It's been a while since I posted anything and I wanted to give a quick update. It's been a busy summer but not with countertop activities. My group has developed a permeable reactive concrete (PRC) that is designed to treat groundwater and surface water. We are currently and successfully trialing a technology that could easily clean up mine pollution such as from the Colorado mine spill this summer. Moving that technology to market pretty much uses all of my time and unfortunately not good for pictures or blogging. I've turned down several countertop jobs so the market is still there. When I get back to countertops I will post some updates. Until then hold tight.
The 2323 project has completed. It involved 9 countertop sections, one shower insert, and one window box. The shower and window box were done last and were by far the most complicated.
Here's an in-process shot of gluing up the shower insert mold. Since it was one piece, the mold had to basically come out of the hardened concrete.
It was cold in the shop the night we placed these and it took about 4 hours longer than normal for the concrete to get to a point to trowel the backs.
One thing we know about concrete is that it shrinks. Even with all the relief cuts in the molds, these fought and fought coming out.
In the end everything came out just fine.
So on to some final shots of the installation. Kitchen with metal cabinets.
These countertops had pretty minimal finishing. They got a quick wet grind with 100 grit, slurry to fill any bug holes, then a final grind with 200 grit before sealing. I used ICT from Blue Concrete. This has been by far the best non-film forming coating I have used on countertops. These countertops have been in over a month with normal wear. Plenty of normal kitchen use means spills don't get immediately wiped up, more like dry out and get cleaned up a few days later. Nothing that has gotten spilled has made the slightest difference. I will have some more on that later. I placed a series of test samples and am going to do a round of testing for non-film forming coatings, similar to my previous sealer evaluations.
That is polished/ground only to 200 grit. These got ground after curing 2 days. Normally a shine like this would take to much older and harder concrete. The nice thing is that with my new mix there is less than a week from templating to installation.
The shower pieces installed.
The shelves are tempered glass held in place with stainless pins.
The master bath vanities are pretty simple. The platinum grey works well with the walnut and blue scheme.
Hey, I can see the light at the end of the tunnel on this project. Of the ten total pieces for the job, seven have been installed and three need to be placed.
If you haven't tried lithium silicate densifier, get a gallon and give it a shot. It basically increases the degree of hydration at the surface to make the concrete harder and less porous. I've used these on pavements for a number of years, but when you actually put it on by hand you can feel the concrete tightening up. I have been doing two applications at 50% strength, letting it sit for a day, and then two applications at full strength. They tend to slightly darken the surface which helps bring out the color.
I haven't been forming holes for faucet on these. I think it is easier to cut cut them in later. I bought a cheap diamond hole saw set at Harbor Freight for like $10 which works well enough.
A few installed and the sink getting siliconed to the bottom.
The bathroom sinks are a basin that just sits on top.
After applying the densifier I then have been applying a few coats of silane. I have been playing around with application techniques for the silane water proofer. This is after cutting it with some water and buffing lightly with a mild abrasive pad.
Well like usual scope creep has reared it's ugly head. Well since this is my project and money I guess that is ok. This project has now gone from six pieces in the kitchen to include some vanities a shower box and an integral window box.
I've seen some guys recently cover the melamine edges with painter's tape and am giving it a try. So far it seems to help with cleanup some and probably prevents some swelling.
The first two pieces were a large plain countertop and the sink section. The mix is my el-cheapo ($5.5/sf) GFRC mix with some Cheng integral color.
They were stripped after 2 days and lightly wet-ground. There were only a couple bug holes and prep was very minimal. The cell phone didn't take too good of pictures of the ground texture and I will have to remember to bring the real camera along next time.
The next step for these is burnishing and sealing. When GFRC works well it is unbelievable how little work is involved after placing.
The next project is underway and will be moving quickly. It's a renovation with six pieces in the kitchen and two in the master bathroom. The original steel cabinets are being reused and have been powder coated turquoise. The countertop color will be platinum grey. I've modified my low-cost Type S mortar GFRC mix to use Cheng Promix for the color and don't need any additional admixtures. I could formulate my own pigments, but for the time and project size their kits are the easiest. I always have way too much pigment leftover when I do it myself and this cuts down on long-term storage. Tests on this semi-original mix were 5000 psi at 7 days so I think we are fine.
There are four standard countertop pieces and a 36 inch deep island with a waterfall edge.
Those stainless steel ball tools make caulking a breeze and are one of the best $1.99 I have ever spent.
Here's a shot of the kitchen before cabinets were set. The wall are grey, white upper cabinets, some custom walnut cabinets, and turquoise lower cabinets. The bright grey countertops will look great.
I'm using a new sealer combination on this one. The three part Richard James system worked very well on the last big sink but it is film forming. The owner on this one doesn't want that look in the kitchen. I've been working with lithium silicate densifiers for curing conventional concrete and have been very impressed. They improve overall durability and stain resistance. I'm going to combine lithium silicate with a silane to get a finish that shouldn't need much attention over time.
Recently this question was posted on the blog. Assuming you haven't read everything on the blog in detail, I thought this would be a good question to reiterate some commonalities and differences between "outside" concrete and "inside" concrete. Do you add #3 re-bar to that? I want to do this for an outdoor bbq island. Can you get a concrete pumping company to come and form it, or is that something you need to arrange ahead of time? I'm assuming you need a nice smooth finish on it so drinks don't spill.
First, the main difference between exterior and interior concrete is what is termed exposure condition. Imagine two pieces of chalk, one inside and one outside. Which lasts longer? The inside one of course, but why? Water. Water is the primary mechanism of deterioration for concrete. It carries bad stuff in, like chlorides and sulfates. It carries good stuff out, like calcium hydroxide. It can also cause physical deterioration, think the grand canyon. And most importantly for many of us, it expands when freezing. So the biggest difference between interior and exterior concrete is the need for air entrainment in exterior concrete for freeze-thaw durability. If you are in warm areas then there isn't as much of a difference.
Secondly, on the topic of who to do it. Concrete is supplied by a ready mixed concrete producer or you can make it using bagged concrete and a rented mixer. It all depends on the volume. A normal mixer you can rent from Home Depot holds around 2 cubic feet of wet concrete . There are 27 cubic feet in a cubic yard and a concrete mixer truck holds up to 10 cubic feet. So that is 135 batches in a rented mixer. There is a significant up-charge if you are only ordering a small amount of concrete because the producer would rather have their trucks fully-utilized. A general or specialty concrete contractor would be appropriate to form the bbq island and would generally coordinate ordering the concrete if a ready mixed supplier is needed. If there is no way to get the concrete from the truck to the bbq then they may rent a concrete pump truck for a few hours. Yes, all that needs to be arranged ahead of time and probably through your contractor.
Realistically, unless you are pouring the world's biggest backyard bbq, ready mix concrete with a pump truck is not needed.
(Photo courtesy of Concrete Exchange)
Thirdly, the topic of reinforcement allows a short soap-box sermon. Rebar, steel reinforcement, is put in concrete to carry tensile load and minimize loss of life during extreme events. If something happens, earthquake, extreme snows, overloading, etc., our concrete structures are designed to crack which signals occupants to get out. The design codes specifically forbid over reinforcing. If too much steel is present then the occupants don't see the cracks before the building/structure falls down. So more is not better when it comes to reinforcing concrete. Also, steel doesn't do anything unless the concrete cracks. No cracks mean the steel isn't needed at the current time. That begs the question, why reinforce a bbq grill? Hopefully there isn't a concern for loss of life. Most likely the in-service loading will be very, very, very well under the capacity of the concrete. Really any reinforcement is there to hold it together on the off chance there is a crack during transportation or finishing. If that is the case do you need rebar or will something else work? With rebar you have to tie it off so it is located at a particular position in the slab. This can be a challenge for experienced contractors let alone a novice at home. I prefer to use polypropylene fibers. They are mixed into the concrete, don't corrode, and can bridge lots of little cracks at the same time. FYI, I don't use rebar in floor slabs, driveways, or parking lots. Most highways also don't use rebar either. Rebar is commonly used in structural applications, not thin slabs.
Lastly, unless you are putting concrete countertops on a boat or plane, smoothness isn't going to impact drinks spilling. However, you probably don't want a broomed finish on a bbq grill top. The smoother the concrete the easier to clean up spills.
Yes, I'm still here. We sold our house, bought one, and are in the middle of a major renovation. In the meantime we are living in an apartment and all of the countertop making equipment is in storage. I will be placing countertops for the kitchen and will start making progress as soon as the cabinet bases are set. We are keeping the original steel cabinets and having them stripped and powder coated.
The house was built in 1950. It is an expanded shale, lightweight cmu with a 2 inch air gap to brick. That combined with some interior spray foam means we will be very energy efficient.
Have no fear, there will be plenty of future concrete projects.