Questions about acclimating air dried slab

[wbarnes]

I just got a walnut slab yesterday locally that has been air dried for about 8 years (or so they say). The slab is approximately 6/4 thick, 10’ long, averages 13” wide, and the moisture content is around 12% according to my meter checked in several places. My garage/shop isn’t insulated or conditioned, so I doubt the moisture content will change much but I still plan on letting it sit in the shop for a week or so before using it.

Would cutting the slab into two 5’ pieces be ok to do at this point? Would it help it acclimate faster, or introduce possible problems? I will be using the slab to make a desk. My thinking was that by cutting it into two pieces I would be able to bring it into the house to sit and acclimate where the desk will eventually be. Good idea or no?

This is my first time working with a slab and with anything air dried, so any comments, recommendations, general knowledge is much appreciated.

 

[Warped Woodwerks]

Seems like the moisture content, 12%, is a little high, imo.

(anyone) Isn't it "best" to be in the range of 7% - 9%?

 

[JNCarr]

Agreed, a little high. The attached is a handy reference.

 

[wbarnes]

Seems like the moisture content, 12%, is a little high, imo.

(anyone) Isn't it "best" to be in the range of 7% - 9%?

I actually just went to the garage and checked again now that I’ve cleaned the slab off. Seems some dirt/debris that was on top of the slab threw my reading off more than I thought it would and the moisture content is +20%. Rookie mistake. Looks like it’ll be sitting in the garage for a while and I’ll need to find another option for the desk I need to build for my wife.

How long should it take a slab to dry from 20% down to usable levels? Seems there may be an online calculator somewhere?Also remeasured and it is closer to 8/4.

 

[wbarnes]

Agreed, a little high. The attached is a handy reference.

Thanks for the reference. Living on the coast, the temp. is 80*F today and humidity is 75%, giving me a stable moisture content of 14.2%.

 

[JNCarr]

One of the pitfalls of using that chart is relying on the number at a single point in time. While the temperature has minimal effect, the LONG TERM RH% has a large impact. So if it's been relatively dry for the last two weeks and today it's 75% humidity, the moisture content will be off, since the wood has not had time to reach equilibrium. I would watch it for at least the next 2-3 weeks to see if it trends with the chart or you start seeing it drift.

 

[Willemjm]

I just got a walnut slab yesterday locally that has been air dried for about 8 years (or so they say). The slab is approximately 6/4 thick, 10’ long, averages 13” wide, and the moisture content is around 12% according to my meter checked in several places. My garage/shop isn’t insulated or conditioned, so I doubt the moisture content will change much but I still plan on letting it sit in the shop for a week or so before using it.

Would cutting the slab into two 5’ pieces be ok to do at this point? Would it help it acclimate faster, or introduce possible problems? I will be using the slab to make a desk. My thinking was that by cutting it into two pieces I would be able to bring it into the house to sit and acclimate where the desk will eventually be. Good idea or no?

This is my first time working with a slab and with anything air dried, so any comments, recommendations, general knowledge is much appreciated.

If you are near me in central North Carolina, 12% is pretty close to moisture content for lumber this time of the year if it is not stored in an air conditioned environment.

So if your shop is not conditioned, there will be no difference if you store it inside for a while.

Before I had a conditioned shop, I built with lumber between 11 - 12% moisture content all the time and I never had an issue. You have to just honor wood movement and build your projects to allow for that. Even if stored in an AC environment, your construction should still allow for wood movement.

In Central NC, once placed in a home, the 12% will go down to around 8 - 9% in summer and 6 - 8% in winter. As a rule of thumb, that will give you movement of around 1/8" over 20" across the grain between seasons.

OK, Just noticed your 20% number. That is too high to build with, unless it is a barn.

 

[Matt Furjanic]

Do you have an attic in your house? If so, put it in there for a couple months, and this time of year, it will probably dry to <8%. I store a lot of lumber in my attic, and it is always thorougly dry.

 

[wbarnes]

Do you have an attic in your house? If so, put it in there for a couple months, and this time of year, it will probably dry to <8%. I store a lot of lumber in my attic, and it is always thorougly dry.

I do have a very open attic that I could store it in. I may have to cut it to smaller lengths to get it in. Is there anything particular I should do help prevent warping, cupping, etc.? It doesn’t appear that the ends were sealed. Should I seal with latex paint first to prevent rapid drying?

Thanks to everyone so far for the helpful replies.

 

[John Jimenez]

I like your idea about cutting it in half…may help to prevent some warping as it dries if you take it inside where the humidity is controlled. I dry my slabs in an unfinished basement with a dehumidifier running and the slabs weighted down. A couple of considerations about bringing it into your house or even your garage is that air drying doesn’t necessarily kill bugs inside the wood like kiln drying does. You may want to treat it with boracare water mixture before bringing it somewhere you don’t want bugs. Just my cent and a half.

 

[walnutjerry]

I actually just went to the garage and checked again now that I’ve cleaned the slab off. Seems some dirt/debris that was on top of the slab threw my reading off more than I thought it would and the moisture content is +20%. Rookie mistake. Looks like it’ll be sitting in the garage for a while and I’ll need to find another option for the desk I need to build for my wife.

How long should it take a slab to dry from 20% down to usable levels? Seems there may be an online calculator somewhere?Also remeasured and it is closer to 8/4.

When I worked with the millwork company we had a dry kiln. The lumber needed to air dry to 10-12% before considering putting it in the kiln. That usually will take 6 months for each inch of thickness I have been told. We also looked for 8% MC coming out of the kiln. Even after all that it is recommended by some to place it in the room where the piece is to be used for 6 weeks before processing and building. All that said-----------I have built a dry sink using air dried spruce pine sawed off the family farm which never saw a kiln or acclimation period in any particular room building before building. It had drawers and raised panel doors. There has been no issues with warping, drawers sticking, or glue joints separating. That was probably 40 plus years ago. Go figure!!

 

[CJ Bach]

Percentage will be different in different environments
The supposedly big devil in the detail is if it is acclimated to the environment it is in.
Arizona will be lower than humid mid nc.
Work it if it is workable just use the moisture meter to get a decent idea if one is close to the guildlines when gluing and error on the dry side if using polyurethane or epoxy as one must not lock in any extra moisture as it will eventually cloud or create cracks and oo…

 

[gmakra]

How accurite is your moisture meter?
Does it have pins or is it pin less?
The point is you can have 3 meters side by side and they will all read different.

If it been air dried for 8 years your probably good to go.

 

[wbarnes]

How accurite is your moisture meter?
Does it have pins or is it pin less?
The point is you can have 3 meters side by side and they will all read different.

If it been air dried for 8 years your probably good to go.

I have a pinless Klein meter. Not sure how reliable it is and nothing to compare it against. Readings are all over the place though from >35% (max of the meter on hardwood setting) to around 12%. Checking some kiln dried ash and white oak I’ve had on the rack for about a year it shows 4-6% consistently, which seems too good to be true. So my thought is the meter may be off by a few percent, so not that accurate maybe but at least precise.

 

[bob vaughan]

An old Delmhorst pin type meter I used to have had a correction table in the instructions for the specific meter in question. This chart exemplifies the possible variations in readings according to the temperature and species.

 

[wbarnes]

I ordered a 4 pack of cheap hygrometers/thermometers on Amazon to check the humidity in the attic, garage, crawl space, and inside the house to determine the best place to dry the slab. I’m assuming inside will be best, but I figured it wouldn’t hurt to check everywhere.

My plan at this point is to first make a diluted borate solution using boric acid and borax and spray both sides of the slab. From my research and finding a couple older forum threads, it seems that this should take care of any bugs that may be in the slab. Then, I’ll cut the slab into two 5’ sections and add a thick coat of latex paint on all ends. The slab will go in whatever location has the lowest sustained humidity and I’ll check it several times a week. I plan on setting a small fan on low to keep air moving around the slab if it isn’t inside the house. I’ll also add some weight on top to help prevent warping.