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    Default Timber sealing (ends) - an observation which leads to a question...

    I've been sealing quite a bit of Spotted Gum after jointing it in the last week (750kgs down to 566kgs). I've been using enamel paint to seal it (because it was there) and I note that on the ends that I have docked with a fine toothed drop saw the paint sits right up on top of the end grain and doesn't soak in at all. This is in complete contrast to the end that are rough cut where it will soak up 2-3 coats, and the first coat gets sucked inside within 15 minutes.

    FWIW the Spotty is about half dry (unmetered).

    So, it seems to me that there are a couple of things going on here:
    1. there is more surface area on a rough cut end
    2. the fibres on the rough cut are obviously torn rather than cut which would lead to more exposure of the inside of the fibre for moisture movement.

    This leads me to wonder whether or not this cuts both ways for moisture movement?

    That is, is it likely that there would be less moisture movement outwards through smooth cut end grain than rough cut, and therefore less likelihood of checking?

    Where I'm going here is can I get away with less sealing on a smooth cut board (i.e one thin coat rather than a thick one)?

    Sounds logical, but weird stuff happens, and I'm sure you'll all enlighten me .

    Also, given that the timber is about half way through drying, if unsealed ends haven't checked thus far, is it likely that they won't check from here on?
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    Quote Originally Posted by FenceFurniture View Post
    Also, given that the timber is about half way through drying, if unsealed ends haven't checked thus far, is it likely that they won't check from here on?
    BINGO!!!According to all the expert opinions and studies I've read that would be the case. Drying faults such as end splits, surface checking, and collapse all occur at high moisture levels when there is a lot of moisture "sucking out" and a steep moisture gradient between the interior and exterior of the timber exists. They aren't visible to the naked eye until later in the process, but that's when they start and then they progressively worsen as the timber continues to drop moisture until they become visible. This kind of degrade happens when the timber is losing free water not bound water (water from between the cells, not inside the cell walls). The misconception is that people believe that the splits dont happen till later in the drying process because they cant see them until then, but in fact if you can get the timber to around 20% without developing splits and checks and collapse then from there on what is occuring is loss from inside the cells... shrinkage. What we see however is the timber opening up at that point along the stress lines created at those higher moisture levels and we assume that the fault has occured below 20%. Shrinkage will open pre-existing splits up wider, but it doesn't seem to create splits.If you can prevent the splits starting in the first place then there is nothing to worry about later on.Same with surface checks, and this relates to the difference between smooth and rough cut ends: there were a number of studies done in the USA regarding pre surfacing of Red Oak prior to sending it to the kilns. Red Oak is a species particularly susceptible to checking and splitting during drying, and the studies found conclusively that passing it through a plane to give it a smooth surface dramatically reduced the loss to such faulting on the back side of the drying process. Surface checking and end splits are basicly the same process on different faces of a board, so it makes sense that smooth cut ends would be less susceptible to end spliting through less exposed grain. and a reduced surface area.

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    Good stuff - thanks very much John.
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    Default One thing leads to another...

    John, would this have any bearing on the amount of twisting, cupping and other rotten behaviour or is that just down to the spring and tensions within the boards?
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    Hmmmm Food for thought indeed! Think I might do some experimenting myself on the next lot of logs I bring home
    .
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    I can imagine that rough-cut, fuzzy end grain would tend to act as a lamp wick for cellular water.

    I've been carving quite a lot of birch (Betula papyrifera) over the past 18 months. In history,
    it was all stacked and stickered, sawmill rough, up on a mountain side for an indeterminate number of years, no cover at all. The ends are quite a lot smoother than the faces, the timbers all about 5cm x 15cm x 150+cm. We all remarked on how few splits there are in the ends.

    The ends are going to dry faster than the core. It's possible that mechnical drying shrinkage in the ends retards water loss.

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    http://www.utas.edu.au/__data/assets...ing-part-1.pdf

    http://www.utas.edu.au/__data/assets...ing-part-2.pdf


    These are links to the Australian Hardwood Drying Best Practice Manual parts 1 & 2, which covers the issues of drying stresses from a whole of process point of view. A lot of it probably isn't applicable outside a commercial operation, but bits and pieces are and certainly the principals involved don't change regardless of scale.

    The thing with wood drying is that its a very complex, not really well understood subject thats had billions of dollars throw at it worldwide over the years and sometimes the answer is still often "we think" rather then "we know". I have a limited understanding of the topic in the way that Joe Average carowner understands how his car works... he can start it, put it in gear and go from A to B without fully understanding the intricacies of various petrochemical reactions occuring based on his fuel of choice. I can mostly dry wood ok without fully understanding the intricacies of diffuse porous vs ring porous cell structures on drying.


    End Splits & Surface Checks = too rapidly drying. Solution... end sealer and slow drying rate during initial stages. End seal is best applied within about an hour of the tree falling, per some paper i read a while back. Personally I end seal immediately after felling and feel its made a difference.

    Cup = cutting wide boards from small trees resulting in differential shrinkage. Solution... cut small cross sections from smaller logs. I tend to work on keeping a ratio of 1: 4, and certainly not less then 1:3 to get a consistent product ( ie 6" wide boards require a 24"diameter log, and not less then 18" diameter to avoid cupping. I can saw them out of smaller logs, but the degree of cupping makes it economically unattractive to me for a premium product. Bigger is better when it comes to logs)

    Bow and Spring = compression and tension in the log. Solution... roll log during cutting and oversaw as required, but also it can be as simple as making sure that sapwood - which dries faster then heartwood - is turned to the inside of packs so it doesnt dry as fast as the wood surface on the outside, particularly in block stacked packs of structural timber.

    Twist = spiral grain. Solution... oversaw, or in some cases use it for firewood.

    "Wavy" boards = improper stacking. Solution... pay more attention to your stickers, but also it can be hit and miss from badly tuned saws.

    All at once = improper storage. Direct sunlight is the biggest stuffer of GOS timber there is, and strong dry winds in the initial stages of drying are a close second. Shade and a roll of hessian goes a long way, and in the heat of summer wetting that hessian to increase humidity in the front of a stack can make a difference. So can the order of stacks... partially dry stacks placed in front of wetter ones impede airflow and so slow the drying rate down. (Wet stacks in front of dry is a waste in any case... you load the air with moisture at the front and the air cant carry moisture out the drier back stacks anyway.)


    I keep threatening to run a batch of flooring through to presurface it. I see a few positives, based on the US red oak studies done by Gene Wengert. Even consistent product makes for even consistent stacks, volume reduction = faster drying (and at todays electricity prices if I could make a nominal 27mm GOS plank a spot on 23mm that would be a reduction of around 10% on the electrickery bill to kiln it), but less degrade would still have to be the economic key though, given it means two passes through the moulder to make a T& G board. One day when there's nothing better to do....

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    Thanks very much for that research John, much appreciated.

    Quote Originally Posted by Robson Valley View Post
    I can imagine that rough-cut, fuzzy end grain would tend to act as a lamp wick for cellular water.
    Yes, exactly. I think that has far more to do with it than the increased surface area (although still no doubt a factor).

    Here are some pics to illustrate what got the grey matter agitating.

    Rough cut, with two coats of gloss enamel paint:



    That end had never been sealed since milling, and you can see a split has well formed, running right across the end, with other minor splits waiting to get going.

    Smooth cut with just one coat (and the opposite end of the same stick, where I docked off either a split end or a useless shaped end):



    and another smooth cut with one coat:



    When the smooth cut ends are angled into the light you can see the gloss of the paint, but the rough cut is still matt finish after two coats.
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    Hmm painting the ends with normal paint is better than nothing, it's much better to use the proper stuff that penetrates and remains flexible, but on ends that have already split is a waste of time and useless for comparison purposes
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    Quote Originally Posted by dai sensei View Post
    Hmm painting the ends with normal paint is better than nothing, it's much better to use the proper stuff that penetrates and remains flexible, but on ends that have already split is a waste of time and useless for comparison purposes
    Understood Neil, but just trying to show the difference in how the paint sits up on smooth end grain rather than being absorbed in, and thinking that this must work both ways with the moisture movement.
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    Quote Originally Posted by John.G View Post
    .........and at todays electricity prices if I could make a nominal 27mm GOS plank a spot on 23mm that would be a reduction of around 10% on the electrickery bill to kiln it), but less degrade would still have to be the economic key though, given it means two passes through the moulder to make a T& G board. One day when there's nothing better to do....
    The other benefit(s) would be more boards per billet, and less degraded boards. The initial pass wouldn't have to be through the moulder would it? Just over a planer?
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    Default Recommended sealant?

    it's much better to use the proper stuff that penetrates and remains flexible
    Can anyone please recommend a suitable sealant with these properties?

    Also, when the time comes to dress the boards, how do you remove it?
    regards,

    Dengy

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    What sealant you use depends on how much you care and how much money you have.

    There are some commercial latex bassed sealants that are...um......rubber.

    contact cement that is a bit dodgy would work well.

    I and others in the past have used disolved poly styrene.....Keep a lidded drum with thinners in it and add any poly styrene packing you get to the drum....add more thinner when it starts to get a bit thick or the neew styrene des not disolve fast enough) ......although it can be a bit crispy when dry......it can be made more flexible by adding some sort of plasiciser (oil or wax)

    Many use variuos waxes.....parafin wax is easily available, but can be a bit hard.....mixed with bees wax, it is softer stickier and more flexible.

    Acrillic paints are far more flexible than enamel and more impervious to moisture.

    then ya get into tar and all sorts of other filth.

    They all work to some degree or other.

    mostly people cut the ends off to get rid of end seal.

    The waxes penetrate fairly well and probably both tooling the least.
    Lots of woodturning blanks are dipped in wax....most just mount em straight up in the lathe and start cutting.




    I definitely agree that the sooner you get that end seal on the better......some timbers you want at it as soon as the log hits the ground.

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    Quote Originally Posted by Dengue View Post
    Also, when the time comes to dress the boards, how do you remove it?
    If it's a wax or similar I just run over it with a paint scraper to remove the excess and then let the thicky jointer do the rest. Generally have to dock the end anyway because it's too rough and definitely won't be square after dressing the faces even if it's a smooth cut.

    After scraping off you could use white spirit to get most of the rest, but i don't usually bother.
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