Relative Humidity differences : woodshop VS. fitting room troubles

[Alex]

Hi Everyone,

This summer, I started a new framing studio, which came with a lot of changes. One of the biggest changes was moving into a new industrial unit that includes a large woodshop and a separate, dedicated clean room for fitting and finishing. I’m really happy with the setup, but now that winter has arrived, I’ve run into a problem.

The woodshop is too large to heat effectively. While it doesn’t get freezing cold, the issue I’m facing is with the heated fitting room. I’ve noticed that the faces of my frame corners are cracking, and only recently did it occur to me that the difference in temperature and humidity between the two spaces could be causing this (along with other factors which you can read here and which I’ll update on soon).

Here’s the situation: all my mouldings are raw wood and stored in the unheated woodshop. The wood is cut, assembled, and sanded there before being moved to the heated fitting room for finishing and fitting. I’ve been monitoring the humidity levels in both spaces. In the woodshop, the humidity ranges between 50% and 60% on particularly wet and cold days. In the fitting room, the humidity fluctuates between 40% and 60%, depending on the weather and how long the heater is running.

The heater in the fitting room is an industrial blower, and I don’t feel comfortable leaving it on overnight. As a result, the temperature and humidity in the fitting room often drop back to the same levels as the unheated woodshop overnight.

When the heater is running, there’s typically a humidity difference of about 10% between the woodshop and the fitting room. The same applies to any frame left in the fitting room overnight.

Could this humidity difference be causing the cracking issues? If so, what should I do to address it? It seems like the fitting room might be too dry, while the woodshop might be too humid.

Any advice would be greatly appreciated!

 

[Prospero]

I have exactly the same problem. I store a lot of raw wood mouldings in an unheated shed and
saw it up there. Then I bring it into my warm indoor workshop to join it. This time of year I like to
leave the cut rails indoors to normalise for a day or two before joining. It's all due to wood shrinking
laterally and it will do this more than you think. The wider the moulding the more cracks toward the
inside of the frame. In fact the production stop I made for my saw setup is a piece of softwood about
90mm wide which runs in a channel. This time of year it's tight in the channel but in Summer there is
a quite large gap.

I once cut two fresh rails and joined them straight away to two rails that had been indoors for a while.
The corners didn't crack but the frame twisted about 100mm out of true. Very embarrassing.
Sticking to letting the rails dry out a bit I haven't had that problem since.

 

[Larry Peterson]

I store a lot of raw wood mouldings in an unheated shed and
saw it up there. Then I bring it into my warm indoor workshop to join it. This time of year I like to
leave the cut rails indoors to normalise for a day or two before joining.

Bingo.......That's what floor installers do.

 

[Rick Hennen]

When we create decorative woodworking pieces for the hospitality industry that involve tight fitting joints or inlays we always allow the raw wood to acclimate to the indoor temperature and humidity for a few days before working it into the required sizes and shapes. After a few days we use a meter to check the moisture in the wood to see if the different pieces are similar. Once those are fabricated we then try to keep them at that same temperature and humidity until they are delivered. At which point we forewarn the end user of the possibility of changes in the joinery or seams if they are not maintained at a similar temperature and humidity. It's just the nature of wood.

 

[David Waldmann]

There are two entirely separate but related issues to deal with.

While you correctly identified the production issue, what happens when it leaves your shop? That is very much outside your control and I can guarantee that many customers have RH levels vastly different than your own.

While I agree that we want to present the customer with a "perfect" product, the fact is that most of the time the frame is going to move/change/crack over time in its resting place, unless that environment is tightly controlled to match your production environment.

Side note: temperature alone makes almost no difference to (solid) wood movement. What causes a problem is when the same air changes temperature, as this affects relative humidity, which is what causes movement in wood.

 

[Jim Miller]

In my experience, the best way to avoid problems with temperature and/or humidity changes is to slow the rate of change. In your case, I suggest tightly wrapping the hygroscopic (porous) materials in insulating packaging, such as corrugated boxboard, Styrofoam, heavy blankets, etc. before moving and then let them rest in the new environment, allowing the materials to acclimate as slowly as possible, perhaps overnight.

 

[Bruce Papier]

This doesn't involve moulding, but it shows how tricky a "perfect environment" can be. We framed a large number of pieces for our local art museum over the years. They had a couple of people on staff who did framing, but sent the big, complicated stuff to us. We had framed a very large print with a fairly wide 8-ply white 100% rag mat in their standard (thin) metal frame. They had it on display for a while then put it in storage. Some time later, they had another exhibit where the print fit the theme. One of the curators sent me an e-mail titled something like "we have a problem". It looked like there had been some type of explosion inside the frame. The mats had expanded and were curving out from the print all around the opening. My reaction was like one of those you see in cartoons where the character's hat flies off his head and spins around. I told her to bring the print over and we would re-do the whole piece. She said she would send it over the next time see had their truck available.

We never saw it again. The mats had shrunk back to their original size within a couple days. All that happened in a very controlled environment.

 

[Alex]

Hi everyone,

Thanks for all the input. I guess that this confirms I was right about the RH

I have exactly the same problem. I store a lot of raw wood mouldings in an unheated shed and
saw it up there. Then I bring it into my warm indoor workshop to join it. This time of year I like to
leave the cut rails indoors to normalise for a day or two before joining.

I've been thinking this same thing but I have two problems with this. One, does it not kinda defeat the purpose when the rail are cut but they still shrink? It would seem to me that this might lead to anomalies in sizes of the different rails which would make them harder, or even impossible to join properly. Or do they all shrink the same (If they where cut from the same stick of moulding of course)?
The second problem is time. This would add another 24-48h of production time, I also let the glue cure 24h, let the stain cure 24h and so on. So I would rather not add to that. That being said, It would be just a matter of planning as it is just 'acclimatisation time' and I if I had to choose between time and non cracked corners, it would be the lather
I am thinking about bringing a small selection of moulding into the fitting room though to acclimatize

There are two entirely separate but related issues to deal with.

I'm assuming you mean the Hoffmann issue? That is indeed still a bit of a head scratcher but hey, one problem down, one to go (and making progress there)

There are two entirely separate but related issues to deal with.

While you correctly identified the production issue, what happens when it leaves your shop? That is very much outside your control and I can guarantee that many customers have RH levels vastly different than your own.

While I agree that we want to present the customer with a "perfect" product, the fact is that most of the time the frame is going to move/change/crack over time in its resting place, unless that environment is tightly controlled to match your production environment.

Side note: temperature alone makes almost no difference to (solid) wood movement. What causes a problem is when the same air changes temperature, as this affects relative humidity, which is what causes movement in wood.

I completely understand and have reflected on this many times. However, I still believe that frames leaving the workshop immediately after being finished should at least be free of cracked corners, even if this might occur soon after due to the client’s (poor) relative humidity conditions. At the very least, while they’re under my care, I feel it’s my responsibility to ensure they don’t crack.
Very good to know about the cold by the way. I've been wondering about the effect of temperature itself as that will be even harder to control then humidity due to the size of the space.

In my experience, the best way to avoid problems with temperature and/or humidity changes is to slow the rate of change. In your case, I suggest tightly wrapping the hygroscopic (porous) materials in insulating packaging, such as corrugated boxboard, Styrofoam, heavy blankets, etc. before moving and then let them rest in the new environment, allowing the materials to acclimate as slowly as possible, perhaps overnight.

I’ve been thinking the same thing. Our showroom is, quite literally, an unheated glass greenhouse (not the best idea, I know), which also serves as our customer entrance. It experiences extreme conditions—freezing cold, intense heat, high humidity, and severe dryness—yet the frames displayed there have taken years to show even the slightest cracking.

Interestingly, despite the far greater long-term RH variation in the showroom compared to the difference between the woodshop and fitting room, the gradual nature of the change in the showroom seems to minimize the impact. On the other hand, moving assembled frames from the woodshop to the fitting room creates an RH and temperature shock, which seems to do more 'damage'

This doesn't involve moulding, but it shows how tricky a "perfect environment" can be. We framed a large number of pieces for our local art museum over the years. They had a couple of people on staff who did framing, but sent the big, complicated stuff to us. We had framed a very large print with a fairly wide 8-ply white 100% rag mat in their standard (thin) metal frame. They had it on display for a while then put it in storage. Some time later, they had another exhibit where the print fit the theme. One of the curators sent me an e-mail titled something like "we have a problem". It looked like there had been some type of explosion inside the frame. The mats had expanded and were curving out from the print all around the opening. My reaction was like one of those you see in cartoons where the character's hat flies off his head and spins around. I told her to bring the print over and we would re-do the whole piece. She said she would send it over the next time see had their truck available.

We never saw it again. The mats had shrunk back to their original size within a couple days. All that happened in a very controlled environment.

Oh, I’ve got a similar horror story. We framed a large artwork for an artist (60" x 45") who had sold it to a major collector. Naturally, the artist was incredibly anxious about the framing being perfect. We completed the frame, but a week later, we received a panicked message from the artist, complete with detail photos of the frame. The inside of the glass (yes, actual glass, not acrylic) was completely fogged up with condensation—so much so that it was dripping. You couldn’t even see the artwork through the mist.

Cue total panic. We had no idea what could be causing it. Assuming the collector’s house might be the culprit—perhaps an older property with damp walls—we asked for details. But no, the artwork was in a modern, state-of-the-art, climate-controlled apartment complex that also housed other framed art, none of which had the same issue.

At a loss, we went to pick up the frame to redo it. When we arrived, we noticed that, because of its size, the collector hadn’t hung the piece on the wall but instead set it on the floor and leaned it against the wall. Turns out, the apartment was heated with underfloor heating, which had effectively warmed the frame and "baked" out every bit of moisture trapped inside.

We rehung the work on the wall, and just like that, the problem was resolved. The condensation dried up completely, and we never heard about it again.
No cracked corners though!

Back to the issue at hand. I’ve been considering getting a dehumidifier for the woodshop to lower the humidity a bit. I know I won’t achieve perfection (unless I invest in a super expensive one), but I assume every little bit helps in bringing the RH levels of the woodshop and fitting room closer together.
Would it also make sense to look into humidifying the fitting room to try and bring both environments closer to 50% RH? Or is that unnecessary, and should I instead focus on letting the wood acclimatize in the warmer fitting room? That said, I don’t really have the space for that option, so it would be a bit of a challenge.

 

[Prospero]

A 'rule of thumb'. If I go out to my outdoor shed and the door sticks (like it does at the moment) I know the moulding inside needs to rest
awhile in the warm before joining. In summer the door does not stick so you are good to join right away.

*Wood shrinks very slowly but exerts a enormous force. Even if it does shrink it tends to not break the glue bond.

 

[JFeig]

As a picture framer who is more than double your age, I grew up before what is today common, climate control although there were furnaces for heat. Most of the materials that you work with are natural materials(wood and paper). It is one thing to have an unheated storage area and it is another thing to manufacture a product in the same area. Even 100 years ago, ask any of the people in your area if a factory was heated or not in the winter. My guess is that they were. Such products as furniture, ceramics, printing, were heated and the raw materials were allowed to stabilize before being worked on.
You might store the lumber in an unheated structure; however, the joining and finishing needs to be done in a heated environment. To use a 500 year old saying -- "you are being penny wise and pound foolish" (adjust for the modern Euro.)

--- AI search
The phrase “penny wise and pound foolish” originated in England and is approximately 500 years old. It first appeared in print in 1598 in Francis Meres’ translation of Luis de Granada’s “Sinners Guyde.” The phrase originally referred to being thrifty with small amounts of money but wasteful with larger sums. It alludes to the British currency system where a pound was once worth 240 pennies, or pence, and now is worth 100 pence.
---

 

[Alex]

As a picture framer who is more than double your age, I grew up before what is today common, climate control although there were furnaces for heat. Most of the materials that you work with are natural materials(wood and paper). It is one thing to have an unheated storage area and it is another thing to manufacture a product in the same area. Even 100 years ago, ask any of the people in your area if a factory was heated or not in the winter. My guess is that they were. Such products as furniture, ceramics, printing, were heated and the raw materials were allowed to stabilize before being worked on.
You might store the lumber in an unheated structure; however, the joining and finishing needs to be done in a heated environment. To use a 500 year old saying -- "you are being penny wise and pound foolish" (adjust for the modern Euro.)

--- AI search
The phrase “penny wise and pound foolish” originated in England and is approximately 500 years old. It first appeared in print in 1598 in Francis Meres’ translation of Luis de Granada’s “Sinners Guyde.” The phrase originally referred to being thrifty with small amounts of money but wasteful with larger sums. It alludes to the British currency system where a pound was once worth 240 pennies, or pence, and now is worth 100 pence.
---

I totally get what you are saying, and to some extend you are right. I've gone and invested in the big space, not really thinking ahead to this problem which may end up defeating the point of the big space to some extent.
That being said I think there is some nuance I need to bring in to this. Although the space is unheated at the moment (and might not be efficient to heat in the future) it is in a brand new industrial unit that is enclosed by 3 other industrial units on all sides but the front. What this means is that it is insulated quite well. We've been having freezing temperatures here all month and the temperature in the unheated space does not drop below 55-60°F which for me is a manageable temperature to work in when doing woodwork. I don't think that this would be the case in those factories hundred years ago. That would be more of and outside temp. is inside temp. stituation. So I get that a space requires some heat to do the work we do but I figured that a minimum temperature above a certain point might be workable as well. This however didn't take RH into account. All the paper and cardboard is sorted in the heated part.
So if what @David Waldmann said about temperature is correct (and I assume he knows his stuff really well!) than heating the space would be an ineffective way to solve the problem. Getting a dehumidifier might be a better, more cost efficient way. Also it might be more 'precise' as a furnace might dry the air out more than you would want. It's kind of what is happening in the heated fitting room.

 

[JFeig]

You just added a new fact to this discussion being the lowest temperatures of the "unheated area". In my current location, my winter thermostat temperature is set at 20°C (68°F) during the day and 62°F (17°C) at night. My "workshop" is in my cellar (basement).

 

[wpfay]

Note: wood contracts and expands across the grain, not with it. If cut in one environment and moved to another, allowing time to acclimate, joining can be difficult if not impossible without recutting the miter.
I have experienced this firsthand with hardwood moulding chops cut at a dry climate at an high altitude, and acclimated in my shop at 10’ above sea level, and in coastal Florida.

 

[Alex]

Note: wood contracts and expands across the grain, not with it. If cut in one environment and moved to another, allowing time to acclimate, joining can be difficult if not impossible without recutting the miter.
I have experienced this firsthand with hardwood moulding chops cut at a dry climate at an high altitude, and acclimated in my shop at 10’ above sea level, and in coastal Florida.

Good thing to get this cleared up. Like I mentioned above this seemed like an issue to me.

 

[Nikodeumus]

On a somewhat related note.
I just recently moved a 60 year old piece of furniture my father made when he was 19.
It went from a climate controlled apartment, stayed over night in a van (outside temp only 2c),then into my non climate controlled cabin.
Now, 2 of the drawers don't close all the way.
After it acclimatizes to the new environment I'm pretty sure it will be fine.
Luckily, I can easily do some planing or sanding if it still sticks after a week or so.
That isn't usually an option with frames.

 

[Larry Peterson]

Now, 2 of the drawers don't close all the way.
That isn't usually an option with frames.

What, your frames don't have drawers, eh?

Or you can repurpose the drawers.............

 

[David Waldmann]

Very good to know about the cold by the way. I've been wondering about the effect of temperature itself as that will be even harder to control then humidity due to the size of the space.

Just to be clear, temperature affect RH. If you have a perfectly sealed space, and the temperature goes Up, the RH goes Down. And vice versa. The key point/word/letter is RELATIVE humidity.

 

[Alex]

You just added a new fact to this discussion being the lowest temperatures of the "unheated area". In my current location, my winter thermostat temperature is set at 20°C (68°F) during the day and 62°F (17°C) at night. My "workshop" is in my cellar (basement).

Well maybe that bring up something else.
What are the 'ideal' conditions in terms of temperature, RH, Wood moisture content?
Maybe it would be good to know what would be the ideal 'base' to aim for.

 

[Alex]

Just to be clear, temperature affect RH. If you have a perfectly sealed space, and the temperature goes Up, the RH goes Down. And vice versa. The key point/word/letter is RELATIVE humidity.

yeah that is clear. But that would mean that wood at 50%RH and 50°F would remain unaffected if the temp goes up to 68°F but the RH remains at 50% (I know that is a logical fallacy as the Humidity is relative to the temperature and the encrease in temperature would affect the humidity but I mean this just for arguments sake and also It seems this could be manipulated through (de)humidifiers.

Also I bought myself a wood moisture content measuring device and did took some measurements. They vary quite a lot and to be honest I have no clue what would be a good moisture content for what wood. The woods I have in stock are Maple, Ash, Oak, Walnut and obeche for strainers (I also carry Mansonia but I'm not sure if you have any experience with this).

 

[Prospero]

In ages past homes had a more stable climate - usually cold and draughty.
Since the advent of central heating homes are usually much warmer and dryer.
Nowadays people buy antique furniture that has resided quite happily in some
old house for decades (centuries?) and wondered why it started to crack.
This was particularly noticeable on pianos which never stayed in tune.
The fact is, it's not so much the climate itself as the sudden changes that do the harm.
Have a room toasty warm in the daytime and turn the heating down at night and you
get big swings. Wooden things do not like it.

 

[JFeig]

museums recommend 40%-60% @ ~20° C with no more than 3% variation per day.

 

[Prospero]

For the record.... Recently there has been a 'cold snap' in my neck of the woods. Very cold
and very damp. The shed readings were hovering around freezing with 90% humidity.
Inside about 19ºc and 40-50% humidity.