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Edpm or grp ?


Pocster

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Hey all

 

My architect has spec’d edpm but talking to some roofers they say that’s the wrong way to do it and should be grp ..

 

So I’m not sure now !

 

My flat roof can be parked on and has 4 skylights .

 

so bottom up structure is :

 

reinforced concrete 

high compressive insulation 

osb ? If using edpm or just grp 

reinforced poured concrete 

chippings 

sand 

driveway blocks 

 

I guess the risk with edpm is tearing it during installation via the rebar or the pour .

One ‘roofer’ said the edpm would perish in this situation ( but wouldn’t say why ) - I can’t see why as it’s essentially a rubber sheet .

 

Perhaps it doesn’t matter - different roofers prefer different methods ? 

 

Any views / considerations I might be missing ?

Quite a few companies had no issue with edpm !!

 

cheers 

 

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Personally I'd go for GRP, for a couple of reasons. 

 

You can DIY GRP fairly easily, as long as you stick rigidly to the instructions and make sure that the weather and the substrate is absolutely dry.  Any moisture can mess up GRP when it's being laid, but other than that is is extremely durable and tough, probably tougher than EPDM.

 

EPDM is very durable, but it's also quite dependent on the skill of the people installing it.  It's probably not that easy a DIY job, although possible, and does, in my view, need a higher skill level in order to get a reliable job.  I've not heard of someone messing up a GRP roof (although I'm sure some have) but I have heard a few tales of leaking EPDM roofs, all as a consequence of the installation, rather than the material.

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I think you’d still need the OSB layer if using GRP. You need a solid, sound and flat surface for the best results. 

If it can move/flex it WILL crack.

Personally I’d go with EPDM which is more rot proof and more flexible. 

 

Edit: @JSHarris is correct that GRP is better for DIY. It’s blooming hard work though. 

Edited by Barney12
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3 minutes ago, Barney12 said:

I think you’d still need the OSB layer if using GRP. You need a solid, sound and flat surface for the best results. 

If it can move/flex it WILL crack.

Personally I’d go with EPDM which is more rot proof and more flexible. 

 

Edit: @JSHarris is correct that GRP is better for DIY. It’s blooming hard work though. 

 

It is hard work, especially if, like me, you decide to do your first ever GRP roof in midsummer, on a hot day, with a friend who assumes that because he's laid up a couple of fishing boat hulls with a chopper gun he's a GRP expert.............

 

To our credit, we laid that roof over 30 years ago, and when I last saw it, around a year ago, it looked just as good as when we laid it.

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Needs a comment from @SteamyTea, who has professional experiresponsibility me with GRP but perhaps not under concrete.

 

I would be suspicious about GRP as it is brittle at the joints. Need to be sure no one walks on one, and that it is protected by the concrete.

 

Presumably you are casting drains into the concrete surface.

 

F

 

Edited by Ferdinand
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2 hours ago, JSHarris said:

Personally I'd go for GRP, for a couple of reasons. 

 

You can DIY GRP fairly easily, as long as you stick rigidly to the instructions and make sure that the weather and the substrate is absolutely dry.  Any moisture can mess up GRP when it's being laid, but other than that is is extremely durable and tough, probably tougher than EPDM.

 

EPDM is very durable, but it's also quite dependent on the skill of the people installing it.  It's probably not that easy a DIY job, although possible, and does, in my view, need a higher skill level in order to get a reliable job.  I've not heard of someone messing up a GRP roof (although I'm sure some have) but I have heard a few tales of leaking EPDM roofs, all as a consequence of the installation, rather than the material.

Spot on there An EDM is not for DIY Use

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3 hours ago, pocster said:

My flat roof can be parked on

Is that a typo and you mean walked on?

3 hours ago, pocster said:

osb ? If using edpm or just grp 

reinforced poured concrete 

chippings

Is this a 3 line list, or a single sentence?

Surely if you mean your 'roof ' is more a 'utility deck' you need a 'specific to concrete' type of membrane, not standard roofing edpm?

I might be way off here and reading it all wrong (due to gin) but i'd ask your structural engineer if this is a roofers job at all.

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Are there any modular / rigid GRP systems available that come on the back of a lorry that would be suitable?

 

If they can make GRP boats or roofs for bay windows (as we used to do) it should be straightforward ... though in 2018 costs might kill the idea.

 

(Persuades himself not to post vintage Aldi advert for gin)

 

Ferdinand

Edited by Ferdinand
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Thanks guys 

I was going to install myself but ‘ worried’ myself away from that idea 

edpm would be 1 sheet with cut outs for the roof lights . I think I would osb under it ( on top the insulation ) . Thought also about something on the edpm to protect it from concrete pour .

As your replies suggest it is not an obvious choice which to use .

once edpm done I intended to shutter the lot and run water over it to check for leaks .

got to be brave !!!

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If this is internal to the concrete deck then I would protect the waterproof layer with fibre board or EPS and then cast the next layer over the top using a waterproof concrete. It may be belt and braces but it won’t leak ...!

 

This sounds more like a job for a basement waterproofing product and not a roofing product. 

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1 hour ago, PeterW said:

If this is internal to the concrete deck then I would protect the waterproof layer with fibre board or EPS and then cast the next layer over the top using a waterproof concrete. It may be belt and braces but it won’t leak ...!

 

This sounds more like a job for a basement waterproofing product and not a roofing product. 

Problem is there’s no obvious roof/ ceiling waterproofing product - certainly not to use in this context . After all it is just a flat roof - but more concrete on top . I guess I’m just worried once edpm down I can never get to it if there was a leak - same no matter what product I guess .

i did look into waterproof concrete as well as a belts and braces approach - architect thought it was a waste of money as edpm installed correctly should last .

too be honest as it is it only leaks around the sky light holes and where the original pour has shrunk and pulled away from any steel . Was also intending to put non permeable pavers on top . But of course that’s the opposite to suds - so not sure they exist .

the area does have a fall of around 2 degrees so will have drainage channels on top the edpm in front t the house ( too be safe ) and one at the front - so ‘sat’ water shouldn’t be an issue .

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As this is going to be a buried barrier, I would GRP it.

If there are areas of high load, or point loads, then extra layers can be placed there.

One advantage of a buried layer is that there are no UV problems to worry about, so a vinyl ester resin can be used.

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I'd wholeheartedly agree with @SteamyTea.  CFS do some good roofing kits, I've used a lot of their stuff over the years, and for this job I'd be inclined to give them a call for advice.  My experience has been that they are very clued up and happy to help, but I'll caveat that by adding that my nephew worked there for years.  Here's a link to their roofing section: https://www.cfsnet.co.uk/acatalog/CFS_Catalogue__FLAT_ROOFING_21.html

 

They have some guidance on roofing with GRP here: https://www.cfsnet.co.uk/acatalog/1project-roofs.html but I would be inclined to ask them about your specific requirement, where you're laying concrete on top of the GRP, as the choice of resin may be more critical.  I agree with ST that vinyl ester resin would seem to be the best bet.

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1 minute ago, pocster said:

ive read it’s just a liquid pour ; is that right ????

Not for GRP, which stands for Glass Reinforced Plastic, sometimes known as FRP, Fibre Reinforced Plastic.

Even been called composite or laminated.

 

I think when we refer to GRP on here, most of us are thinking about a glass fibre matt (not Fibreglass as that is a trade name) which is impregnated with a liquid resin, usually polyester, but may be vinyl ester (better strength and longevity as long as it is out of sunlight) or epoxy resin (more expensive and often harder to do right).

 

There are some newer acrylic resins that are water tolerant, but I would have to investigate them more.  There are also polyurethane resins that have some good characteristics, but for roofing, polyester (cheapest and most widely used) or vinyl ester if you need extra strength and are worried about long term submersion in water.

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1 minute ago, SteamyTea said:

Not for GRP, which stands for Glass Reinforced Plastic, sometimes known as FRP, Fibre Reinforced Plastic.

Even been called composite or laminated.

 

I think when we refer to GRP on here, most of us are thinking about a glass fibre matt (not Fibreglass as that is a trade name) which is impregnated with a liquid resin, usually polyester, but may be vinyl ester (better strength and longevity as long as it is out of sunlight) or epoxy resin (more expensive and often harder to do right).

 

There are some newer acrylic resins that are water tolerant, but I would have to investigate them more.  There are also polyurethane resins that have some good characteristics, but for roofing, polyester (cheapest and most widely used) or vinyl ester if you need extra strength and are worried about long term submersion in water.

Thanks !

been looking at some grp install videos now !

so osb on top insulation still ?

Do I really need to do the whole roof in one sunny day ? I.e osb ; mat , resin , final coat ?

have to look into how up stands are dealt with ...

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Ok ! Grp some questions !

osb - fine ; do I fix ? I.e screw through osb and insulation into concrete ? Or just lay ontop ? ( assume tougue and grove best ).

do I ignore expansion gap at edges due to pour on top ? . My 4 edges are 2 wall abutment and 2 run off ( I think !! )  - so I use appropriate trim ????

assume wall abutment trims are mitred to go around walk on glass upstands ? ( can’t seem to find a video of grp install around up stands ) 

 

cheers 

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@pocsterI am a bit tied up at the moment, but shall come back and give my thoughts on how to do your layup.

Any chance that you can post a picture or sketch up of the two run off areas and any these up stands.  It may help clarify what you are trying to do.

 

Basically GRP is easy to put into a corner/edge, harder to put over a corner/edge.

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