Why Use Cartridges?
The most common errors using two-part resin systems packaged in cans or bottles involve measuring and mixing mistakes. Over the years we’ve seen just about every conceivable way to make these errors. These include everything from forgetting to include either the resin or hardener by grabbing the wrong bottle, reversing the ratio, or simply getting the ratio wrong when measuring. Mixing errors include inadequate mixing, not scraping the sides and bottom of the container and not wiping the stir stick during mixing.
Air is always introduced when mixing any two-part system in an open container. The air escapes when a coating or laminating epoxy resin like Clear Coat or SilverTip is applied in a thin film. It will not escape from a thickened epoxy adhesive like GelMagic, a fast curing epoxy like Quick Cure, a honey-like material like T-88 Structural Epoxy Adhesive or a urethane like SilverThane SA-2100. Air is prevented from escaping both because of the viscosity of these materials and the fact that they are used for bonding in a closed joint. Air entrapment results in a weaker joint – the joint may be adequate for the intended purpose but it is still weaker than it would be without the entrapped air. With some non-porous materials like aluminum, steel, plastics and certain hardwoods the dispersed air may weaken the joint enough to cause failure under high loads.
Then there is the “countdown” factor: The true viscosity of two-part systems begins rising the moment the parts are mixed and continues to do so until the material has solidified: Time is not the friend of epoxy or urethanes sitting in a mixing pot! Material removed from the pot ten minutes after mixing is not the same as that removed right after mixing. As these systems cure they are less able to wet out substrates and increasingly poorer bonding can result. The repetitive nature of measuring and mixing two-part systems is, frankly, boring. Once you’ve done it a dozen times you’ve got it mastered. You get complacent and make errors. It is much more fun to apply the material, close the joint, clamp it and stand back and admire your work. If the job is small you can spend twice the time measuring and mixing than doing all the fun stuff like applying the material and closing the joint.
Then there is waste: One almost always measures and mixes more than they actually need to do a given job for the simple reason that the clock is ticking on closing a joint and one does not want to pause and have to go through the process of measuring and mixing a smaller second batch with another set of possible errors. With smaller jobs the waste can be three to five times the amount of adhesive actually necessary to make the joint simply because it is impossible to thoroughly measure and mix material from bottles and tubs in amounts much smaller than a fluid ounce.
Wouldn’t it be nice if there were a way to eliminate the chance of measuring and mixing errors, maximize the resin strength by eliminating air, always use freshly mixed material, enjoy top of the line products, save time, eliminate waste and have more fun? There is such a way. It’s called using dual cartridges. To use one you simply drop it into a caulking gun, prime it and screw on the tip to dispense thoroughly mixed and precisely measured material free of air. You put the mixed material right where it is needed with little waste. Using dual cartridges is fun and is the quick, confident way to kick back and watch things cure!
“All this but for what cost’, you wonder. A half-pint kit (8 fluid ounces) of T-88 Structural Epoxy Adhesive sells for about $21. It consists of two 4-ounce bottles with Yorker spouts with caps enclosed in a light cardboard box. The comparable cartridge contains 8.34 fluid ounces and sells with a mixing tip for about $22 – about 4.8% more. But, you get about 4.3% more material in the cartridge AND a mixing tip. It’s a six of one and half-dozen of the other comparison.
“But, the tip can’t be cleaned. What if I need another tip?” Tips are available separately. They cost $1.75 each in a six-pack. One fluid ounce of T-88 in the half-pint kit costs about $2.60. Waste 2/3 of a fluid ounce doing a larger job and you’ve paid for the tip.
“Aw, but you can’t use the material left in the tip!” True, but the square turbo tip retains only about one-quarter fluid ounce that you can’t squeeze out. But, if you mix a couple of fluid ounces in one of our four ounce plastic cups you’re going to leave this much clinging to the sides and bottoms. So it’s a wash either way.
“But, a half-pint kit is more than I need anyway. Why don’t you package kits in smaller bottles?” You’ve got us there! We don’t do this for the simple reason that we’d still need two bottles, the Yorker tips and box to package them in. The price would not go down by much. (Check out things in your local grocery store to see what we mean!) But, we do package most of our larger “cartridged” products in 50ml dual cartridges and these are really cool! You need a special gun for these cartridges but we sell it for $21 – much less than you can find it elsewhere. The idea is to get the gun in your hands so that you can use current and future 50ml cartridge packaged products.
“So, all the products available in cartridges are also available in bottles or tubs, right?” Wrong. Our SilverThane urethane product line is not available in either bottles or tubs. Currently our only SilverThane product is SA-2100, our UV resistant marine sealant/adhesive. We’ve got two new exciting SilverThane products waiting in the wings. In addition, we’ve been working on several metal bonding epoxy adhesives that are unique. These products will only be available in cartridges: we don’t want their performance compromised by the introduction of air; and, in the case of urethanes, by moisture in the air.
“It sounds like I ought to get with it and give cartridges a try”, you exclaim. Right on! Check it out.
- STR Staff