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Mounting and Strengthening Your Sign
Precision Board Plus HDU high density urethane is comprised of millions of tiny cells. These cells are created during the chemical foaming reaction process and, for the most part, are separate from each other. This condition creates a closed cell structure which does not allow anything to absorb into it and results in long life expectancy.
Due to the cellular nature, high density urethane must be treated differently than wood. Unlike wood, Precision Board Plus HDU Plus has no grain, it cuts easier, sandblasts and routs faster and smoother, plus carves quicker with less effort and wear on the carver. This cell structure, however, requires special consideration when mounting and attaching the sign.
Following are some of the more common mounting conditions and recommendations:
Signs mounted directly to the building wall.
Flat mounting directly to the wall is best accomplished using studs as hangers. The first step is to put the studs into the wall. Concrete nails work well in masonry walls, use galvanized nails into wood wall. After the studs have been installed the sign should be leveled and pushed back onto the studs with enough force to cause a small locating indent at each stud. Be careful not to damage the sign. Using these indents for proper hole location, drill a hole about 1 1/2 times larger in diameter than the stud. Depth of hole to be about 1 inch if thickness allows. Fill the holes with silicone caulking and slide the sign over the studs. Verify sign is still square, support as necessary, and let cure overnight before disturbing. Leaving the heads on the studs allows the silicone to grip the sign and keep it from being pulled off the wall during high winds. The silicone maintains a strong yet flexible attachment that allows for any wall movement. This type of installation also keeps from having to drill and repair attachment holes through the sign surface.
Do not attach a weight bearing screw or bolt directly into high density urethane. Because urethane has a cellular structure and doesn’t have grain, any weight bearing screw or bolt must have extra support around the threads. Hanging signs are typically hung from eye bolts that are either screwed directly into the sign or that are welded onto the supporting steel framework that is screwed into the periphery of the sign. Attaching eye bolts or weight bearing screws into urethane should be done by drilling a hole about 1 1/2 times larger in diameter than the eye or screw and about 1/4″ deeper than the length. Fill this hole with a very strong 2 part epoxy, such as EP-76 and insert the eye or screw down to flush with the surface. Try to keep the fastener in the center of the hole. Excess epoxy can be smoothed around the eye with any suitable tool dipped in mineral spirits. The epoxy holds the threads of the fastener and greatly increases the holding surface around the inside of the hole. This makes the fastener able to take much more load and eliminates the loosening effects caused by expansion and contraction of the fastener.
Strengthening wide expanses of high density urethane
Because urethane does not have grain, it also has less beam strength than wood. Wide, unsupported, expanses need to take this into consideration. This situation can be addressed in several ways depending on the design of the sign and the unsupported expanses.
Three possibilities are:
1. Add a metal band around the periphery of the sign and attach it as mentioned above.
2. Add a metal extrusion in the shape of a T along the entire bottom edge of the sign. A slot is cut up into the bottom edge of the sign that is slightly wider and deeper than the leg of the T. This slot is then filled with a strong, hard, two part epoxy, like EP-76, and the T inserted into it. The excess epoxy squeezed out of the slot welds the other two legs of the T to the bottom edge of the sign adding rigidity without any visual impact.
3. Bond urethane sheets to a center sheet of exterior grade plywood or equivilent. Make sure that the bonding adhesive is waterproof (i.e. PB Bond or PB Fast Set).
Sandblasting, Carving and Routing Tips
Sandblasting Precision Board Plus HDU HDU uses the same techniques as when blasting any lightweight wood. HDU is made up of millions of tiny cells so blasting is much easier and the sandblaster can get much closer to the work surface. Since HDU doesn’t have any grain, it is important to set the air pressure to about 40-60 psi at the pot. This reduced pressure still allows for fast blasting and subtle detail can be created during the process. The blasting medium, or grit, should be either aluminum oxide or medium grit silica sand. Be sure to also check out our blog post: How To Make A Sandblasted Precision Board Plus HDU Sign.
Carving HDU is almost the same as carving wood but it is much faster and easier. The same types of chisels, knives, and other surfacing tools can be used. It is easier on the carver however since it has no grain direction. Severe radius turns and angles are easier to do and the carving tools don’t have to be kept as sharp to achieve fast, clean removal. A more creative approach can be used when carving Precision Board Plus HDU because of the ease of removal. Precision Board Plus HDU substrates save time because they can be purchased in large, thick sheets which eliminates the need for laminating and planing.
Routing and cutting HDU is the same as wood only is much easier on the router or saw motor. Deeper passes and faster feeds are all possible because of the no grain cellular makeup. Precision Board Plus HDU is easily cut or machined with standard cutting tools. If you need help with cutter selection, go to Onsrud’s Router Bit Search Tool and search high density urethane.
Smooth Finishing and Priming with FSC-88 WB
- Sand any saw marks, heavy texture, or roughness from surface to be primed. Use 120 grit sandpaper.
- For deep cuts or abrasions, pre-treat by spot priming with FSC-88 WB, or in extreme cases FSC-360 WB knife grade filler. Allow to dry and lightly sand before continuing. To make FSC-88 WB a thicker consistency for use as putty, pour a small quantity on cardboard and let set until desired thickness occurs.
- Apply liberal coat of FSC-88 WB by brush, roller, or spray gun. When applying by brush or roller, scrub in the first coat to wet out the cells. Allow to dry to tack free – about 15 minutes, recoat as soon as surface changes from gloss to flat matte. Spraying results in faster drying because of the higher solvent content and spray atomization.See FSC-88 WB Product Data Sheet for spraying details. Do not sand between coats.
- Apply a second medium heavy coat of FSC-88 WB by brush, roller, or spray gun. Do not allow it to run. Allow to dry to tack free – about 15 minutes. When a totally smooth surface is not required, skip step 5 and go on to step 6. Do not sand second coat if proceeding to third coat.
- If required, apply a third medium heavy coat of FSC-88 WB. Remember: All sanding must take place in the filler before getting back to the original PB surface. Since Precision Board Plus HDU is made of millions of tiny cells it is impossible to sand the Precision Board Plus HDU smooth.
- Let dry over night.In areas of detail, i.e., relief cuts, vertical sides, and other hard to reach surfaces, allow the FSC-88 WB to dry a little longer. Use a brush wet with water to gently smooth out the filler. With a little practice you can use this technique to eliminate all sanding of these hard to reach areas. Let dry over night.
- Sand smooth with 120 grit sandpaper or 120 grit Drywall & Plaster sanding screens.
- Lightly sand with 220 grit sandpaper. FSC-88 WB is totally dry when no balling up occurs on sandpaper. If it does, let dry until it does not occur.
- For complete drying use a larger shop fan to blow across surface. Do not place item in direct sunlight as the FSC-88 WB might dry to quickly causing blistering in the primer.
- Wipe with tack rag and proceed with top coat system.