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Cracked Header Repair – DIY No Welding

Add exhaust repair putty to the chopped fibreglass

In Short

Adding fibreglass to exhaust repair putty massively improves the quality & strength of cracked headers repairs


Chris Fix has done an excellent video on how to do a cracked header repair but it misses out one crucial point.

To get the basics, watch his video from start to finish it has gold sprinkled throughout.

Great video with great advice but one thing can make the repair MUCH better.

Making The Cracked Header Repair Better

In the Chris Fix video he shows how to seal up the header.

He uses the exhaust repair putty directly onto the leaks in the header.

In my experience of cracked header repairs, this does not work. Applying the exhaust repair cement directly onto the header does not work for long.

The header gets too hot for the putty in normal day to day driving, the exhaust putty shrinks and then it cracks into small pieces and then it breaks off completely and you are back to square one.

My Top Tip

My top tip to avoid this cracking problem is to mix the exhaust putty with fibreglass before you apply it to the exhaust header.

My source of the fibreglass. DEI Radiant Matting but any fibreglass material should work
Cut off small pieces

I have DEI Radiant Matting sitting around so I used that by cutting it up into small pieces. If you don’t have fibreglass matting, exhaust wrap should also work, basically any fibres that can withstand high heat.

Cut up the fibreglass until you have something like this

I cut the fibreglass into a pile then I add the exhaust putty a bit at a time until it has just enough paste to stick to the header and its flexible enough to fit into the gaps and holes.

Start by adding a bit of putty and mix it in
Mixing in the putty/cement breaks up the fibreglass even more. Keep adding the exhaust cement until you get to……
…this. Just enough exhaust putty to bind all the fibreglass together and sticky and flexible enough to stick to the cracked header and to fill in the holes and gaps

The fibreglass is what is going to give the exhaust putty its strength and it is what is going to stop the exhaust putty from cracking. You want to use as little putty as you can get away with, the less putty there is in your mixture the stronger it will be and the less change it will crack.

And that’s basically it. Apply the putty mix to the header in the same way as the Chris Fix video.

I did the exact same thing as Chris Fix except I mixed the exhaust putty in with fibreglass to give it strength.

Compared to Putty Only

I tried with putty-only twice and the cracked header repair didn’t last more than a few weeks.

By mixing in the fibreglass the cracked header repair lasted months.

Not a Permanent Header Repair

In my experience this is not a permanent repair but I drive the car quite hard ie full throttle and high revs, if you don’t do this the repair could last forever.

Whatever the case, mixing fibreglass into the exhaust putty made the repair last much longer.

This page was last modified Oct 21, 2021 @ 12:52 pm

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