Lead flashing vs. plastic bonding

[thomas.rynne]

Hi, I have a single story kitchen extension with a tiled roof which is leaking and causing a significant damp problem in the room. The leak is at the join between the main house and the slooping roof. I think the leak is caused by the lack of lead flashing along this join. I've previously been planning to fit one but because of time pressures at the moment I got someone round to give me a quote.

He suggested using a plastic alternative. I can't remember the name for it but it sounds like a bitumen based product which creates a bond between the wall and the tiles and seals the gap -similar to the black tape you can buy in DIY shops but a bit tougher. He quoted 350 pounds for this and said doing it in lead would cost 700. He'll guarantee the plastic bonding work for 10 years and although he would fit a lead flashing he can't guarentee it because when the concrete dries it will fall out.

I really don't know which option to choose. I feel a bit wary about choosing the plastic option even though its cheaper and has a guarantee. Does anyone have any experience with this alternative to lead flashing?

Although the lead flashing could/will fall out eventually I can put it back myself -which isn't too big a job. If the plastic breaks I just have to start again. However, 10 years is quite a long time and a saving of 350 pounds is quite significant.

Also, lead flashing is cut into the brick so I always imagined it caught some of the falling moisture in the wall which the plastic version will not do- am I correct?

thanks for any advice Thomas

[Andy]

No advice on those particular options, but you could use the fake lead flashing which is anodised aluminium backed by bitumen. May need surfaces to be painted with a proprietary primer first if they are dusty or difficult to adhere to. A hairdryer might help the bitumen backing adhere in this temperature, as will pressure. Not as good as proper lead flashing of course, but easy enough to fit, fairly cheap (

[Dave Plowman (News)]

Find someone who knows what they're doing.

[Dave Liquorice]

What breakdown between parts and labour? I suspect the tape he can whack on in a morning the lead might take a day or two. Who is backing the guarantee, an insurance company or him? If him what happens if he goes bust or disappears...

Personally I'm old fashioned when it comes to this sort of thing and would only accept properly chased in, wedged, and formed lead. These days lead will last for donkeys years, the pointing might need redoing but so will all the pointing at some point...

[Mark]

Trust me, black sticky tape and this builder should be avoided. lead flashing is the only way to fix this, and you should be able to get it done for well under £700.

-

[thomas.rynne]

Thanks for all the advice. I think I might have gone ahead with the tape, against my instincts, if I hadn't asked here.

Given the time I could waste trying to find a reliable builder I'm thinking of doing it myself. Is that realistic? Can anyone recommend a book/web site which describes the process.

I'm guessing you chissel out the mortar from between the bricks and push in strips of lead, folding each one over the bricks and then across the tiles. The bit I'm not so clear on is the join between the lead and the tiles. Does the lead just rest on the tiles? I've been looking at other roofs from a distance and the lead seems to form a straight line down the roof. Is that done by cutting each strip of lead to the right shape?

Also, is the lead just held in by the mortar or should I wedge it with something before I put the mortar in? How far in should the lead go?

thanks again, Thomas

[meow2222]

Not that clear what you mean, but it doesnt sound right to me.

Each lead strip will end up with a 1 sided herring bone pattern of cuts in it.

Is this a party wall by any chance? If it is, I'd go with the sticky tape, as lead is liable to involve you in the complexities and expense of party wall legalitiies. Sticky tape doesnt require any party wall complications, lead does since it means cutting into the wall.

If you get on a ladder and have a closer look at some stepped lead flashing you'l soon see how its done.

NT

[Dave Plowman (News)]

Stepped flashing is where you cut the lead to fit the existing brick courses. The other way is to cut a parallel groove with an angle grinder, etc. Stepped uses more lead - but looks better IMHO.

Rake out the mortar to a depth of at least an inch. Make a cardboard template first to get the angles correct, then transfer this to the lead. It's a very easy material to work with.

Like I said about an inch. The usual way to secure it before re-pointing is with wedges made from the lead offcuts. Make them about an inch wide and fold over in a 'Z' fashion. Then ram them in place with a drift and hammer.

It would make things easier if you could examine an already done job closely - perhaps with binoculars.

[chris French]

In message , " [e-mail]" writes

Wickes have a fairly good leaflet about it:

Direct to file:

[thomas.rynne]

Thanks for the link. I have a fair idea what I need to do now but it's raised some more questions.

How long is this likely to take? Given that the roof is about 3 meters will I get it done in one day (7 hours)?

Do I need to buy a dresser and/or bossing stick or can I get buy with a mallet and a bit of wood?

Should I use clips to hold the flashing down on to the tiles (as described in the wickes leaflet)?

Should I use sealant instead of cement for the pointing (as described in the leaflet)? I don't think I've ever seen flashing which doesn't use cement but if sealant works better I'm happy to use it. Sometimes the new alternatives can be worse though (like the stickey tape which started this thread).

[Christian McArdle]

My god! Is this a stepped flashing or a straight line join?

Anything other than proper lead flashing looks cheap and nasty.

Lead flashing is dead easy to do. I really enjoyed flashing in my conservatory. Although a stepped flashing would be more difficult than the straight one I needed, I almost wished I had needed to do one as I found the leadwork really enjoyable. A really nice material to work with. Easy to cut, easy to bend. Stays exactly where it is told.

Don't skimp on the patination oil, though. I missed a bit, and it is really quite obvious if you look.

Christian.

[Dave Plowman (News)]

Should be fine.

A dressing hammer - plastic - only costs about a tenner but isn't essential. However, making wood 'bits' to do the same job might not be worth the bother.

I've never seen these. Lead stays in place without any clips on the tiles.

The traditional way is just mortar. It's worked for hundreds of years. And of course is the same as the pointing between brick courses.

[Peter Lynch]

When I did my flat roof (many years ago), me and a mate did the whole width of the house in less than a morning. This involved angle grinding a few cm. of motar from between 2 rows of bricks, folding/inserting the lead flashing (with folded bits to keep it in, as mentioned) then using a quick-set mortar to fix it in place. If it's easy to get access and the weather is OK, I'd guess 1 person could do 3 metres in well less than a day ... unless you're getting paid by the hour :-)

[Chris Bacon]

The "clips" referred to are probably lead strips nailed in place and bent back over the flashing, like the ones used to replace a single damaged slate. They are used for quality leadwork - however, whether they're needed for the OPs work I don't know, as I don't know what that work is!

[Christian McArdle]

I used the special lead sealant, which is basically silicone stained lead colour. It is probably much easier to use, but more expensive, than traditional mortar. My basic procedure was to angle grind out the mortar to just the thickness of the blade, insert the lead, shape the lead and then seal. No need to rake out the whole lot to be repointed.

Christian.

[Dave Plowman (News)]

Right. My house is Victorian so once you're through the pointing raking out is easy.

[Nick H]

Just to clarify, are you talking about the horizontal flashing along the top of the roof or the sloping one down the side.

If its the horizontal flashing then you should be ok in a day. You wil

need to do it in two pieces as the lead shouldn't be used over 1. mtrs to allow for expansion, overlap the two pieces by 100mm.

Ive got various bossing tools but for a long time used a piece of 2

1 and a hammer, be careful not to hit the lead with hammer or mark it to much as it can look messy.

The wieght of the lead will hold it down to the tiles but make sure yo dress it nice and tightly into the wall particularly at the angle wher the tiles meet the wall and then just lightly dress the lead down ont the tiles, you will need to work back and forth a few times to get it looking neat.

Ive used sealents many times and they do a good job if you make sur the brick joints are free of loose cement and dust, I use a low modulu silicone in a suitable colour.

Pionting with cement is not difficult but again clean out the joint well and clean any cement of the lead afterwards.

BTW you should form up each piece of lead on a bench first, measure th upstand, rough angle of roof and the depth of the chase and then ben the lead into pretty much the right shape before taking it up onto th roof, you can then tuck it into the chase, wedge it with lead offcut and then carefully dress it into place.

The big secret with lead is take your time, if you work the lea carefully you will get it to the shape and position you want withou damaging it, if you rush it will look s**t

Good luck

-- Nick H

[<me9]

If organised and you have everything worked out that /should be ok, unless the unpredicted turns up.

For flat work, most can be done with a decent bit of finished timber and a hammer (or mallet) Edges should be rounded, or else marks will show.

I have clipped down, but not necessary unles in an exposed area. Lead is

*heavy* If dressed down properly there's no place for the wind to get underneath.

I've found the Wickes sealent excellent, if a little expensive. Don't forget to wedge the lead int o the joints first (with lead wedges).

Remember, do *not* exceed the maximum lengths of lead recommended. If you do so, it /will/ crack. You use a little more, but it will last you and probably your children out.

[<me9]

Words of wisdom there, Don't skimp on the raw materials and you'll enjoy woking with it, and know you've done a lasting job, as long as the rest of the structure survives.

[Christian McArdle]

So's mine (well actually Edwardian, but still built with lime). Unfortunately the very rear wall (but luckily no others) has been repointed with cement at some point, and this was the wall that needed the flashing.

Christian.