I have 2 Sign foam signs (30" X 55") glued to a 3/4" plywood center, for strength (sign is between to brick pillars)the paint keeps blistering on the top, my guess is the screws into the plywood are drawing in moisture. I removed the sign last year and sealed everything with PB's Hardcoat, repainted & re-installed. Well the paint is blistering again, I'm thinking of maybe an epoxy coat on the top of the sign? Any suggestions would be greatly appreciated. Thanks
Posted by Dale Feicke (Member # 767) on :
Do you have any pictures, Bruce?
This is just an educated guess, but I'm wondering if all the glueing, sealing and hardcoating is actually causing the problem by trapping moisture?
On various sandblasted projects I've done over the years, it has been advantageous to let things 'breathe'...
Sounds like somehow the plywood is absorbing moisture from somewhere. If it cannot evaporate, it will find other ways to get out, and/or it could cause the wood to swell.
[ May 03, 2010, 12:31 PM: Message edited by: Dale Feicke ]
Posted by Wayne Webb (Member # 1124) on :
Not being mean but, why would anyone use something that will expand/contract, hold moisture, outgas, and potentially rot inside an HDU sign? I use only aluminum extrusions in my HDU signs and have never had a problem.
Posted by Joey Madden (Member # 1192) on :
I must agree with Wayne Webb and I would like to hear the answer on why would anyone use something that will expand/contract, hold moisture, outgas, and potentially rot inside an HDU sign.
Posted by Glenn Taylor (Member # 162) on :
I do the same as Wayne. Aluminum extrusion is the best way to go, IMHO.
Posted by Dave Sherby (Member # 698) on :
Same here. Aluminum or steel. I like steel just a bit better because I'm not set up to weld aluminum.
Years ago, I took the advice of a Letterhead that said to use MDO plywood as a backer for HDU. I learned my lesson on that sign and went to aluminum or steel and haven't had any problems since.
Posted by Steve Purcell (Member # 1140) on :
I'd strip the edge, and brush in some West System (wet) 2 or three coats while it sinks in. Level it out with 407 or 410 fairing, sand smooth, and paint.
If you're fastening into the MDO, put some WS into the pilot hole.
I know that the SF guys don't recommend MDO as a backer - but I've been doing it for over 20 yrs without a problem. Just be sure to seal all exposed areas.
Posted by Raymond Chapman (Member # 361) on :
For years we used MDO without any problems, but then began to see our signs warping and some hairline cracks in the edges of those that had MDO sandwiched between two layers of HDU.
We now use aluminum or DiBond. Some use steel because the guy that does our frames, brackets and such does not work in aluminum. Lots of primer and paint keeps everything from rusting.
I was probably that guy that gave the advice...and it was good advice at the time, but something must have changed in the MDO, adhesive, or paint....or a little of everything.
[ May 03, 2010, 01:41 PM: Message edited by: Raymond Chapman ]
Posted by Chris Lovelady (Member # 2540) on :
do not put something together that will rot with something that won't.
we use a webbing and gorilla glue to glue 2 peices together with and aluminum for edges were hardware will go through to prevent taring. i have found this the most superior way and it will not break. we did a sample at the shop then jumpped on it..no breaking!
p.s if expansion is an issue use PB brand construction adhesive...it is urethane based!
[ May 03, 2010, 02:12 PM: Message edited by: Chris Lovelady ]
Posted by Dirk Rampling (Member # 9233) on :
Question for Ray
What are using to bond dibond to hdu?
Posted by Mike Faig (Member # 6104) on :
PL Premium Urethane Construction Adhesive for urethane to urethane construction. Sometimes I'll finish assembly on support structure after all painting has been done. In that case I'll dribble some water and GG into the holes and allow for expansion to fill in the gaps before sealing with caulk. From this angle, you can see the 1/8 x 2" flat steel is unfinished and ready for the final assembly. I don't have pictures of the final assembly to post.
Posted by Raymond Chapman (Member # 361) on :
Answer to Dick: West System Epoxy. Scuff up the DiBond and make sure all the dust is off the HDU. Apply epoxy to both side and assemble. We just put a bunch of gallon paint cans on top for clamps until the epoxy sets up.
Posted by Wayne Webb (Member # 1124) on :
VERY nice, Mike!
Posted by Dirk Rampling (Member # 9233) on :
Thanks Ray
Posted by Rusty Bradley (Member # 6938) on :
Raymond...I don't have the West System Epoxy you recommend and would like to glue tomorrow...will gorilla glue work for bonding dibond to HDU?
Posted by Joe Crumley (Member # 2307) on :
Rusty,
As you know, Gorilla Glue expands making difficult to use on large flap panes. You'd need to apply considerable pressure to keep it flat.
I agree with Chappy about the use of epoxy. However there is precious little difference, if any, between West epoxy and other brands. Your local hardware is likely to have just what you need.
Of all the brands I've tested, MAS is the one I prefer because it's low VOC'swww.masepoxies.com/
[ May 06, 2010, 06:16 AM: Message edited by: Joe Crumley ]
