Humidity

[Tod Gilding]

does anyone know how long wood should be in an appropriate RH or should I say ,how long does it take for my guitar components to adapt to lower humidity.
I cut and prepare my braces, backs and sides etc in my shed and then move them to an area of around 48% RH for assembly,but how long should the wood be in the lower RH before I start to build the guitar ?
The RH around my area has been lingering around about 67% ,but today it dropped to 48% and I was wondering if I could have started to glue things up today in the shed without moving them. Is 6 hours or so enough ?

[charangohabsburg]

does anyone know how long wood should be in an appropriate RH or should I say ,how long does it take for my guitar components to adapt to lower humidity. [...] Is 6 hours or so enough ?

I would not risk that.
It depends a bit on wood species and thickness. I would allow at least 48 hours for back and sides (feeling saver with 72 hrs). The top by itself (spruce and similar) may be "faster" but the bracing is thicker, so I still would give it 2 full days at least. The bridge (thicker than veneer) needs some more days.

I observe stability of moisture contents by weighing pieces on a precision scale (cheap, $10 range, from eBay, displays in 1/100 gram increments up to 300 grams, accuracy is better than 1/10, more than enough). When RH and the weight of the wood specimen (using such a precision scale) don't move from one day to the next I consider the wood having reached EMC (Equilibrium Moisture Contents).

[vandenboom]

fwiw, I try and leave all the wood for a guitar under construction in the more ideal humidity setting eg. 45-50%. I usually do this at least 2 weeks before wanting to use it - I'm not saying it needs that long, don't really know. Then when I'm ready to cut/sand etc outside in higher humidity, do it promptly, and take it straight back inside. Haven't tried the weighing approach.... Frank

[Trevor Gore]

does anyone know how long wood should be in an appropriate RH or should I say ,how long does it take for my guitar components to adapt to lower humidity.

"The Book" says 5 days for previously "dry" wood at ready-to-glue thicknesses. Who am I to argue?(!) Have a top or back turn inside out just once and you never take short cuts again.

Yes, I know many of you will have got away with less, but it is very dependant on where the wood has been prior, its thickness and species. Better safe.

[charangohabsburg]

Have a top or back turn inside out just once and you never take short cuts again. [...]

Yes, this is certainly the most solid learning method - maybe the only one that really works.

[ozwood]

I don't have a dry room , the shortest time I have left it in the shed to stabalize was 4 day's at 45 - 48 % and that made me a little nervous, and I have a logging function on my hygrometer, so you need to be sure you've had , I think at least , bare minimum 4 day's below 50 % to be safe . I waited 3 months to finish my last guitar just waiting for dry / low humidity weather .

That's my Two bob's worth.

Cheers,

[kiwigeo]

I buy sh*tloads of wood and then make sure I'm in a job where I don't get alot of time in my workshop....that way any piece of wood I pick up has been acclimatising to workshop conditions for at least 6 months......in most cases 6 years.

[Dominic]

I do the same as Marcus, when I get wood I inspect ever set and try to determine run-out and check other visual markings. I mark what they are Sitka, cedar etc, date, how much they cost including postage and most importantly, how much they weigh. Then every now and again I'll re-weigh them so they end up with a bunch of number showing decreasing mass. At some point the tops stop losing mass which indicates they have reached some equilibrium. Now I will also start to measure their elastic constants, density etc and try to better match tops to various sized guitar designs.

Canberra is great for guitar making, usually pretty dry air. I have a couple of electronic meters and they both seem to under estimate RH. I got a decent hygrometer from LMI and it shows RH around 10 ppts higher than my electronic ones. Even so, it sits around 50% most of the time so it does not take much to lower it with a small machine which goes in my spare bedroom where I keep all my wood and guitars I am working on.
I think it is worth recording what we can as most of us make too few guitars to pick up the nuances purely by repetition.
Good luck with everything
Cheers
Dom

[Tod Gilding]

Thankyou all for your replies much appreciated. However since posting this question I have done a fair bit of research on the topic, It seems that it is not as simple as just monitoring the RH, it is the EMC ( moisture content ) that will play havoc with our wood MC is affected by RH and Temperature ,I'm finding that this is a very involved topic that will need a lot more research on my part.
The more that I learn about this the more confusing it gets, for example, we here in Australia, it appears, are building our instruments under the same controlled conditions as builders In the US,but the completed instruments will be expected to live in a very different environment.
I have found that the most populated areas of Australia, The East coast from Melbourne up as far as Noosa, does not vary much and can often have the same Temp and RH,but move inland and the RH drops off dramatically and the Temperature can rise just as dramatically,I am not finding many vastly populated area's in Australia where the RH and temp match those that can be found in major area's in the US, I need to do a lot more research,but it seems that here in Au we should be building under slightly different conditions to those in the US.

[jeffhigh]

Todd I had not realised that temperature effected EMC so I looked it up.
Yes it does but the effect over most normal temperatures is much less significant than the effects induced by RH changes
You are dead right that what counts is the actual moisture content of the wood, but this is difficult to measure in the thin timbers we are using without destructive testing such as taking a sample and drying it completely.
So we tend to settle for reaching emc in a certain Rh at a comfortable room temperature.
I tend to build a bit dryer than the 45% that is often recommended.
I also think it is not just the natural environmental conditions that give trouble in the USA, but also the preponderance of central heating which is often creating a warm superdry environment.

[woodrat]

Hi Jeff, you make some interesting points there re: environmental factors. Just a small anecdote to add to that...I was in the UK in January and was staying with a friend who had a drafty house, it is a Victorian terrace house that hadn't had the windows ripped out in the 80's and replaced with pvc double glazed ones. Anyway I carry a small hygro with my guitars and I noticed that on the days that we had heavy frost the house was robbed of its moisture through the windows because they leaked so much.On the days that were "warmer" ie. no frost the humidity in the house came back to where it had been prior to the frost. In the Northern hemisphere where the winters are severe and they heat like you mentioned low humidity in houses can occur....I concur!

John

[Tod Gilding]

Yeah Jeff, Your Also dead right, but what I'm getting at is, if you build an instrument at Caves Beach In December At 45% RH, on completion it could (would) be going strait to 80% RH or more,If I am understanding this correctly, That is a Dangerous increase, and unlike anything a builder in the Northern hemisphere would have to consider. As I said,I need to learn a lot more,but I think here on the Australian East coast we may be better off building at around 50 - 55 % RH if the instrument is to live in this area.

By the way,that figure of 50-55% is just a guess, I don't know what it should be, but it should be higher surely,when you consider our environment here.

I will do a lot more research. and thanks

[Bob Connor]

It's not so much the instrument that is built at 45% RH going into 80% that will be a problem as the wood will expand and will probably at worst require lowering the action

What you need to worry about is an instrument built at 65%RH (which is about average for the eastern seaboard of Aus) that is taken to an area of 25% RH, like an airconed house or out into the outback. The wood will shrink and the top and back may crack. Any convex tops and backs will sink making the action to low or at worst the top or back will split. The frets may start sticking out the side of the neck as the wood shrinks there and the frets may become loose causing rattles and dead notes.

The reason that between 40 and 50%RH is suggested is that it is in the middle of the ranges that of RH that we could expect and therefore is more likely to survive any extremes if moved to those areas.

If you are sending instruments to geographic areas of low RH you should include some sort of humidifier in the case. In these circumstances the instrument should be kept in the case when not being played.

Hope this helps.

Regards

[woodrat]

If you are sending instruments to geographic areas of low RH you should include some sort of humidifier in the case. In these circumstances the instrument should be kept in the case when not being played.


Regards

Yes Bob, That is the best advice. Last year I took an instrument to the Kimberley in the dry season and the RH was about 15%. I had no problems with it. I have a great little device called an "Edney" paper hygrometer that is a small English made Hygrometer that was used (back in the day when people cared!) to measure the environment where a companies stationary was kept. When calibrated it is very accurate and great for traveling as it is only about 60mm across and 12 mm deep. I have found that cases seem to always have an RH around 45-50%...in other words...yes keep them in their case and they will be a happy guitar.

John

[jeffhigh]

Ever have a hot dry wind come in
Couple of years ago, here on the humid coast, I had one which dropped the RH down to 15%
One guitar had it's back crack, between brace locations
Looking back I realised that while I had braced ot dry, I had not glued it to the rims at a controlled rh
Whilst the idea of building a guitar for a specific region appears to have merit, you have no real control over what it experiences during it's life especially in transit or on stage.
Building at over 50% is a recipie for disaster IMHO.

[Trevor Gore]

As others have said, the reason to have your wood in equilibrium at 40-45% RH is that it delivers the required ~8% EMC over the range of normal temperatures (~0C to 30C). Hence, conversely, if you build with wood that is at 8% EMC (all through) the wood never has to tolerate the dimensional changes associated with more than ~50% swing in humidity from its build condition, which thus minimises the potential to cause damage to an instrument.

Extreme dryness for extended periods will crack wood (as we all know). Extended periods of high humidity seldom causes structural problems, but associated with high heat, some glues will give up. Hence the choice of choosing to build in a humidity slightly lower than the mid point of 50%.

Here in Sydney, outside my workshop, I see humidity ranging from below 20% (the electronic hygrometer says just that!) to above 95% with the temperature ranging from ~5C to 40C, and once out of the workshop, that is what my guitars have to survive. And they do. You need to be brave to build outside the normal 40-45% RH range (8% EMC).

[Tod Gilding]

Thanks for that info,I get it now.

I wasn't considering That drying can be far more detrimental than than a higher RH.

And Trevor, if I am ever able to get my WAS & TAS under control,I may be able to afford your books,and won't have to ask these stupid questions anymore.

Thanks again to all

[rocket]

Martin is the king of stash when it comes to stockpiling tonewood
Rod.

[Mark McLean]

Have a top or back turn inside out just once and you never take short cuts again. [...]

Yes, this is certainly the most solid learning method - maybe the only one that really works.

I am the latest member of the learn-this-the-hard-way-club. I work in a poorly sealed, unlined external shed with no climate control. I am well aware of the RH issue and thought I was clever enough to avoid problems. I have a RH meter in the shed and I watch the BOM observations closely and I wait until we have dry weather before I do any RH-sensitive stuff, like gluing bracing or closing the box. But - how much waiting is long is enough?

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I assembled the back and sides of my latest project. The top was ready for bracing but then we had a long stretch of damp and humid weather in Sydney. Seemed to be for months. I cut and shaped the top bracing and then waited......... It finally got dry. RH down to 48%. Next day I glued it up, then some carving and shaping - all OK. It had a pretty good 30' radius. Then some more rain so I had to wait before I closed the box. 2 weeks later it was dry again (admittedly only for about 24 hours - way too soon in retrospect) and I glued the top.

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We have now had a solid week of warm and dry weather. Take a look at it now. Both the top and the back are concave.

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I guess both plates are stuffed. I will probably remove them from the sides, route/sand the bracing off and start again.
The lesson is that you certainly need a number of days at low RH for wood to settle. The 5 day rule sounds like a good one.

Just found a dehumidified on E-Bay, in the next suburb, for $80. It is going to be a good investment!

[Tod Gilding]

I'm Sorry To see that Mark
I would like to know. exactly how long it takes for our wood to adapt, I hear a lot of stories about backs splitting in a very short period when the humidity drops , it just seems that if you have a braced board the wood adapts and brakes in no time, but if you are waiting to glue something it takes forever

[Bob Connor]

Pity about that Mark but better finding out now than when it's finished.

Just a comment about the bracing.

Is this a OOO model? If it is I would probbaly put another finger brace in as they are quite useful in countering bridge/bridgeplate rotation. Yours like a little light on in that area to me. The rest of it looks great.

If it's a OO or o model please ignore me.

Regards

[Mark McLean]

Thanks Bob. It is a Gibson L-00 size and the plans only have one finger brace. But, as you can see, I copied your lattice bracing so I have departed from the plan already. Maybe another finger brace would be appropriate. It is interesting that with an increase in RH to around 60% today the plates are convex again. It is a fickle thing. Anyway - I am learning stuff, so that is good.
cheers
mm

[Bob Connor]

I think the extra finger brace wouldn't hurt, even on an L00 Mark.

They are very accessible through the sound hole if you think they need reshaping after the instrument is built.

Regards

[Craig]

That's a bloody shame Mark . Beautiful looking work too !

Anyway - I am learning stuff, so that is good.
cheers
mm

A fantastic attitude Mark