What is the dif between Silicone I and II?... Has anyone had failures with either? I'm doing a project that needs to been done very right, and would appreciate some help.... This project is a 2 inch HDU frame(raw) onto sanded Dibond and a 4x5 feet blank of HDU on both sides of the same. Thanks, Jack
Posted by Felix Marcano (Member # 1833) on :
Bump-o-matic!
Wish I could help Jack, sorry.
Posted by Chuck Churchill (Member # 68) on :
I am not sure that I know what the differences between I and II are but I do know that II works great for all kinds of applications. I have installed lots of signs inside and out with GE Silicone II. I can only think of one where we had a failure. It waa a 2'+x8' piece of 1/4" acrylic on a south facing exterior marble wall. I think th acrylic extanded to much in the heat and managed to break the bond with the silicone. Then again maybe my installer didn't put enough on.
I would think if you call the GE office listed on back of the tube they could send you some literature on what I and II are supposed to be used for and their characteristics.
Posted by David Harding (Member # 108) on :
I originally emailed some semblance of this to Chuck since I was having login problems but Steve & Barb fixed those...Thank you Steve & Barb!
Chuck,
The failure on your 2' x 8' sign was probably caused by two factors. The first is, as you stated, the expansion and contraction of the acrylic sheet, which can shear the adhesive bond. The second could well be a reaction between the silicone and the Marble. Marble is calcium carbonate, silicone contains acetic acid, which eats away at Marble. Sometimes, you will find a pasty white substance at the point of failure. When I have to attach something like acrylic to Marble, I use PL Premium, a urethane based adhesive. It is sometimes available in Lowe's or Home Depot. If PL is not available, check the labels on the various Liquid Nails type adhesives to find the one that says "outdoor" and concrete or Marble.
If the stone you attempted to stick the sign to was, in actuality, Granite, then silicone would be no problem. I often see Granite referred to as Marble.
I do not usually use a plastic piece outdoors at the size you mentioned because of the problems with mounting it to stay and look acceptable under all temperature conditions. A method of mounting acrylic would be by drilling oversize holes and mounting with fasteners and washers slightly on the loose side to give the plastic room to expand and contract. Illuminated signs with plastic faces work because the face is not secured tightly. It is in a track or retainer that is enough oversize to allow the plastic to move at will without hindrance.
The coefficient of expansion for 1/4" acrylic varies from 3.8 to 6 in/in/̊F x 10-5,depending on the brand of plastic. Translated into English (I cannot do that French thing up in Canada, however I could do a Spanish thing here in Texas), from 0 F to 100 degrees F, the plastic will expand between 3/8" and 1/2" in length. If you installed it at 50 F, it could be up to 1/4" longer in the summer and 1/4" or more shorter in the winter. That, in itself, sounds like problem enough but if you somehow pin the ends so they cannot move (such as by bolting or gluing firmly to a wall), the extra 1/4" length bowing outward at the middle translates into about a 3" bow, which also adds to the stresses involved in trying to pull your creation away from the wall. To visualize the amount of bow, place a yardstick on a desk. Push one end of the yardstick 1/8" toward the other end and see how much it bows in the middle. The 1/8" squeeze bows the stick a full inch. The same thing is happening to your sign.
With the above paragraph in mind, you would need to drill holes at least 1/2" diameter if you use a 1/4" fastener. You would also have to center the fastener in the holes to allow for expansion clearance and make sure the screws and washers were not so tight as to trap the substrate from movement. Many times you will see wavy plastic signs on walls. It is because of mounting them with no room for expansion. These stresses, caused by lack of expansion clearance, also contribute to the plastic breaking at the holes, another common sight. Adding fasteners in the middle to pull down the bow does not do the trick, for now you will have two bows, one at each side from the center to the end. Keep in mind that the yardstick bowed an inch over the length of three feet. Your sign face wants to do the same.
For exterior signs of 2' x 8', there are plenty of substrates available, such as Dibond, Aluminum plate, HDU, that do not have nearly the expansion coefficient that Acrylic has. Keep in mind that ALL materials expand and contract in temperature changes and there will be some bowing at high temperatures, even if barely noticeable. Aluminum's expansion coefficient is about a quarter that of acrylic, steel is about half of Aluminum. The polyethylene core of Dibond has approximately the same expansion rate as acrylic, however it is much more malleable and compressible so it works well sandwiched between two pieces of Aluminum.
Posted by Dave Johnson (Member # 2535) on :
Check these sites for information on silicone sealants and caulk.
