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Epoxy For Natural Stone

Epoxy For Natural Stone

A lot of people contact us and ask, “I see you have lots of epoxies, but I don’t know which to use. Can you help me?” Here is everything you need to know about epoxy

When you are gluing granite to granite in any structural application the only glue that should be used is epoxy. You can define a structural application like this - if you could wave a magic wand and make the glue disappear, would anything fall to the floor? If the answer is "yes" then it is obviously a structural application.

Other glues like polyester resins just do not absorb into the silica substrates of granite and therefore epoxy is the only permanent glue for this material. While other glues may be used and possibly will stay there they can also lose their bond to the stone for no apparent reason causing failure. This can be a problem when something falls to the floor, especially if your toes are there!

Epoxy, also known in the stone industry as A-B, consists of two parts. Part A is a resin and part B is a hardener. The ratios can vary from 1:1 to as much as 5:1, but if you are using a glue that is 30:1 it is not an epoxy (although there are other two-part glues; polyester resins, cyano acrylates and even some urethanes to name three). As a rule epoxy contains no styrene and is much stronger than other glues. In fact, when mixed properly and used for a lamination of granite to granite the epoxy will actually dry stronger than the granite! It is so strong that if you glue granite to granite and allow it to cure then break the granite the epoxy will not break, but the stone will break on one or both sides of the glue joint.

Epoxy comes in different viscosities for different applications. The three viscosities used in the stone industry are flowing (which is the consistency of syrup), knife-grade (which is the consistency of warm peanut butter), and penetrating (which is the consistency of water). While some of the applications for these will overlap here are some guidelines to go by.

If you are doing a lamination (gluing 2 pieces of granite together to make it appear twice as thick) you should use a flowing epoxy as it will conform to the voids more easily and will ooze out of the seam uniformly so that when you scrape the stone with a razor blade across the seam it will be flush. When you use epoxy in this application you want a uniform edge. While you could use knife-grade here there is a much greater chance that you’ll end up with little air pockets on the visible part of the lamination seam which you will have to fill in later. All of our customers that laminate granite use flowing glue for laminations. Flowing epoxy can be used in almost all horizontal applications like laminations or fills. Our flowing epoxies are all transparent, some dry with a hue and some are water-clear.

If you are working on an uneven surface, a horizontal or angled surface (non-horizontal) or a chip repair you can use knife-grade glue. The best advantage of this glue is that it will pretty much stay where it is put; bearing in mind that gravity does affect it of course. The thickening agent used in knife-grade epoxy varies from cabocil to ash, but in any case it does not dry transparent as all of the flowing epoxies we carry do. It may dry translucent, but in the best cases it will dry a clear white (think of looking through an ice cube that is suspended in drinking water).

If you have a crack in the stone and it is too narrow to get either knife-grade or flowing epoxy into it you can use a penetrating epoxy. This glue will seep into a hairline crack, bonding everything it touches on the way down and into the stone. This glue will never get rock-hard. It always maintains some elastomeric quality to it so that it will move when the stone has deflection in order to help prevent the stone from breaking again. This is important as anytime a stone has been cracked or cut into it has been weakened.

Most do-it yourselfers use the knife-grade as it is easy and user friendly. If fast-setting is preferred we sell a fast setting mercaptan epoxy that dries in less than 30 minutes and will not stick to polisher surfaces. Most pros reading this are nodding their heads and already know what they need to use for their applications. If you have any questions please feel free to contact me at mark@defusco.com



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