GRP roof disaster zone

David Costelloe · 17 Aug 2021

April 2016 - new 100m2 GRP roof for £23k.

Condition damp, cold and rainy, but the contractor only worked in the dry (allegedly)

2021 - Not leaking, but it now looks to be in a rare old state

Can anything be done - hopefully the OSB deck is still dry.

What caused this disaster?

What is to be done?

oldbutnotdead · 17 Aug 2021

Get a hose on it for starters, a fair bit of that is just debris. After that- hmmm. Topcoat looks as if it was too thin in places (where you can see the bare laminate and OSB) and too thick in others (where it's cracked).
The laminate itself looks decent enough (hopefully £23k was roof from scratch on a new build not just recover), grind off topcoat & recoat should do it, maybe put another layer of mat on just to play safe.
You'd want a nice hot sunny week to make sure it's bone dry before you start the job.

EDIT Ooh, just zoomed in a bit more on your first pic- is that a big raised ridge or 2? If yes then the laminate has failed (water penetration), grind back to bare at those points and relaminate.

David Costelloe · 18 Aug 2021

The previous three layer felt and 50mm of insulation blew off on the morning of Easter Monday 2016, with one corner ending up on the other side of the house. So the contractor replacement fixed insulated OSB boards (c. 120mm) to the concrete roof, taped the joints and GRPed it. It looked great new, but it bears many horrors...

Anyway, I'm going to try Desmopol (a polyurethane membrane that forms from a liquid) as a longer term fix - we needed an emergency fix two years ago and it seemed to the needed job. Regards DC

oldbutnotdead · 18 Aug 2021

Give it a good clean first, the PU stuff will bond better. Acetone wash on the laminate/topcoat should key it in even better (tho do a small bit first, acetone is used when relaminating to open up existing structure so new resin bonds properly, may not work with PU).
Pity you didn't get back to the original contractor- those big ripples are defective installation (damp boards), 3 years is no life at all for GRP roof.

David Costelloe · 18 Aug 2021

I tried to get them back when water was pouring into the house in 2019. Said they would attend, but did not, so I had to have an emergency repair done, technically invalidating a worthless guarantee. The work was so bad, I would not let them up there now.

The latest development was a leak from a gulley outlet that drained into an internal downpipe. After investigation and removing the boxing the cause was that the outlet pipe was not long enough to insert inside the down pipe - one pipe sat on the edge of the other, and had moved allowing a decent proportion of of the run off from a 100sqm roof (four outlets on the roof) to drain into the boxed in channel. From inside the house, you looked up and saw daylight. Admittedly I had made it worse - I thought the pipe might be blocked and backing up, and had a drainage guy use a drain unblocker from below (no roof access, three storey house). Then some brave soul got on the roof with ladders, shone a torch down the outlet and could see part of the outlet pipe outside the perimeter of the downpipe.

You live and learn.

oldbutnotdead · 18 Aug 2021

Mmm. Original lot made a nice bit of profit off that job even allowing for access, scaff etc. Wonder how they fixed the boards to the concrete..hopefully a lot of Gripfill rather than gravity

David Costelloe · 18 Aug 2021

Screwed into the concrete and glued....

Rufus Raintight · 18 Aug 2021

What new realms of hell is this! Do you know the make of GRP system they used? and did they lay the product over the existing surface?

David Costelloe · 18 Aug 2021

Brand name was something like "Crystic", with a ten year guarantee. Laid on new OSBs, staggered pattern, taped etc. Looked OK to an inexpert eye when completed

Rufus Raintight · 18 Aug 2021

David Costelloe said:
Brand name was something like "Crystic", with a ten year guarantee. Laid on new OSBs, staggered pattern, taped etc. Looked OK to an inexpert eye when completed

Is that picture of the can of resin with the drill mixer you repairing the area with desmopol?

David Costelloe · 18 Aug 2021

It is the start of desmopol being added. It's not me - getting on the roof via ladders is not my forte.

Seeing the photos, do nothing was not an option.

BTW, if you do these jobs off a ladder, get smaller 6kg tins, not 25kg which are tricky to get up safely (rope, pulley, man on ladder guiding the can up the wall or ladder safely)

oldbutnotdead · 18 Aug 2021

Crystic are a known brand, trouble is the warranty only covers defective materials (eg resin not going off properly) not defective installation (laminating damp boards)

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GRP roof disaster zone

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