Can You Weld Rebar?

Rebar is invaluable for building projects and being able to join two pieces can add to the overall stability of the construction. Welding the rebar is a great way to achieve this, but can you do it? The short answer is yes, you can, but not all rebar will react the same way.

What is Rebar?

Rebar, or reinforcing bar, is a steel bar which adds tensile strength to concrete. It fortifies the concrete to make it more compacted and stronger.

There are different types of rebar, and while they are all suitable for many construction jobs, some are better than others for larger constructions.

Types of Rebar

Mild Steel bar

This is possibly the most widely used. It has good tensile strength, it is easy to work with and it is cheap.

• Texture: The surface is plain and round in shape.
• Width: Available from 6mm to 50mm
• Uses: Mild steel bar is mainly used where steel bars are needed to slide in to a metal sleeve. This includes dowels at expansion joints, contraction joints in roads and in column spirals.
• Properties: It is easy to cut and will bend without being damaged.

Deformed steel bar

There are different types of deformed steel bars, and they are both designed to reduce slippage. They’re also the best when it comes to welding.

• Texture: The surface has ribs, lugs and indentations.
• Width: Available from 6mm to 50mm
• Properties: Better strength than mild steel bars.

TMT Bars (Thermo-Mechanically Treated Bars)

These have been heat treated, which adds extra strength to the concrete. TMT bars are easy to bend, flexible and a good choice for welding.

They are used for RCC work and have excellent qualities:

• Superior strength
• Welding ability
• Excellent bending ability
• Good ductility
• Resistant to corrosion
• Will withstand earthquakes

HSD bars (High Strength Deformed Bars)

These are cold twisted steel bars. They have a low carbon value and are used for reinforcing residential and commercial constructions and bridges.

Just like TMT bars, the have their own excellent properties:

• Superior bonding strength
• High tensile strength
• Better welding capacity

You may also come across other types of rebar but these are not so widely used.

• European Rebar. This is made of manganese so it does bend, but it is not suitable for places with extreme weather conditions.
• Carbon steel rebar. This is also known as black rebar. While it has good tensile strength, it is prone to corrosion.
• Epoxy coated rebar. This is carbon steel rebar which has an epoxy coat. While this does reduce the corrosion, the coating is still delicate.
• Glass fiber reinforced polymer. This is an alternative to steel. Made from fiber glass, it does have good tensile strength.
• Galvanized rebar. This is coated with zinc, so it resists corrosion. It is also an expensive option.
• Stainless steel rebar. This is resistant to corrosion, harder to damage and can be bent. It is also the most expensive option.

Why do you need to weld rebar?

Rebar adds strength to concrete, but there are advantages to welding it. Welding the bars can provide more rigidity to a structure. If you’re creating a rebar mat or cage and transporting it to site, welding will also make this stronger so it is less likely to come apart.

As with all projects, before you start, always make sure you have exactly what you need and that you have the appropriate materials.

• First, make sure you have the right kind of rebar.
• Some rebar will need to be reheated, so check whether or not you need to do this before you start.
• Check your filler. Do you need welding wire or rod?

How to tell if rebar can be welded

Obviously, the main criteria for welding rebar is the metal content. You may need to refer to Structural Welding Code AWS D1.4, but if you use a low-alloy steel rebar, then it is weldable and you don’t have to worry about any special considerations.

Rebar with a high carbon content is not suitable for welding.  You need a carbon content of less than 2.1%.

There are some easy ways to see whether your rebar is weldable or not.

• If rebar is of welding quality it will be grade-W and will be marked with a W. If the rebar does not have a W on it, then it is not suitable for welding
• Another way is to look at the end of your rebar. If both ends are the same color then it cannot be welded. If one end is red and the other is a different color, then it is suitable for welding.

You should also look at the joint you are looking to weld.

• You can weld lap joints, butt joints and splices.
• Parallel bars must be parallel and perpendicular.

Which filler to use

As with all welding jobs, it’s vital to choose the right filler and this depends on the welding method you are using. IF you’re using A615 Grade 60, the table below shows what should be used.

A full table of which filler should be used with different grades of rebar is available from the American Welding Society.

Preheating

Some rebar will need to be preheated to make sure you get a good bond. The main things you need to consider are the size of the rebar and the carbon content.

Rebar with a low carbon content will require more reheating so you will need to check the certificate if you can.

Welding rebar

Once you have your rebar and you’re ready to begin, prepare everything you need first.

You will also need to ensure that your rebar doesn’t move or you could end up with it out of line. A good way to hold it in place is a jig. If you are welding two bars next to one another, make sure they are exactly parallel before you start.

If you’re welding a joint, make sure the rebar is angled correctly before you start.

It’s always best to test your weld first rather than make a costly mistake.

Frequently Asked Questions:

What happens if I weld the wrong rebar?

If you use the wrong rebar, this will affect the tensile strength of the concrete and cause it to crack. Always check you have the exact rebar in the specifications.

My rebar bent while I was welding it. Is it ok?

You will need to check with the engineer. They calculate tolerances very precisely and any bend could affect the overall strength.

How do I know which filler to use?

The AWS has information to help you make the right choice of filler. They have a table which outlines which filler is required for different grades of rebar, and the best fillers to use. Try to keep to their guidelines when you’re welding rebar to ensure you get the best tensile strength.

Which type of welding do I use to need to weld rebar?

AWS guidelines say you can use three types of welding on rebar

• Shielded Metal Arc Welding (arc or stick welding)
• Gas Metal Arc Welding (MIG or wire feed)
• Flux Core Arc Welding

Conclusion

Welding rebar can be daunting when you first start. Any mistake could be costly, or could jeopardize the strength of a structure. If in any doubt, the AWS do publish guidelines to help you choose the right type of rebar and the method to use. The engineer on your project is also a good person to connect with if you have any questions.