Surface preparation Your wall needs to be very flat. This plaster mix won't fill gaps, so make sure the wall is at a finish quality of level 4 or 5 as understood by drywall and plaster contractors. If you try to level an area by applying a thick coat of this mix, you will spend the rest of the evening babysitting the area, frequently recompressing it to prevent cracking.
Mist the wall with water before applying the plaster. If you don't, the water will immediately be wicked out of the wet plaster, causing it to stick to the trowel on the smoothing pass seconds later. The moisture in the wall also aids adhesion.
Don't apply the lime plaster directly over gypsum drywall. It will crack and chip off in a few days. You will need to apply a quartz primer first, and ideally a skim coat of gauged lime plaster over the whole wall. I know this because I tried various types of wall board as test panels.
Application technique Basically the plaster is troweled on in very thin coats. Think heavy-paint thin. It is the variation in trowel techniques and aggregates that produces the varied finish effects. Since the permutations of techniques are endless, consider the mechanics of the process to guide you to your desired finish. Ultimately, though, this is an art that requires practice. If you are easily discouraged, spend the money on an experienced professional applying a proven product.
My observation is that controlling the finish is all about controlling imperfections. When you trowel on the plaster, the resulting surface has minor imperfections in the surface height. Subsequent applications of plaster will fill in the low areas and may even leave high areas exposed. The variation of exposed layers and tapering of thicknesses creates variation in tone in the finished surface. Burnishing creates the variation because higher burnishing pressure deepens the tone. Higher points in the fluctuating surface get more burnishing pressure and deeper color, even if you used only one tint in a perfectly mixed plaster for all the layers.
We can affect the imperfections by controlling how we use the trowel, and also by the aggregate in the plaster. The length of trowel passes changes the size of the area of similar imperfections, so it changes the density of tonal variation. The angle of the trowel changes the pressure at the working edge - higher angles have higher pressure thereby exposing more of the underlying layers. A flatter trowel will float more wet material aver the surface. The stiffness and size of the trowel used controls pressure as well. The direction of the trowel pass will affect how that layer reflects light - almost as if it changes the orientation of the marble particles. Larger aggregate creates larger variations in the finished surface, and also increases the abruptness of those variations. Abrupt variations lead to more contrast and even the illusion of lines and hard edges.
Use short, crossing strokes with a fine aggregate plaster, and the result will be a dense but subtle variation in tone. From a distance the color will look uniform, but will come alive like paint cannot. Use fine aggregate layers over a course aggregate base coat along with pigment changes, and you can achieve high contrast like that from the exposed sedimentary layers in a slate or shale.
Do be careful to not overwork the underlying layers. As the moisture evaporates and wicks out of the plaster, it will begin to burnish with the trowel. That will adversely affect adhesion of subsequent layers.
Burnishing This is when the surface comes to life. Referring to the photos in my previous post, that wall was a pretty uniform light drab brown before burnishing. Almost all of the tonal variation appeared during burnishing. Regarding pressure, one pass with a few pounds of force on the trowel results in 50%-75% of the surface taking on a sheen. The task is tedious, not strenuous.
I use a flexible pool trowel that allows me to work in a circular motion. A stiffer trowel dictates that it be dragged in one direction per pass, otherwise it digs into the plaster. Either way, I start with a very light pressure to knock down the high spots, then increase pressure until I get the desired depth. If the surface has a low spot that defies burnishing, use a little 600 grit paper to level the area first.
Perhaps it is the type of lime, use of sharp sand, or lack of finesse, but I have a little difficulty burnishing before the surface is completely dry. Most of an area will burnish fine, but then the trowel will stick or catch, pulling off a small area of plaster. Patching is easy, but I prefer to burnish the dry plaster. The main drawback to burnishing dry is that the high spots are much harder to work down, so sanding will occasionally be required to get a uniform burnish.
One more note about materials - did you know that the marking "chalk" used on sports fields is many times actually marble dust. I've found 50 lb bags of Imery's marking powder (marble) for under $10.
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( 3 / 309 )Well, bummer. I had a long post typed in but when I hit submit, my session had expired. DoOver.
Here is a picture of the results from my homemade venetian plaster:
The base layer uses 1/2 part masons sand in place of 1/2 part of the marble dust. In retrospect, course marble dust would probably work better if I'd had it. The sharp silica sand tends to get grabbed by the burnishing trowel, and can "pop" or scratch the surface if too much pressure is applied while burnishing. You can also see the vertical lines caused by the wet trowel chattering over the sand grains. The lines are coloration only, and can't be felt by touch. We like the effect.
The color is "BROWN" liquid integral concrete pigment from Menards. I added the pigment last after everything else was well mixed. I did not fully mix in the pigment, but left a little variation in the bucket. The base layer was textured slightly with a natural sponge roller.
The second and third layers used all marble dust for the aggregate. I tweaked the pigment levels about 50% up and down in the top layers to get contrasting shades. I mixed the pigment well for these layers.
As the following picture shows, the homemade VP burnishes easily. I used a thin stainless steel pool trowel for burnishing. This trowel is very flexible, and does a better job of burnishing low areas. I only spent a minute to work this 2'x2' area into a nice shine. As you can see, some areas are a touch low, and don't get burnished right away. A few passes with 600 grit sandpaper will smooth things out enough so burnishing has better coverage.
Enough with that, here is the recipe:
Lime Putty (1 part) Make this by sifting hydrated lime powder into distilled water until it won't accept any more (dry powder floats on the surface for more than a minute). Cover the container and leave it sit overnight. The next day, the lime will have settled, so add more dry powder to refusal. Repeat until a rest overnight no longer results in appreciable water on the surface (maybe 3-4 repetitions). Now let it sit for a few weeks covered airtight in a cool place. Water and a thin floating crust will form on top of the putty. Pour this off and mix the putty well. Either use the putty immediately, or replace the 1" of water on top of the putty and reseal the container for long term storage. It only improves with age. (Basic method described to me by The Plasterers Arms over at FauxForum)
I used Western Miracle Lime. Yes, it is high magnesium dolomitic lime. No, it doesn't appear to detrimentally affect the plaster.
Marble Dust (1 part) I use Imery's, which is available from various distributors nationwide (they make cultured marble sinks with it). It is also sold as pool aggregate. Get a variety of gradations from medium sand (0.5 mm or so) down to the finest sold. $50 should get you several 50-100 lb bags.
Linseed Oil (~1/10th part) Just plain old boiled linseed oil from the paint store will do fine.
Olive Oil Soap (a smidge) I use Kiss My Face brand from the local natural foods store. Prepare the soap by shaving it and combining with an equal part of distilled water. Melt over a double boiler. The consistency after cooling should be like grease. A smidge is two tablespoons per gallon of plaster. (Method described by Eli Lucero at FauxForum)
Lime-safe Pigment I use the liquid integral concrete pigments. These won't fade in the presence of lime. You can add up to 15% by weight of lime, or 5% of the overall plaster batch weight. Fresco pigments should work as well.
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( 2.8 / 271 )I removed a rib capstrip that had been destroyed when I was removing the rudder skin. I fashioned a new one from spruce and glue it in place. I also cut out a new rudder skin that conforms with the plan shape better.
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( 2.9 / 476 )Drilled the holes and glued them in.
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( 2.8 / 355 )Based on design calculations for the strut and root attach fittings, I had two choices - use five 1/4" bolts in bare wood, or use three 1/4" bolts in 1/2" phenolic bushings. Since drilling holes in the spar makes me nervous, I went with the option that required less drilling. The problem was that I did not have 1/2" phenolic rod - only 3/4". A few minutes with a lathe solve that issue, and I am now ready to install the bushings into the spar.
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( 2.9 / 297 )I got a shipment of GL2 birch ply that should keep me busy for quite a while. I have been trying to find an inexpensive source for the plywood, and I think I've done the best I can do - Plywood and Door Manufactures Corporation in Chicago, IL. They sold me the 1/16" 50"x50" sheets at $23 each, plus shipping. With the freight, the cost was still well below that charged by the usual suspects. I had the plywood one day after I ordered it.
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( 2.9 / 380 )I glued in the leading edge stringer as well as an additional lamination on the wing tip bow. The reason for the extra lamination was that after shaping the nose area of the tip bow, there wasn't enough area for the leading edge skin to attach. The extra 6 inches of lamination along the underside of the leading edge gave 1/4-inch of glue area for the skin after shaping. That should be sufficient for the low stress joint.
I am trying a new (actually old) adhesive - Weldwood Plastic Resin. I really like T-88, but it isn't available locally. I can get it in St. Paul, MN at Rockler, but they only carry the very expensive 8-oz. kit. I can currently get WPR at the local Ace Hardware store, and it is MUCH cheaper. I think the plastic resin works fine, though I can see where it would be unforgiving of gaps.
Speaking of locally (well, kind of local) available products, I stopped at McCormick's Lumber in Madison, WI this weekend to get some 1/16" birch plywood. They were out of the plywood, but they did have a very nice selection of Sitka Spruce. The quarter-sawn rough-cut boards were 1"x9" in lengths from 14' to 18'. I didn't have to go into the stack more than a few boards to find one that will make some nice longerons.
Yes, the spruce is more expensive than the lumber at the local lumber yard (we do still have a lumber yard in Eau Claire, in addition to Menards) - but I haven't had much luck finding wood that I would make a spar or longeron out of. The structural grade douglas fir at Lyman Lumber was one exception - I found a few 2x10s that I could have used. Each timber could have yielded a couple one-piece longerons or caps, maybe double that with scarfing and laminating. That douglas fir was better than half the cost of the nearly perfect spruce - not worth my time to save so little.
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( 2.9 / 179 )I sprayed the leading edge ply with near-boiling hot water to soften it, then used a dozen cargo straps to pull it into position around the leading edge ribs on the wing.
The radius is pretty sharp for the 1/16" bias-ply birch. It took a fair amount of coaxing to get the skin tight to the ribs, especially from 2" to 6" back from the nose on the top. In the image above you can see where I needed to use some oak boards under the straps for extra pressure in that area.
On the strut-braced wing with two struts per wing, the leading edge is not normally load carrying - the chordwise moment is directly carried by the struts. So why use the expensive 45-degree plywood? The primary reason is because the bias-ply holds shape better between the ribs with less tendency for warpage. The other reason is that it does offer some degree of structural redundancy. Even though the skin cannot resist the moment from all the design flight loads, there is a good chance that it would be sufficient to resist 1G loads in the event of a rear strut failure.
1 hr.
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( 2.9 / 154 )I cut and fit the nose stringer. The 12-foot stock I had was just a few inches short of extending from the root rib out to the wing tip bow, so I scarfed on a short extension.
I also ripped the 45-degree birch ply into wide strips for the leading edge. These strips were scarfed end-to-end to make one large piece for the leading edge skin. The plans call for two butt joints in the leading edge skin over heavier nose ribs with cap strips. Aside from the PITA scarf joints, I feel that the one piece leading edge skin will be easier to build and will form a smoother leading edge.
It is interesting to note that the 45-degree birch ply has a very pronounced sheen that the 90-degree ply does not. The 45-degree ply is mil-spec, whereas the 90-degree stuff is GL-2. I'd wager that the mil-spec material is more sensitive to needing the surface scuffed. Testing that I did with the GL-2 ply and epoxy didn't show much difference in bond between scuffed and un-scuffed.
2 hr
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( 3 / 146 )With a little gentle application of a heat gun to soften the glue along with a sharp razor, I had the starboard skin of the rudder removed in about a half hour. As I suspected, the interior of the rudder had not been varnished. Strictly speaking, that enclosed area doesn't require varnish. However, varnishing the interior does help with dimensional stability of the plywood skin as humidity changes, thereby preventing oilcanning and warping.
I am now able to access the trim actuator. It is a simple powered lead nut salvaged from something. The linkage to the trim horn consists of a leadscrew on one end that threads into the actuator. My problem with this setup is that there is no limit to the motion. In a trim runaway situation, the actuator would keep going until something broke - I'm fairly certain the motor has sufficient torque. This will be replaced with a standard MAC servo or equivalent.
I removed the light and associated wiring. I plan to use an LED tail light, but I haven't decided which one to use yet.
I also removed the sharp leading edge piece. Once the new skins are in place, the plan-specified rounded leading edge will be shaped. The rest of the workmanship appears above average.
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