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I started doing mosaics made up of thin scrap aluminum.

This question is about my first first mosaic 'prototype' that I am doing which measures 28 x 34 inches. The aluminum scrap material weighs very close to 3 pounds.

I enjoy building these, but it is a money making venture, so I need to keep the cost low and aesthetically, I like a minimalist frame. So, the design constraints are:

  • Keep the cost under $20

  • Build time: <1 hour with practice (simple home garage workshop, tablesaw and tools)

  • Aesthetically simple design

  • 28" x 34" mosaic (plus maybe the frame border)

  • Weight of mosaic pieces: ~3 pounds plus adhesive

My first thought was to glue the pieces to to ~5/8" BCX plywood painted black (BCX is sanded smooth on one side); I like the simple look of it, but at 28" x 34" (plus maybe a border) I am afraid it will warp. I am open-minded and will consider any material, not just wood.

UPDATE: The scrap pieces used in the mosaic are small (2 inches or less), so some type of backing will be necessary.

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computercarguy's answer covers a lot of territory. I'll supplement that with a few other ideas.

  • It sounds like the artwork has an "upcycled" appearance, being made from scrap pieces. You can carry that theme into the frame by making it out of scrap materials, also. For example, a simple picture frame made from pallet wood.
  • You can stick with the metal theme by making a simple frame from metal, possibly recycled. A few possibilities: metal tubing (square or round), angle iron, simple wrought iron design, or rebar bent into a rectangle.

    Joining aluminum to another metal, like steel or copper, it would be a good idea to keep the metals out of direct contact because they can interact and corrode. You could do that by applying a finish to both surfaces first, or use a layer of a material like epoxy to join the surfaces. If you screw the art to the frame, you can separate the metals with a thin plastic washer that you cut from something like a clear PETE plastic bottle like soda or bottled water comes in. If the sculpture is mounted to a backing board, you can avoid the issue by fastening the backing board to the frame.

  • An alternative is to go in the other direction with the frame. If you make your own, you can make a pretty nice frame with under $20 in materials. It doesn't need to be fancy, just precision-made with a nice finish. Coupling art made from upcycled scraps with a fine frame can make the result look more upscale.

  • You don't necessarily need a backing if the components are strong enough to not bend under their own weight and are securely joined. Pieces like you describe are often done without one. You can do it with no backing or frame, or no backing but fastened to some kind of frame at a number of points around the outside edge. You can get ideas from a place like Touch of Class; Metal Wall Sculptures.
  • If the materials in the sculpture aren't strong, or might be subject to handling, another approach is to put the finished piece in a shadow box. It might be enough to just use an open, box-style frame. Or you can add protection by covering the front with glass or clear plastic.

    A shadow box also introduces the ability to augment the art with lighting. You can embed LED strip lighting into a shadow box frame.

  • Another idea for a backing -- a mirror. You can build the sculpture by gluing the pieces to the mirror, or glue the finished work to the mirror. The mirror's reflection can add a degree of complexity to the appearance.

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Wood

BCX shouldn't warp on you, especially at 5/8" thick. It's rated for outdoor usage*, so as long as you treat/finish it correctly, you shouldn't have a problem with it warping. You could probably get away with 1/2", depending on how much weight you actually add with the mosaic.

As far as finishing/treating it goes, that depends on how you are using it. Gluing things to one side will usually seal that side, depending on the glue you use. Using a standard wood glue might not stick to your mosaic pieces and may not seal that side, but using a silicone or epoxy glue will seal it, while also likely sticking to your mosaic pieces.

Simply painting the wood should be enough to seal the edges and back side. You can also stain and use other finishes, like shellac or varnish, if you want a different look to the back. If your artwork is going to be outside, make sure the finish is rated for the normal moisture and temperature range in your area. Example considerations: don't use an interior paint for an outdoor exhibit, don't use a finish that isn't water resistant if it's going to see a lot of precipitation or humidity, don't leave bare wood in a low humidity and high heat desert, and don't bother with an expensive or time consuming finish for an indoor exhibit unless you really want to.

You can get chemically treated plywood for outdoor use, but paint and glues might not stick to it. And if it's chemically treated, you don't want to paint or seal all edges.

*Types of Exterior Plywood

CDX is the most common exterior plywood grade. It comes in 3/4-, 5/8- and 1/2-inch thicknesses. Appearance stamps on plywood range from cabinet-grade (A) to construction grade (C and D). Exterior plywood carries an X stamp, which identifies it as suitable for use outdoors. Beside CDX, you can also find better grades, such as ABX, ACX and even BCX.

https://www.hunker.com/13401518/what-types-of-plywood-can-be-used-outdoors

Metals

You can also think about using a sheet of aluminum or steel, although that'll likely cost you more than the plywood. I'd suggest 1/4" thick for rigidity purposes. You might be able to get away with 1/8" or 3/16" thick, which should be less expensive, but then you could get into more issues with expansion and contraction of the piece warping it, if it's going to see extreme temperature differences.

With steel, you'll still need to seal the unglued side, since it'll rust even indoors. That's as simple as painting it, most of the time. If you want a better look or a more durable finish, you can even powder coat it. Aluminum doesn't need a finish, but it can look better if it does. Or you can do a wide variety of finishing to the aluminum itself, such as brushing, scuff sanding, or polishing. Aluminum can also be anodized a variety of colors.

With both steel and aluminum, to reduce costs, you can use expanded sheets, but then you risk warping again, as well as the glue not having as much surface area to grip. And if you want something that gives more surface area, don't really care about costs, and has a really neat pattern, you can use diamond plate.

Even 1/4" steel and aluminum can be cut with a circular saw with an abrasive disc, an acetylene torch, or plasma cutter.

Plastics

There are definitely reasons to use a sheet of plastic for your backer. It can make it light weight, transparent or translucent, weather resistant, chemical resistant, warp resistant, and a few other things, too. The problem with plastic backing is that it's harder to find glues that'll adhere to plastic and other materials, such as metals. It's not impossible, but they are usually more expensive and may not work as well.

Even though plastics won't warp from humidity, they can still warp, or even crack, due to temperature. Many plastics are stronger than glass, but they still tend to have properties similar to glass. A piece of polycarbonate is much stronger than acrylic and many acrylics are much stronger than glass when it comes to an impact, but due to age and high heat, can turn yellow or become brittle. There's outdoor rated plastics for signs, but they cost more, too. Outdoor rated plastics may also be harder to find and when you do find them, you might only be able to buy them in 4'x8' sheets.

Plastics likely won't need a finish, unless you want to protect them from UV or reduce glare, and even then, you can sometimes get it from the manufacturer with that coating. Outdoor plastics usually have UV coatings on them already. Plastics with a P95 or P99 coating have an anti-glare coating on one or both sides. Frosting is also an anti-glare treatment and has a completely different look, like frost on the grass in your lawn on a chilly winter morning. The other (P95 and P99) coatings are clear and don't interfere with color or translucency.

For the size you're looking at, 1/4" thickness might be all you need, but 5/16" to 1/2" might be better to add rigidity. Plastics tend to cost more linearly as you increase the size and thickness. A 1/2" piece of acrylic will usually cost twice as much as a 1/4" piece the same dimensions. However, 1/4" plastics are much more common to find and can come in a wide variety of colors, while most of the 1/2" plastics I've found come in clear, white, and black, with few exceptions, unless you want to spend some serious amount of money (over $500 for a 4'x8' sheet) to get it.

Believe it or not, plastics can be cut like glass or wood. You can score plastics and they will snap on the score line like glass. (And just like glass, if you don't do it right, it won't break on the score line.) They can also be cut using a finish blade on a circular saw. Some plastics, not all, can be cut using a laser cutter, although you need a pretty large area laser cutter for the size you're looking at. Many plastic suppliers will do cut to size for you, too.

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I would suggest to build the frame from slats of wood. You should be able to find them quite cheap.

You fix the support for the mosaic on the frame - "sheets" of fiberglass mesh. The mesh is very light and gives extra strength to the frame. Also cheap and easy to find.


For the frame itself, there are two options.

  1. Create a working frame from any wood (suitable to your needs), apply a decorative second frame on top.

  2. Create one frame (or buy it readily made to the proper dimensions, or order one), apply the mesh on it. Continue working with the "final" frame.

For option 2, you may want to protect the surface of the frame with something (e.g. kitchen plastic wrapping foil), to avoid damaging it with glue, scratches and what-not.

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  • +1 for fiberglass mesh because I was trying to think of method similar to how a 12" x 12" group of 1"x1" tile are held together. Gluing the moasic to a thin mesh would allow customer to choose a mounting frame that is to there liking when they order. If you get a chance, elaborate on "slats of wood". A picket from a fence is a 'slat' but so is a skinny little piece of lattice. – Roger Feb 19 at 18:22
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    @Roger: English is not my first language, and the word needed is indeed a "specialty" one. I used "slat" because it was the first entry in the dictionary, and the pictures showed something similar with what I intended :) Actually, any wood that fits the purpose is good - considering size, weight, quality... – virolino Feb 20 at 6:00

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