I've been constructing my double-sided hdu signs panels like this for the past year or so...for strength a 1/2" MDO core is sandwiched between two 1" pieces of hdu...as pictured...a 1/2" thick strip 2" wide is glued around the perimeter therefore totally encasing the MDO and keeping the core water tight...my fear is that the MDO might possibly expand inside the core due to heat and pop open a joint allowing water to enter...I have only one locally that I can check on...the glue joints are tight but it has not been very long in the weather...do you think I have anything to fear.
The method above is time consuming and maybe overkill...pictured below is a much simpler method which I think several of you guys are currently doing...of course the MDO edges are exposed and would have to be sealed...I would prime and use a paintable caulk on the edges...which method would you prefere and would you seal the edges on the bottom method with something other than what I have suggested.
[ December 18, 2009, 12:18 AM: Message edited by: Rusty Bradley ]
Posted by Sal Cabrera (Member # 1236) on :
Hi Rusty, I had done some signs just the way you mention, I do use gorilla glue to glued the materials and the way I seal the top of the sign with bondo auto body filler and the sides sometime with caulk but I prefer Bondo top and sides it dose sealed perry well, after I sand it to a smooth finish with my orbit sander,then following with two coat of bull's eye primer and finished. it is a little time consuming but it worth the effort. that is the way I do.
Posted by Bill Lynch (Member # 3815) on :
I don't encase the sides like that, but it looks good. We seal the edges with epoxy. I have two signs where the paint finish (gripguard) developed a few cracks. This occurred with a dark finish facing the sun, in colder weather. The first one I thought may have been from the paint being too thick. But after a second did exactly the same thing I'm wondering if it is from the different expansion/contraction rates of the HDU and MDO.
Posted by Rusty Bradley (Member # 6938) on :
I would like to use the bottom method this time because it is so much more simpler to build...but only if I can get a good seal on the edges...the different rates of contraction and expansion between MDO and HDU that Bill speaks of makes me wonder...wouldn't it be best to seal with something flexible as opposed to something that cures rigid...in other words seal with something that would move accordingly with the material to prevent cracking.
Posted by Rene Giroux (Member # 4980) on :
Hey Rusty, I understand your need to re-enforce the core of a D/F HDU sign panel. I did it your way a few times but now it incase a steel structure. Steel is dirt cheap, much stronger and you just fit the two sides of HDU one on top the other and use Gorilla or epoxy better yet, construction adhesive like urethane-PL in a caulk like tube.
The black lines illustrate the inner steel structure. I used 1"x2" steel tubing on the flat side so I only have to rout out 1/2 the thickness on both pieces. 3x5, 1/4" plates at the ends make a strong support between posts or anything else. I used PL glue with a bunch of screws on one side with the holes blocked out with Magic Sculpt.
Might be too late if you already started this one, but the next time... inner structure. For now, if the wood and the HDU are flush out, just seal with epoxy and paint.
cheers
Posted by Kelly Thorson (Member # 2958) on :
I make mine like Rene's. Makes it nice for painting a two sided sign as you can prop up the mounting brackets and flip.
Posted by David Harding (Member # 108) on :
West Systems has an epoxy called G/flex that bonds tenaciously and remains flexible.
Posted by Bill Lynch (Member # 3815) on :
Thanks David, I'm going to check that out.
Posted by Wayne Webb (Member # 1124) on :
I do mine like Rene's, except I use aluminum instead of steel.
Posted by Rusty Bradley (Member # 6938) on :
David...that sounds like what I need for this job...I'll check it out...thanks...you guys are the best.
Posted by Dan Sawatzky (Member # 88) on :
Rusty
If I'm doing cut out letters or smaller signs that need reinforcing I do it like you do... with MDO encased inside with no edges exposed. For larger signs I use a steel frame and do them like Rene does or more often with the steel armature sticking out the back rather than the sides making the mounting much more invisible for the most part.
While I may use a little more time and material our signs are finished and often textured all the way around. It makes for a quality product that separates us from our competition. I'm already the most expensive in town so price isn't a factor. Folks who truly want quality are prepared to pay for it in my experience.
-grampa dan
Posted by Dennis Raap (Member # 3632) on :
I also build ours like Rene have been for a quite awhile works great. Posted by Cam Bortz (Member # 55) on :
I've done them every way you can think of, and here's my experience (as opposed to opinion). 1. MDO, or even just regular exterior plywood, is fine for a core or backer. Seal the edges with Titebond III waterproof glue. The difference in expansion rates is negligible. Mostly I use plywood as a backer for a SF sign, in that I have material that will hold fasteners. 2. Steel. On DF signs I use steel flat bar, 1/4 x 1 & 1/2". I have the ends, where I want to mount the sign, sticking out (for a hanging sign they stick out the top about an inch). I also have a couple of pieces of the same stock going across the sign. To install the steel I route a channel on the back of one face, and bed the steel in the channel with epoxy. I have signs out there as large as eight feet long, between posts, that have done just fine for eight years or more. 3. Adhesives: I've used Gorilla Glue, flooring adhesive, Liquid Nails, you name it. The best and most reliable is West System epoxy. Gorilla glue is strong and reliable, but it's expansion pressure can force your panels apart as it cures, unless you use a LOT of weight or clamping. With larger signs I've gone so far as to sandwich the faces between MDO, lay the whole thing of the floor, and brace them with 2x4s between the floor and the ceiling joists. With epoxy you don't need to go through these shenanigans.
Posted by Doug Allan (Member # 2247) on :
where do you guys get your west systems epoxy?
I went to our Letterville merchant page, wrote a nice note introducing myself, & asking about making a purchase... never got a reply, wrote back a second & maybe a third time... no reply!
Posted by Rusty Bradley (Member # 6938) on :
Cam...am I reading that dimension right...the steel flat bar you use is 1/4" thick...that seems rather thin but if has worked for you I trust your experience...just want to know if I'm reading that right.
[ December 19, 2009, 11:41 PM: Message edited by: Rusty Bradley ]
Posted by Dave Sherby (Member # 698) on :
Doug, boat building & repair places almost always stock it. It's boat builders favorite epoxy.
Posted by Jean Shimp (Member # 198) on :
Rusty, For single face signs we use 1/2" thick PVC instead of MDO. You don't have to worry about sealing the edges on PVC. So far PVC has been working well for us in our climate which is not too far from you.
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