Timbers expansion Question.


Hiya Folks, Working now on a project that isn't quite "Fine Woodworking". Building an adobe (heavy bricks made from mud) wall. Over the gate portion, I intend to set two or three 6"x10"x6 ft. ponderosa pine beams horizontally. On top of these, I'll put additional adobes. Ultimately, the entire structure excluding the wood will be stucco'ed. I intend to leave a gap on the sides of these beams for expansion but am not entirely sure what to do for the bricks sitting on top of it. I thought about putting a layer of asphalt roofing material down allowing the wood to slide if you will, under the weight of the bricks (maybe 200 lbs?) but am not sure if that will hold up or even allow the wood to move. Would a thin sheet of plywood, masonite, or ?? sitting on top of the beams be a better option? I'm used to allowing for expansion with table tops, not timbers! Any help is most appreciated. Cheers, cc
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the timbers expand the most in the direction from the heart of the tree to the bark- that is the tree gets fatter or slimmer as it takes up or loses water. the wood doesn't expand enough to measure end to end. you don't need to leave room at the ends, but it will lift the adobes above as it expands. the most likely failure you'll see is cracking of the stucco around the lintel.
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Yeah, that's what I'm trying to avoid but I don't want to get too fancy with a solution either. I may just put it in and worry about cracks later. They make a matching caulk (to the stucco) so that may be the answer. I do plan to leave some space around the beam for horizontal expansion but just didn't know how to handle any vertical (not lengthwise....wasn't concerned with that) without shoring up the adobes above the beam (more effort than I need!). Cheers and thanks. cc

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Considered an arch instead of a flat surface? Post to alt.home.repair also.
On Sat, 6 Aug 2005 08:36:31 -0600, "James \"Cubby\" Culbertson"

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We considered an arch and the wife decided against it. Everyone's got an arch on our street I guess. I was originally planning to do a full arch with only adobe but then this idea came up. I probably won't post to the home.repair group as I'm doing the work today. Just thought I'd ping the wood experts around here as to how to minimize the effects of shrinkage/expansion in this application. Cheers, cc
wrote:

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My house is almost 150 years old. The construction is brick with massive oak lintles. There are cracks above every single one. This leads me to the concusion that wood lintles supporting masonry is just a bad idea. Timbers tend to be pretty wet, not like the nice kiln dried hardwoods that you know and love in the shop. The will shrink. That wil leave the adobe unsupported.
If the lintel is decorative and there is something else holding up the stones above, the there will just be a little seam above the lintle to fill. That could work.
Cheers,
Steve - who thinks there is a reason why everybody else has an adobe arch.
wrote:

intend
asphalt
up
masonite,
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Yeah, every house around here has these same beams, lintels, etc... and every one has little cracks around it. Especially indoors. It's unfortunately a fact of life for us here as that is the standard construction. I put my bricks around the beams with space and kept morter out as best I could. I'll come back with caulking after the stucco and we'll see what happens. And yes, you're right about the wetness of the beams. They pretty much cut them right there and hand them to you with no drying whatsoever. Cheers, cc
ps. Not everyone has an adobe arch, but a lot do. Many have exactly what I'm doing :)

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On Sat, 6 Aug 2005 08:36:31 -0600, "James \"Cubby\" Culbertson"

If I understand you correctly, the wood will be free to act independently of the stuccoed portions.
If the adobes above are not tied into anything else, they will simply ride up and down on the pine as it gains and loses moisture.
My only concern would be to tie the adobes to the top of the beam, so that they are not just a monolithic entity waiting to bean some unsuspecting visitor to the hacienda.
I'm from the East Coast, and thus know zip about adobes, but, if they were bricks, I'd tie them in with masonry ties, and not run them too high.
Masonry should be separated from wood, and in this case, you will need to use something that will be self sealing, so that the fasteners that tie the masonry ties into the wood will not pass water.
Around here, I'd use Ice and Water Shield (a roofing product), or a strip of EPDM roofing.
If you cut a quirk along the top of the beam, you could use plastic sheet (under the other barrier) as an additional membrane between the masonry and the wood ), and this could be left large enough to wrap and protect the wood during stuccoing.
When the stucco is set up, you can cut the plastic inside the shadow line of the quirk, and, since your other membrane will have already been cut to an exact fit, you should have a decent structure, and clean wood.
Tom Watson - WoodDorker tjwatson1ATcomcastDOTnet (email) http://home.comcast.net/~tjwatson1/ (website)
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When working in a traditional material and style, there is generally a reason that those methods developed as they did. An arch was put in because it worked, not because it met some designer's need to differ.
Wood and mud and straw and stucco are going to change with moisture. Frankly, so do bricks and mortar, or steel, concrete and glass.
When we mess with the wisdom of our fathers and grandfathers, we risk learning lessons they already paid for, sometimes dearly.
I didn't mean for that to sound as though I was preaching, but I don't know quite how to edit it differently.
Patriarch
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Thanks folks, The interesting thing, and I agree with Patriarch about not messing with proven methods, is what I'm doing is no different than what they've been doing for hundreds of years. Yes, there are arches out of nothing but adobe but most structures all contain wood and as far as I can tell talking with the adoberos around here, they just set the adobes directly on the wood with morter (and everything's tied together with morter as well I might add, ie. no floating blocks). I'm gonna go ahead and add a membrane as Tom mentioned as I don't see how it could hurt. Cheers, cc

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