6 Mil black or clear plastic?

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Little Digger

Member
Sep 3, 2015
123
Southwest Virginia
I know some cover their piles with clear plastic and others with black plastic, but I'm wondering if there really is a difference between the two as far as trapping heat.

As we all know, black attracts heat so I would think the black plastic would trap more heat than the clear (milky) plastic. I had used black tarps to top cover the wood piles, and had seen temperatures reach above 160 degrees, and I vaguely remember seeing 185 degrees.. On the other hand, I read someplace that black reflects heat, and that the heat doesn't go deep enough into the wood pile.

What I'm thinking is this, use the 6 mil black plastic for the firewood kiln sort of thing instead of the clear unless the consensus is to use the 6 mil clear (milky) plastic. Plus, would the black break down quicker than the clear due to the UVA and UVB rays? Or would it last longer?

I've seen pictures where people had tried the clear shrink wrap where the tops deteriorated and left the piles unprotected for a little while, and the same for the clear plastic. If I remember correctly, I think it was over the course of 6 months.

With all of the rains we've had recently, a total of 21 inches over the last week and a half, I'm debating using the kiln method to keep my wood dry for the coming years, or at least until I build a firewood shed. One specifically for firewood and no other storage. I probably won't have time to build that type of shed for at least a year with my other to-do's so I'm exploring other options.

I know my firewood will dry back out, though a week and a half of constant rains and viewing the water just run off the covered tops and down the open sides really has me thinking of a better solution. I did completely cover my current seasons wood with plastic and will remove it Monday when the weather breaks. Then give it a few days and possibly stage it on the porch after I check the porch for structural integrity. (it's 1 and 2/3rds cord) I already have 1/3rd of a cord in the house.

So which should it be, 6 mil black, or 6 mil clear (milky) plastic? What is your opinion?
 

tigeroak

Feeling the Heat
Nov 4, 2012
355
kansas illinois
I don't use it but if I was it would be black as it will be hotter than milky white as white reflects.
 
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Wood Duck

Minister of Fire
Feb 26, 2009
4,790
Central PA
You really want clear plastic. Black plastic absorbs solar energy and so it gets hot, but the heat is on the surface of the black plastic. Of course some of the heat gets to the inside of the plastic too, but the heat is generated on the outside surface. With clear plastic most of the energy in sunlight goes through the plastic and is absorbed by the wood. The hot wood then radiates heat back, but radiant heat doesn't pass through the clear plastic so it is trapped. This is the greenhouse effect and will help heat up the wood as much as possible. With milky plastic I think you'd get some of the sunlight reflecting off the surface and some passing through. This would give you a greenhouse effect but you'd be working with only a fraction of the total energy in the sunlight because some would reflect away. I don't know how much would reflect, but it could be half of the energy.

Between black and milky I guess I'd go with milky, but clear would be my first choice.
 

peakbagger

Minister of Fire
Jul 11, 2008
5,432
Northern NH
Covering a pile is mostly to keep water from getting on it. Any heat trapped is going to trap moisture unless there is active ventilation. Black plastic is UV resistant and will last longer, clear plastic is not and therefore will fail quicker negating the primary goal which is keeping the water out.
 

Soundchasm

Minister of Fire
Sep 27, 2011
1,297
Dayton, OH
www.soundchasm.com
I read a little scholarly work on burning out gardens, and clear resulted in higher ground temperatures than black. I keep buying the 50' rolls of 36" (approximate dimensions) milky stuff, and I keep using the pieces over and over and over. Cut to length, and staple both sides on a single stack.
 

fire_man

Minister of Fire
Feb 6, 2009
2,369
North Eastern MA
I hate paying for them, but I have only had good luck with quality heavy duty Brown tarps set over sheets of plywood/OSB. I figure it's cheaper than a shed and has been pretty fool proof to guarantee dry wood.
 

maple1

Minister of Fire
Sep 15, 2011
10,522
Nova Scotia
I use a tarp the same width as the pile & nothing else. Spread it out on top & cover it with one more layer of wood. It doesn't move, and the top layer of wood keeps most of the direct sun off which is what destroys tarps & plastic first. Either that or rips from failed tie down attempts.

I don't think in most cases it would matter if you use clear or black plastic or tarp. But if your aim was to get heat into the pile with the help of plastic, you should use clear. That's what greenhouses use.
 

fire_man

Minister of Fire
Feb 6, 2009
2,369
North Eastern MA
I had to add the plywood/osb because critters were chewing giant holes in the tarps from below:(. I was being so careful to cover so I'd have dry wood and the holes just funneled the water into my wood and soaked it. The other benefit is the plywood top stabilizes the stacks so after seasoning/settling for 4+ years they never fall over.
 

Hickorynut

Feeling the Heat
Jan 10, 2012
344
western ky.
Covering a pile is mostly to keep water from getting on it. Any heat trapped is going to trap moisture unless there is active ventilation. Black plastic is UV resistant and will last longer, clear plastic is not and therefore will fail quicker negating the primary goal which is keeping the water out.
Well, I have used black plastic for many, many years. And it has lasted for 5 to 6 years and even more. It definitely has some UV resistance. One fella I know used clear and said his shredded in a couple years, just crumbled. I use 6 mil by the way, not sure how thick his was....
 

Wood Duck

Minister of Fire
Feb 26, 2009
4,790
Central PA
Covering a pile is mostly to keep water from getting on it. Any heat trapped is going to trap moisture unless there is active ventilation. Black plastic is UV resistant and will last longer, clear plastic is not and therefore will fail quicker negating the primary goal which is keeping the water out.
Have you read the threads on solar kilns? The short version is that you don't need active ventilation for a clear cover to have a large impact on drying wood. It seems counterintuitive to me, but it apparently works. I plan to try it one of these days.
 
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