yo1dog

Mositure in SYP for workbench

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Questions first, details second:

  1. Is 8-10% and 12-15% MC SYP dry enough to use for a workbench in a non-insulated garage shop in Austin, Texas?
  2. Given that the MC ranges across a board, which figure should I use? Max? Average? What about small wetter spots?
  3. My cheap moisture meter states "Measurement accuracy: ±4% for both hardwood and softwood". Does that mean a reading of 10% could actually be 6% or 14%? Does that make it almost useless for determining if wood is dry enough for woodworking?

I started building a Roubo-inspired workbench during my vacation which has 1 week remaining (back to work on 1/14). I was really hoping to have it done by then. The plan is to build a 4.25"x28"x6' top by gluing up 8/4 Southern Yellow Pine. The base will be made from doubled up 8/4 SYP as well.

I chose SYP because it is pretty darn cheap here in Austin, Texas and is recommended by Christopher Schwartz in his book on building workbenches. I was sourcing from lumberyards when I found my local Big Box store sells construction grade "kiln dried" #2 prime SYP for dirt cheap. I picked through the stacks and found some decently straight and clear 2x10x12' flatsawn boards that I could rip in half.

I wasn't considering moisture content because it was advertised as "kiln dried". When I got home I could feel that one of the boards was noticeably damp to the touch (not sure how I didn't notice at the store). I bought myself this cheap $45 pinless moisture meter to check it out. I moved the meter over the face from one end to the other. That board ranged from 35-40%... Luckily, that board was from a different bunk/stack than the rest. Of the others, about 1/2 read between 8-10% across the board with spots at 11% and the other half 12-15% with spots at 16%.

This is my first large furniture project so I started reading up on acceptable wood moisture content. I learned a lot but was also inundated with often conflicting information lacking context. Some put a dead stop on figures like 9% or 12%. My case may be atypical since I am building a beefy workbench and not fine furniture. As such, I don't mind cosmetic flaws like small cracks that might result from the wood settling as long as they are not detrimental to the integrity. Also, the bench will not be indoors and instead in my non-insulated garage shop and exposed to the changing humidity. This site states "In most of the U.S., when wood is outdoors but protected from the rain, the wood will attain an EMC of 12% when the RH is 65%" "in more humid locations ... wood outdoors can attain 16% EMC." So maybe the wood is actually about were it should be for outdoors in Austin? Idk

It seems quite a few people have built workbenches using construction grade SYP from a Big Box store without reporting any issues. Am I overthinking and over-worrying?

Let me know what you guys think and I appreciate any input.

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Build it with confidence, with the location of the bench in an unregulated non-insulated garage you'll be fine. Those numbers should be acceptable. The only thing I'd check is if the numbers are all similar based on your cheap moisture meter. The cheap moisture meter may not give you accurate readings, but it will give you readings that will show you if the moisture content is similar. 

Ideally I would have left the wood sit in the garage a few weeks before construction, but with what you are building you could get away with out this step. 

Sounds like you have Schwartz's book or have referenced his book, he goes over moisture content and I think he would also say you can build this with confidence.

Finally, industry specifications for moisture content in "kiln dried" softwoods does not match that of hardwoods. The acceptable moisture content of "dry" softwoods is maximum moisture content of 19%.

http://www.alsc.org/greenbook collection/ps20.pdf

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Consider that even very dry lumber will 'acclimate' to its environment, and gain or lose moisture as dictated by that environment. The SYP will make a very stable bench. You may need to re-flatten the top over time, but that is true of any wooden workbench.

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http://www.csgnetwork.com/emctablecalc.html

You can use this to determine what moisture content the wood should be at. If you read the manual for the meter it will probably give you some adjustment for different densities of wood. this will get you closer to it's actual MC. The range of 4% they list can be to a number of factors more in the wood than the meter. The best way is to use the meter as a comparison. Have dry wood in your shop that's been there for a long time of a similar species or density and measure that and compare it to your new wood.

If the SYP is that high in MC depending on your EMC it's going to dry some. The best thing to do is let it dry before building the bench but you don't have to. I built mine wet the major down side is your going to have to flatten the top again. This is all dependent on what your shop EMC is mine in the winter can get as low as 6%. Down where your at that your winter EMC could be 15%

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Thanks for the feedback.

Today it is 66°F and 87% humidity. The calculator puts the EMC at 19%. I looked up the average humidity and temperature in Austin for each month and it looks like the EMC ranges from 11.7-12.7%. Then I found this chart which has done all that work for me and puts the range at 12.1%-13.7%:

Quote

Equilibrium moisture content (EMC) of wood exposed to outdoor conditions in the United States, estimated by mean monthly temperature and relative humidity.


Austin, Texas
Jan,  Feb,  Mar,  Apr,  May,  Jun,  Jul,  Aug,  Sep,  Oct,  Nov,  Dec
13.3, 13.2, 12.8, 13.0, 13.7, 13.3, 12.6, 12.1, 12.6, 12.8, 13.0, 13.0

 


I measured a couple pieces of whitewood/SPF that have been in the shop for a few years and got 6-8% MC. Much lower than I expected given the EMC values above and much lower than my SYP.

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TLDR-a. I air dried my Ash for as long as I could stand. Built my slabs a few months before the wood was ready, i flattened it, think I re flattened about about 8 months, haven't thought about it since. I would do nothing different. 

 

 

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I must admit, your lighting solution is ingenious!

Nice to see your top coming together!

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To toss my 2 cents in on your original question, it's important to know what the relative moisture content is for your shop.

Test some lumber that's been there for a good long time.  This will tell you what that number should be.

Before I moved, my number was around 11%.  I don't have an accurate number for the new shop as I haven't been in it long enough to answer that question for myself.  I get around that by using kiln dried lumber that's had a little time to acclimate in my shop..

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2 hours ago, Chestnut said:

DANG! The pile of sawdust around your PJ882 is awesome! Looks like your having some fun.

Haha that was before I bought this portable dust collector. I thought I could keep coasting without one... this project pushed me over the edge. Once I get my shop setup a little more I'll be setting up a real dust collection system.

 

2 hours ago, ..Kev said:

I must admit, your lighting solution is ingenious!

Nice to see your top coming together!

Sarcasm haha? Actually, I got a few of these LED shop lights for Christmas that I still need to put up.

 

2 hours ago, ..Kev said:

To toss my 2 cents in on your original question, it's important to know what the relative moisture content is for your shop.

Test some lumber that's been there for a good long time.  This will tell you what that number should be.

Before I moved, my number was around 11%.  I don't have an accurate number for the new shop as I haven't been in it long enough to answer that question for myself.  I get around that by using kiln dried lumber that's had a little time to acclimate in my shop..

I tested a couple pieces of whitewood/SPF that have been in the shop for a few years and got 6-8% MC.

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Not that you're going to turn back now but, if my relative MC for my shop was 6 to 8%, I would be a little more concerned using material that was at 14%.

That's why it's important to know these numbers for your shop.

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3 hours ago, yo1dog said:

*shrug* we'll see

From experience worst case you'll have to reflatten the top. Mine is crowned by about 3/8" so if you can error thick on the top it'll leave you with more material to flatten if needed.

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