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Ok, folkses. I've seen enough about this to post a not so humble opinion. After dozens of 4x8s and similar sizes in varying thicknesses, and a multitude of very large mural carvings in 4" to 8" material, I can definitely state that you MUST back every freestanding carving/sandblasted in HDU. The exception will be (of necessity) a double sided with rods inlet into the center of the sandwich. If I might qualify that last one, we ALWAYS laminate a sheet of marine grade plywood in the center in addition to the mounting bars/rods. In addition to that we typically use 2"x2"x1/4" steel angle running the entire length of the large murals. These are called "strongbacks", and our mounting system incorporates matching rails on the posts or wall. The "GPI" Mural is so mounted, and that's on a flat wall. In addition, you must also back any HDU signage that's mounted to a flat wall no matter what the size.
I've seen and experienced enough of the 4x8 variety having to be replaced or repaired because of a sharp impact to some point of the face resulting in an instant crack. 15# and up will flex a minute amount before cracking, BUT.....but a sharp impact will crack it every time. Case in point: A local sign shop who buys HDU from us periodically asked for mounting advice. We gave said advice with the explanation and he departed forthwith, some $$s lighter. Two weeks later........ "Hey! The damned thing cracked! All that happened was a golf ball hit it on the course and it cracked right in half! What's the deal?"
He hadn't taken the "deal" to heart. I sold him another 4x8 of Precision Board and he stopped at the lumber yard to buy a sheet of MDO. A golfer's hook shot made me a few more bucks.
In every single case, we ALWAYS laminate first. Clean the Precision Board and mist with water, mist the rough side of the plywood, crosshatch with PB240 adhesive and clamp lightly. In the dead center Latigo uses a large body washer and a screw sufficient in length to go into the plywood backing, lightly cinched down. Use weights instead if you must. NOW you can cut to size or configuration. I don't care if its 6" material. Back it. You'll get no warping or cracking with an impact.
I give classe in this medium, folks. If you're a newbie, pay attention. If you're convinced you'll never back a freestander, explain your logic and how many you have out there before you tell me to "go back myself"
School's out!!
k31
-------------------- Pierre St.Marie Stmariegraphics Kalispell,Mt www.stmariegraphics.com ------------------ Plan on knowing everything before I die and time's running out! Posts: 4223 | From: Kalispell,Mt 59903 | Registered: Mar 2000
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well i for one will listen! i'm extremely cautious and trust nothing...my luck sucks so i'll do whatever it takes to secure my position. i don't like doing things twice and the word refund isn't something i want to hear unless i'm on the receiving end. thanks for sharing your wisdom!
-------------------- Karyn Bush Simply Not Ordinary, LLC Bartlett, NH 603-383-9955 www.snosigns.com info@snosigns.com Posts: 3516 | From: Bartlett, NH USA | Registered: Jan 2001
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Yo mama, Joey Thanks, Karyn. ....and, in response to an emailed question.... If your panel is to be 12' long, cut your plywood into two 6' lengths so that you have a 2' overlap of the backing. Same misting, crosshatching with adhesive, etc. If you're into a 5, 6 or 7' height by 16'or larger, piece the backing with overlaps on the Precision Board. This size mural does require strongbacks or a similar reinforcing/mounting system. If we end up doing a meet in Lost Prairie in '04 there will be a full 8'x20' or larger mural demo.
-------------------- Pierre St.Marie Stmariegraphics Kalispell,Mt www.stmariegraphics.com ------------------ Plan on knowing everything before I die and time's running out! Posts: 4223 | From: Kalispell,Mt 59903 | Registered: Mar 2000
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On 4x8s and smaller we use 5/8ths minimum here. On larger murals we use 3/4". I prefer not to hear about them once they've left the shop. On the GPI Mural we used 1' plywood and the Precision Board was 6 thick.
k31
-------------------- Pierre St.Marie Stmariegraphics Kalispell,Mt www.stmariegraphics.com ------------------ Plan on knowing everything before I die and time's running out! Posts: 4223 | From: Kalispell,Mt 59903 | Registered: Mar 2000
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Ok Prof. Peirre, A few questions if I may? (Disclaimer: not trying to be a smartass here or argue with Pierre or any other such nonsense … these are genuine concerns on my part.)
I’ve always been concerned with this sort of lamination because of the inherent differences in the materials used. Do not HDU and MDO have different rates of expansion and contraction? I’d assume that they do since they are completely different materials. So, if this is the case, would not the stresses involved during said expansion and contraction be detrimental to the integrity of the sign?
I keep thinking about a science lab class where we took a strip of metal that was composed of copper laminated to another white metal (Tin or aluminum maybe? Cut me a break this was in something like the 6th grade) and gently heated it. The thing curled up like a pig’s tail due to the differences in the expansion rates of the two materials. My thoughts then, lead me to believe that something similar could happen with the laminated HDU/MDO. I’m thinking that the finish along the edges could be compromised and crack at, or near the joining of the two materials as they move against each other.
While we are considering the edges; what methods and materials do you suggest to finish the edges? The MDO must obviously be filled and the edges sealed, no?
Thanks for your time and input.
-------------------- Jon Androsky Posts: 438 | From: Williamsport, PA | Registered: Mar 2002
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Johnathon, two quick answers. With some 90 carvings/murals under our belts, we have yet to experience a delamination. Expansion of either of these substrates is so minimal as to be non-extant. The PB240 permeates both the Precision Board and the raw wood. Sealing the plywood edges? Yup. We have a positive, fail-proof method. You'll have to go to our website to read about it. I'm no longer a merchant here and not allowed to expound on the product.
Back when we used to discuss Pelucid openly, my intent was to share our discovery with other sign shops. We were actually selling it to letterheads at dead cost. No markup. After the webmaster insisted that I become a Merchant or quit discussing it, I became a Merchant. It cost me $365.00 a year for the pleasure of supplying it to letterheads at no profit. That got old real fast, so I did not reenlist as a Merchant. The logic of all that escapes me, but I won't discuss it here any longer. Not if its going to COST me money to help letterheads.
Go to my website if you want to read about how we handle carvings and substrata.
k31
[ August 12, 2003, 04:53 PM: Message edited by: pierre ]
-------------------- Pierre St.Marie Stmariegraphics Kalispell,Mt www.stmariegraphics.com ------------------ Plan on knowing everything before I die and time's running out! Posts: 4223 | From: Kalispell,Mt 59903 | Registered: Mar 2000
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Maybe charging us a little more for the Pelucid would allow you to be a merchant again. Would hate to see it kept a secret. The knowledge of Pelucid and other things on the BB are worth being a resident. Thanks for introducing me to the stuff. Check is on the way.
Thanks Mr. P!
Debbie
-------------------- Debbie Posts: 674 | From: USA | Registered: Feb 2001
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Thanks, Debbie. In order for us to afford the Merchant Status we'd have to sell 5 times as much pelucid as we did the year we were a Merchant. There are so many "computer only" shops here on letterheads that our market with actual paint shops is very limited. The vinyl shops won't take the time to overcoat one of their signs. Even if they wanted to they're in such sterile, office type settings that it wouldn't be practical for them anyway. We're a dying breed, Deb. I'm so very fortunate that my kids are keeping the fire burning here in Montana. Long live the brush and chisel!!
heh.............
k31
-------------------- Pierre St.Marie Stmariegraphics Kalispell,Mt www.stmariegraphics.com ------------------ Plan on knowing everything before I die and time's running out! Posts: 4223 | From: Kalispell,Mt 59903 | Registered: Mar 2000
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Long live the brush and chisel!! 
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