Bituminous mastic versus acrylic based roof coating

amandstu

I have bought tins of both of these and wonder is one better than the other in different settings.

Does the acrylic form a tighter bond?Is it more elastic?

Both tins seem to be reinforced with fine fibres and the price seems to be the same.

I am using them to patch up where the torch on felt covering the Bangor slates has opened up over and also on the flat roof at the bottom of the slates(where the sloping roof meets the flat roof and on the flat roof itself)

But ,in general I wonder what might be the advantages of one product over the other?

listermint

Felt over slates ?.. any pictures?

amandstu

https://www.boards.ie/discussion/comment/121585170#Comment_121585170

Nor really.I don't like using the camera on the smartphone.

If you can imagine a normal sloped roof with slates and an adjoining flat roof which meets the slates just where the eaves would normally be.

Our roofer mended this flat roof some 25 years ago using torch on felt and continued the torch on felt up into (ie over )the slates which is about 9 feet ,I'd say and down the other side as well-actually they continued into the valley between the two sloping rooves we have but left the front of the 2 nd roof (the 2 rooves run parallel) uncovered with just the original slates.

The thing is ,on the first slated roof that he covered with torch on felt he only went as far as the part above/behind the flat roof and so the roof with the slates is only half covered along the length.(the slated roof is twice as long as the flat roof)

The torch on should ideally cover the whole area of the slated roof but it doesn't.

So where the torch on covering meets the bare slates (half way along the slated roof) rain has been getting in.

I don't feel up to reapplying the torch on onto the slates and so I have been slapping on the mastic I was asking about-both along the line where the torch on ends and the bare slates "resurface" as well as the seam between the flat roof and the slated roof above and behind it.

I have applied torch on myself in the past but I also have friends who have set fire to a customer's roof and so I am just doing this temporary job with mastic for now :-)

Deregos.

What brands are the two bituminous and acrylic coatings you've purchased?

Tec7 used to do a good bituminous roof coating with fibreglass strands but I don't see it stocked anywhere anymore.

amandstu

https://www.boards.ie/discussion/comment/121585284#Comment_121585284

Yes I used that in the past .It was in 10 (20?) nlitre tins and I would buy it again if I could find it.

The two brands I have now are (for the acrylic) Cromapol

and for the Bituminous Mastic it is Cromar.

Think the company is Cromar for both.

5 litres tins cost 45 eu.

GreeBo

I would have thought the felt would have been better going under the slates? Its going to be hard to seal that joint permanently IMO as they rain is constantly seeking a way in and whatever you put there is exposed to all weather conditions.

Because of how it was done, even the smallest leak has nowhere to go other than into the attic/roof space.

amandstu

https://www.boards.ie/discussion/comment/121585685#Comment_121585685

You have given me an idea.I can look into the attic on a wet and windy day and look under the slates to see where the (very small now) amount of rain is still getting in on those days..

listermint

https://www.boards.ie/discussion/comment/121585685#Comment_121585685

Exactly my reasoning for looking for a photo. It sounds like it was done horrendously. But without a photo can't really tell. At this point I'm saying 'roofer'...

amandstu

https://www.boards.ie/discussion/comment/121586272#Comment_121586272

He is pretty reputable. This was 25/30 years ago . He has done a few jobs since and is still going I think.

He did explain to us that half patching the flat roof was not ideal(it it fully done now) but it was probably because we were skimping on costs at the time.

I expect we didn't want all the Bangor slates covered as well .It is a very old building.

Wasn't torch on fairly new at that time?

listermint

https://www.boards.ie/discussion/comment/121586947#Comment_121586947

Torch on is decades old. He should have lifted the slates and gone under with it. You don't torch on over slates or tiles. Especially not half way up a pitched roof. Where does the water go but behind it.

amandstu

https://www.boards.ie/discussion/comment/121586972#Comment_121586972

It wasn't half way up.It was half way along.

The full "height".

But it did join the unslated section of the pitched roof at an angle (perhaps 45 degrees from vertical) and so some of it(the edge) was indeed receiving rain coming down off uncovered slates.

I have put mastic on the vertical joins between the 3 or 4 slates and am looking at the apex (called the coping?) as well in case the wind forces rain in at the very top.

But if strong winds blow up from the bottom of the slates there is nothing I can do realistically.

The torch on should have been put on vertically I think ,but there is an inconvenient chimney stack that seems to have prevented this.

pic to follow

amandstu

Done a pic,anyway

20240108_152611.jpg

listermint

Ouch, for me I'd bide a bit of time for weather to get clearer and have those tiles lifted. The old stuff needs to come off and any new stuff run under those slates.

I wouldn't torch on top of what's there. Water will find it's way in. The transition allows for that. Original guy did a mickey mouse quick fix job on that.

amandstu

https://www.boards.ie/discussion/comment/121587536#Comment_121587536

Thanks.It is a while since I inspected the attic but I seem to remember that there is nothing behind lots of (all ? I can't remember) the slates anyway (along the whole inside of the very large roof)

If those large Bangor slates are keeping out the rain for the far greatest part ,might it matter if a little gets in so long as it is very little and just in the storms?

It must be coming in all over in high winds but it has never been damp when I went up (unless a slate had come off)

listermint

Biggest problem is water can get in behind that slate to 'goo' transition and then on to your valley. It may be sliding into an older valley bitumen or lead beneath. But it all has to come off to see. You should get away with it fine until weather improves for roof work.

10-10-20

https://www.boards.ie/discussion/comment/121587536#Comment_121587536

Agreed. That was a plaster-patch 25 years ago as a way of getting the OP down the path of affording a proper job. Its time has come to be done properly.

GreeBo

https://www.boards.ie/discussion/comment/121587496#Comment_121587496

The problem is that "half-way along" is effectively "half way up". If you take a point half way up the roof there is tile with a torch on felt joint below it. Water is running down that joint and finding a way in. Once its in it has nowhere to go unless you happen to get lucky and it finds another way out.

Really the whole thing needs to come of, you need a roofing underlayment underneath the slates, vertical battens to allow water to escape. Horizontal battens on top to take your slates/tiles. Sounds like you would also need to have the valleys rebuilt.

As above, based on the amount of water you are seeing, you should be fine to wait until summer to get this done.