Desmopol roofing Polyurethane membrane
Discussion
Folks, the short version of this is I'd like to know the price of this stuff, 25kg tub + accelerator.
Long version:
The recent storms haven't been great for building roofs, but sure have been great for testing them!
I'm having a few issues with the build of a new dormer on my house. The flat roof is leaking like a sieve. The builders have already applied the Desmopol product as the final coating, but despite this the water is still able to find its way through. It's a warm roof: board > DPM > insulation > board > desmopol. 12" upstands along a ~6m interface with a ~40deg pitch roof.
Builder doesnt seem to be in control and maintains that the water can't be getting in through the new flat roof because this desmopol stuff should have sealed it. I don't think he can have studied his work that hard because when I had a look it seems to be full of pin holes. The area is ~21m2, which by my calcs after finding the product data sheet requires ~32kg of the stuff to give a 1.1mm thick finish. That depth is the minimum as per the data sheet, ideally I want it to be thicker than the minimum allowed. He has barely used 1 25kg tub.
So I want to convince him to apply another layer of the stuff. What are my chances of convincing him that its reasonable to insist he goes and buys another tub (+accelerator for the cold weather). Is this stuff mega money? I don't want him to use the extra 6kg tub that it looks like he got to just patch up some areas, IMO it needs redoing completely, certainly for my peace of mind. I'm not sure that there are any alternatives: we have discussed some but on reflection it seems to be that a re-coat is what is needed. I certainly don't want any bodge fixes!
Other maybe relavent info: the "flat" roof is supposed to have a 1:50 fall, and indeed suitable fairings have been installed on top of the joists. However the joists seem to me to have about a 1:50 fall themselves in the wrong direction, meaning the boards and overall roof have ended up just about flat. not a problem for the desmopol, according to the data sheet, but certainly not what the drawings say.
Thanks in advance
Long version:
The recent storms haven't been great for building roofs, but sure have been great for testing them!
I'm having a few issues with the build of a new dormer on my house. The flat roof is leaking like a sieve. The builders have already applied the Desmopol product as the final coating, but despite this the water is still able to find its way through. It's a warm roof: board > DPM > insulation > board > desmopol. 12" upstands along a ~6m interface with a ~40deg pitch roof.
Builder doesnt seem to be in control and maintains that the water can't be getting in through the new flat roof because this desmopol stuff should have sealed it. I don't think he can have studied his work that hard because when I had a look it seems to be full of pin holes. The area is ~21m2, which by my calcs after finding the product data sheet requires ~32kg of the stuff to give a 1.1mm thick finish. That depth is the minimum as per the data sheet, ideally I want it to be thicker than the minimum allowed. He has barely used 1 25kg tub.
So I want to convince him to apply another layer of the stuff. What are my chances of convincing him that its reasonable to insist he goes and buys another tub (+accelerator for the cold weather). Is this stuff mega money? I don't want him to use the extra 6kg tub that it looks like he got to just patch up some areas, IMO it needs redoing completely, certainly for my peace of mind. I'm not sure that there are any alternatives: we have discussed some but on reflection it seems to be that a re-coat is what is needed. I certainly don't want any bodge fixes!
Other maybe relavent info: the "flat" roof is supposed to have a 1:50 fall, and indeed suitable fairings have been installed on top of the joists. However the joists seem to me to have about a 1:50 fall themselves in the wrong direction, meaning the boards and overall roof have ended up just about flat. not a problem for the desmopol, according to the data sheet, but certainly not what the drawings say.
Thanks in advance
roofer said:
If it's not mixed, or installed at the correct rate, timing, it will pinhole.
Before re coating, it should have a re activation primer used, to make sure the coats fuse.
It has to be mixed with the right amount of activator for the temperature that day.
Oh, and it's s
t.
Sorry to go slightly off topic, but in regard to that last sentence about the quality of the product...what in your opinion would be the best product for a flat roof these days? I might end up re-doing the garage in the next couple of years.Before re coating, it should have a re activation primer used, to make sure the coats fuse.
It has to be mixed with the right amount of activator for the temperature that day.
Oh, and it's s
t.The best quality products are usually out of the domestic budget range.
If you go to your local Roofing stockist, they will have some IKO T.O system product which will last 20 years plus if installed correctly.
As will any SBS modified bitumen membrane systems. Polymer modified Asphalt is excellent, and can be easily overlaid 30 years later.
At the end of the day though, any product needs fitting correctly. And there are so many slashers in the domestic level of the market, it's a minefield.
If you go to your local Roofing stockist, they will have some IKO T.O system product which will last 20 years plus if installed correctly.
As will any SBS modified bitumen membrane systems. Polymer modified Asphalt is excellent, and can be easily overlaid 30 years later.
At the end of the day though, any product needs fitting correctly. And there are so many slashers in the domestic level of the market, it's a minefield.
Think about stripping and starting again.
I say this, as you have a sort of warm roof, but with another board (I am guessing plywood or OSB) below the top layer of waterproofing. If it has been leaking, there is the potential for a lot of water to be trapped inside the buildup. If it is all sealed up now, there is not much opportunity for that trapped moisture to dry out potentially leading to delamination and/or decay of the upper board material.
Ideally, strip and remove the top layer of board and re-cover the insulation with a waterproofing system that can be stuck or mechanically fixed to the insulation. This will depend on the insulation type and that might also need to be replaced.
You should never have a layer of wood-based board above the VCL in a warm flat roof. If the roofing material needs to go on a board, then you should construct a cold vented roof system.
I am not saying it will definately have problems, but just re-coating and trapping moisture in the roof is a high risk plan!
I say this, as you have a sort of warm roof, but with another board (I am guessing plywood or OSB) below the top layer of waterproofing. If it has been leaking, there is the potential for a lot of water to be trapped inside the buildup. If it is all sealed up now, there is not much opportunity for that trapped moisture to dry out potentially leading to delamination and/or decay of the upper board material.
Ideally, strip and remove the top layer of board and re-cover the insulation with a waterproofing system that can be stuck or mechanically fixed to the insulation. This will depend on the insulation type and that might also need to be replaced.
You should never have a layer of wood-based board above the VCL in a warm flat roof. If the roofing material needs to go on a board, then you should construct a cold vented roof system.
I am not saying it will definately have problems, but just re-coating and trapping moisture in the roof is a high risk plan!
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