Frequently Asked Questions

Question:       D/2 Biological Solution – Rust/Orange Staining After Use

I used D2 on my aunt’s gravestone this morning by spraying it and leaving it on the stone.  It appeared to work fine so I left it to do its biological work.  I next sprayed it on my grandfather’s grave located next to my aunt’s and it immediately turned the stone a rusty color.  I believe it was because of lichen on the stone.  I scrubbed the stone with a soft nylon brush and used a lot of water to remove the lichen but I was not able to remove the rust color stain on the large stone.  Do you have any suggestions for me on how to remove the rust-colored stain on the stone?  Should I spray more D2 on it and let it sit there?


The rusty color or sometimes orange color is due to the lichen and biological material that is dying. We sometimes compare it to a leaf that dies, turns orange and rust color, that means it’s working. With a few more rains and sun spells it should flush out of the stone pores and go away.

Question:    Glacier or Last Patch Gel for outdoor kitchen

I am doing an outdoor kitchen, and wondering which product is best for seaming.

Glacier or Last Patch Gel?


Either product can be used, both are UV-stable (will not yellow in sunshine).  We would suggest Last Patch Gel.  The main difference is strength. Glacier is a rigid, structural, permanent adhesive, you will never open the seam without breaking the stone so if you ever foresee that need, use Last Patch.  Last Patch Gel is very strong, but not strong enough to be considered a structural adhesive.  You will most likely not break the stone if you try to open the seam in the future (unless you have a very soft stone).  Last Patch Gel is also much more flexible than Glacier, so if your outdoor kitchen will experience extremes of temperature throughout the year, we would recommend Last Patch Gel as it will offer more movement capability than Glacier.

Question:    Re-Attaching & Patching Limestone

What would you recommend for re-attaching limestone and for patching the areas that can’t be reattached? It’s outside in a northern climate so it has to be able to handle freeze/thaw conditions!


Re-attaching the stone use Bonstone Ultimate.  Patching missing areas use Historical Restoration Mortar (HRM)

Question:    Tell me about Glacier?


This one is NOT an epoxy. Why is that a big deal?  Two reasons:  1. Because epoxies will yellow after exposure, Glacier will not.  Makes Glacier the “go to” product for anything that will be used outdoors.  2. Epoxies will soak into and darken (“stain”) the edge of the joint on some porous stones, like limestone or especially white marbles, makes a very objectionable dark line at the joint.  Glacier will NOT do this.

Glacier has an extremely fast cure.

Glacier is used in:

  • Outdoor applications
  • White marble fabrication
  • Whenever a very fast cure is required.

Question:    What’s the difference between Last Patch & Historical Restoration Mortar


LAST PATCH family includes Last Patch Gel, Last Patch Dymond, and Last Patch Limestone.  These are all fast-curing urethane materials.  Major benefit of this technology is uv-stability (non-yellowing), fast curing, and ability to cure at low winter temperatures.

Last Patch Gel is clear and is used as a surface patching material for shiny stones, mostly polished granite.  Also used in headstone repairs such as filling-in spelling mistakes.  Preferred over Last Patch Dymond because it is easier to sand-blast, that’s how they carve the letters and numbers into headstones.  The sand simply “bounces off” Dymond.  Another use for Last Patch Gel is to fill holes in stone, for example when they remove a sign from a wall, the bolt holes are still there.

Last Patch Dymond, a much harder, faster-curing version of Gel.  Becoming more popular than the original (except for headstones—see above).   All of the Repair Kits include Dymond, not Gel.

Last Patch Limestone—basically a textured and colored version of Gel.  We add tints to give color, and powders to give texture.  This product is much preferred for grainy stones like limestone and sandstone, since (once it’s cured and sanded), the result more closely resembles the actual stone.  The other products are too smooth and too shiny.

HRM—Historical Restoration Mortar.  We developed this product when the recession hit in 2008.  People were telling us that they love Last Patch, but it’s expensive. They realized it may last 100 years, but they didn’t necessarily need that durability for a lot of the projects. So, we developed HRM.  Now, HRM is NOT a clear product, so it does NOT compete with Gel or Dymond, but it is a VERY good alternative to Last Patch Limestone.   It gives pretty much the same properties; fast cure, uv-stability, mimics the stone color and texture, and at a reduced price (about 30% less).   HRM is an entirely different chemistry than LP Limestone.  It is a lime- based mortar, with an acrylic latex hardener.   Being water based, however, you CANNOT use it in the winter, it will freeze before it cures.

Quick comparison of LP Limestone and HRM, and reasons one might choose either product:

  • Best strength, longest expected lifetime: Last Patch Limestone, much stronger than HRM.  We say LP Lime will last 80+ years; HRM 20 years.
  • Easiest to work with:  HRM, by far.  The mix ratio (A:B) is pretty critical for LP Lime, get it wrong, and it won’t cure.  But HRM is very forgiving, you can add as much or as little of the latex to adjust the working viscosity to your liking, and it will not materially affect the strength.
  • Substrate preparation: both products require clean and dust-free.  But LP Limestone MUST have a dry surface, like all urethanes, and moisture present at the surface will interfere with proper cure.  HRM has a definite advantage here, being water-based itself, it tolerates dampness very well.
  • Color and texture, once cured, HRM looks good, no further work required.  But LP Limestone cures to a grainy, shiny product. To get the right color/texture/gloss, you have to grind it flush with the surface.  Not only is this an additional step, but it’s very difficult to do this on a curved surface, like a column.  HRM is SO much easier for these applications.
  • What if it rains? The patch might look good dry, but when it gets wet, we want the patch to look the same as the wet stone, we want the patch to darken like the stone does when it gets wet.  HRM excels at this; LP Limestone is just OK.
  • Lastly, a property called “breathability”, defined as the ability (or resistance to) the movement of water vapor through the patch.  Many specifications call for a breathable product, they want any moisture in the stone (from rain or snow, for instance) to be able to evaporate through the patch, rather than try to “push” through a non-permeable patch and thus “pop” the patch.   HRM is breathable, LP Limestone is not.

Question:    What’s the difference between Fast Set Extreme and Ultimate?


Fast Set Extreme:  Epoxy adhesive for stone, knife grade, very fast curing.  One of the very few epoxy products on the market that will cure in temperatures below 50F. (Most will simply “freeze in place” at those colder temperatures.  Extreme will even cure at temps as low as 20 F).   Legacy product, been around for over 50 years. Lots of history.

Ultimate:  a rather new product (about ten years), based on a newer chemistry.  It is NOT an epoxy, but actually a hybrid product of several chemistries, that we have dubbed “modified polyurethane hybrid”.      It is a knife grade product, very fast curing (even faster than Extreme), and will also cure in below-freezing temperatures.  Ultimate is available in several different colors.

So, why would you use these products?

Here are the main advantages of Extreme (compared to Ultimate):Long history of successful use.    Ability to adhere to slightly damp stone (Ultimate MUST have a very dry substrate to work, any dampness and it will not adhere).

Main advantages of Ultimate over Extreme:   Much faster curing.   No odor, can even be used indoors (Extreme smells) UV-stability, means that the adhesive will not turn yellow after exposure to sunlight (Extreme will discolor), Ultimate will not.  One other unique advantage of Ultimate is that, due to its uv-stability, it can also be used as a surface patch.  Using Extreme in this manner would result in a patch that will discolor.

Question:  What’s the difference between Edge, Clear Gel and Express II


Edge System has a flowing viscosity, medium-fast curing, very clear, extremely strong.  Legacy product that has set the bar for the industry, has a history of over 25 years

Clear Gel is a Knife-grade version of Edge System

Express II is available in both flowing and knife grade.  Same as the above 2 products, but the cure is twice as fast

So, why would you use these products?

If you want maximum confidence (longest history of successful use), use Edge System or Clear Gel.  It’s kind of a personal preference whether you want Flowing or Knife Grade.  Some people think Flowing gives them a tighter joint, but flowing makes a mess, drips everywhere!  Knife grade is non-sag, so no drips.

If you’re in a hurry, use one of the Express II products.   Even though they are newer, they’ve still been out there for nearly 20 years, so it also has a long history of successful use.

Lastly:  The Express II products are a little more expensive.

Question: “Using NautiThane.  Instructions call to “sand between coats”—is this necessary for proper adhesion between coats, or is it just to ensure a smooth coating?”


The sanding is only to ensure a smooth coating, it is not necessary to achieve adhesion between coats.   UNLESS you are applying a touch-up coat, after the previous coat has been exposed to weathering for some months.  In that case, it IS necessary to sand lightly (“scuff coat”) to ensure good adhesion between the weathered layer and the fresh coat of NautiThane.


Question:  “Used NautiPoxy to previously-coated wood.  Sanded down to bare wood, then applied the epoxy—it was fully hard and cured the next day, but looked very mottled.  Did I do something wrong?”


No, this is normal.  NautiPoxy is a thin epoxy, designed to penetrate and fill the pores of new wood to improve its strength, water resistance, and durability.  If applying to wood that has had a previous coating, even if sanding to “bare wood”, you most likely still have the pores of the wood completely filled with the previous coating. NautiPoxy cannot penetrate in this case, and simply builds up on the wood.  With this thick of a coat,  it is not unusual for the NautiPoxy to not properly  flow-out,  and you may get some craters,  depressions, waves, and other defects, resulting in a somewhat “icky” appearance.  This is totally normal, nothing to be concerned about—because you are going tpo sand the NautiPoxy anyway before applying the NautiThane topcoat.  So, just sand the icky-looking NautiPoxy until smooth.  There is no need to go all the way back down to bare wood, just sand enough until it’s smooth and uniform in appearance (you want to, at the very least,  make sure all the shiny spots are sanded smooth).

Question:  I have a large fabrication job, requiring massive chunks of stone and numerous anchors being installed simultaneously.  It’s also very hot (temperature) here.  Looking for a adhesive to provide extended working time, in essence a slow glue.


We have the perfect product, Bonstone Anchor.  Anchor is a 2-component structural adhesive that combines the strength and durability you’ve come to expect from Bonstone, with an extended working time to give you more “breathing room” in fixturing and clamping,  especially when the thermometer really starts climbing.  Anchor is not new, in fact, in homage to our dear deceased founder, King Harte, it is one of our oldest products.  The formula has remained practically unchanged since King himself invented it back in the 60’s.  As they say—“if it ain’t broke, don’t fix it!”