How to seal a cracked concrete slab roof?

[Dadam]

Our house has a lean-to coal shed at the side which is now used as a utility room. It has a concrete slab roof with a crack across it which leaks and drips a lot in this weather. The crack has been there years. A few years back I climbed up and a slathered a load of mastic type stuff (think it was emergency roof repair mastic) over the crack. It did work and lasted a couple of years but is leaking again.

What is a permanent fix that doesn't involve a complete new roof on the thing?

 

[Dadam]

I think it was this stuff I used. It was a really thick sticky black jollop.
I was wondering if something thinner would be better so it would penetrate deeper and fill it better. Maybe a silicone type exterior sealant from a sealant gun?

 

[fossyant]

How big an area ? Would something like this work - could be spendy.

https://roofin.co.uk/shop/supaslate...JSsPO6defRQrKTMWuKcGWHgEdF0aLhRoaAhzhEALw_wcB

 

[Gunk]

What is a permanent fix that doesn't involve a complete new roof on the thing?

unfortunately to fix that properly it’ll need a felt or fibreglass roof over the top of it

 

[Dadam]

The area is about 5’ by a few inches. Tiles won’t work as it’s flat

 

[Dadam]

unfortunately to fix that properly it’ll need a felt or fibreglass roof over the top of it

Not happening, it might be knocked down for an extension in a few years. So not “permanent” as such but few years hopefully.

Is it not possible to fill and seal to stop it leaking?

 

[Gunk]

Not happening, it might be knocked down for an extension in a few years. So not “permanent” as such but few years hopefully.

Is it not possible to fill and seal to stop it leaking?

You could try a flexible epoxy concrete filler.

 

[Gunk]

https://amzn.eu/d/iW7jTPW

 

[Drago]

Fill your crack, then get it fibreglassed. The roof, not your crack.

 

[bikingdad90]

Bitumen mastic? It’s a rubber crack filler and waterproof.
Round my area you often see it between joins on a path where it has been cut and lifted for telephone lines etc.

 

[si_c]

If the roof is concrete (a picture would help) then I would chip out the crack a little bit either side with an SDS drill, clean the larger crack, and then mix up a batch of concrete and fill. If the crack goes all the way through then some timber on the bottom of it to prevent the repair flowing through. Edit to add: I'd put some plasticiser into the mix as well - this will make it slightly more flexible when working and when it's cured it'll be more durable.

If you have the tools then the cost is pretty much the concrete and plasticiser, so probably around £50 or so.

That plastic roof repair is likely better used on a felt type roof.

 

[presta]

I'd have thought the hot-melt bitumen that roofers use would be the stuff, but your problem might be cleaning the old mastic off the concrete first, so that it'll adhere and seal.

 

[silva]

A crack means two parts, that can move relative to eachother, and is possibly a manifestation of stress caused by such movement due to temperature and/or material (differences).
Thus a sealant that is and stays elastic, and whoms bond to the concrete is strong enough to force the sealant to stretch. There are primers for concrete (=alkali), that prepare its surface to bond with the sealant. The sealent itself should be rubber-alike, polymer based, ment for the building materials ex. Some sealants state primer not needed, but still needs primer cleaning functions. Ex. https://ramsauer.ru/assets/files/206/parabond_construction_eng.pdf
These polymer-based sealants are very sticky, a hassle and risk of damage when having to remove them so it's taking some care.
Can be painted over, and in case water can stay for a while, will protect the sealant from this longer term exposure, which degrades most/all glueing agents.

 

[berty bassett]

Just clean all dust off , slobber felt adhesive all over then just stick shed felt down, it will do a repair that will give you peace of mind - or you can buy a kit on line with all glue and rubber that will be safe for 25 year and won’t cost the earth