When we embarked on the DIY blackboard slate countertop project we had a general idea of how to do it, but in the end had to make a bunch of decisions, trial and error, research and pure guts.
Step 1: Cleaning the slate
These blackboards were from the 1940s, and had been glued to the wall with who-knows-what adhesive back in the day. Then at some point they had white boards glued on top of them! In other words, a TON of stuff to remove. You can read more about that process here
Step 2: Building the understructure
Just like a tile countertop, we needed to build up a structure for the slate to attach to. This was pretty straightforward (especially after doing the brick fireplace the same way). A sandwich of ¾” plywood, backerboard attached with thinset and screws, and then taping any seams. This flat, level surface then gave us the template for the slate. We took the opportunity to make the new surfaces a half inch further offset from the cabinets below giving the counters a bit more surface area and a more attractive overhang.
The best part of making our our counters is we could experiment as we went, and truly get it exactly how we wanted. If we had ordered them, we may not have been able to look ahead as far to see how we wanted it.
Step 3: Cutting and Installation
We used a borrowed diamond stone cutting saw (like a mini circular saw with a water attachment) to cut the slate. Matt would measure out the pieces we needed, set them up on sawhorses in the driveway and cut away. He scored guide lines with a metal scraper since drawing them on would wash off with the hose water from the saw. He also learned that using a guide was critical. We used a combination of a standard clamp guide from Harbor Freight, and some old trim clamped on with c-clamps to ensure a straight cut. This step required LOTS of patience and attention to detail. There were certain pieces we had picked out for particular areas due to the grain in the stone, so we only had one shot.
Installing the slate was just like large format tile. We used large format thinset and a wide notched trowel. There were some great resources online demonstrating the importance of how you lay down the thinset and how it impacts the strength of your floor/counters etc.
We set the slate with as minimal of grout lines as possible, starting with the edge pieces. This would ensure that the top pieces would overlap perfectly to create the counter edge. Clamping them in place was critical to ensure they would not slide as the thinset set up.
Once the sides were installed and cured, we could move on to the top pieces.
Step 4: Finishing
After experimenting with some trial pieces, we decided to slightly sand a bevel into the leading edge of the counters. This smoothed out the look of the stone and also should reduce chipping in the future. To achieve this, we used a belt sander to take off a fine bit of slate. It made all the difference in taking this project to a pro level. Some we sanded once they were set, some we did before.
Step 5: Sealing
After reading up on options, we decided to just finish our counters with mineral oil. And well, honestly have not done that yet. We still plan to, but they are performing so well just as they are.
By doing this project ourselves we save a TON of money, got the material we wanted (dark, solid, natural stone), saved materials from the landfill and truly achieved a unique one of a kind feature for our home. We still have a pile of leftover slate so we may do this again for an outdoor kitchen…
Questions? We would be happy to answer them!