Black Jacking Shed Felt Roof?

paperclap · 28 November 2022 at 2:39PM

Hi all,

So have had a few leaks in our shed. Not sure how old the existing felt is, but where moss has built up from the neighbour's overhanging trees, it's degraded some of the felt, and caused leaks.

I've now removed the overhanging trees. Done some patch work with some felt. But, thought may be best to simply Black Jack the entire shed roof, as there's a fair few leaks dotted about.

I know the best solution would of course to be rip the old felt off, and replace with new... but I'm thinking short-term, cheapest option, to see us through this winter. Maybe a year or more, if the Black Jack lasts!

Was thinking either EverBuild's Black Jack 905:
https://www.toolstation.com/everbuild-black-jack-all-weather-roof-coat/p60252

Or, 901:
https://www.toolstation.com/everbuild-black-jack-black-bitumen-paint/p88792

Both £30 for 5L. But, the 905 only gives you 1.25 square metres per litre... whereas the 901 gives you a whopping 5 square metres per litre!

The shed is 2.4m by 9.6m. So 23 square metres.

Any recommendations on the above, or any advice?

casper_gutman · 28 November 2022 at 3:21PM

Either option sounds like a bit of a bodge, but might possibly buy you some time. I'd imagine that to be effective (even in the short term) at spanning over splits in the felt any brush-on product would need to be applied thickly to build up a fairly thick layer, so the product that quotes lower coverage might be better for that reason.

However, it might be a false economy. The more expensive blackjack stuff is costing you £4.80 per square metre (£30/(1.25*5)). Shed felt can be had for lower cost, e.g. https://www.screwfix.com/p/roof-pro-green-shed-felt-10-x-1m/820ht is £23.99, or £2.40 per square metre - half the price of the blackjack! Better quality felt could probably be had for more money, but even the cheapest stuff will surely be more reliable than worn out felt plus blackjack and shouldn't take much monger to apply.

Mutton_Geoff · 28 November 2022 at 3:23PM

I'd go one further, strip the whole lot off and pay about £100 for a single piece of EDPM and bonding adhesive. That'll last you the next 50 years. Roofing Superstore etc sell shed size pieces of EDPM.

Belenus · 28 November 2022 at 3:24PM

I know the best solution would of course to be rip the old felt off, and replace with new... but I'm thinking short-term, cheapest option, to see us through this winter. Maybe a year or more, if the Black Jack lasts!

That might be key.

I don't know how effective or long lasting Black Jack will be but my instincts are that spending £30 for a short term solution might not make long term financial sense.

Additionally, applying Black Jack is likely to be a tedious and unpleasant job compared to stripping and replacing felt which you may need to do anyway sooner rather than later.

On the other hand £30 is not a lot so, if you are happy to do the work, go ahead with that if you really don't want to re felt now.

Consider EPDM as an alternative to felt. It is more expensive but lasts far longer.

cymruchris · 28 November 2022 at 3:35PM

Image: https://us-noi.v-cdn.net/6031891/uploads/editor/pk/noyp8eh8eyyx.jpeg

I used Thomson’s 10 year roof seal - and it’s worked perfectly. I had a number of leaks in a shed felt roof - couldn’t work out exactly where they were - put a decent coat of this over the whole roof - it looks better - and now it doesn’t leak. It’s been on 6months so far. It wasn’t hard to apply, but I needed a bit more than the tin recommended.