My block built chimney is leaking a little water into the loft. It is where the haunching at the back of the chimney that covers the lead flashing has blown from the blocks leaving a small gap for the rain to penetrate. I am going to replace the cement to reseal the flashing but have no waterproof PVA available to create a key. Will I be OK using B&Q multipurpose or Wickes Universal PVA instead? I will be using waterproofed 4:1 cement for the job but imagine is would be advisable to use PVA first for a good key to the leadwork and block.
if you install a metal bead (bell bead) around the chimney and nail it just over the lead flashing first, it will give you a key to work with, then use 1 shot waterproof in your mix of sand and cement,4/1, It will probably take a couple of coats, so you can apply the first coat,then use your trowel to scratch the first coat, which will give the second coat a key, once set
I had to do the work last weekend and did something on a similar theme to your suggestion. No bell but I formed a curved rib to cover the lead and add some depth and strength to the cement which was made with waterproofer added. Managed to get the job done in one hit which surprised me. There are a few fine cracks in some of the remaining render but nothing blown - I reckon the previous owner may have had a chimney fire because the clay pot is badly cracked too. Do you think it would be a good idea to make up a waterproofed cement slurry to paint on before proper painting?
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