Green Hemlock board & batten - finishing schedule ?

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Forum topic by Charlie posted 05-27-2013 12:02 PM 5823 views 0 times favorited 1 reply Add to Favorites Watch
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1100 posts in 1708 days

05-27-2013 12:02 PM

OK, so I’ve started putting up 1” thick rough sawn hemlock boards (battens later) and pretty much went with the advice of “put it up wet and let it dry on the wall” method. The boards are fairly fresh cut. Yes, I know it’s going to shrink. This is on a garden shed for my wife. The original plan was (is?) to paint it. She was told and is ok with leaving it until late summer/early fall or even letting it go until next year to let the hemlock dry and “settle in”.

She saw me oiling a cut-off with linseed oil (just had to see what it looked like) and she liked that it didn’t darken the wood, but popped the grain some. She said, “Can we paint it with that? And if we do, can I still paint it later if I want?” I know we could still paint it later… oil-based primer and then a good exterior paint, but I wondered if oiling it sooner rather than later would have a negative effect on drying. I’m not talking about oiling it now while it’s still pretty fresh, but rather in a month or so. Would oiling it help to prevent some of the cracking/checking that I feel pretty confident will be coming? Would it still allow the wood to breathe enough to dry?

The pine facia and any other exposed “normal” lumber used for trim is getting primed and painted. Maybe as soon as this afternoon (at least primed well). I just don’t want to screw up the hemlock as I know it has some considerable drying to do.

Why paint and not stain?
Fair question. I’m having an issue with carpenter bees eating my workshop. They don’t touch anything painted, but stain doesn’t even phase them. They chew right through it. They’re not bothering the stained T-111 siding, but they LOVE getting under the eaves and eating my sub-facia. They don’t touch the plywood soffit…. because it’s painted.

I’m told they really don’t care much for hemlock, but that may only be because it’s green. Once it dries it may be more attractive. So it may get painted if for no other reason than to prevent the bees from eating it.

1 reply so far

View Dan Krager's profile

Dan Krager

3229 posts in 1656 days

#1 posted 05-27-2013 02:28 PM

Hi Charlie, Happy Memorial Day. If you are a vet, THANK YOU for your service!
I don’t have direct experience with wet hemlock, but I use wet hardwoods all the time, some in good furniture (gasp!) If you handle it well and select carefully, it’s not a problem.

As you know, splitting is the result of tension created by movement, usually shrinking in situations where part of the wood cannot keep up with the other part. Lots of things contribute to that and if you carefully anticipate the forces, you can minimize the tensions. Shrinking due to loss of moisture is one thing. Every board will behave differently depending upon how it was sliced from the log. Wood shrinks tangent to the rings, so a “planked” board with center pith (quartersawn) is less likely to split than a board planked farther from the pith. Splitting starts at the ends because moisture loss is greatest from the cut open pores. Seal the pores and you extend the time it takes to split. Exposure to sun on only one side creates tension and while cupping is the usual result, center splits develop shortly especially if both edges are secured and it cannot physically cup. Narrow boards, 2”-3” cannot develop enough tension to split. So, I would suggest that you put either narrow boards on the the sunny side(s) or select the stack for the “quartersawn” center boards (where the grain goes face to face at less than 45 degrees). Finally, nail your boards in the center only and cover the edges with battens allowing about 1/4” between the boards.

If you can replace the moisture with something permanent that doesn’t shrink (polyethylene glycol), then you have “plasticized” the boards and they will not split or move. You don’t have time for that process here. Raw linseed oil (not BLO) on outside and heavy on the ends will help a lot. After a while a coat of wood preservative on the outside will help too. Painting later on is a good idea.

So, using what you already know about wood movement, you can keep your boards looking their best by using good strategy to minimize and accommodate the forces involved.
Good luck.

-- Dan Krager, Olney IL There are three types of people...those who are good at math and those who aren't.

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