Below we have provided a listing of some of the most frequently asked questions. These have been refined from real user queries and we trust that their queries will help you with any such concerns you may have.

If you cannot find what you are seeking please do not hesitate to contact us.

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We would hammer home one vital message – for roofing installation your roof must be dry. If the forecast says it’s going to rain probably best not to start at all – if it might rain unexpectedly mid job be well prepared, have some visqueen type sheeting available to cover up (before the rain actually starts.)

Fibreglass FAQ’s

You have multiple fibreglass roofing kit ranges – what’s the difference?
  • Classic kit – Blended resin engineered especially for roofing – very cost effective, yet really good quality.
  • Deluxe kit – the very highest quality kit – 25yr product guarantee – 100% pure resin – lloyds approved- add value to your property.
  • Platinum Fire Rated kit – the very best of Deluxe combined with the top rated fire retardant topcoat!


How much Hardener/Catalyst ?

RKD understand that this element probably causes most concern when installing a fibreglass flat roof. This is the area where most potential issues can arise in the roofing installation. So first tip –

  • Always make sure that you thoroughly mix catalyst into resin and topcoat (resin in a pot or bucket – not in the tin)
  • Always use a proper catalyst dispenser to ensure your measure is accurate
  • Remember too much catalyst can cause failure to cure just as easily as too little.
  • Potlife – resin will cure quicker if left in the bucket (about 20mins) so mix little and often as you go.
  • The climatic conditions (temperature) will effect curing time – generally the hotter the faster. (Are you in direct sunlight?)

There is not an exact definition of how much catalyst to add to resin as it depends on the temperature and local conditions. This is why you mix little and often, it allows you to adjust the catalyst percentages as you go.

Resin and topcoat catalyst addition is the same – your base layer and topcoat should cure in about 30 – 40 mins if the mix is right

The industry provides two types of catalyst – Summer and Winter – RKD provide winter catalyst by default fro November to Feb/March


Summer Catalyst Addition chart


Can I apply the topcoat layer of fibreglass roof on another day – will my roof still be waterproof?

We receive this query quite often, especially from customers who are first timers and those with larger roofs and limited daylight in the Autumn/Winter months.

The Simple answer is yes and yes – however you will need to be aware that there are extra elements to consider.

Firstly, with the resin/matting basecoat layer correctly applied your roof will be fully waterproofed.

Secondly, moisture – the roof and basecoat must be dry before topcoat application – moisture will prevent the topcoat from curing.

Topcoat – just a general note, although when mixed with catalyst the topcoat is applied just like a coat of paint it doesn’t just add a colour finish. The topcoat is designed to increase structural integrity of the roof and chemically bonds to the basecoat/resin layer. It also adds UV damage prevention attributes.

Catalyst ratios are the same for topcoat as the resin layer, but take note, conditions may be different on another day so check your charts and the climatic conditions.

If you apply topcoat same day or within circa 12 hours there’s no need to sand the laminate for bonding purposes. Outside this time frame you will need to light sand and wipe down with acetone. Sanding gives a key, acetone helps the topcoat to chemically bond to the resin matt/base layer.

However many installers like to give a light sand to check for any bumps and smooth trim edges etc. (obviously clean off with acetone properly)

Again for topcoating always wear mask, goggles and gloves from A-Z. As with laminating get your tools ready and to hand. Mask off with masking tape any edges to insitu fascia boards etc.

You recommend using 18mm OSB3 Tongue and Groove deck – but I’ve already laid 8 x 4 OSB3 plain boards?

This is very common, 8 x 4 sheets are often more readily available and installation over an 8×4 sheeted deck is easily overcome. We recommend T&G because they include natural expansion properties within edging joints. With 8 x 4 sheeting expansion is generally included by allowing a 3mm gap between sheets.

This gap will therefore require fibreglass bandaging to ensure full fibreglass roof integrity. Bandaging is applied by laying the bandage over the join and applying catalysed resin to it, letting it settle then paddle rolling just as you would for the base coat layer. Thus any bandaging installation becomes an ideal test bed for catalyst addition .

All RKD fibreglass roofing kits allow increased quantities of resin and bandage to cope with nominal wastage and edge trim sealing. If your roof is above 15m2 and you have  8 x 4 deck each kit also includes an opportunity to purchase a little extra resin or bandage to resolve this requirement

I will need to purchase edge trims, but which ones and what size?

GRP Fibreglass Trims generally come in 3m lengths. We stock a full range –

Advisory Guide

  • Small roofs/Bay roofs. – 65mm depth – Use the A170 Drip and the B230 Raised edge trims together
  • Standard roofs (most common) – garage/extension etc – 90 mm depth – Use the A200 Drip and the B260 Raised edge trims together
  • Warm roofs – 140mm depth – Use the A250 Drip and B300 Raised edge trims together
  • C1,C2,C4 preformed corners work with all the above
  • D260 Wall fillet combined with a C100 flashing trim are the most common solutions for adjoining walls and upstands
  • Use D300 Wall fillet combined with a C150 flashing trim wall fillet where an existing chase from a felt roof is evident
  • Use F300/600/900 where flat roof adjoins a tiled roof

Rubber FAQ’s

What will the ClassicBond EPDM bond to?

ClassicBond EPDM is best bonded on to timber surfaces such as roofing grade plywood or OSB3 (Oriented Strand Board) sometimes called sterling board.  It can also be bonded to light weight concrete and other non porous surfaces such as Fibreglass and tissue faced insulation.

Most Importantly – What Surfaces Cannot Be Bonded To?

ClassicBond EPDM can not be bonded to bitumous surfaces or remaining bitumous residue on a roof deck – such as:

  • Roofing felt
  • Asphalt
  • Liquid mastics

The EPDM will tend to draw the oils out of the bitumous material which causes the EPDM to lose its molecular structure and fail.

As such care should be taken when removing the old Bitumous roofing membrane as it may leave a residue which can damage the EPDM membrane.

Pragmatically and to ensure issue free installation RKD  recommend over boarding old roof coverings using an OSB3 recovery board or insulation boards.

What is the difference between ClassicBond and Firestone EPDM?

RKD  get asked from time to time what are the differences are between the two systems. Obviously we stock ClassicBond so to offer a critique would be unprofessional. So here are some salient facts.

In essence ClassicBond and Firestone Rubbercover are the market leading brands for EPDM Rubber Roofing Membrane Systems.

CB membranes are 1.2mm and 1.5mm thick

Firestone membranes are 1.14mm and 1.52 – so little difference here

ClassicBond is manufactured in the United States by Carlisle Syntec,. They are the largest producer of EPDM in the world. ClassicBond is the original EPDM  – it was first used on commercial roofs in the 1960’s. Firestone was launched at a later date in the 1980’s.

With its longevity ClassicBond can claim to have a proven 50 year life expectancy with many roofing instances still completely viable.

Both ClassicBond and Firestone Rubbercover are BBA certified and approved by the NHBC. (Obviously when installed in accordance with the manufacturers guidelines.)

ClassicBond’s BBA Certificate No. is 11/4853

Firestone Rubbercover BBA Certificate No: 89/2216

Service life expectancy

The above BBA certificates record the following –

Firestone RubberCover has a service life in excess of 30 years

ClassicBond has an expected service life in excess of 35 years.

What is the biggest size epdm roofing sheet I can buy?

The biggest sheet size available from RKD is as follows.

Note – All sheets can be joined where the roof size is bigger than the maximum sheet size:

ClassicBond  1.2mm – 15.25m x 30.5m (50ft x 100ft)
ClassicBond 1.5mm – 15.25m x 15.25m (50ft x 50ft)

The biggest EPDM one piece sheet sizes available in the Roofing Kits Direct range  come from our ClassicBond range.

RKD understand that covering your roof with a new membrane that has no onsite joins is perceived reassuring and offers piece of mind. However RKD would note that jointing technology in any of our EPDM systems comes as strong as the membrane itself.  Therefore multiple sheets joined together onsite actually offers a more practical solution – large membrane sheets do offer a handling challenge.

In pragmatic terms, whilst 15m x 30m sheets are available, RKD believe that this will be a rare occurrence. We therefore offer to cut sheets to size for you. You can order any size you wish up 15m x 30m!

Typical Weights are: –

1.5kg/square metre & 2kg/square metre for 1.2mm & 1.5mm thick respectively

Can Rubber roofing sheets be joined?

Yes – RKD rubber membranes can be joined. Our joint technology offers joint bonding as strong as the original sheet and not detrimental to the waterproofing or strength capacities..

Jointing is used –

  • Where the roof is bigger than the largest membrane size or
  • Where it would be beneficial to install the membrane in smaller sections.

Not every roof is a nice flat rectangle, master the forming of corners, splicing etc and you can readily join sheeting to tackle your particular needs.

Membranes can be joined using splice (Seam ) tape or covertape. The important aspect to remember is that surfaces are primed as tapes will only adhere to a primed surface.

Do I need Special Tools for EPDM Rubber Roofing

For the standard 1 piece installation you really only need basic tools which Many diy’ers will have to hand.

  • 9″ Paint Roller for you to apply water based adhesive
  • 4″ Mini Roller for you to apply contact adhesive
  • 2″ Paint Brush for you to apply primer to clean EPDM
  • A good pair of scissors or utility knife for cutting or finally trimming the membrane

If membrane joints or patches are needed a seam roller is required.

RKD have always found that a nice soft broom is really handy when smoothing membrane out over laid adhesive.

Overlay FAQ’s

How is the liquid overlay affected in our cold winters?

Classic Liquid overlay will remain elastic down to -40°C so is not affected by cold weather in the UK

What’s the difference between Flexitec and Classic Liquid

Both systems are rapid curing.

Both system cover a plethora of surfaces.

Both systems utilise thickness and an extra layer to promote longevity.

Classic Liquid is a straight out of the tin product

Flexitec uses a hardener to facilitate curing.

Whilst Classic Liquid has a reinforcing fabric this is only utilised when covering felt or asphalt roofs.

Nominally Flexitec uses 225g reinforcement fabric in all installations.

  • Similar to GRP fibreglass, Flexitec 2020 is genuinely rapid-curing (30 – 60mins walk-over time) with an extra-tough finish.
  • Similar to liquid overlay systems it’s flexible and can coat a range of roof surfaces.

Both systems rely on the roof to be covered being waterproof and sound in nature

Neither product should be used if the original roof or timber substructure is suspect.



Are Liquid and GRP overlay better than fibreglass or rubber roofing.

In RKD’s opinion this very much depends on individual circumstances.

This can also depend on the capabilities of the installer and the complexity of the roof.

Both Flexitec and Classic Liquid are very straightforward to apply.

Fibreglass and rubber roofing need to be installed to a clean dry timber deck which in many circumstances mean stripping an old felt roof and replacing timber or overboarding.

However Overlay products are quite expensive so there is a trade off between ease of use and budget.

As with most roofing it usually depends on the installers preferences and confidence in capabilities



can be easier to apply for the DIYer than fibreglass and can deal with multifaceted roofs with projections etc more quicklyy than fibreglass or rubber.



How quickly will an overlay product be weather proof?

Both ClassicLiquid and Flexitec installations are good to go in about an hour post install

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