Repairing a corrugated asbestos-cement roof

[nothanks]

I have a large shed (far too large to consider re-roofing) which has a corrugated asbestos-cement roof that probably dates from the 60s. It's in quite good condition but there are a couple of cracks and one 4" hole where a pipe used to pass through. It seems the repair options are either Flashband (+primer), an EPDM patch, making a GRP patch, covering with a bit of corrugated roofing, or using galvanised mesh and cement. What else should I be thinking of? Any recommendations?

[Tricky Dicky]

Depends a bit on the aesthetics, patched in cement/asbestos roofs tend to look crap. If that is not an issue then a lot depends on how long you want the repair to last because inevitably you will end up repairing it again. Those roofs tend to weather over time the eventual surface does not provide the best substrate to adhere on and being the material it is not really feasible to clean it.

Richard

[Harry Bloomfield]

[e-mail] was thinking very hard :

Box section, corrugated painted metal roof as a replacement, it is not that expensive.

[newshound]

Rather than flashband I would be thinking about the fabric with mastic tapes, Sylglas to DIY-ers or Denso tape to professionals. Together with a bit of corrugated sheet of the correct pitch for the 4 inch hole. Probably not galvanised mesh plus cement, too likely to crack over time.

[nothanks]

I've already re-roofed one smaller shed with 32/1000, but this one is LARGE (an old chicken house).

[nothanks]

I plan to wire brush it (wearing mask and working up-wind) around the damaged areas, then to seal it with either a PU varnish or proprietary primer.

[nothanks]

Why would you prefer Denso tape to flashband?

Currently, for the hole, I'm favouring a corrugated off-cut screwed and Stixall'd to the inside and then the depression at the top filled and profiled with polyester resin (car body filler) ... but all suggestions welcomed, especially from those who've already solved the same problem.

[harry]

I fixed mine with flashband. The stuff lasts a long time.

[Thomas Prufer]

I repaired a difficult-to-replace bit of asbestos cement roofing with fiberglass mats and resin, as used to repair rust holes cars. This soaked into the cement well, creating a good bond, and has lasted ~10 years so far. Came in a kit with resin, hardener, and mats...

Thomas Prufer

[Brian Gaff]

The problem with this stuff is that as the building settles, the roof is under stress and fixing cracks etc, is only postponing the inevitable. I think it goes brittle with age myself. The only, not very pretty thing I did for some years till I was ready to let it go was to use plastic corrugated stuff over it, tucked under the apex strip. Fillers, glue and other clever things seem not to bond to the powdering asbestos very well. Brian

[Brian Gaff]

Hmm, well, its actually not that dangerous, as its particles not fibres, bout the kind of dimpling it has on its surface seem not to be able to be removed and if you do it seems that its still powdery underneath. I guess some modern paints might be better though. Brian

[Andrew]

Drips condensation during cold weather though.

[tabbypurr]

If replacement isn't practical, a cheap effective option is: Apply bitumen paint Apply cloth Apply bitumen paint Sprinkle on sand.

NT

[newshound]

Because I think you would get it to stick much better to the irregular and friable surface.

I'd agree with that, except that stixall might well be enough. What are you going to screw it to? Or do you mean put a few nuts and bolts through the two layers? I would be OK with that. The problem I can see with filling the depression with car body filler is that I am sure cracks will open up. As an alternative, how about filling the depression with mastic? The main thing is to get a good fillet over the lap joints. Or, as I said, sylglas or denso.

[nothanks]

Thanks for that. I'll think about using GRP on the top.

[nothanks]

Yes, roofing bolts to hold the wiggly tin. Perhaps a bit of GRP over the top.

[Harry Bloomfield]

As does asbestos. Steel can be fixed by either buying the insulated version, or adding insulation.