisture other wise you get mold.

The drying times for wood depend on species, there is a very good publication you can get from the Forestry Products Lab; titled "Drying Hardwood Lumbers" , another one is "Kiln Operators Manual" both offer good ideas on drying lumber.


Mark

[WkndCutter]

Wood is going to dry out as fast as the conditions it is in allow for.  As long as there is good air circulation slow is good but the wood will dry out at a rate depending on the environmental conditions the wood is stored in, how it is stacked/stickered...

Mark has the right idea though about preventing mold.  Both books referenced are good guides also.


Andy

[jimF]

other reasons to increase drying rate :is discoloration from oxydation reactions (although I prefer this), increased final drying stresses, if you are in the business decreased production and increased inventory costs.

[Larry]

Mold, although undesirable isn't much of a defect in hardwoods as it rarely effects the finished product.

Stain is a defect that ruins hardwoods unless ya plan on painting them.  General rule is light woods such as maple, ash, basswood, and hackberry need to be dried fast to avoid stain and keep the white.

I've pretty much figured out every way possible to mess up hardwoods.  Ash with reverse sticker stain caused by to slow of drying.  The stain went all the way through the board.  Shown with a good board in the middle.

[Charles]

then I have a question of similar nature.
I dry for myself and have a small 300bf kiln that I set dry bulb for 105f. Why can't I dry at 85-90f. Is there a temp to low. I was thinking that because this is a small homemade unit, it would be easier on the equipment if the temp was lower. I have dry/wet bulb, heat control and fan control etc. Not having a problem just thinking maybe "off", temp would be 90f and "on" be 85f. The evaporator temp is 22f less than the ambient at 95f so that's not a problem. Can the temp be to low I know it takes longer to dry but that is not an issue. I guess the question is can you dry lumber to 6% at 90f cause I know you have achieve 30% RH. Can you get this at 90f. Or do you have to achieve a certain temp to get the bound water to move. And I am lucky at 105f. Also I usually dry air dried and am very aware of mold.

thanks
charles

ps larry
Am interested in what is too slow drying to get the sticker stain on the ash

[jimF]

Charles, assuming your lumber is exposed to the ambient air vapor pressure, you would need to have a dew point temperature below 50F to get about 4% EMC which is what you would need to dry to 6% MC.  Lower temperatures help reduce oxidative stains but if you dry too slow because of low temperature and not low enough EMC the increased resident time increases oxidative stains.   I know this is all qualitative but I know of no research that has quantified all these variables to various degrees of stain.  Bound water can be removed at low temperatures if the EMC is low.

[Charles]

Thanks Jim
I"m going to stick with 105f I've never had a problem and don't need one. Never thought about the low temp and stains.
Thanks
charles