| Author |
Message |
Robin E. Snyder
Senior Member
Username: robin
Post Number: 578
Registered: 08-2004
| | Posted on Saturday, November 08, 2014 - 11:31 am: |    |
I have a project using large Ponderosa Pine logs for an exterior trellis (Albuquerque). Current moisture content is 20-25 percent and, based on supplier input, it will take about a year or so for the logs to reach moisture content around 19 percent. The design team is ok with this. The question came up whether to use linseed oil to help prevent future cracking/checking, or whether to use sealer. Some of the logs at the existing building have mold growth (I have read linseed oil can contribute to this) so that may be a factor. I admit, I know very little about wood treatment. Any experts out there that can assist? |
Mark Gilligan SE,
Senior Member
Username: mark_gilligan
Post Number: 700
Registered: 10-2007
| | Posted on Saturday, November 08, 2014 - 01:12 pm: | |
Do you have any technical data to suggest that either linseed oil or sealer will prevent future checking or cracking?
Will suggest that the high moisture content of the wood will make the wood more conducive to rot and mold. |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1607
Registered: 03-2002
| | Posted on Saturday, November 08, 2014 - 03:45 pm: | |
Boiled linseed oil has been used as a sealer historically. Here in New England, where old houses have wood gutters (not very practical, eh?) they would often be sealed with it. My understanding is that it oxidizes similar to oil paint (which, of course, was once made with linseed oil binder). I don't know what raw linseed oil would do.
It would seem to me that these products may somewhat slow down checking, but they are porous, so moisture will still leave the wood. Once the bulk of the moisture in the wood has evaporated, it will shrink, and the frequent result of that is checking and splitting. Also, once a check starts, the sealer is no longer effective at the check, and evaporation will continue more rapidly at that point. You can readily see this in weathering painted wood.
One thing sealers may do is control the way the surface weathers and changes color. Here in New England, white cedar shingles are a frequent siding material (think dune shacks in Provincetown, MA). Some types of sealers, sometimes with bleaches, will help to control the inevitable weathering to a more uniform silver grey. Not sure this works on Ponderosa pine, or in Albuquerue. |
Steve Taylor (Unregistered Guest)
Unregistered guest
| | Posted on Sunday, November 09, 2014 - 07:06 pm: | |
Logs are probably going to check no matter what you do to them. Wood shrinks at different rates radially versus tangentially,versus longitudinally as it dries. It also dries from the outside in, and the moisture wicks out of the ends so they dry faster than the parts in the middle.
Slowing the process will minimize the size and number of the cracks, and the smaller the board the less it will check. Sawn lumber is frequently painted on the ends to slow down the process.
There is no sealer or paint that will prevent moisture migrating out of the wood. Most finishes will slow the process. I saw something a few years ago that suggested that wax (I don't remember what kind of wax) slows the process more than any paint or varnish.
In any case, if they want this trellis made out of peeled logs they're going to get cracks. Consider it part of the rustic look. I would be more concerned with how the thing is attached to the ground, or whatever it's going to sit on. The joinery should be detailed so that moisture doesn't accumulate around joints where it will wick into the wood. Wood will last a very long time if you keep it dry; not so much if it stays wet.
Steve Taylor |
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