MOT Sill Welding

So my car failed on the sill having a hole in it. I'm after some advice on what I can\can't do as to repairing it. I'm thinking using some 1mm (could I use 2mm?) rectangular plate to fully cover the hole and then weld all the way round it totally sealing it up.

Was quite surprise to see that this area has been welded before!

I've taken a wire wheel to it to clean it up for your perusal.

Does it have to be flush or can I lay the new plate on top of the hole and weld round it so its slightly raised? I have included a picture with a red line to show the size of the patch how I propose to cover the hole.

Any help appreciated.

 

1mm will be okay over the top, patches need to be welded all the way round with no stitches or tacks. I can see more rust inside so you will need to keep going back to good solid metal so you don’t keep blowing holes.

 

look closer i can see more repair needed from just your pics that you have show

 

How much do you love this car,how long you think of keeping it,do you want it to just past the MOT,you doing the work,all these need to be answered.
Its been done before,so the chance its got worse are high,ie that hole will get bigger,the inner sill at the bottom and to the right is you main concern,and i bet you thats rotten.
So,if you dont care about the car that much or not bothered what it looks like and needs its MOT for work etc,patch right over it,you'll have to nurse a weld to the right there
Where in Kent btw?

 

Near Folkestone - don't love the car that much at all! Just need to get it through the MOT.

 

Then my man,its a big patch

 

At the bottom right there are 3 layers of metal. The top layer is just floating. You need to separate and remove the top 2 layers, clean up the thickest bottom layer, then extend your proposed patch downwards with a flange ( which can be plug-welded ).

 

I was just starting to think that way myself - I have some 1mm thick box section and thinking of cutting it so that there is a 90 degree or so 'lip' of say 8mm along the longer side of the patch.

 

I wasnt going to tell you as i wanted you to look and see where you thought it might want doing

part of reason for my post is to get you to look and see where and what you think was needed to be done

its also a lesson on where else to look before you start

 

As the man said patch it up and lots of black sticky stuff

 

There are several points I'd raise, you need to be brutally honest about finding where the corrosion ends, modern plasticised(?) Underseal type paints can maintain the panel shape whilst the steel has rotted away beneath it, work your way along the sill pushing firmly with your thumb/paint brush handle, the rotted section Will give quite readily; you'll soon learn to recognise the sound and feel of rusted steel breaking up, and the indent left;
Welded patches fitted before I'd remove, to weld the steel needs to be as clean as is possible, preferably bright and shiney, though when it's car bodywork thin, burning through and sucking contaminants from the reverse side is all too easy, but you can only do what you can do
Maybe consider cutting the old sill off altogether and fitting a pattern part, it's not nearly as much work as you imagine, you have the chance to inspect/repair the inner sill, the whole outer sill is new and won't need repairing in another place next year,