We are using Laminators Econolite substrate scuffed with scotchbrite pads painted with automotive paints; sometimes a 2 part paint sometimes base coat clear coat... we apply sign vinyl and clear coat over top of the whole thing on complex jobs that we want to last a long time. We mount with stainless steel screws. On 2 of the signs very close to the ocean there are bad corrosion problems. On one the corrosion is under the laminators white factory paint (sign face side), it starts at the outside edge of the sign and comes inward like there are thin worms underneath. On the other one a few of the screws have the corrosion around them again underneath the factory white paint. Since the signs are complex it is really distressing to have to re-do them and worse I can't figure out what is going on, so I won't do it again! Laminators says their products are not warranted near salt water... this makes no sense since many cities have salt water in the air on stormy days and they sell it in those cities... further my competitors use Econolite as well, but don't use stainless steel screws which produces a nice drool line of rust from their screws down the face of the signs, however there is no corrosion. I am wondering if I am creating a form of electrolysis between the different metals (aluminium & stainless steel) and this is my problem? If it is does anyone know what type of screw works better? I am thinking maybe a ceramic screw that is now used on pressure treated posts.. I could really use some help on this one as I see that some other older posts talk about using stainless steel screws on aluminium sheets... one a wet month, we can get up to 34 days of non-stop precipitation.
Posted by Jerry VanHorn (Member # 4704) on :
If I am not mistaken, is the Econolite a corogated plastic with aluminum laminated to the faces?
We use Dibond, a solid core material. I would think that would be better. I live in Ohio in the middle of a corn field so we don't have the salt issues.
good luck
Posted by Brian Crothers (Member # 2888) on :
Yes that is the product... However they each have an aluminium face on both sides, so if it is electrolysis the problem would be the same for each in a wet envoirment.
Posted by Ricky Jackson (Member # 5082) on :
Brian, You are right about the two different metals; it's called "dissimilar" metals and it will create galvanic corrosion where two metals have different electromobile properties. If you can use the ceramic screws, go for it. I still don't see how the panel could fail under the paint unless you're just talking about next to the screws. If it is failing elsewhere you probably need to seal the edges where the metal is bonded to the other substrate. Considering that over 50% of the population (almost every major city) of the U.S. lives within 25 miles of salt water, that's a pretty poor warranty if you ask me.
Posted by old paint (Member # 549) on :
anything that exists near saltwater WILL GET THIS PROBLEM!!! rickys right about dissimilar metals, and i lived in sarasota fl for 19 years and i was never more then 5 miles from the bay or gulf. on boats they have things they call ZINCS. these are a chunk of metal i think is lead/zinc combination the boat people attach to boats for the dissimilar metal problem. instead of it attackin the alum(lot of used in boats and boat motors)and stainless steel(mostly all fastners on a boat are this or brass)it will "eat" the ZINC. you could try that or before you hang the the sign find some PETTIT ANTI CORROSION paint and paint the cut edge of the alum.
Posted by Brian Crothers (Member # 2888) on :
Thank you for the replys. Some of these boards are near salt water for several years & do not have any corrosion at all. So it could be a bad batch of product, a cheaper aluminium grade, thier glue formula changed or the s/s reacting with the thin pice of aluminium. And yes, the corrosion is UNDER the paint and is some case up to 30" from the nearest screw, but origonating from a painted edge.
Posted by Bill Lynch (Member # 3815) on :
I hadn't heard about the "Not near salt water" part of their warranty, I'll be asking my rep about that. It sounds like the edge of the aluminum that is exposed to the air is where the corrosion starts and travels from. An edge cap w/ silicone and a dab of silicone in the holes prior to fastening may help. But I just don't think you should have that much of a problem after that amount of time.
Posted by Brad Ferguson (Member # 33) on :
I have had this problem with Alumalite as well, though it didn't happen much. I never figured it out. I would be suprised if a stainless screw was the culprit. The corrosion I have noticed didn't occur at a fastener anyway, but near an edge. The aluminum on these laminates is very thin--.010" or so. I've not seen this type of corroding on heavier thicknesses.
I no longer use Alumalite much. I much prefer Dibond, except for temporary stuff.
Brad in Kansas City
Posted by Rick Sacks (Member # 379) on :
I use aluminum and stainless screwws all the time and never have seena problem. I live on the coast where there is considerable salt spray. I don't use the product you mentioned though, and think if there was a problem with electrolysis it would occur at the location of the diss similar metals, just like it does with brass and iron plumbing fittings.
Posted by Stephen Broughton (Member # 2237) on :
Found this:- However, galvanic corrosion can be prevented if certain steps are taken. One being by electric insulation between the metals, where the insulation has to interrupt the metallic contact completely.
In large constructions where electric insulation is difficult it is possible to use an electrolyte insulator between the two metals for example by painting to interrupt the connection. Often it is beneficial to conceal the surface of the cathodes (that of the nobler metal), however another possibility is the installation of an intermediate layer
Would a rubber washer between the aluminium sheet and s/steel screws work?? also found this:- The corrosion resistance of aluminium varies widely depending on alloy, environment, design and protective measures taken. However, it is possible to give some general guide-lines.
A clean aluminium surface is reactive and will react spontaneously with water or air and form aluminium oxide. This oxide is very stable and has in addition a very good adhesion to the metal surface and thus protects aluminium from corrosion or further oxidation. This means that aluminium has good corrosion resistance in environments where the oxide layer is stable.
The oxide layer will deteriorate in environments with high or low pH or where aggressive ions are present. Below a pH of 4, acidic conditions, and above a pH of 8,5, alkaline conditions, there will normally be an increase in the corrosion rate of aluminium, but this also depends on which ions that are present in the environment.
Aggressive ions will break down the oxide layer locally and start local corrosion attacks. Among the aggressive ions, chloride (Cl-), is the one with the most practical importance, because it is present in large amounts in both sea-water, road salts and some soils and in lower concentrations in other natural sources.
A so called general corrosion attack proceeds at about the same rate on the entire metal surface. Because of the stability of the oxide layer, general corrosion will rarely be a problem on aluminium, except in very alkaline or acidic environments. Aluminium may however experience local attacks in connection with formation of small anodic areas as a result of a local breakdown of the oxide layer. Some of the most typical local attacks on aluminium are pitting corrosion, crevice corrosion, intergranular corrosion and galvanic corrosion.
hate to bring bad news though.
[ October 12, 2005, 10:26 AM: Message edited by: Stephen Broughton ]
Posted by Donna in BC (Member # 130) on :
I just quoted a sign made from econolite. I'm not happy to see problems can occur! Is nothing fool proof?!?
No salt out here. Just RAIN.
Posted by Rick Sacks (Member # 379) on :
I think your aluminum was poorly prepared for paint by whomever did the priming.
Posted by old paint (Member # 549) on :
if iam not mistaken..ECONOLITE is only powder coated on on side....the back is bare....ALUMILITE is powder coated on all four sides....then the coro is attached.
![[Frown]](frown.gif)
hate to bring bad news though.