Should I use GRP to repair leaking fillet on concrete roof?

[481]

Our garage flat roof is made of 100mm thick concrete (1950s) which tends to leak where it butts up against the side brick wall of the house.

I repaired it 15 years ago with a 45 degree mortar fillet about 100mm wide (front surface) - but now this is leaking in a couple of places from cracks ranging from barely visible to maybe 1mm (ie no major structural degradation but enough to let water creep in).

I'd like to do another 15 year fix but preferably without hacking the fillet out and redoing it. What would people recommend?

1. DIY GRP?
2. Some sort of bitumous tape?
3. Paint on something out of a tin?
4. Rubber?
5. Something else?

In all cases I was planning to do a thorough clean and priming with G4 sealer. The fix would not be seen by anyone BTW so I don't mind what it looks like.

Any suggestions or Top Tips?

Thanks!

 

[Nige F]

Acrypol

 

[oldbutnotdead]

Lead if you want 50 years out of it. Fillets are a pain if there's any movement in the structures. Best to remove the fillet but if you can't/don't want to then chase above the fillet, use 220mm Code 4(so there's 100mm on the flat bit of the roof) and use Leadmate to seal the lead into the chase. Job jobbed.

 

[481]

Thanks for the advice folks.

For the record - in case anyone can benefit from a review of my experience - I decided to use Acrypol+, on the grounds that it was the simplest solution.

The best price I found, with next day delivery, was from an online UK roofing superstore. This worked out about 25% cheaper than local roofing specialists.

After a thorough clean and a couple of weeks without rain, I first applied the Acrypol AS8000 primer, to be on the safe side, followed by a single coat of Acrypol+. The primer went on fine, and was ready for top-coating after a couple of hours. The main downside of the primer was the incredibly strong solvent smell - even on a windy day it was almost overpowering when working close to it.

The top coat is incredibly gungy, and there's a bit of a knack to applying it which I probably didn't learn. Around the fillets (ie the edges of the roof where it hits the wall) it was a bit like applying icing to a cake. I used a 2" brush but it took a while to work it into all the corners. However, it did look like it was binding together really well (there are fibres embedded in it) and it comfortably filled cracks a few mm wide without a need for any scrim.

I painted up to a horizontal level of half a brick above the top of the fillet, creating a sort of upstand which I hope will mean I can get away without ever having to chase in any lead-work into the wall.

I thought it would be worth protecting the entire flat concrete roof at the same time (ie not just the fillets). Here, the primer went on fine with a roller, but I struggled to get good results from the topcoat using a roller - it really needs to be dolloped on thick, and it was hard to get a smooth finish once it started to dry a bit (it didn't like being re-worked with a roller).

As a result, the bits we did with a roller felt like they were too thin and they didn't fill all the little pockmarks in the concrete surface - but I'm not too worried about that because it did fill the small number of surface cracks that had occasionally been allowing water to drip in through the roof itself. I think Acrypol referred to a proprietary squeegee applicator which I guess would work better if you wanted to get an even, thick finish on flat surfaces.

The final thing to say is that both the primer and - especially - the top coat are incredibly messy and sticky. Don't even think about cleaning any of the brushes etc after use - just pick some old stuff you can throw away immediately after use.

Overall cost of materials worked out around £10+ per sq metre, including primer, topcoat and the cost of two brushes, two roller sleeves and a roller tray!

Time will tell how long it lasts but it looks like a tidy job and the topcoat is gungy and sticky enough to inspire confidence.

HTH and thanks again for the advice.