Fire Table – Concrete Sealing

Fire Table – Concrete Sealing

As I said in my last post, today’s post is about sealing the concrete insert of our new fire table. And as I also mentioned last week, I made a mistake while sealing the concrete. But we’ll get to that. First, let’s talk about different concrete stains.

There are basically four types of concrete sealers, as I found out while researching the best one for my project. The four types are penetrating, acrylic, polyurethane and epoxy. Each one of these performs the sealing in a different way. Acrylic, polyurethane and epoxy stains all build a protective film on the top of the concrete to provide protection, albeit using different chemical compounds. Penetrating sealers, typically some sort of silicon compound, provide protection by reacting chemically within the concrete. These don’t leave behind a protective film like the other stains. A key benefit of the penetrating sealers is their ability to let the concrete continue to breathe, or allow moisture vapor to escape. This is important for pieces that will experience the freeze thaw cycle. Probably important for an outdoor fire table in Denver, Colorado. Here is a great summary of the different concrete sealers.

Based on my quick summary, it is probably clear that we decided to go with a penetrating sealer. I read a bunch of reviews and finally ended up going with Ghostshield Siloxa-Tek 8500 (not an affiliate). It provides all of the protection we wanted, while also not changing the appearance of the concrete. On top of that, I was able to order a sample to complete my whole project, since our concrete insert is very small. In fact I have about ¾ of the bottle left for future applications.

Let’s get into sealing. Before applying the sealer, the concrete did not repel water droplets.

The water just spreads out and begins to soak into the concrete.

The sealer requires two coats, one applied about 15 minutes after the first one. To start I laid out the concrete in our office so that the sealer could dry and cure in warmer temperatures. 

What I thought was a great setup to allow easier sealing of the sides.

Notice the paint chip under one of the ends to protect the concrete from getting scratched on our old trim piece? I used the trim to get the concrete off of the drip cloth. The paint chip ended up being a mistake that I’ll touch on later. 

For a concrete piece this small, I used a brush to apply the sealer.

Seal coats applied before the concrete dried back to its original color.

I started by applying both coats of the sealer to one side and letting it dry. After than, I flipped the insert over to apply to the other side. Check out how well it repels water with the sealer applied.

Perfect beads of water as the sealer prevents it from soaking into the concrete.

The research part of the concrete sealing was by far the most time consuming part of this process. Once the sealer was in it took just a few hours to get everything sealed. But I can’t finish this post without mentioning my mistake. Remember that paint chip? Well, it soaked up the sealer as I applied it. As I left the insert to dry, it basically acted as a sponge and held excess sealer against the surface it rested on. This surface happened to be the top of the insert. I wanted to do the bottom first to figure out exactly how to apply the sealer. Unfortunately, that decision backfired. 

After flipping the concrete to start sealing the top side of the insert, I realized that the paint chip of excess sealer had caused a dark spot on the insert top. Not great. I did try to lighten the stain with some concrete cleaner and grout cleaner with no luck. It was a good lesson to think through every bit of a drying setup for a sealer (or stain or paint) that can leave behind dark spots if not dried properly. Ultimately though, it’s not that noticeable, especially when it is set in the table with the fire pit in place. Lesson learned with basically no harm done, the best kind of lesson!

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