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  1. #1
    Join Date
    Mar 2012
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    australia
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    Default How to remove moisture in shed to stabilise timber slabs?

    My very old tin shed is 9mx6m with a concrete floor. I'm betting there is no moisture barrier under the concrete considering it is a rough job and probably 40 years old. It is full of shelves and equipment so I'm not going to empty it, apply good wall and ceiling insulation then replace everything. Humidity in my house is around 60 to 70% most of the year but humidity in the shed is all over the place. A couple of days ago (winter here in West Australia) it was 93%.

    I mill and dry my own timber and then build furniture from the final product. (DIY, I'm no professional). I like to thickness the dried timber slabs to 2 or 3 mm thicker than final dimensions and leave the pieces in the shed for a week or two so that internal stresses can reveal themselves. Then I cut to final dimensions and start fabricating. This was mostly done in warmer and drier months but now i have the opportunity to DIY over winter as well.

    The problem is the timber will not be suitably acclimatized in a shed with such high humidity. As soon as the finished product is moved to the house it will dry out, shrink and cause problems.
    So the questions is: can anyone recommend an effective method or piece of equipment that will reduce the moisture content of air in a cold/hot shed with no insulation?

    I had considered the option of moving all the timber pieces to the house for acclimatization then moving them back to the shed for fabrication but that is not viable. (It would be if I were a bachelor !).

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  3. #2
    Join Date
    Feb 2006
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    Perth
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    Default

    The first thing you can do is improve your ventilation to the point where the humidity inside the shed is about the same as outside.
    This then becomes the same as air drying (ie outside drying) but of course being covered and away from direct sunlight this will reduce cracking etc.

    It doesn't matter that the humidity or temp goes up and own , what you don't want is for these to stay too high for extended periods or you will get mould/cracks etc

    Whiile you are at it you can improved your fine dust control as well.

    If you have a DC outside your shed running that to ventilate your she will be expensive.
    If your DC is inside your shed, adding ventilation will reduce teh fine dust build inside your she.

    Nominal you want be tween 10 and 20 room air changes per hour for fine dust control.
    As your she is 9 x 5 by say 2.7 that's 121.5 m^3
    10 to 20 room air changes per hour is thus between 1215 and 2423 m^3/hour.

    For humidity control about 5-6 room changes per hour should be enough
    Now you dont want this for drying timber so install 3-4 small fans (or one big one and 1 small on) and when you are not making dust just run (the smaller) one of them.

    If the timber is stacked too close together eg up against a wall this can still lead to problems.
    Thany timer stacks should have a decent gap (150mm) from walls and of course with at least 20 (preferably 25) mm gps between slabs. The spacers should be no less than 500mm apart and all directly above each other include a set of spacers at the very ends. If you can organise some weights like concrete slabs on top of the pile.

    Circulation inside the shed is recommend for even humidity and temperature (ie one she of a she can get hotter in the morning and arvo) a couple of fans that continually circulate air is a good idea. In wood kilns circulation is critical for even humidity and temperature control an reduces cracking

  4. #3
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    Mar 2012
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    australia
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    Default

    My apologies Bob since it seems I was not very clear. The timber slabs I'm referring to have already been air dried/cured in a separate open walled shed (while being stacked correctly, etc as you explain). My dust collector is outside the enclosed tin shed/workshop.

    Now I'm using those dried slabs to build furniture in my enclosed tin shed/workshop. After trimming and thicknessing these slabs to rough dimensions I keep them in the workshop for a week or two to stabilise. Then I cut and thickness to final dimensions, build the furniture piece and on completion it gets installed in the house.

    The workshop is nowhere near air proof - two sliding doors cover the front 6m and there is no airtight seal between the wall sheets and the roof sheets. There is also a personal door at the far end of the workshop opposite the sliding doors and this door has gaps all around it. A 150mm open "chimney" ventilates the roof ridge. I'm guessing there is plenty of air flow but perhaps not enough.

    I'm wondering if a dehumidifier inside the workshop operating 8 hours each day may be a solution and I'm hoping someone may have already tried this and can report on their success or otherwise.

  5. #4
    Join Date
    Nov 2021
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    Sunshine Coast, QLD
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    You need to measure the conditions in your house where the furniture will live, if you have space store it where it will live and not in your shed (for a few weeks), by leaving it in your shed you are just climatizing the timber to that space and not where it will end up, so unless you can create your house conditions in your shed you will be gaining nothing.

  6. #5
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    you can move the wife out for a few weeks
    I would love to grow my own food, but I can not find bacon seeds

  7. #6
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    Aug 2007
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    Saskatoon, SK, Canada.
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    Just a thought. Instead of a dehumidifier to try to dry the entire shop would you have room to make a box (kiln) large enough for your project wood and use a small dehumidifier in it? It wouldn't need to be big enough to hold an entire glued up project unless you take a long time to complete assembled pieces. Maybe the size of a work bench with front doors that you can still work on top of. You can return the boards into it at the end of each session. It would be a lot easier to control the temperature and humidity in a small kiln keeping it the same levels as the house.

    Pete

  8. #7
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    Feb 2006
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    Perth
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    Thanks for the clarification about the dryness of the timber..

    Unfortunately it sounds like trying to hold back the ocean.

    A dehumidifier to reduce humidity for the whole shed would make sense if you had a fully sealed shed (including the slab) but it sounds like your floor is just going to keep pumping water into the shed and in that case you will need a big humidifier just to handle that.

    Additionally when it's windy, especially while raining, the wind will pump humidity into the shed through the gaps which may just overwhelm a small humidifier.
    You might even get sufficient or even faster "dehumidification" after these increases in humidity when ambient humidity drops, by just forced venting the shed.
    But relying on Gaps in a shed to ventilate can only "assist" ventilation if there is some air movement outside the shed.

    If you use a dehumidifier you will still need internal air circulation. If you put the dehumidifier alongside the timber stack you could end up with drier air on one side of the stack resulting in problems.
    Running a humidifier running for 8 hours is unlikely to work. This means for the other 16 the floor and gaps will rehumidify the air and along with a constant supply of humidity from the floor an gaps the dehumidifier will take many hours to recover teh she air humidity.

    A sealed box to store timber would make sense for long term storage but as soon as you pull the timber out of the box and work it your high humidity environment will affect it while you are working. As Pete says if you can put the pieces back in the box when you are not working them that would certainly help. Could you possibly divide up your shed with a couple of walls a make a smaller working area? Seal the floor and gaps in that area and dehumidify that?

    Have you got a humidity meter? Where in WA are you - I could loan you one of mine if that helps.

  9. #8
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    Mar 2012
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    Thanks for the offer Bob but I already have a meter. It's an analogue meter but suitable enough to see the difference between the shed and the house. These last few days see a humidity of around 73% for the house and in the shed about 95% humidity (early morning) down to 80% (afternoon). It's all pretty variable of course given it's winter.
    Maybe the best option is for me to forget about woodwork during winter and have a holiday instead!

  10. #9
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    This is not an uncommon problem. Earth floored sheds are often used for timber drying and storage. If these sheds do not have consistant flow through ventilation, be it natural or artificial, the humidity levels become such that proper drying is almost impossible. A simple solution is to lay a moisture barrier directly on the ground, directly below the stacked timber and extending beyond the stack in all directions by about a metre. Stack base should be 400mm above ground level. Consistant through ventilation is critical, be it natural or fan forced and if fan forced, reversible by having fans at both ends.

  11. #10
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    Perth
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    Quote Originally Posted by harry wall View Post
    Thanks for the offer Bob but I already have a meter. It's an analogue meter but suitable enough to see the difference between the shed and the house. These last few days see a humidity of around 73% for the house and in the shed about 95% humidity (early morning) down to 80% (afternoon). It's all pretty variable of course given it's winter.
    Maybe the best option is for me to forget about woodwork during winter and have a holiday instead!
    How does the she humidity compare to what's outside your shed?

    If it's on average less then ventilation will help

    Take yesterday in Perth.
    From 1:30 am to 7:30 the BOM reports it was 99%
    BUT
    From 9:30 to 6pm it was 75 or less and got down to 48 at 2:30pm

    If you had a sealed box to store the timber in, you could have removed the timber and worked on it between 9:30am and 6pm.
    BUT
    You would have needed ventilation fans and started then up at say 9am and let them run for about an hour to reduce the air humidity inside the shed.
    Then monitor the humidity through the day and if it went up too high put the timber away in the box.
    That doesnt help when you are assembling but its better than nothing.

  12. #11
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    Feb 2006
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    Perth
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    Quote Originally Posted by rustynail View Post
    This is not an uncommon problem. Earth floored sheds are often used for timber drying and storage. If these sheds do not have consistant flow through ventilation, be it natural or artificial, the humidity levels become such that proper drying is almost impossible. A simple solution is to lay a moisture barrier directly on the ground, directly below the stacked timber and extending beyond the stack in all directions by about a metre. Stack base should be 400mm above ground level. Consistant through ventilation is critical, be it natural or fan forced and if fan forced, reversible by having fans at both ends.

    I agree it's largely about ventilation.

    I looked at the BOM humidity data for Perth for June.

    While it has not been consistent throughout the day, the average humidity at 9am has been 80, while the average humidity at 3pm has been 58. The average of these two is about 70 which is what the OP wants.

    This of course is not the average humidity during the whole day because there are often long periods at night eg between 8pm and 8 am, where the humidity stays high (>90%) and remember the wood will take on the humidity of the overall atmospheric average which will be well above 70. However, If he can seal the wood away during those high humidity times he can easily work in the lower humidity envelope during the day.

    A storage a box with a low wattage incandescent lamp would probably work. During assembly, a covering with the same low wattage globe under it could also work. Some experiments need.

    A simple arduino controller coudl be used to monitor humidity and switch the lamp s desire.

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