Porous garage roof

Wooster · 3 Sep 2009

This is my first post - so be gentle with me...

I have a pre-cast concrete garage with a 'fibre & cement' roof. (It's the modern equivalent to the old style asbestos roof.) It's 14 years old, and the roof has become porous. In heavy or persistent rain the underside become damp. Mould has started to form on the underside. Replacing the roof is very expensive. Like for like is £400+, just for the parts. (And if it will only last another 14 years...)

Some sort of sealer might be an option, but they get mixed reviews: http://www.screwfix.com/prods/46708...psons-High-Performance-Roof-Seal-2-5L#reviews

There are less expensive roof products, but they are not strong enough to walk on - and I need to do this to trim my fir trees once a year:
http://www.screwfix.com/prods/37174...ng/Coroline-Green-Sheet-2m-x-950mm-Pack-of-15

So I was wondering... Could I use creosote? Clean the lichen (etc) off and paint the roof like a fence. Creosote waterproofs fences - the water beads up afterwards. The roof panels are mainly cement / concrete, so (surely) the creosote won't do them any harm.

Or am I missing something obvious?

Your thoughts would be appreciated.

joe-90 · 3 Sep 2009

It might be worth looking into using SBR primer. If applied from above and below it might just do the job.

Nige F · 3 Sep 2009

You walk on an "asbestos" roof

With crawling boards I hope. Can`t buy creosote now, only a substitute

noseall · 4 Sep 2009

Gravity is the greatest asset to any vertical product.

Deluks · 4 Sep 2009

Shouldn't be letting water in after just 14 years. Could there be water getting in another way and condensating on the underside? Just a thought.

If it is leaching through the sheets then overboarding with cheap corrugated pvc of the same profile (usually 3") should buy you another ten years use.

Wooster · 9 Sep 2009

First of all, thanks for your replies and thoughts.

I'll certainly look into SBR primer. I've never heard of it before.

Yes, I know about crawling boards. But some of the possible replacement roof panels won't allow you to even use crawling boards. They are simply not strong enough.

It certainly isn't condensation. The panels are wetter (and have the mould growth) only in the troughs of the corrugations - where it is wetter. The 'peaks' of the corrugations are are relatively OK. Water isn't getting in anywhere else.

I love the idea of putting 'cheap corrugated PVC panels' over the existing roof panels. Regretfully, I must have imperial corrugations - they are about 7" between peaks. Non of the replacement panels seem to be the same size.

Any further thoughts would be appreciated!
:D

Deluks · 9 Sep 2009

Another quick thought, could it be possible that the sheets haven't been fully supported during installation, this could mean that the spans are too wide between supports or that the roof isn't up to the load. Either of these scenarios could result is the sheets being under stress and hairline cracks appearing.

There is only one real solution, replace the lot. Have you looked into the cost of board and felt? You could get away with using a cheap felt for the first year or so, and then going for a good quality system when you've saved up a bit. You can get plywood or OSB from about £12-£15 a sheet if you shop around.

Wooster · 9 Sep 2009

Thanks for your reply.

Yes, I had thought of roofing felt - onto of flake board if i wanted to keep it cheap. However, one reason for wanting a 'quick fix' was the hard work of getting the old roof off - and fitting a new one. My garage is 19ft long and 13 ft wide.

The roof frame is angled iron (1" by 1") so it's pretty strong. It might not have had enough securing bolts, however, and (yes) it might have flexed in strong winds and introduced micro cracks.

Still might try creasote (substitute!) over a small area, just to give it a try. No one seems to have come up with an answer as to why I shouldn't use it.

Thanks again

Deluks · 9 Sep 2009

I very much doubt it will work. It's very thin stuff and will probably come through the sheets as the rain has done. This will stink out your garage and the next time it rains everything will probably be covered in watery brown oil.

There are specialist products for roof coating. Google Acrypol, Wickes also have some roof repair products on their website.

Wooster · 10 Sep 2009

Thanks for your thoughts.

I've looked into Acrypol before. It's probably wonderful stuff, but it would cost £200+ to 'do' my garage roof. (I phoned their technical department and asked about coverage.)

But you are probably right about using Creosote. Smelly and oily - and it won't fix micro cracks.

I've looked at the wicks site http://www.wickes.co.uk/All-Weather-Roof-Repair/invt/191215 and have asked them about the coverage to work out haw many cans I'd need.

Thanks for your interest.

Deluks · 10 Sep 2009

Did you make it to page 2, http://www.wickes.co.uk/Solvent-Free-Waterproofer/invt/164041

Specifically mentions cementious sheeting on the tin

Wooster · 11 Sep 2009

No, I didn't make it to page two! Looks a very interesting product - maybe just what I'm looking for.

Many, many thanks for your help and suggestions.

alittlerespect · 13 Sep 2009

Do a web search on 'liquid roof membranes' to get more information on available options.

Regards

diynot

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Porous garage roof

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