Repairing kader on PVC canvas

Repairing kader on PVC canvas

Welding repair kader onto roofs and walls

This is an article for anyone who maybe interested in repairing the kader on their own pvc canvas.  Please don’t take any of this as the gospel “correct” way of doing things, it is only meant to give you an idea of how you might like to proceed based on how we have done things to date.  The main reason for writing this was because I found it very difficult to locate a good source of info for the questions that came about from having a go.

A quick mention for our marquee facebook group, without the knowledge of some of the people on there I wouldn’t of been able to progress at this.  The Facebook group is free to join and is meant for anyone who owns a marquee company or has a interest in the trade to use as a place to hang out.  Find it here –

Firstly the tools you’ll need:

The great thing about doing this type of work is that the tools required for the small scale stuff (which is what i’ll be talking about) are relativley cheap to buy and there isn’t alot required.  Here’s what we use to weld pvc along with a short description about each.  I’ve included relevant suppliers of materials where I think it may help, there will be other companies supplying the same products and i’m sure some will be cheaper.  These are who i’m currently using.  Maybe if you find a quality supplier you wouldn’t mind sharing any tips or info in the comment section at the end of the post.

Ok here we go….

  • Stanley knife – straight edge blades and carpet hooked blades.

Straight forward with these, as it says.  We use cable ties direct (here) for blades

  • Biro and ruler

Hope I don’t have to explain what these are!

  • Long length of straight metal used for scoring.

We have a piece of tubular metal which we have picked up somewhere along the way.  Its about 4.5m long.  If you dont have anything long and straight to score along then use a maquee purlin as an alternative.

  • Repair kader

Kader comes in various size core diameters and flanges.  You want what I believe is called a repair kader.  You’ll want the same size core as you currently have welded on your canvas which in my case is 7mm and a finish of 8mm.  This should be the same for most of the 3m, 6m and 9m profiles if you are using frames from suppliers such as Roder, Custom Covers, Techtonics etc.  However make sure you check.

Kayospruce Ltd – is where we get our repair kader from.  It works out about £1 per meter or there abouts.

  • Heat gun

The heat gun we use is a Leister Triac BT that we picked up one year at the Showmans Show.  These are the same branded guns that some of the manufacturers use for minor repair work so they should be capable of doing the job as well as other small time repairs you may need to carry out.  Price wise you can get them for around £350 brandnew which is my opinoin is worth the cash as you will easily recoup this in repair costs. I know ours was bought at the discounted show price but I dont recall the exact amount.  It’s also worth noting that they regulalry come up on eBay for around half the price, second hand.  – Leister heat guns on eBay

  • Rag and white spirit

Available from most hardware shops, B&Q etc.  White spirit is used to clean and prep the areas to be welded making sure they are clean and dirt free.  Other thinners can be used.  Any clean rag will do.

  • Spring loaded clamps

Some times called market stall clamps, use these or something similar to hold the new kader in place.  Easy to get cheap on ebay – market stall clamps

Clearing a work space and getting started.

Not to be under estimated, you need a good amount of space for this.  Obviously more so for the roofs then walls.  We like enough room to be able to fully extend any roofs, our largest for repair being 9m.  At the unit we have a second flooring area which is very slightly wider than 3m and a little over 9m long giving us just enough width and just short on length as a roof for a 9m structure is some where around the 9.5m length.  The area is kept for repairing canvas and so we have nailed large sheets of hard wood to give us a clean smart working area.

Walls are done on the same work space and we have plenty of room.

We shall be mainly talking about roofs as the walls are straight forward in comparison.  So take your roof and lay it out to the max.  If like us you have the room then take 2 ratchet straps and place one in each corner, securing it to the same ring you would connect the rope to pull the roof over a marquee.  At the other end secure it by either finding an anchor point or like us put a temp fixing in.

By tightening the ratchet straps to put some tension on the canvas it will pull out the kader straight making the removing of old kader easier.

We dont find putting tension on the walls necessary.

Removing the damaged Kader

With the canvas laid out, next we need to mark the kader with the biro to create points we can then then line up with our metal guide ready for cutting.  This can be tricky because the point at which to cut can vary depending on the original manufacturers kader application.

The easiest way to gauge this is to take a piece of repair kader and open it up.  You’ll notice the flange doesn’t open right back to the kader.  Your aim is to make the position of the new kader lie in the same place as the old.  The place at which to cut the old kader is where you want the new kader to butt up to which will be at the point I just spoke of, where the flange stops opening.  When butted up to this point does the new kader lie in line with the position of the old kader?  It should do, if not adjust the point that will become the cut so it does.  Now take a ruler and measure how far the gap is from the old kader to the cutting point.  On a standard manufacturers kader this is generally around the 1cm mark.  Now moving up the old kader, mark 1cm (or your worked out measurement) from the kader inwards placing a mark at regular intervals.  Approx 1ft apart should be good.

Incase you didn’t fully understand that I thought i’d make this quick video to help.

With the marking out done, get your metal guide and place it between the marks.  A tip here is to not try and line them all up at once.  Likely hood is that as you are repairing a roof that has been in use for a couple of seasons or more and the line of the kader isn’t straight.  Therefore joining all the dots at once wouldn’t be possible.

Using a straight bladed Stanley knife, slice carefully along the metal guide keeping weight on it so as not to move it off coarse.  You may find it easier to clamp it down depending on your setup.  This didn’t work out for us to well.

Unpick the Fittings

I hate this bit but its got to be done.  Unpick the velcro strips and the flaps that join on to the next roof.  You maybe wondering about unpicking the fittings that we have the ratchet straps too but we don’t do these until we have welded the majority of the new kader on, then take the ratchet straps off, unpick these and finish off the kader.  This just means we keep the roof tight during welding.


Welding on the new kader

Cut the repair kader to length by rolling it out alongside the roof and cutting with a knife.  We always leave a few extra centimeters each end.  Using the clamps line up the new kader and clamp onto the roof, don’t worry to much about position at this point as we adjust as we go. (check out the pic)

Fire up the heat gun

Let the fun begin.  If you have a heat gun like ours you’ll be switching it on a minute or two before you need it to allow it to get to temp.  Just for information the setting we use is number 6 or slightly over, obviously yours maybe different.  You will notice that the pvc on the inside of the repair kader has a lower melting point than normal pvc so a lower temp maybe suitable on your gun.

Starting at one end and slightly in from the the end of the roof (about 1/2 foot)  I first check the kader is butted right up tight to the roof on the inside of the kader flanges.  Then apply a clamp a short measure onwards to hold in place.  Weld and repeat until you reach the other end, leaving about 1/2 foot again.  We leave the end because we still have the ratchet strap connected to the roof via the rope link.  We need to detached and unpick the link strap, weld the kader then replace via sewing.  You will also re-sew on the flaps and velcro.  We replace the velcro with new, both on the roof and the flap whilst it’s off.

Once the roof has been welded this side you will need to flip it over to do the other.  You will not need the clamps for this as the first welded side will hold everything in place.

Here’s a short video of me welding a 6m marquee roof to give you an idea of the process.

That should be it, roof complete.  If you have achieved a roof then a marquee wall is small fry.  You can do these on your work space area or on tables as they are alot more managable.  The great thing about walls is there’s no unpicking and the whole process is very quick compared to the roof.  There are other components when it comes to walls however, such as replacing rings, the fastening string and roof to wall toggles.  Maybe that will be another article!

I really hope you found this helpful in some respect and please do comment below, leaving any thoughts, tips or advice you may have to share.

Until next time….

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