Liquid solution to weeping flat roof ?

[Jethro_uk]

Does anyone know of a liquid that can be poured onto a flat room to somehow seal what must be a pinhole leak ?

[pamela]

We had a bad leak from a flat roof on an extension and had it tanked with fibreglass and resin (like a boat). It was impossible for water to get through that but it didn't work.

Later we found the rain was soaking through the brickwork of the low perimiter wall surrounding the rood and into the celing of the room below. Maybe a membrane barrier had torn or hadn't been fitted. Sealing the wall with bitumen paint solved the problem.

Not that I did any of this but over the years I watched it puzzle a lot of previous attempts which had all failed to prevent the leak.

[Dave Plowman (News)]

Most likely at a joint or bend somewhere if a felted roof. Acrypol is very good - and you can get a scrim for it to reinforce it between coats, which is a good idea over a joint. If the felt seems otherwise good.

[tabbypurr]

bitumen is far cheaper of course.

[Chris Hogg]

Many years ago in a previous house, we had a shared drive and adjacent garages. The neighbour had his garage roof replaced, but the roofers did a very poor job, and it leaked at the join between his and my part of the roof and there was a visible gap at one point. I poured some Isoflex into the gap, quite a lot of it in fact, so much so that it even dribbled down the inside of my garage wall. But it sealed the leak!

I imagine the Thompson equivalent is just as good, and cheaper

[Jethro_uk]

Does it seep into the joints ? I know there are any number of "sealing" products which you paint/skim/roll over the felt. I also know from bitter experience with my parents flat roof over 20 years that they all leak.

I had a feeling I'd read off something for boats.

The proper job is to refelt, which might be a "round tuit" job. After I've made good the temporary (lasted 3 months) flashing repair I had to do last year.

[Mr Pounder Esquire]

Many many years ago I worked as the maintenance guy in a big hotel in Blackpool. But not for long. The flat roof leaked badly, very badly. The owner spent thousand of pounds on repairs with different companies. The water still pissed in and all over the guests. Hotel is now closed down.

[tabbypurr]

patch repairs are known for quick failure. But it would be hard for a single all-over layer of new felt to not work. However leaking decks can be rotten, and a new felt layer can trap water, accelerating further rot.

Last time I patched a leaking felt roof we had to use whatever was on hand. It just wasn't practical to do anything else. So on went: sand & bitumen to fill a hole bitumen (in solvent) bedding sheet more bitumen sand. Voila, ad-hoc roofing felt.

NT

[Dave Plowman (News)]

Hot bitumen? Not something most can DIY.

[tabbypurr]

bitumen with solvent.

NT

[Brian Gaff]

So the moral is, before spending money try to find out where the leak actually is.

Brian

[pamela]

We had many tradesmen tell what was causing the leak but when they implemented their proposal the leak continued. We then invited surveyors and various independent specialists to determine the source of leak but they couldn't agree amongst themselves. Oh well.

[Dave Plowman (News)]

Yes. If the felt looks to be in good condition, likely a join has given way. Worth giving them all a coat of Acrypol. If that works, do them again with some scrim over them too. That should see the felt out.

If the felt looks rough, best to bite the bullet and replace.

[tabbypurr]

What is the upside of acrypol over bitumen?

[Andrew]

I've tried that. Utterly useless. After about a year it will will craze and crack like mad if put on bitumen, and it's not exactly cheap either.

The best stuff I have used is Thompsons emergency flat roof repair . It looks like thick bitumen paint and you put it on with a trowel and it seems to dry very quickly.

Long(er) term, use something like Isoflex liquid rubber, but make sure you use their special primer first. Larger Wickes sell it, but B&Q no longer do.

Give the Isoflex a realy *good* stir and get some elbow length rubber gloves like the ones petrol delivery drivers use because it is messy stuff.

The special primer is very liquid so if you can wait for the coming cold dry sunny spell to allow everything to dry, the special primer by its very nature will seep into the defect and seal it on its own.

Wash the brushes in thinners or petrol or they just go solid.

[Andrew]

None. There is only a downside - after about 1 year it will crack and craze. Been there, done it, have the ....

[Andrew]

Thomsons emergency flat roof repair it you know where the defect is. Really good stuff.

[Andrew]

+1. V Important to use their special primer too, which costs just as much, but its like applying 2-pack PU paint.

[tabbypurr]

most such roof gloops are bitumen in solvent, some with added chopped fibres. Why are people so keen to pay extra for nothing?

Liquids that seal a crack will fail if the crack moves open any more. A single layer of felt lasts years. Even a patch of ad-hoc felt lasts years & costs nothing but the bitumen and a bit of rag.

NT

[Dave Plowman (News)]

Worked very well here. Had two problems on a felted roof which is now over

25 years old. One may have been from new as it depended on a combination of rain and wind from a certain direction and was minor. The other (first) was the felt split where it was turned up under the lead flashing. Both were fixed with a combination of Acrypol and its scrim. Perhaps the scrim is why it hasn't cracked.

First repair is over 5 years and counting.

The second one was difficult to find as it only happened rarely. At the transition where the flat roof meets a downward sloping tiled part. With lead over the transition. That, too seems to have worked.