Q: Our shop has been getting a lot of resined slabs lately, and I am a little confused as to why slabs are resined, to begin with. I would be interested to know why they are resined and what problems fabricators are having with these resined slabs?
A: In the past few years, I have had many fabricators ask the same question. Of all the fabricators I have spoken with, some have no problem at all with resined slabs, while others are having nothing but problems. The following are some of the pros and cons of resined slabs. The following article is not intended to solve this problem or to render an opinion but to put forth arguments from both sides. In other words the good, the bad, and the ugly. The resining of stone slabs is not as new as some might think. Resining started back in the 1960s on marble and about 10 years ago with granite. Today, the resining of slabs is commonplace, and it is predicted that almost all stone slabs will soon be resined.
What is resining?
The resining process uses polyester resins. There are several methods that are used to apply and cure the resin, from hand-spray applications to automated lines. The slabs are first honed and dried, and then the resin is applied. The slabs are then cured in heated ovens, and after the resin is cured, the slabs are sent to the polishing lines where they are polished. Some factories also apply a thin layer of wax to the surface after polishing to help protect the stone during shipping.
The resining of slabs has allowed slab producers to eliminate lots of waste and sell slabs that would otherwise be rejected. Brittle materials can now be used due to the resining process, which helps hold the brittle material together like a glue.
Resined slabs are also less likely to become damaged during shipping. Resining of slabs has also reduced the price of slabs, which is one reason the industry is seeing such a big growth in slab sales in recent years. Resined slabs are also less porous, and many resined materials do not need to be sealed, since the resin acts as a sealer for the stone. In addition, Filippo Emanuel of Tenax USA listed the following benefits in a recent article in Stone World (June 2003, page 100): Several materials are naturally fractured and could not otherwise be sold or marketed even if they are superior in terms of color, durability and other qualities.
There is a growing tendency in producing thinner slabs to reduce transportation costs and open up new markets and different stone uses. The waste from manufacturing slabs of particular materials (especially some marbles) could represent 35 to 40% of production, thus considerably increasing the cost of the remaining slabs. Many different kinds of granites have natural micro-fissures that compromise the final polished effect, thus reducing the beauty of the material. There are materials just too fragile to be polished, leaving no solution but to close down quarries. Some granites have fissures that pass through the slab and considerably decrease the strength of the slabs and pose a hazard when used as outside paneling. Limited reserves of a particular color of stone leave only the worst and more damaged veins to be quarried.
The Bad and The Ugly
Over the past few years, several problems have arisen with resining slabs. The following are some of the problems that have been encountered:
One of the major complaints associated with some resined slabs is that the resins used are not UV resistant. I have heard of several fabricators who store their slabs outside for several months, and when they go to use them, they discover that the slabs have darkened. This is especially true of slabs that are covered. In one case, a slab of stone was partially covered with another
section of stone. When that small section was removed, it was discovered that the portion of the slab that was not covered had darkened. This is the result of UV light reacting with the resin. The lesson to be learned here is not to store slabs outdoors in direct sunlight. This is especially true of light colored materials such as Giallo Veneziano and others. However, Emanuel points out that there should be no resin on the surface of the slab. “If there is, it means that the manufacturer did not do a good job removing it,” he said. “That is when fabricators start having problems with darkening effects.” If done correctly, the resin is inside the cracks and the pits, but nowhere else. An additional problem is with profiles. Several fabricators have had experiences with the profiled edge turning out lighter than the rest of the stone. “The problem with the edges is that the resin will darken the top of the slabs regardless of the UV,” Emanuel explained. “It is just the effect of the different reflection of the light when a material is imbibed with resin. When you cut the edge, there is no resin on the side — regardless of the UV exposure. That’s the reason why the edges are lighter.” Over time, we have found that the edge will darken and match the face of the stone.
A quick fix to this problem is to use a color enhancer to darken the edge.
2. Sealer interaction.
Our technical hotline has received several calls where impregnators have been applied to a resined stone, and the material clouds, discolors, or fades. After testing several slabs and sealers, I have discovered that some solvent-based impregnators will react with the resin, causing it to break down and turn color, cloud, or fade. This is a problem that is difficult to repair. We have
found that the application of a color enhancer will sometimes hide this problem. My recommendation would be to use only water-based impregnators on resined slabs.
3. Polishing and refinishing problems.
In a recent countertop repair seminar, one of our students brought in a resined section of stone he wanted to try and refinish and polish. We discovered that this material had such a heavy application of resin that when he tried honing the top, the resin became gummy. Once the surface was cut and polished, it was very difficult to match the remaining surface of the stone. As of this writing, I have yet to find a solution to this problem other than to refinish and polish the entire slab so it all has the same polish. Please keep in mind that some of these problems may be the result of improper application and not necessarily the resin itself. Just like any other industry, quality control can be an issue, and sometimes a slab or two may slip by. This is why it is important to deal with reputable slab distributors and to carefully inspect each slab upon delivery.
Only time and history will tell if the resining process is good, bad, or ugly. Of course, resin chemistry will most likely improve, as well as the application process. In the meantime, stone fabricators should be aware of these problems and learn to deal with them.
Frederick M Hueston is the founder of Stone Forensics and has over 30 years of experience in the stone business. He has written over 30 books and hundreds of articles. He currently is Chief Technical Direction for SurpHaces and Director of SurpHaces Learning Institute. He hosts a weekly radio show, The Stone and Tile Radio Show and Podcast.