FAQ Answer to Question on Grouting Compounds for Mixed Media Installations

Hi Don,

I read your webpage and I was wondering if you might be able to help me with a grout issue.

I am working with wood, glass, and marble in mosaics. The biggest issue I have is the natural expansion and contraction of the wood. Clear silicone is great for adhering glass, but I'd prefer not use that as a "grout" for the mosaics. Main reason is that it's toxic and will not be easy to clean off the glass or marble unless the installer enjoys very tedious work (I like tedious...mosaics obviously, but installers don't).

I've been in the mosaic field for 15 years and no one has been able to figure out a reasonable solution to this issue. Hence, no one is making wood, glass, and marble mosaics. I found a grout specific to wood, but it is not a good product...it stained black walnut to an ash grey and weeks later it was coming out of the joints.

I've attached a picture so you can get an idea of what I am dealing with.

If you have time and wouldn't mind helping me with this issue, I would much appreciate it. If not, no problem.

Thank you,

Katherine




Katherine, I’m sure you’re well aware yours is an age-old issue for artists, builders, architects and anyone who’s attempted to put two or more things together to form a whole for more years than history can record.

I’m a big believer in using the simplest method that will get the job done. I like “dry setting” stone for example because it’s the most forgiving (when done right) in all but the most troublesome situations. Still, it won’t work in every instance and is a difficult skill to master (at least for some).

It could work in your situation depending on the application. It would not work, of course, if the item were to get moved around a lot. I’ve utilized the dry set method on tables for example, with more than a modicum of success. The ancient stone setters used sand as a grout almost exclusively. When elastomeric properties are needed within the grout material itself, “bark” was often utilized. Probably the best known of which is cork. Finely ground bark or cork can be used in a loose mixture like silica sand or bound together to form sheets, strips or rolls to fill a variety of hole or gaps sizes.


The picture you sent me did not come through well, but of what I could tell, the gap you are attempting to fill is quite sizeable. Standard wood filling compounds will not work well in “large” gaps. They are made to take a stain and finish like raw wood and hopefully “disappear” or at least blend well with the piece or pieces they’re filling. Where you have large or expansive gaps to fill, the grout (if you must use one), can greatly benefit the overall system when made of a contrasting color, texture or pattern to what’s being filled.

We frequently use ground cork to make a flexible grout for wooden “rounds” or end grain block installations where the gaps are often quite large. Where wear is paramount and flexibility less so, we’ll resort to a highly plasticized mixture of cementitious grout and poly binder. We find such grouting materials can take foot traffic well and work better in many indoor installations where moisture can get trapped (such as entryways) and not easily pass through (as with most exterior applications).


Our company manufactures a variety of wood fillers, several of which are quite elastomeric. Two of our products, EZ Trowel FloorFill and Patch-It, contain 3 times or more resin than standard wood floor fillers. This greatly enhances their elastomeric properties. These products not only work well in standard wood flooring situations but also in highly resilient wood floors (e.g. sports floors) where standard wood floor fillers will simply pop out during active use.

There are occasions where we will mix wood, metal, stone and glass materials together to form a highly stylized or artistic floor. The grouting mixtures in these installations vary, but we often find a highly plasticized cementitious grouting compound the most advantageous all around.

Of course the tighter the pieces joined together, the less the issue of rejecting the grout (assuming a stable or immovable substrate). If pitch and yaw presents a significant problem with grout ejection (e.g. a yacht, houseboat, pier pole or similar construction), an elastomeric binder is a must. That’s one of the principle rationales behind dry setting and how exterior dry set systems have lasted for so many centuries. It facilitates the pass through of rainwater preventing (or at least reducing) freeze/thaw dilapidation and lends itself so readily to repair.

There are also many indoor wooden floors, as well as floors constructed of both wood and stone that rely on dry setting compounds which have endured exceptionally well for centuries. That’s my acid test for longevity…actual useful life.

Even dirt has been used with both stone and wood for countless centuries. I recently came across a near 200-year-old installation near my home of beautiful wooden marquetry set in bone dry dirt. I found no indication whatsoever of deterioration within the structure. Now that kind of fortitude truly impresses me.

Hope this helps,

Don Bollinger