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Using Compounds like Epoxy and Mortors
Sach teaching student in Guelph to carve stones.
Note carving tools on white cloth pad.
Epoxy and Limestone Mortor.
WARNING!!! We are still trying to work this out ourselves. If you have large numbers of stones to do, it takes a long time to use the proper limestone mortors, mixing them up with the correct stone dust, etc. However, we have also been shown the damage of using the wrong premix compounds.
This area will be updated as we gain more information.
- Most premix compounds (putty like substances) are not water permeable. This problem we have found is NOT explained well on most sites. Once we began to hear the description in detail it made more sense. We always thought. Water should work through a stone from top to bottom or bottom to top (it can go both ways), and work it's way to the edges and dry there right? So why this water problem. What is not explained on other sites is exactly that. The water will find the edge of those non water permeable compounds and work it's way to the edge. Dry. And leave salts and other compounds on the stone. And it is those locations that can cause harm. It will take a long time. But gradually you will see small rounded edges on those stones. right where the water works it's way to the edge. But if you let the water work through the stone, there is less of those compounds in one spot, and thus less damage.
- So, premix compounds in stones that DO NOT allow water penetration should be avoided when possible. There is a water permeable compound out there being sold by a company that tell you that you must pay huge money for their courses or they will not sell you the compounds. You just add water. We have used that compound extensively and had good luck with it though we have not taken the courses. If you can purchase it we do recommend it.
- There is also another compound that is a premixed powder as well. All you have to do is to add water to make it into a paste as the one above. And we have gotten reliable information that this works well for almost every application. Yes, you have to mix it. However, this is a simple one step mix and we believe it may be at least a partial solution to problems. It is by a company named Daubois. They make both a pointing limestone [ XHN-60 ] and bedding mix limestone mortar [XHN-101 ] to set stones into bases.
- One thing we have learned is that limestone mortar can often be used to attach pieces back together but this of course is a technique that takes a fair bit of skill.
- Re Epoxy. We have found the following. Probably the best solution is to put in stainless steel or fiberglass rod. Epoxy around that. Then fill the crack. BUT! Remember that the disadvantage is that the rods may break out the stone much worse again if that break is challenged again at some point. If all goes well, the stone may last longer with rods. But if that stone is challenged and is broken again, it may be ruined to the point of not being repairable again the next time. Also if you have huge numbers of stones to repair as we do, you may need to ask yourself is it better to repair more in a way you have a hope of getting many finished, or is it better to repair in a way that you will never be able to repair a tiny percentage of the total number you need to do.
- Re Epoxy Types. Caution... NEVER NEVER NEVER use Silicone as an epoxy to glue monuments back together. It does not allow water movement almost everywhere, yet it will have small pin holes in places that tend to run the water in, thus causing the worst of both cases. It is the absolute worst thing that you can do to a monument!
We have used about 6 different epoxies, and in all cases, used materials that share similar characteristics for strength. The differences are mostly related to setting times, viscosity, and cost. It is imperative to select the right epoxy for the job. Our repairman with the most experience in our group writes as follows. I recommend a concrete epoxy, capable of setting in a moist environment, with a high shear strength [ typical of most concrete epoxies ] and a setting time of at least 30 minutes. In all cases, the epoxy bond is comparably strong. However, if a failure occurs, it is generally related to blunt force trauma to the monument, typically from lawn mowers, and rarely from vandals. When I say refer to a failure, in every case, the failure is not the epoxy joint, but rather breakage occurring approximately 2 mm above or below the epoxy joint in the monument itself. To repeat, the epoxy does not fail, but rather the monument material itself fails. Monuments made of granite rarely break, and we've found that trauma breakages occur in marble, limestone, and sandstone in order from strongest material to the weakest. One other case for epoxy failure may occur if the actual monument has become grossly weakened from long term exposure to water. A typical example would be a marble slab monument, buried in the earth and constantly exposed to moisture for well over 35 years . As well, the poorer the quality of the marble the greater rate it deteriorates with moisture. In these cases, the epoxy joints are only as strong as the material that is being repaired. We have found if a blunt trauma occurs, even a light blow, the monument will break again, approximately 2 mm above or below the joint - the epoxy itself does not fail, but rather the stone fails. The poorer the condition of the monument, the less dense the stone is and the epoxy does not have a solid material to bond together.
The materials Loctite E-30CL and #M Scotch-Weld DF-460 are more viscous and tend to easily run, especially on a hot day. They both tend to change from clear to a yellow colour as they harden. The primary draw-back is they come in small tubes and are very costly . They will suffice in very small repairs. Again though, this repair is costly for the small amount of surface area repaired. Another product used successfully is from a company called RedHead . They offer a full range of products much the same as the products mentioned above. RedHead A-7 works well, has a rather strong odour, comes in small and medium sized tubes, and tends to be costly. My favourite epoxy is RedHead G5 . Although you need to buy a dispensing gun for it, the catalyst/base combined tubes come as 22 fluid ounces [ 650 ml ], is the most colour stable, offers a 30 minute set time [ faster on a really hot day ] and is reasonably priced. The bottom line is, this product [G 5 ] offers the most material at the best price, and will cover large surface areas of broken monuments .