Is GRP a good roofing material?

GRP flat roofing Prose and cons


  • Now easily available in DIY shops
  • Good and strong
  • Tested over many ears to perform
  • Comes in any colour
  • Can be formed into any shape
  • Will hold standing water


  • Very rigid and brittle if laid to thin
  • Has to be laid by experienced people
  • Has to be built up to form a good surface and this takes time and materials
  • Weather and temperature dependable

Other options to consider

  • 3M SD650
  • GacoRoof
  • Kemper

All three are based on the principles of GRP resins and glass fiber but they have been modified to be flexible.

My opinion.

If the GRP roof is laid correctly and to the correct depth they are good roofs however I only ever see well laid GRP roofs when Im down the coats these are normally laid by boat builders and are formed from may layers of GRP,  forming a good strong shell.

If you have lots of money and want a really nice looking roof then GRP is the way to go.

Flat roof survey or report

It’s not often we get asked to look at a flat roof as large as this and unfortunately our free estimate wont cover the cost of surveying this roof and reporting back the findings.

This flat roof is a round 1500m2 and is covered with an old type flat roofing membrane with welded joints, this type of roof is still being fitted but we consider it to be one of the older generation flat roofing materials.

I’ve taken a walk around the inside of he building and seen where the water is penetrating, externally I have examined the roof and can see lots of  design faults, I will be submitting a preliminary report  suggesting that thermal imaging of the roof is undertaken to show where the insulation is saturated this will help identify the areas of the roof where the roof has taken on water, then we can  scrutinise each joint and visually inspect the membrane for holes punchers  or rips.

At this stage I think we will be cutting out all the wet insulation then repairing the roof using a liquid roofing systems such as GacoRoof.

Related articles

Liquid roof covering by GacoRoof over a parapet wall

In this video I show you just how flexible the GacoRoof covering is

We have just covered an old asphalt roof in wembley with the new liquid waterproofing system, we dressed the parapet walls with the system so we didn’t have any flashing details to deal with.

No flashing no messing about complete encapsulation, the flexible roofing system will allow for expansion and contraction  over the seasons





Parapet wall and flat roof before and after


Using a liquid roofing system we can encapsulate the parapet walls with ease


Take this old asphalt roof in Wembley, the asphalt has sagged and cracked away from the parapet wall


Cracking is evident and the ceiling below shows water-damage.


The brick parapet wall is  solid construction but the flat roof is built on timber and will settle over time, the asphalt will melt in the summer and go brittle in the winter, with the thermal movement the  cracking occurs.


So after cleaning of the roof taped patches are applied to the cracks before the new roofing system is installed to the roof.



On this roof we are using the GacoRoof a silicon-based liquid roofing materials from the USA . GacoRoof is very flexible and can withstand   the movement described above.


The other interesting factor to all of this is the color of the finished roofing materials GacoRoof  has a white finish and reflects the sun’s heat stopping the  old roof from melting


liquid flat roof gacoroof london 14



Preparation before a new liquid flat roof

We are on day to of this roof, the old roof is an old asphalt roof and was leaking from several places.

In this video I walk you around the roof showing you the condition of the old roof, some of the cracks and detailing.

The new liquid roofing system we are about to use on this roof is imported from the USA and is relatively new to the UK

It’s a silicon-based flat roofing materials called GacoRoof and one of its biggest advantages over other flat roofing materials is its amazing flexibility

Before we cover the old flat roof with the new roofing system we have given it a good clean and repaired all the damage that has happened over the years.

This old roof had Ponding or pooling water all down the center, although a problem to the old roof its not a problem to the new liquid silicon roof.

Why choose a liquid flat roofing system for your new flat roof.

Some roofs just look a mess when covered with a sheet roofing materials, if the flat roof is large and the detailing is limited then a sheet flat roofing materials such as EPDM rubber could be used.

If the roof is covered with obstacles such as skylights, pipes, air conditioning units and so on then a liquid roofing system should be chosen.

I alway explain to my customers we don’t choose the flat roofing system for the roof the roof and your budget chooses the system.

The new Liquid roofing system we are using on this roof is ideal as an overlay system for old flat roofs, the advantages of the GacoRoof liquid flatroofing system is that its snow white when completed reflecting all the suns rays int he summer.

Problem with Green flat roof

Green flat roofs may be nice on the environment and nice to look at but when you get a problem they can be very expensive.

This green flat roof is probably going to have to be completely striped as the flat roofing membrane under it is leaking somewhere and we cannot find the problem.

Realistically under a green flat roof you don’t want to have joints that can go wrong at sometime, most new flat roofing materials will last for many years but when they do go wrong they will alway go wrong where there is details.

Remove the details remove the problem.

liquid rubber SD650 By 3m flat roofing 8

EPDM rubber roof inspection

Around five years ago we laid this flat roof using EPDM rubber over tapered insulation, the job was quite complicated as we had to adjust the falls to the original flat roof so all the water would run to the back of the roof. The roof insulation was laid at the front of the roof to a depth of around 350mm, pushing the water to the back of the roof .

I also show you in this video some of the characteristics of EPDM rubber. EPDM rubber is flexible and when laid over soft insulation the completed roof is soft to walk on. Customers sometimes comment on this as if it’s a problem, however it’s not! That’s how it’s designed to be. The complete system is lightweight and designed to go over the top of other roof coverings such as felt and asphalt.

EPDM rubber roof W13, West Ealing

Via Flickr:
EPDM rubber dressed over the top of new insulation to Part L of the building regulations, the EPDM rubber looks good dressed up over these parapet wall and around the chimney pots.
This EPDM rubber flat roof looks good and the area to the chimney pots dressed in EPDM solved a big problem. We laid this roof over insulation supplied by Kingspan insulation,
EPDM rubber roofing material should be trouble free for between 20 to 40 years. The EPDM we used on this roof comes with a 20 year insurances back guarantee and is expected to last for up to 40 years, there are different EPDM rubbers on the market, and they all come with different guarantees, we are trained installers of three different EPDM rubbers some come in small sheets and some come in large sheets, depending on the flat roof what we are to lay the roof over, depends on what EPDM rubber waterproofing membrane we use. Please contact us at London Flat Roofing or call 020 8421 3193 for more information. All comments are welcome so please leave some feedback if you find the information we supply helpful.

Liquid rubber flat roofing SD650 by 3M

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liquid rubber SD650 ny 3m flat roofing 31liquid rubber SD650 ny 3m flat roofing 30liquid rubber SD650 ny 3m flat roofing 29liquid rubber SD650 ny 3m flat roofing 28liquid rubber SD650 ny 3m flat roofing 27liquid rubber SD650 ny 3m flat roofing 26
liquid rubber SD650 ny 3m flat roofing 25liquid rubber SD650 ny 3m flat roofing 24liquid rubber SD650 ny 3m flat roofing 23liquid rubber SD650 ny 3m flat roofing 22liquid rubber SD650 ny 3m flat roofing 21liquid rubber SD650 ny 3m flat roofing 20
liquid rubber SD650 ny 3m flat roofing 19liquid rubber SD650 ny 3m flat roofing 18liquid rubber SD650 ny 3m flat roofing 17liquid rubber SD650 ny 3m flat roofing 16liquid rubber SD650 ny 3m flat roofing 15liquid rubber SD650 ny 3m flat roofing 14

Via Flickr:
The words Liquid Rubber are what most people perceive liquid roofing products to be, realistically out of the 15 or so liquid roofing materials on the market there is only one Liquid Rubber liquid roofing material that I know is actually liquid EPDM rubber, all the rest are liquid emulsion liquid polymers, or some other kind of material.
We are using 3M Scotchkote Urethane Roof Coating. SD650 is a two component, elastomeric, solvent-based urethane for flat roofs and its good, very good! Exactly what you would expect from 3M. It comes with a 25 year guarantee from 3M, when installed by a trained contractor, and yes, we are trained contractors. So if you need any info on the system please don’t hesitate to contact me: Steven Dickinson 07802 300 099 at London Flat Roofing Ltd.

This is a link to some of the videos on Youtube we have, showing this flat roofing system.
Time lapse video of a new flat roof
Cleaning an old asphalt roof
First coat detail round skylight

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