Guide to Soldering Blocks
Soldering blocks are a foundational tool in your shop, but you need to make sure that you have the right one. Different materials will act differently underneath the flame of your torch. Your methods, style, and available tools will all factor into which one is ultimately the best for what you’re creating.
So, let’s take a look at the major types of soldering blocks, what they’re best for, and where to find them.
Different Types of Soldering Blocks
The soldering block is the surface on which you solder, but it needs to do a bit more than just resist heat. While everyone has their own preferences, there are still just a few major materials used when we’re discussing soldering blocks.
The two most common are silica fire bricks and charcoal blocks. Both of these come in a few different configurations, depending on what you’re planning to do. You can also modify the shape of most materials easily for more specialized soldering applications.
Fire bricks are special bricks made for use in high-temperature applications such as refractories and kilns. You’ll sometimes see them sold as refractory bricks or kiln bricks depending on where you’re shopping.
These bricks are made of silica, which means they’re slow to change temperature. Fire bricks are great at retaining heat, but they take a lot of thermal energy to heat up in the first place. This can make them a bit problematic to use with a smaller torch since the silica will tend to “eat” heat until it’s red-hot.
Fire bricks come in both soft and hard variations. The softer ones are crumbly but can be pierced easily with bits of silver or steel to make clamps.
Fire bricks are easy to cut down into smaller pieces if needed, and they retain heat for a long time. This makes them ideal for creating smaller areas where you need a lot of heat, you just need to position the bricks correctly.
Fire bricks have better durability than charcoal, lasting much longer. Hard bricks last longer than soft ones by a good margin but are harder to form into molds or other shapes.
They can be found easily online, usually bought as refractory bricks. The higher temperature they’re rated for, the harder they’ll be. Ratings for 3,000°F and higher are what we generally consider “hard” bricks, while those in the 2,300-2,500°F range are much softer.
Charcoal is the other serious option. These bricks are created with charcoal, either a solid piece (soft blocks) or a bunch of loose charcoal that has been under high pressure (hard blocks).
The main advantage of charcoal is that it creates a reducing atmosphere, meaning that it will help to keep your material from oxidizing while it’s under the torch. This is invaluable at times, and is especially helpful with very reactive metals like copper.
Charcoal, both types, are easy to form and carve. Many a silversmith has begun their melting journey with just a bit of hollowed-out charcoal brick. I’ve carved ingot molds with nothing other than a pocket knife out of them several times.
Charcoal does need a few extra precautions. The first is to always use it in an area with good ventilation, while you should always have this while soldering it’s especially important in this case.
You’ll also need to keep a squirt bottle around in order to stop the block from smoldering after the operation.
Charcoal blocks, particularly soft ones, have a shorter lifespan than fire bricks since they burn over time.
Charcoal bricks are a bit of a specialty item but many online retailers carry them. I recommend finding a hard charcoal brick and treating it like a soft one when it comes to preparation for newbies.
Honeycomb blocks are ceramic and made with a ton of small holes in them. They’re not much different from a fire brick in composition but tend to be much less crumbly.
The holes are of a uniform size, which allows you to make pins for holding pieces in place easily.
Honeycomb blocks are usually a bit thin compared to other types of blocks, so make sure you protect the surface under them.
While ideal, I find that they cost more than other options and require extra protection underneath them to keep from burning the work surface.
While they seem great for beginners I recommend working with something else to start with, especially if you’re still working with a butane or propane/air torch. The holes dissipate a lot of heat, which can make things difficult when you’re using a torch that’s on the lower end of the BTU spectrum.
Their biggest advantage is that they require no modification to work, just a bowl of sand or tile underneath. They also can’t be altered to form molds like other types of brick, which is a big disadvantage for those trying to perform a melt without a crucible and kiln.
So What Type of Soldering Block Do I Need?
It largely depends on preference, but you can draw some easier conclusions by comparing them side-by-side.
For most people, I recommend beginning with soft fire brick. They’re easy to use, can be shaped with almost any tool, and the soft surface makes it easy to improvise clips with pieces of wire or to stick straight pieces of silver into the brick to be held for soldering.
They also don’t require a squirt bottle and are less likely to cause problems when used indoors.
Soft fire bricks do tend to break down quickly, especially if they’re exposed to a lot of flux. The acids in the flux tend to eat at the brick a bit or break off pieces of it when the item being soldered is removed from the brick.
That said, if you’re using a proper fume hood or have a workshop with good ventilation then you may be better served with a hard charcoal brick. When compressed charcoal lasts for quite a while, at least compared to soft charcoal bricks.
Charcoal is a great material when you’re first learning how to use a torch as well. The reducing potential of the charcoal keeps surfaces a little bit cleaner and the charcoal takes on heat readily and stays warm for an extended period.
Soldering Block Preparation and Modification
Of course, no work surface is perfect from the factory so we often have to make small modifications and prep our blocks before use.
Small modifications can be done with almost anything. If you’re handy with a pocket knife they work well for carving into everything from a soft charcoal brick to scraping out a hollow in hard silica.
Protecting the Workbench
Your bricks will get hot on occasion, which means that you need to keep the surface underneath them protected. I didn’t realize this was a concern until I did a large melt and managed to burn off the clear coat under and around my block on the desk I was using.
I still work on a wooden bench, as do most jewelers, and there are a few options to help protect your desk.
A sand-filled bowl larger than your brick is one solution. Others use different heat-absorbing materials in the bowl.
My preferred solution costs less than a dollar: just buy a single 12”x12” tile from a home improvement store. I’m usually able to get them for $0.55-0.85. Any ceramic or stone will do.
These tiles can still break if you do something excessive with heat, but they will keep your desk, counter, or workbench from being damaged by the heat. I generally keep a spare on hand in case one breaks in the middle of a project, but that’s a rare event and is usually precipitated by a stupid move on my part.
In any case, with daily soldering on a roughly painted desk, there’s no damage after a couple of years. A simple tile can solve a lot of problems.
Ease of Access
A lazy susan or other turntables can make using your brick much easier. There are both purpose-made kits or turntables you can buy separately.
Look for metal or ceramic parts. Plastic ones meant for casual kitchen use won’t be able to stand up to the heat.
I don’t personally use one anymore, but not everyone is comfortable with using tongs to reposition a hot brick when needed.
They can be a great asset for those new to soldering. That said, you should be focusing on heating the entire piece when working with silver, brass, or copper instead of heating in one specific area which makes the turntable a bit less useful than it appears at first glance.
That said, they’re a huge asset if you’re working with gold. Gold soldering is often done by going in hot and fast directly on the solder, and a turntable will let you get on the areas that most need the heat without a lot of tricky repositioning.
Safety Warning: Always cut, drill, and otherwise work with silica bricks outdoors and, preferably, with an N95 mask. Silica dust is nasty and can lead to silicosis over time, minimizing exposure is a great idea. For the same reason, you should periodically use a wet wipe to get the dust off your bench instead of just sweeping it.
Cutting fire bricks is easy, no need for power tools. I’ll often use a drywall key saw to cut hard bricks. Something with a thinner kerf like a miter saw will save more material but a $20 hard brick can be cut down into a half-dozen bricks suitable for soldering jewelry. Soft bricks can often be cut with a knife and a sawing motion, although it’s terrible for the blade’s edge.
Silica fire bricks can be stacked to make a small “kiln” type setup. It will take some experimentation to find the exact setup but an enclosed area with a vent will do fine. The vent is to keep the torch from blowing itself out as the air comes back towards it.
Molds can be made from either. A shallow, long hole in the fire brick will let you form ingots. Line the area with flux like you would a crucible and you can melt silver in it. This usually creates a rectangle-esque ingot, but round ones can be made with a circular depression instead. A bit of hammer work and they’ll be ready for rolling or other further processing.
Charcoal is a great material, but I rarely use the bricks as I generally work indoors with an improvised hood.
There are a few things you need to do differently with charcoal.
Cutting up charcoal bricks is easy enough, but you need to be careful to preserve enough depth in them since they wear down so quickly. I prefer not to cut them down and will use one side for molds and the other as a soldering surface when I do keep one around.
Charcoal bricks, especially the soft variety, also need to be bound to prevent them from cracking. The thermal expansion and shrinking from changing heat will cause the brick to crack, often in really bad spots.
Use bail wire or some spare copper to wrap around the outside of the brick. I wrap six times around with 24g copper wire to handle this task, others swear by steel binding wire. This will keep the brick in one piece, even if it does crack.
While charcoal cracks a lot it won’t affect your melt in most cases. Molten silver has a very high surface tension, so it’s not going to run down through the cracks like water would.