Prepping a Bale House for Plastering

Bale walls can usually be raised very quickly, but that's only one step in the process. Before plastering can begin, there are many, many detailing jobs to do. If they aren't done, the plastering will not go smoothly, and it will be difficult to get the results you wish.

As professional plasterers, we often arrive to plaster bale walls that the owner has prepared for us. And usually there are a number of details that we need to do (or redo) before we can begin.

We've compiled a list of wall preparation details that we recommend be completed before calling in a plastering crew (or attempting to start plastering yourself). Remember, if you are planning a volunteer bale raising, try to spread out your volunteers so that you have help getting the bales prepped too.

Pre-plastering prep work to be done by owners:

Bales stacked. Well, you have done your best you and your extensive list of volunteers have done a beautiful job stacking your bales so that your walls are looking as plumb as a nicely stacked bale wall can look! Take an appreciative look at your work and enjoy a celebratory meal together, but don't let those volunteers all leave you'll need LOTS of help for all of the work to follow.

Start with stuffing. Holes and gaps between bales need to be tightly stuffed with straw. We suggest that you stuff as you stack the bales otherwise, it's a mammoth job for someone to do after the whole house has been built. Stuff holes neatly and tightly if you don't stuff them tightly enough, you will have air leaks and insulation loss in spots on your walls, and plastering will be difficult over such voids. You can also stuff holes and low spots with a cob mix, using a high straw to clay ratio.

Window shaping. All window openings should be shaped as desired and covered with plaster lath or mesh (the windows can be sculpted with a weed-whacker or other tool if the bales are on the flat; if they are on edge, you may have to use a big bale beater-type hammer to hammer them into shape, or you might have to resort to tightly stuffing behind lath to get the desired shapes). Diamond lath is usually the best mesh to use, especially on overhead plastering spots (tops of windows). This is definitely one of the more satisfying jobs once you get the knack. If you have a particular shape of window opening in mind, you'll either have to carefully train your volunteers or do them yourself. If there are any wooden sills in your windows, don't forget to check that the barrier paper has been put on before you lay your mesh.

Weed-whacking/bale trimming. All walls should be weed-whacked and straightened prior to hanging reinforcement wire please wear protective glasses, and a respirator for this very dirty job! Generally speaking, it is better to do this job wearing long sleeves and pants, or you'll end ^

18.36: This wall is meshed, masked and properly flashed. It's ready for the plaster starting to cover it.

up with itchy bits of straw all over you! It might be a good idea to have a few different volunteers (maybe just the owners?) do this job as it is quite a hot job, and can be unpleasant in the heat of the summer. On the other hand, it can be quite satisfactory to do this job, with a noticeable difference in the shape of the house as the shagginess of the bales is now looking nice with the new haircut.

Cover and mesh wooden elements. Exposed wood surfaces to be plastered that are wider than 1.5-inch should be covered with house wrap or painted with slip coat, then covered in plaster lath (diamond lath works best). If you can push some straw in behind the mesh, even better. This helps prevent shrinkage cracking of the plaster as it hits a different substrate.

Plaster stops and drip edge. Plaster stops must be installed around doorways, windows, and at the top of the bale wall where needed. These can be temporary strips of plywood, 1-by-2s, permanent flashings, or trim boards. Drip-edge flashing must be installed above windows and doors, and below windows if no other drip sill provisions have been made. Generally, plaster stops of are ideal.

Electrical boxes. Electrical boxes properly installed %-inch proud of the surface of the bales, with vapor barrier hats behind, and surrounded by, diamond lath well fastened to the box and the bale wall. Airtight masonry (or R-2000) electrical boxes truly are worth the bit of extra money they cost. They don't require site-made vapor barrier hats, and they have a flange that acts as a natural plaster stop.

Braces, cabinet reinforcement. Extra bracing, if required for installing cupboards, etc., should be placed in appropriate places on walls, preferably before reinforcement mesh is hung (you can imbed a 2-by-4 or 1-by-4 into the bales as you are stacking them, or you can install vertical 2-by-4s that run from the bottom to top plate (keep in mind that these will mean notching or custom-fitting bales around them).

Reinforcement mesh. If you have to use reinforcement mesh for your building, we recommend using a strong plastic mesh rather than metal fencing or chicken wire. It's much easier to work with. Reinforcement mesh should be hung inside and out, stapled or nailed frequently and securely to top plate and bottom curb. We recommend using air staplers for this job. 18.37: They drive larger staples. If you choose to use a hammer tacker or hand stapler, make sure you have The heaviest several heavy-duty versions. You should work in teams of at least two people for installing the mesh, cabinets need and if you are using metal reinforcement mesh, you may need more workers. Pull the mesh as taut wood as humanly possible. You can either stop at the window openings or continue right over them, sta- strongbacks pling the mesh to the framing and cutting out the parts covering the window later. The tighter you under the can get the mesh now, the less fiddling and stitching later! ^ plaster.

all the plastering provisions in the local building code or that you at least use some kind of mesh reinforcement, such as:

• Plastic mesh. This is our favorite type of mesh. It is the most convenient to install because it comes in 10-by-330-foot rolls, light enough to be handled by one person, and may be cut with a knife or scissors. It is also less expensive than most wire meshes, but may be more difficult to locate, as it is not a commonly used product.

• Diamond lath or expanded metal lath. This is a heavy-duty,galvanized mesh that is commonly available. It is not used to mesh entire buildings but offers excellent support where there is no straw for the plaster to bind with (over wooden surfaces, vapor barriers, flashings). It can also be used to form consistent curves at windows, doors, and corners. This mesh is also placed around electrical boxes to help fasten them to the wall and keep them secure. Use a metal cutting wheel on a circular saw to cut this mesh, as it is long, slow work with hand shears. Using diamond lath over the entire wall would actually weaken the walls by interfering

Reinforcement mesh should not extend beyond the bottom curb or above the top plate. It should be neatly and tightly installed, with any extra mesh cut off. Little pieces of mesh sticking out in these places will remain forever sticking out of the plaster, looking ugly and allowing potential air/moisture penetration.

Pay attention to the mesh at the bottom of the wall where it sits on the flashing: it really needs to be fastened well here, so that it lies flat and flush with the bottom of the flashing.

Stitching the mesh. Reinforcement mesh needs to be quilted or sewn so that it sits flat against the bale wall. Stitches must be tight. No lengths of string should hang down on the wall; after tying off the stitch, cut off excess twine.

After all the other rather labor-intensive jobs involved in getting your walls ready, this is a much calmer, somewhat meditative one. Look for spots where the mesh is sitting far from the wall and place your stitches there. Watch for the needles coming back through the wall towards you; stand back far enough to make sure you don't get jabbed!

Windows. Your decision about whether to install the windows prior to plastering or afterwards will depend on the kind of finish you want. If the plaster is intended to finish against the sides of the window and/or cover a built-in flange, they must be installed first. If the windows will be finished with wood trim, they can be installed after plastering.

Flashings. The flashing at the bottom of the wall can be installed prior to stacking bales, but there is a chance the flashing will get a bit dinged at the bale raising, so most people install it after the bales are in place. It gets attached to the curb with screws or roofing nails. Make sure that the flashing is actually installed so that it will do its job think like water! If the flashing is sloped towards the house, it won't be helpful!

Masking. Windows, doors, and exposed framing lumber must be masked with plastic or cardboard. Use a quality tape to fasten covering to them; cheaper brands will come off, leaving windows exposed and vulnerable to plaster droppings. When you are masking your windows, you need to decide where the plaster will end leave a 1V inch bare for the plaster on the outside of the window frames if the plaster is to cover over them. It is difficult to remove tape from window frames if it is buried under the plaster! ^

with the bond between plaster and straw, since it is difficult to push the plaster through the narrow holes with any force.

• Welded steel fencing. In seismic areas, or where prescribed by code, use a welded steel fencing. Typically available in 2-by-2-inch grid, this is a strong mesh, with wire gauges of 14 to 18. Use bolt cutters for cutting this mesh. It can be expensive to cover an entire building with this mesh, so adjust your budget for this choice.

• Chicken wire. We don't know why some people still insist on using chicken wire on bale buildings. It is difficult to handle because it won't stretch tight or sit taut over the straw; it's awkward to cut and it's not inexpensive.

It has been standard practice to cover any exposed wood with tar paper prior to meshing and plastering.We'd recommend against this. It's better to isolate the wood and plaster with air barrier or plastic. Another option is to paint the wood with a runny slip coat of your plaster. This puts a coating on the wood so it doesn't suck the moisture out of the plaster and gives the plaster a better surface for bonding. The

Flashing needs to be masked; again, set the masking tape back a / inch, but don't tape the flashing too far in advance of the plastering, as it can be difficult to remove after baking in the sun for a long time. Same goes for the windows! If you have a dedicated cleaner, you can skip masking the flashing. Never skip masking windows, doors and thresholds!

Finished floors need to be masked as well. Set the floor tarps back half an inch from the bale curbs.

Plaster will be spilled during the process. The time you take to mask will be paid back in time spent not chipping and scrubbing cured plaster from surfaces. Remember that the tape lines you create will define the edges of the plaster; if you want it straight, tape it straight.

Scaffold setup. Scaffolding should be erected 8 to 12 inches away from the walls, with the ladders on the outside, except for the top row. Scaffolding should be ample enough to surround house; sky jacks or scissor lifts can be more economical than scaffolding on large two- or three-story buildings.

Site. Trenches, holes, and excessively rough terrain slow things down. Have the site excavated, if possible, to provide a flat, level, safe terrain for scaffold placement.

Extra time spent on prep really pays off; the finished walls will reflect the effort. So, good luck, hang in there, and hopefully you've been able to cull a keen group of volunteers to help with all of these tasks.

— Tina Therrien, The Last Straw, no. 45, 2004. ■

18.38: The quality of masking of windows and doors dictates the quality of the finish. Good scaffolding helps plasterers do their best work.

18.39: Mesh goes on quickly with an air stapler and is held secure by long staples. Note that the mesh is pulled tight enough that is lays flat even before it's quilted.

best option of all is to staple some loose straw over the wood so that the plaster is not applied to two different substrates at all.

All mesh will need to be securely fastened to your top plate, foundation curb, and window and door bucks. It can be stapled or hung from nails that have been driven at an angle into the top plate at 6- to 12-inch intervals. If the staples shoot through the mesh, turn down the air pressure. Once attached, the mesh can be pulled taut at the bottom of the wall and fastened securely. In some situations the mesh will install better horizontally.

If you are using a mesh with large holes, you will need to double it over wooden, metal, and concrete elements, or else fasten heavier diamond lath over top. Be sure you allow the doubled or heavier mesh to extend into the straw wall by about six inches. This can be useful where you expect the wall to take some punishment, such as around doorways and exposed corners, and where cracking is most likely, such as at the corners of windows and doors.

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