As the stone industry grows, there are more and more importers and suppliers opening up and selling slabs. Unfortunately, a number of these companies are supplying stones that are problematic.
For this reason the fabricator needs to carefully inspect stone slabs before accepting the stones for fabrication. The following are some general guidelines for what to look at when purchasing stone slabs.
Slab size can be very important, especially as a determining factor in whether or not you get the job. First of all, if the slab is too small to make certain sections from one piece, the client may opt to find someone with larger slabs. Second, size can determine your waste. If there is a lot of waste, your cost goes up, and when your cost goes up, either your prices go up or your profit goes down. If you are bringing slabs in for stock, you should anticipate its most probable use and determine your needs and waste from that.
Polished is probably the most popular finish for stone in commercial and residential use. Other finishes include honed, thermal (flamed), sawn, bush-hammered (pitched), sand-blasted, etc. There are also different degrees within most of these finishes. If you own a reflective light or gloss meter, this factor is much easier to determine. Some quarries, factories, brokers, importers or distributors may alter a slab to make it appear better than it really is. In the long run this practice can cost you time, money, aggravation and, more importantly, your reputation.
Most people try to darken typically dark stones or apply waxes or coatings to make the polish appear better. If you suspect a stone has been altered, you should not accept it or else have the supplier prove it has not been altered. One way to test a material is to rub your finger across it to check for smudges. If the slab smudges, use a solvent, such as acetone, mineral spirits or neutral (pH = 7) wax or sealant strippers to determine what the slab really looks like. This practice may also help determine the proper color of the stone. If you have the capability to face polish the stone, you could polish the face along the edge, back or other inconspicuous area. The best method for avoiding these problems, though, is to deal with a knowledgeable and reputable supplier.
Consistency, for this application, is synonymous with balance. If a slab has good balance, you will have less trouble getting a two-piece countertop to match at the joint or a fireplace header and legs to look right. If you cover most of the slab with a piece of plywood, which has randomly cut out sections in it, you could more easily determine its consistency. Unfortunately, sometimes you don't know the consistency until the pieces are cut and being membered up with the piece that will adjoin it after installation. It is always a good idea to look at the consistency as the pieces are being cut and before doing edge work, cutouts or taking them to the jobsite. Because stone is a product of nature, very few slabs will be as consistent as you would like.
Beauty is in the eye of the beholder. What some people call an imperfection others may consider desirable, but some imperfections are just that -- imperfect no matter how you look at it. The following is a list of some of the major imperfections I have found over the years:
• Fissures and cracks, or veins that look like cracks
• Large brecciate sections (in either a veined slab or one with typically small brecciations)
• Holes, fills or pits
• Inconsistent veining
• Size (too small) or irregular shape
• Discoloration or a weathered polish
• Dry or mud veins
• Mineral deposits
• Thickness or gauging problems
Two machines that would do well in this industry are the stone stretcher and the stone planer. You would need a stretcher for every slab that is too small and for every piece that is cut too short, and the planer would be useful to ensure all adjoining pieces are the exact same thickness. However, since these machines do not exist, you must take great care to reduce your risk of needing them.