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  1. #1
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    treated wood some info needed

    I have a project I am desiring to build, as soon as possible, and that is a pergola.

    I would like maybe some information if anyone here can provide it, I have looked on the web and found some things but not anything specific on these questions.

    First some background info:
    I plan on making a pergola that has a 12 ft span between the main columns, and it will be approx 5 ft wide. I plan on useing 6 x 6 x 10 treated square posts, and 2 x 8 x 16 foot treated mainboards on top, which I will take 1.5" x 7.5" off the top sides of the posts and placing the mainboards against that (so it's basically inset into the top of the post) and using one on each of the 4 sides of each main post (notched and interlocked sorta of, with probably two 1" dowels or pins glued and flushed to hold them to the 3 x 3" center) hope I'm making this clear. I will then use a normal pergola design sorta like the one here:
    http://www.trellisstructures.com/per...golas-no11.jpg

    my apologies to the real woodworkers here, but I will be painting this.....I know this is so beautiful and would be natural, but I'm trying to make it cheaply, and will be using treated wood like I said.
    anyways on to the questions:

    1) If I buy treated lumber from say consumers lumber or builders square for this pergola, will I be able to paint this quickly, or do I have to stack the wood and dry it out, without worrying about the paint falling off? how long would I have to let it dry out before using it?

    2) will I have a problem with shrinkage or other things?

    3) will I need stainless nails? for the mainbeams (the outside boards) I am actually contemplating like I mentioned using a tight wooden dowel or peg to secure it. there will be two boards parallel in each direction, and I planned on periodically having 3" boards between them to secure one board to the other probably with dowel as well at least 3 dowels probably a 5 dice pattern. the 'latice' work is going to be treated 2x2's and I will probably mortise and tendon them in, probably not secured with a dowel, and 2x4 for the wider parts.

    D I have any worries about wood twisting, or something i haven't thought of? thanks all.

  2. #2
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    RE: treated wood some info needed

    You'll definitely see shrinkage and some twisting/cupping/warping as the PT lumber dries out; it's usually shipped nearly dripping wet, and just as fat & heavy as it cam be... and impossible to paint with any success.

    I say... if you'll be using PT, then build it and let it stand as built for at least one full year before trying to paint it. That's problematic, of course, because there'll be a thousand little places where paint SHOULD go to do the job well, but CANNOT go because stuff's attached together already.

    One thing strongly in your favor - if you use dowels, they'll already be as dry as they'll ever get... whereas the PT lumber will be as wet as it'll ever get. That means that after you've driven the dowels, the PT will shrink down onto the dowels & lock 'em into place irremovably.

    I'd still use metal to hold it together, though, and stainless fasteners would definitely be my choice, since this thing is overhead and if someday it falls because fasteners rusted through, somebody's gonna' get flattened.

    -- Tim --

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  3. #3
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    RE: treated wood some info needed

    Don't build it "cheaply"; build it "inexpensively." There's a difference.

    Is there a reason you're planning to use treated wood? It's understandable in the few areas of a pergola that would be in contact with the ground, I guess, but for the whole structure? Seems like expensive overkill to me.

    Unless I'm going to plant the wood in the ground (actual ***ground contact application***), I never use pressure treated wood. It's more expensive, and because it's soaking wet it's heavier and more difficult to machine until it dries. And yes, you will have to worry about shrinkage, warpage, movement, etc. as it dries.

    phil



  4. #4
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    RE: treated wood some info needed

    Yeah, if you're gonna paint it, you can use just regular construction grade lumber. Cheaper, and without having to do all the waiting for it to dry before painting. Use a good quality exterior grade paint and be ready to repaint every several years.

  5. #5
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    RE: treated wood some info needed

    Just as Tim said. One thing to find out is the preservative used on the wood. Most of the newer treatments require the use of at least triple dipped galvanized fasteners; stainless is preferable. Further you must use a minimum of G185 galvanized hardware (also called Zmax by Simpson).

    DO NOT use any aluminum next to ACQ or CA-B treated wood as they are both very corrosive. I'm not sure of the MCQ treatment used on the east coast so you'll want to check. The other treatment used on SYP is called L3 which has no copper in it. I've heard its not very corrosive.

    Finishing PT lumber is a matter of allowing the wood to dry completely. Most manufacturers suggest using an alkyd primer once the drying is complete. Then follow with your topcoat.

    Hope this helps

    Mike

  6. #6
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    RE: treated wood some info needed

    >Don't build it "cheaply"; build it "inexpensively." There's
    >a difference.
    >
    > Seems like expensive overkill to me.


    hmm excellent point....and so therefor my idea has changed. the four 6 x 6 x 10's shall be PT.....the rest will just be regular decent construction wood. I just figured PT would last longer I suppose, but well if it's painted, and cared for, then it should last well beyond the rest of my lifespan anyways shouldnt it, and I wont have to worry about using stainless nails either will I?

    Should I anyways? would there be another reason to?

    Ok then, with the new idea, will the wood still be wet as heck or is that just a problem mostly with PT?

    oh one other concern of mine. does anyone see a problem with the spane being 12 ft using 2x8x16's?


  7. #7
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    RE: treated wood some info needed

    It's specific to PT. Everything else you buy really SHOULD arrive no more than about 7% EMC (Equilibrium Moisture Content, a measure of kiln-dried wood) but WILL probably arrive at about 10% because it's stored in open air. That's still very dry.

    I'd still use hot-dipped galvanized nails to hold it together, even if you'll be painting over the nailheads. No need for stainless except in the PT.

    Paint EVERYTHING (except the PT) BEFORE IT'S ASSEMBLED. Prime, paint, cut, prime & paint the cut surface, assemble. Otherwise, moisture will sneak in where you haven't painted & blow the paint back off the surface. That's the leading cause of blistered house paint, right ahead of poor priming. If stuff's painted completely and well, paint lasts a long, long time. If it's painted poorly (which is typical), it's only good for a couple of years before it wants painting again.

    -- Tim --

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  8. #8
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    RE: treated wood some info needed

    In the above picture of the pergola, how do they do the joints with the supports off the mainbeams (I call the mainbeams the long ones on top, in my case I will be using 2x8x16's)? are they done by notching out both boards, and fitting together like:

    http://lh6.ggpht.com/andrew.garboniv...4/pergola1.jpg

    If so does the weaken the board a lot? (IE if a 8" board is botched half-way, does it make it a 4" in strength pretty much? should the main board be notched from the top or the bottom? (I'd figured top )

    any other suggestions/etc?


  9. #9
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    RE: treated wood some info needed

    Go ahead and build it with PT lumber. Wait 1 month in summer or 2 months in spring or fall for the PT to dry. DO NOT PAINT. Use stain made for pressure treated lumber instead. I use Olympic golden oak stain and it comes out great on a deck I built for my friend. Just put the stain in a garden sprayer and go to town.

  10. #10
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    RE: treated wood some info needed

    Let's go with... the layer of evenly spaced planks will be "rafters", covered with a lattice for shade. Under those are "joists", including the four "rim joists" around the perimeter. They rest on posts.

    So... I think you're asking about the corners of the rim joists, where the seemingly-impossible corners are, with horns extending out in both directions. I'm pretty sure half of those horns are purely decorative, probably toenailed in place post-facto from the backside.

    If you use the joinery you've pictured there, it'll significantly weaken the joists... and I mean SINGIFICANTLY weaken them. Not only will such a notch diminish the shear strength by half, it'll diminish the mudulus of elasticity by far more than half because the "stress skins" on the two edges will be only half as far apart. Too, the square-cornered notch provides an excellent spot for splitting to start; if one must diminish the width of structural members, ideally no abrupt 90-degree notches should be used because cracking & splitting tend to happen right at those 90-degree corners.

    Since those horns - extensions of the rim joists - don't appear to serve any structural purpose, nailing them in place as applied trim should be fine. Keep the horns that appear the most structural, and apply the rest.

    -- Tim --

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