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Oak door expansion

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Wurm

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The pictures are of the lower section of a stable door that I have cut and is ready to glue together, but I have recently been told that I should leave a slight gap between the slats so as to allow for expansion. Can anyone here verify that, and give an idea of how much gap I should leave? I can still run each piece down the table saw if necessary (although I would rather not since it will give me another chance to make a mistake).

The slats are 1" thick and are currently showing 14% moisture.

It is only the second item that I have made out of wood, the first having been an airing cupboard, so all advice is appreciated.
 

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Trevanion

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Is this an internal door or external door as that makes a massive difference. What is the length of your tongue and groove? I’ve quite often seen doors where the boards have shrunk to the point where you can see daylight through the boards. If it was a tongue with 10mm depth I would go tight on either side and 2mm between each board, if it’s a 5mm or so tongue I would definitely go 1mm between each board as 14MC is about right for it to stay fairly stable but it is on the moist side in my opinion, so they’re likely to shrink. If it’s an internal door I would go tight as possible as they will definitely shrink, I would even leave them in the house for a week before pinning them in place.
 

Mrs C

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I have done 3 external oak doors, 10mm tongue and left 3mm between each. They have been hung for 3 years and get the extremes of weather and have been fine.

If you haven’t already thought about it you need to pin each on centrally to stop them wandering.
 

Mike Jordan

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The weather mould seems to show that it's an external door so I would go with the last advice and allow three mm between each board. The destructive power of expanding timber is enormous. Many years ago I made a tall side gate from European ash, every winter the boards expanded more than I had allowed for and forced a bow of about 20mm into the front face of the gate. It was made with wedged mortise and tenon joints which remained solid for about fifteen years before rot set in and caused me to make a replacement in Iroko.
You appear to be using another form of jointing so a better level of expansion gap than mine would be a sound idea.
Mike.
 

dzj

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Here's an article that'll help you calculate the amount of annual expansion/ shrinkage due to change in moisture content:
https://www.popularwoodworking.com/wp-c ... vement.pdf

There are charts American Forestry Association have issued that'll help you determine annual change in MC in most world locations, but I don't have this link.

If your door will get drenched by rain, a 4-5% increase in width is not unheard of.
 

Wurm

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I found the information from the US Forestry Service and it says 15% - 20% for Cardiff, which is probably a little drier than here in the west where the humidity mostly lives between 70% and 100%. The last few weeks have been abnormally dry which is probably why I am showing 14% on the thinner sections and 18% for three inch sections.

Some of the slats are quarter sawn so using the formula from the popular woodworking site that means I should leave 1/20" gap.

The graph below is consistent with that, but what neither it nor the US Forestry Service say is how quickly the moisture content rises when exposed to the misting rain that is so common here and can last for two or three days at a time, and the reply here that I should allow for 5% movement suggests that I should leave a gap three times that. The tenons are 1/2" so there would be plenty of scope for doing so. My current thinking is that I should err on the side of caution.

With regard to pinning them, I am guessing I should drive a nail through the frame that will go through the tenon of each slat. Can anyone recommend a particular size of nail?
 

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deema

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I’m a bit further up than you, but it’s still either warm or cold rain most days in Cheshire! The oak doors I’ve made have had a coat or two of Osmo oil, or Tung oil on them and normally settle at around 15% moisture content.

I’m assuming the slats are tongue and grooved? If you pin each slat the nail will corrode away very very quickly leaving a horrid black stain due to the acid in the oak. The amount of gap you leave will need to allow for circa 5% moisture change ie, up to 20%, it’s very unlikely that will will dry out to less than 12% on the driest periods. With this in mind I would bed the end of the centre slat in a dollop of clear exterior silicone (put in the slot, not in the tenon to avoid it wiping off as you put it in and messing up any finish) and then calculate the expansion based on half the overall width.

Finish the slats and groove with your preferred coating before assemble.
 

topchippytom

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Its an external door so a lot depends down to moisture content and how the door is sealed/varnished ect,I would tend to keep tight this time of year due to the warm weather but winter is coming and how exposed to the elements is the door.
 

dzj

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Erring on the side of caution is what I would also do. Particularly if your door isn't protected by some kind of canopy/ overhang.
 

Wurm

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I installed green oak lintels and beams of 4" section nine years ago which all show 17% - 18% from being in the cottage with no windows during that time, so I am guessing that is the average about which most of the exterior oak will settle (assuming my meter is accurate). I have been planning to oil the oak but not use any other treatment.

I am coming to the conclusion that I should leave 1/8" gap between the slats, put a spot of glue on just the centre of the tenons top and bottom, and hold off on installing the door until the shelter above it has been built (which I cannot do until the roof has been done, which is a bit of a pain).

I really appreciate all the responses here since I am well out of my depth on this job, and thank goodness I found out about the need to allow for expansion before glueing it together in its current form.
 
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