How to cut a clean, even 'chase' for lead flashing

Discussion in 'Roofing and Guttering' started by Safety First, 19 Mar 2020.

  1. Safety First

    Safety First

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    Newbie...
    Apron flashing to polycarbonate roof lean to. Wall is rough cast render.

    I set a shortish peice (mistake#1) of wood as a height guide onto ledger board and used a 5" diamond blade to cut a line. Worked not bad.

    Then cut about 8mm off guide board and repeated to make hopefully a 10mm ish max slot to put lead and hall fixings into.

    Instead I have a wandering mess from 8-20 mm.

    Looks awful. Too big in places for hall clips. Lead is going to wander around to the line.

    I can cut it again higher and and cover the bad chase using a wider piece of lead- was only giving a 3" drop so it's all for the best

    Not usually so cack handed but it was really difficult.

    Is there a tool /method I need?

    Think hall clips need 8-16mm...

    Thanks in advance.
     
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  3. palaceray

    palaceray

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    You should buy a proper chasing blade from somewhere like screwfix. You will only then need to do 1 Cut across
     
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  4. catlad

    catlad

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    Just get some flashband and cover the mess up.
     
  5. Safety First

    Safety First

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    Perfect. Cheers.:LOL:
     
  6. Safety First

    Safety First

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    Ah there we go. Never heard of it. ... Will go for that. Thanks.
     
  7. Safety First

    Safety First

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    Confused now.
    I was using a plain angle grinder and a normal diamond 5" blade...
    These chasing blades screwfix are thinner than the blade I already have.
    I could try to squeeze two blades together on the spindle :sneaky:
     
  8. Safety First

    Safety First

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    So,
    Not sure anyone else is going to have the same issues that I did, but I filled the too low, crazy wandering chase with mortar to put strength back into the render.....so I can cut another one about 2.5 inches higher. This will give about 5 inch drop-still none the wiser what the drop does!
    And tomorrow I'll be fitting 3 diamond blades onto the angle grinder and using a much longer 5x1 inch board sat on top of the ledger board as a guide.

    Obviously not ideal but I can't work out any other way of making the straight line in the render.
    Sods law the bricks under the render are all over the place.

    If the bricks are not rendered I guess you can usually rely on them being laid well and so offer a mortar course to clear out and flash into at any height you pick, but that will be straight.
     
  9. noseall

    noseall

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    The lead upstand should be 150mm up from the roof deck. This is to protect the wall from rain splash, because you will have removed the render below the chase and reinstated the render bell cast at the new chase height.

    Above that should be a cavity tray, on unprotected walls.
     
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  11. Ian H

    Ian H

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    I would advise against that. It would be a disaster if the 3 blades didn’t work as 1 for a fraction of a second.
     
  12. Safety First

    Safety First

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    Thanks for the heads up. I would advise against it too. I shall feed back with the result but anyone that takes a single anecdote as a working method needs their head examining. And now is not the time to need the NHS.
     
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  13. datarebal

    datarebal

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    three will not clamp up together without distorting.. risky.

    your angle grinder will be unlikely to cut a good chase through rough cast and into underlay brick bed.
    beg , buy or borrow a tool capable
     
  14. Safety First

    Safety First

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    Ok. Wow, took me a minute to work that out... I get you. Never was a bell cast to raise but there should have been. Ive increased the lead width from 240 to 300mm. As I should have 7 inch run, 6 inch drop, 1 inch in the wall, I need to leave something short.

    I think I can put a bead of silicone under the lead at the top of the polycarbonate. Opal so won't see it.
    So maybe 5" run will be fine.
     
  15. noseall

    noseall

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    I'm reluctantly saying this but our 115mm Silverline thick diamond mortar joint disc is actually very good.
     
  16. Safety First

    Safety First

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    IMG_20200322_142356.jpg
    Goggles, mask, ears, gloves.... Scarf wrapped around my neck and tucked into jacket.

    As pic it was possible to do up the spindle nut Nat West tight and there was still some thread peeping.
    I figured that catastrophic failure would need heat or twisting. It never got even warm. That said the scarf was ready to take chunks of disc just in case.
    Did a great job in the end.
    Some of the bricks were like glass though and others were much softer.
    Brickie said on a wall they knew was being rendered they'd sling them in on the p155 and use overbaked ones too.

    I ran along the edge of a 1x6 sat and clamped on ledger board to get guide mark, then removed board and came back with long sweeps getting to max depth. This added more width to chase with each pass and mean I didn't wander badly. There was no middle bit to cut out after but a sig amount of dust.

    Key to getting away with it was ensuring all 3 blades were evenly held.

    Taking the guard off helped see what I was doing...


    As if!
     
  17. datarebal

    datarebal

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    How about a picture of the finished job
     
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