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Boat Welding How To

All paddlers know what a pain in the behind it is when you split your boat and then trying to find someone to repair it for you. Well take a look at this how to and you may be surprised how easy it is to do it yourself.
I am not a welder by any stretch of the imagination, which makes this how to all the more interesting as, if I can do this plastic welding lark then pretty much anyone can. That said you use this information at your own risk, I will guide you as much as I can with the instruction but I will not be held responsible if you turn your plastic craft into a molten lump of goo on the floor.
Right thats the serious bit over with lets get down to some fun!

The boat I welded in this how to was a Dagger Nomad 8.5. It had apparently been professionally welded before I got the boat and to be fair it had obviously held up to quite some abuse on the river since being welded. Some people will say you cannot really use a boat to its full potential once it has been welded. I personally disagree with this as I have given my Nomad some stick and besides, now I have the kit and the know how to repair it, who cares :-)

What you will need:

  1. Stanley Knife - Or Craft knife.

  2. Shave hook - Must have a point and a straight edge.

  3. Flat metal object - I have used a plasterers float as I found it the best for the task, which I will explain later. It needs a handle on it as you will be putting it against a hot surface.

  4. Plastic welding rods - I have used HDPE (High Density Linear Polyethylene) which is the closest match to the boat I welded, check with your manufacturer for best match. You can pick these up off Ebay for about £6 for 40 in various colours. If you can't get a colour match for your boat then get clear rods.

  5. Hot air welding gun - With variable heat output and a slim nozzle as seen in the picture. I picked this one up off Ebay for £60, which I feel will way pay for itself, if only in the beers from appreciative paddling mates for fixing thier boats.

What to do:

I had a 60mm split in my boat which as mentioned had been welded before but had started to split again so I decided to give it a go at fixing it myself. See picture below of the split before I started the repair.

Split before I cleaned it ready for welding.

1. Clean up the damaged area. You need to get the shave hook and the stanley knife and give the split and the surrounding area a good scrape to remove all the crap around it. You also need to use the point of the shave hook to create a V groove along the split. This will increase the surface area that the weld will stick to allowing for a stronger weld. It can be pretty scary when you start taking plastic off and digging into the split but be brave and take your time to get a good clean work area. You can see from the pictures below the damaged area after it was cleaned and prepared. You can see the definate V groove I created. You can also see the remnants of the previous weld showing as darker areas.

2. Fire up your hot air welding gun. I set my welder to number 7 on the dial and gave it a good couple of minutes to get to temperature. Before you begin to weld you need to heat up the end of your welding rod, so I used that as an indicator to test that the gun was up to temperature.

3. Lets start welding. Hold the welding gun in one hand at approx 45 degrees to the work area and your welding rod in your other hand at approx 45 degress to the work area. See picture below.
Hold the tip of the welding gun approx 20mm away from your work area. When the heat starts to change the colour of the plastic on your boat (the colour will deepen and the surface will start to become shiny), present the tip of the welding rod into the heat air flow. The rod will begin to melt, at that point use a small circular motion on the rod so that you work the molten plastic into the V groove. KEEP THE ROD AND HEAT GUN MOVING, if you don't you will blow a hole in your boat and it will turn into a gooey mush. Work your way along the V groove. Once at the end quickly put down your welding gun and rod and then place a flat metal plate over the welded area and apply a fair bit of pressure. I used a plasterers float as it had a handle and a large surface area which helped flatten out the bulge that will happen when you heat up plastic. You need to put a good bit of weight on it (I leant on it and I'm a big lad). Keep the weight on for a few minutes to allow the plastic to cool.

4. Scrape away again. You now need to scrape the area again to smooth out the weld. You may find that the welded area is pitted in places, don't worry as you are going to weld over it again to fill in the blemishes.

5. Weld again. As mentioned previously, you will probably find that there are hollow areas of your weld. (See picture below) Repeat the welding process again along the whole weld to raise the welded area and it will also fill in those blemishes. Don't forget to put weight on again and then scrape away to smooth again. I went over my weld a third time but you can decide if you need more or less welds.

6. Thats it you are now done. That was easy wasn't it? :-) Let the area cool fully and you are good to go. I found my weld solid enough and if it gives again, who cares cos I will just weld it again. Below is a picture of the finished job.

Here is a link to a nice video that those clever chaps at Liquidlogic kayaks have done on plastic welding.

Also here is a link to a thread I started UKRGB with some helpful info from other paddlers on the subject of boat welding.