Oxbow16 Posted September 12, 2023 Share Posted September 12, 2023 Hi all I've finished installed soakers to my slate roof at a wall abutment, and I've cut the chase above ready for the flashing. The chase isn't mega straight, especially the bottom line This is mostly due to bits of stone and mortar falling away. And partly lack of skill On top of that, the vertical bit of wall that will be behind the flashing undulates and is anything but flat. I've dressed the soaker upstands tight to the wall. Should I do the same with the flashing or does it not need to be dressed so tightly? Also, I was planning to keep the bottom of the flashing about 10mm above the slates. The upstand would then be around 115mm, with 35mm tucked into the chase. Where the chase is lower than 115mm, does it matter? IE - with the lead at 115mm upstand, but the bottom line of the chase only 100mm, there will be a small void behind the lead. Is that ok as is? Or should I look to pack it somehow? I hope this all makes sense! It's been a long day. I'll try and add some photos shortly. Any advice much appreciated. Many thanks Link to comment Share on other sites More sharing options...
Gus Potter Posted September 12, 2023 Share Posted September 12, 2023 40 minutes ago, Oxbow16 said: I'll try and add some photos shortly. That would help, lets us see what you have on your plate. 1 Link to comment Share on other sites More sharing options...
Oxbow16 Posted September 12, 2023 Author Share Posted September 12, 2023 Thanks @Gus Potter Here's some photos as promised. Link to comment Share on other sites More sharing options...
Oxbow16 Posted September 12, 2023 Author Share Posted September 12, 2023 ... Link to comment Share on other sites More sharing options...
Gus Potter Posted September 13, 2023 Share Posted September 13, 2023 1 hour ago, Oxbow16 said: Here's some photos as promised True to you word! Excuse the spelling, quick response. Visually your soakers don't have enough upstand.. but I think you'll get away with it as the roof pitch is steep. I would recut the top line of the chase. Put a timber batten up the line of the roof, put safety boots on and hold the batten with your knee or get help to hold it at each end.. the easy way and much better, and recut a few mm higher with a 9" grinder with diamond disc, marked for depth of cut. Aim for 25 - 30mm depth of cut into the wall. Get your top side of the chase straight. That is the bit you will see. Get a brush and clean the chase, then get a Henry hoover / Dyson and really get rid of all dust from the chase. I'm not joking! Go to B & Q and get some SBR bond. Apply the SBR bond to the bottom of the chase only. Follow SBR instructions, let it go tacky.. if it dries out it is no good and makes the bond worse! Don't get the SBR bond on the slates and clean your tools pronto after. Cut the batten down to 25 mm less than the depth to the top chase. Hold it against the wall. Make up a mix of 1 part cement with 3 parts sand with some mortar plasticiser. Use the cut down batten as a guide to re level the bottom bed of the chase when the SBR is tacky. Clean up, keep it moist and go for a beer and let the mortar harden for a few days. Now you have a neat top cut and have sorted the bottom part of the chase that you need to be able to jamb the lead into the rebate. If you leave low spots in the bottom chase the water will get back into the wall and the flashing wiil get distorted when you are trying to fix it in place. If doing it DIY fold up your flashings but keep them to 1200mm long in length, then install as per Cookson Lead work guide. Be gentle when jambing the lead into the chase.. then point up and seal the chase. Make sure you use Patination oil and apply it to both sides of the lead (the bit you see and the bit you don't) and edges of the cut lead. This sounds like I'm laying it on thick but you have some good looking stone and slates there.. don't spoil it with crappy flashing work. In this case I would say the flashing should stop 10 - 15mm from the top of the slates.. stops capilliary action. As the soakers don't have enough upstand then just along the top of the soakers run a V shape line of lead mastic at the top edge. You can do this V by cutting a slot in a standard matsic tube nozzle. Ths will create an extra ledge which will mitigate the lack of upstand depth of the soaker. 1 1 Link to comment Share on other sites More sharing options...
Oxbow16 Posted September 13, 2023 Author Share Posted September 13, 2023 Thank you so much for taking the time to respond with such detailed instruction. I really appreciate it A few points in response first.... - The soaker upstands are 75mm which from everything I read is standard? - Yep, I've used patination oil on the soakers and will do the same on the flashing. I did think best not to use it on the bit in the chase, as I had planned to used lead sealant there and worried about adhesion. I've got some of this to use: https://www.screwfix.com/p/geocel-trade-mate-roofers-seal-black-310ml/32561 I read that sealant would be better than mortar as it is more flexible and not prone to cracking like mortar. - For reference, the roof pitch is 9/12 (around 36.5 degrees) - I'll be keeping my flashing lengths under 1200mm. - My plan was indeed to stop the flashing 10mm short of the slates / leave a 10mm gap at the bottom. - I've been using a leaf blower to clean out the chase, followed by a brush. But I think a last going over with a vacuum cleaner is a good call, so thanks for the tip. As for redoing it... I think the problem I have with that is firstly time and money. I'd have to buy another angle grinder, new discs, and redoing it all will eat into the time needed to do the same on the other side (plus a repair is needed there too so it will take longer). The wall then needs some pointing work, which I'll be doing with lime and want to get done before the colder weather kicks in. And unfortunately I don't move quickly, and have to the the job around work and around wet weather. My second issue is that I'm not convinced a new cut would be any neater. At least not with me doing it Some of the stone in the wall is old red sandstone (I think!) and is naturally prone to breaking easily. The mortar is NHL 3.5 and was done less than a year ago. That too seems reasonably crumbly in places. So I do wonder if a new higher cut would end up more or less the same? I'd guess it would. I don't want to be coming on the forum asking for advice, only to get the advice and not take it... But I wondered if anything in my reply changes your thoughts on redoing it? Or for that matter if anyone else has opinions on whether it is vital to redo it? Is the main issue aesthetics or practical (the flashing doing its job of keeping water out)? Could a compromise be... - Use a little sand/cement mortar to patch up any gaps between the top of the soakers and bottom of the chase, as well as in the bottom of the chase itself. (Question - how long would I need to leave the mortar to cure until I could put in the lead if I do this?) - Put in the flashing. Leave the sealant for now. The wall is quite sheltered and has been less protected for the best part of a year. - When I repoint, use lime mortar and small stones as necessary in any of the larger gaps above the chase. - Finish with sealant once all is dry. Or is there any chance I can make do with what I've done and just crack on, going a bit mental with the sealant in the chase to make sure no water can get in? Sorry for the essay and thanks to anyone reading it or pitching in. Cheers Link to comment Share on other sites More sharing options...
SteamyTea Posted September 13, 2023 Share Posted September 13, 2023 The cut, considering the wall type, is probably as good as can be expected by hand. 1 Link to comment Share on other sites More sharing options...
Oxbow16 Posted September 13, 2023 Author Share Posted September 13, 2023 1 hour ago, SteamyTea said: The cut, considering the wall type, is probably as good as can be expected by hand. "By hand" using an angle grinder? Thank you if so Or did you mean by hand with chisel and hammer? Link to comment Share on other sites More sharing options...
SteamyTea Posted September 13, 2023 Share Posted September 13, 2023 32 minutes ago, Oxbow16 said: By hand" using an angle grinder 1 Link to comment Share on other sites More sharing options...
Mr Punter Posted September 13, 2023 Share Posted September 13, 2023 I have just had some horizontal lead flashing done on brick. They used Flashpoint sealant in the gap at the top of the lead. Looked fine to me! 1 Link to comment Share on other sites More sharing options...
Oxbow16 Posted September 14, 2023 Author Share Posted September 14, 2023 20 hours ago, Mr Punter said: I have just had some horizontal lead flashing done on brick. They used Flashpoint sealant in the gap at the top of the lead. Looked fine to me! Thanks The stuff I've got is a bit different from Leadmate, Flashpoint, and the like, by all accounts. It's a bit more general purpose, but I've been told by Geocel that it's fine to use for lead flashing. Did get me wondering though whether I should ditch it and buy something specifically designed for lead flashing only. The one that I've got is Geocel Trade Mate Roofers Seal: https://www.screwfix.com/p/geocel-trade-mate-roofers-seal-black-310ml/32561 Anyone ever used it? Cheers Link to comment Share on other sites More sharing options...
joe90 Posted September 14, 2023 Share Posted September 14, 2023 It says it is compatible for lead 👍, however being OCD I would use grey to blend with the lead and the stone. 1 Link to comment Share on other sites More sharing options...
Oxbow16 Posted September 14, 2023 Author Share Posted September 14, 2023 1 hour ago, joe90 said: It says it is compatible for lead 👍, however being OCD I would use grey to blend with the lead and the stone. Haha - I think that's far enough and not even in the realms of OCD to be honest! But either way, it's available in grey too so all is good 1 Link to comment Share on other sites More sharing options...
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