GRP Resins - any appreciable differences between makes?

[ThreadLock]

Hi Guys,

This year I hope to tackle the garage flat roof - most probably in GRP. It's a simple rectangle, 6m x 5m, with one wall abutment, and no 'features' in the surface (pipes etc.).

There seems to be quite a range of resin 'systems' on the market, all of course claiming to be 'superior' or 'high performance'! Some say they're 'flexible', others don't mention it.

So are they all much of a muchness, or do the newer resins have some advantages. Is it more down to the skill of the installer (!) and quality of preparation, rather than any real difference in resin?

Cheers.

 

[noseall]

Hi Guys,

This year I hope to tackle the garage flat roof - most probably in GRP. It's a simple rectangle, 6m x 5m, with one wall abutment, and no 'features' in the surface (pipes etc.).

There seems to be quite a range of resin 'systems' on the market, all of course claiming to be 'superior' or 'high performance'! Some say they're 'flexible', others don't mention it.

So are they all much of a muchness, or do the newer resins have some advantages. Is it more down to the skill of the installer (!) and quality of preparation, rather than any real difference in resin?

Cheers.

Personally, I tend to shy away from GRP, mainly because I have a top notch felt roofer. It's also the faff of having the right conditions for a successful outcome, i.e. stable temperature at 23.5º C, wind at max 3MPH, relative humidity no greater than 16%, surface dry for the last 22 hours etc.

 

[ThreadLock]

Thanks, noseall - but I thought it was 23.7º C

 

[oldbutnotdead]

If you have a vanilla roof (no weird corners) I'd suggest looking at EPDM or similar rubber roof coverings.
GRP has its place but as above it is finicky- base has to be rock solid, application has to be excellent.
EDIT Back to your original question, I've not noticed any significant differences between brands but I'm only 10 years away from the 1st roof I did so who knows ...

 

[John D v2.0]

Great question and I'm interested in this too as I'm doing a smaller roof and trying to understand.
From my research the standard ones that are about 100 quid for 20kg are the same polyester resin with low styrene.
The flexible ones are a different formulation which escapes me at this time of night.
You can compare the thickness of the matting, 450gsm is more efficient in resin, 600 or 2x450 would be more durable.
But from what I can see it's super finicky and easy to mess up if you add too much or little of the catalyst or get water anywhere. Or use the wrong board.
Good luck!

 

[oldbutnotdead]

GRP (in my experience) is a very good solution for awkward shaped rooves (bay windows are a prime example) and for rooves which will see any appreciable foot traffic.
Lots of people have reported noise problems with large GRP rooves- causes can be deck not secured properly, deck board joints not fully supported (if you've been cheap and used square edge boards not t & g), no expansion joints/clearance from deck to walls)
The recommended deck board used to be 18mm OSB3 BUT the last sheets of osb I bought were very smooth with some sort of sealant on them so I'm not sure whether they'll be suitable (the older type was quite an open structure so the resin would get a good key).
Everything has to be clean and dry, you have to get the amount of resin per sq m right and you have to consolidate to get rid of any pinholes.
Same with topcoat- too thin it'll not last, too thick and it'll crack.
The cost has increased spectacularly.

 

[noseall]

Great question and I'm interested in this too as I'm doing a smaller roof and trying to understand.
From my research the standard ones that are about 100 quid for 20kg are the same polyester resin with low styrene.
The flexible ones are a different formulation which escapes me at this time of night.
You can compare the thickness of the matting, 450gsm is more efficient in resin, 600 or 2x450 would be more durable.
But from what I can see it's super finicky and easy to mess up if you add too much or little of the catalyst or get water anywhere. Or use the wrong board.
Good luck!

When I built my shed below, I considered doing the flattie myself i.e. rubber type roof or GRP. I could barely buy the materials for what my flat roofer charged to do a top notch, three layer torch on jobby.

shed.jpg

• noseall
• 4 Dec 2022

 

[ThreadLock]

Thanks all for your very helpful suggestions.

I've been going round in circles considering the merits of GRP, EPDM and good ol' torch-on felt Do I just get someone in to do it, or 'man up' and have a go myself? It still appears to be 'boom time' in the building trades, so costs seem quite high - and even getting folk round to quote is difficult - which is why I'm considering the DIY route. I do, however, recall the "Dirty Harry" quote: "Sometimes a man's gotta know his limitations"

EPDM does seem more DIY-able, but the surface finish looks a bit 'meh', with somewhat clumsy edge details - at least on the photos I've seem. Maybe it looks better in real life?

GRP does indeed look more finicky, and the usual advantage of DIY - being able to take a bit more time over things - doesn't apply here! Stuff needs doing 'against the clock' for the best results. However, going DIY does at least mean you can pick a good weather 'window of opportunity' of your own choosing!

As for felt - doing a proper 'torch-on' job looks like being a dying art from what I can gather, but would appear fine for a simple 'vanilla' roof like mine. Maybe it's just better marketing of 'higher tech' products which makes felt seem a bit 'old school' - it's a pity noseall's guy isn't based in Lincolnshire

Sorry to ramble on - maybe I'm just (as usual) over-thinking it a bit....

 

[John D v2.0]

Great question and I'm interested in this too as I'm doing a smaller roof and trying to understand.
From my research the standard ones that are about 100 quid for 20kg are the same polyester resin with low styrene.
The flexible ones are a different formulation which escapes me at this time of night.
You can compare the thickness of the matting, 450gsm is more efficient in resin, 600 or 2x450 would be more durable.
But from what I can see it's super finicky and easy to mess up if you add too much or little of the catalyst or get water anywhere. Or use the wrong board.
Good luck!

Just to add to this, the reason I'm only looking at GRP is it's an existing pinholed GRP roof, and I only need to do 2/3 of it and I'm hoping not to touch the lead edge that drips onto the pitched roof on two sides. Not to mention the party wall ridge and the edge that goes under the tiles above.
If it was a complete renewal I would look at other types of roof.
by the time I get up there I may need to do the lot... Let's see.

 

[ThreadLock]

Hi John,

Have the pinholes developed over time, or do you think the initial laying wasn't up to scratch? How old's the roof, and was it 'professionally' laid?

The internet's a great place for information & advice, but so much of it is conflicting

Cheers,
David

 

[noseall]

Have the pinholes developed over time, or do you think the initial laying wasn't up to scratch? How old's the roof, and was it 'professionally' laid?

It was probably only 22ºC and 18% humidity, at the time.

 

[oldbutnotdead]

Did a bay roof last August in that really hot weather- resin was going off so quick I ended up having to double cover it cos the 1st coat (total area 3 sq m) had gone off in the 5 minutes it took to resin the whole thing so couldn't consolidate properly- pinholes everywhere

 

[John D v2.0]

Hi John,

Have the pinholes developed over time, or do you think the initial laying wasn't up to scratch? How old's the roof, and was it 'professionally' laid?

The internet's a great place for information & advice, but so much of it is conflicting

Cheers,
David

The initial laying wasn't up to scratch, it was done under a tin hat by the builder, but it was December so probably cooler than it could have been ideally.
I think they did it in a rush and didn't get the air bubbles out.
It's only 5 years old now. I only noticed it soaking through the OSB last month.

 

[John D v2.0]

Did a bay roof last August in that really hot weather- resin was going off so quick I ended up having to double cover it cos the 1st coat (total area 3 sq m) had gone off in the 5 minutes it took to resin the whole thing so couldn't consolidate properly- pinholes everywhere

Yes that must be gutting to waste materials like that. according to my online research, you have to use an infrared thermometer to check the temperature of the roof deck, if it's in the sun it can be easily too hot to lay, even if the air temperature is alright.
It seems that keeping the sun off while you work is pretty much imperative in warm weather.
I don't think I'd lay GRP as a job because you can only work 100 days a year at best! Since I'm doing it myself I don't have to worry about losing days to the weather.