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I have to do an exterior for a new garage on an older house. The plan calls for an “aged” post and beam stucco look which is quite involved. The garage is currently sided with OSB.
I don’t want to create a mess of triangles for the stucco mesh, so my plan is as follows:
Paper the exterior with 15 lb. Add the horizontal, corners and some of the main verticals using 2x cedar. The corners would be pre-built using biscuits and gorilla glue. Attachement of all wood would be by way of screws from the inside. The fill in surface would then get a mesh and stucco scratch coat. Over this would be the remaining vertical and detail trim using 1x cedar (again screwed from inside?), followed by the final stucco coat(s) in the remaining fill in surfaces.
The cedar is intended to weather naturally (or be lightly stained to a weathered look matching the existing house). Is this a reasonable approach? What are the pitfalls?
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It sounds like you have a pretty good handle on this. I have a few suggestions that might or might not help. I would first maybe think about using #30 lb. felt, and putting the wire mesh on first, then your first trim pieces on top of that. This would give a small "drainage plane" behind the wood to allow any moisture that does penetrate to dissipate. I also often put a small rabbet on the backside of the edges of the wood that go against the stucco, and then use that to get stucco behind the outer lip of the wood trim. This gives you a better joint to caulk, and if the wood shrinks a little, you don't wind up with a crack right through to the tar paper. I agree with you about putting on a scratch coat before you put on some of the other pieces of trim. It goes without saying that it would be best to treat any pieces of trim on all sides prior to installation. Hope this helps some.
*It sounds like what you want is an imitation half-timber look, although post and beam stucco is pretty descriptive. Real half-timber building were built with a timber frame and plastered brick infill. They were notoriously drafty.As Nick says you should key the edges of the trim to allow the stucco to get behind it. A bevel will work.I would think about all 1x trim applied over the wire but before any mud. The scratch coat will not even be close to flat.I question screwing from behind, because this allows only 5/8" of a screw tip in soft 1x cedar. You will have a hard time getting it tight without pulling the screws out or poking them through. Nail it, or screw if you must, from the face. Stucco will stain the cedar. It will weather out evenly in time, but you may want to accelerate this process to make it look good right away.
*Mike, You've really hit the design style nail on the head. I've been unable to come up with a suitable description for the effect. Imitation half-timber fits perfectly. Just for the record, the foundation for this project is being done with a rock veneer up to about 4 feet. On a historical interest, what kind of pattern did they use on the brick fill in all those triangles?If the trim is keyed and mounted to the wire directly before mudding (leaving a wire void behind) doesn't this create potential source of water problems when the wood shrinks?What would be your suggestsions on flashing the top edges of the horizontals? Or would a simple bevelled top edge to divert water away be sufficient?What kind of process would use to accelerate the cedar weathering? Any tips on protecting the surface through the mudding process?
*Scott,The bricks in true half-timber construction were just fill. There was essentially no pattern, just whole bricks and rubble set with lots of mortar. They were almost always plastered so the bricks were hidden.Stucco is meant to shed water but really isn't waterproof. The paper is the ultimate barrier. Joints between the wood and sutcco will not be anymore of a problem than cracks in the stucco. I would be very carefull in doing the paper, thouogh. I don't think 30# is necessary, but with the wood it would probably be a good idea to use roofing felt, rather than sheething paper. If you don't get much direct water it should be fine. I would use a Z-bar at the horizontals to direct any water outward. You should lap the paper above onto the Z-bar. You may want to consider this for the tops of the diagonals, too.It is almost impossible to mask wood where it joins stucco, since the stucco process amounts to wet sanding with very coarse material. Duct tape might work. Baking soda and water will artificially age redwood, but I'm not sure about cedar. If it is rough sawn you can probably clean it with a wire brush. Bleach such as oxalic acid will probably clean it pretty well. Simply brushing cement or your stucco mix and water might work well enough, as time will correct any irregularities.
*If the trim pieces are sitting on wire, how would I lap the Z-bar with paper?Part of the trim is framing 8" glass block windows (there's a whole wack of em). These windows have been framed in to be built on site (bare glass block, no frame). I'm still contemplating how to build in and seal these things (I've got till next summer). Any suggestions?The trim is going to be a little difficult around these openings (again with the trim sitting on wire). I've got just enough spacing in the frame to allow a little more than a 1/2" clearance around the block. One idea I'm mulling around is to use 9" wide shakes to line the opening (thick side in) from the exterior to the depth of the block thickness then simply place the block from the outside and bead the edges. The block will be recessed from the exterior 2-3". Not exactly sure how to flash this.
*You were paying more attention to what I said than I did myself. Obviously the paper can't lap the Z-bar, nor does it need to, since the Z-bar is only to prevent water from getting behind the trim.Glass block in stucco is traditionally set flush with the stucco without trim. You'll have to work out the flashing details, but where the trim is on an edge of the stucco, and not in the field, don't put it on top of the wire.
*Sorry to keep picking on the details (I'm almost there, your help has been invaluable), but regarding the Z-bar. Would you be nailing it directly over the wire or does this involve cutting the wire to insert the Z under the edge? Won't flashing over wire leave the mud vulnerable along the flashed edge (thinner coat, no mesh to grab)? Or does this matter?I see now, with the block trim full depth, I could simply frame in the opening and caulk the block at the trim edge (we're talking more rough timber look here).