Flat Roof Decking OSB-3 vs Plywood | Delamination

OSB or Plywood

Don’t use ply-wood for a flat roof that’s going to be fiberglassed – even marine ply, Cure-it GRP or Topseal. will not guarantee a roof if you’ve used Plywood, it must be OSB-3.

Problems installing fiberglass on the wrong decking boards

Fibreglass should always be installed on OSB-3 sterling board preferably with tongue and groove edges,

Boards with tongue & groove (T&G) edges comes in 2ft x 8ft or without T&G in 4ft x 8ft which can be a bit difficult to handle especially if you’re working two to three story’s high and need to lift the boards up to roof height

norbord products sterling-osb/sterling OSB-tongue-and-groove

OSB3 roof decking for a GRP fiberglass flat roof

OSB or Plywood

The 2400mm x 600mm or 2ft x 8ft boards are the best and the most popular,  (T&G) on all sides and easy to handle,

OSB plywood

The perfect boards for fibreglass resin to bond to, with no surface preparation needed

  • Plywood will need to be sanded before the GRP will bond
  • OSB with T&G profile stops the edges of the boards dishing or warping whilst the fiberglass cures
  • Plywood needs to be finished on the joist/beam or noggin. OSB3 doesn’t its supported by the T&G this helps with the waste off cuts too…
  • All but joints with plywood will need additional CSM (chopped strand matting) bandage

OSB3 (oriented strand board) is by far the best choice for a fiberglass flat roof or balcony

Plywood does de-laminate especially if there’s any moisture ingress like condensation from underneath this will cause the boards to delaminate from the fiberglass check out our video on this problem,

Audr
Audr
08:16 25 Apr 18
Prompt response, arrived to look at job when he said, gave a thorough account of what needed done, we agreed a price. The next fine day he arrived early with another worker and job done before end of day. Prompt, efficient, professional and reliable. My old cast iron guttering now looks like new and doesn't leak....hurray! Thanks James.
james thomas
james thomas
17:48 08 Mar 18
I have used James and his roof firm twice now and have had fantastic service each time. He is very quick to provide advice and all his work is timely and of a great standard . I would happily recommend and will be using him again in future .
Ed Hagerty
Ed Hagerty
19:31 13 Oct 16
We’ve been restoring a house in Cumbria and over the years we’ve had tradespeople from across the spectrum. I can comfortably say that Jim and his team are in the very top of the list in terms of quality, price and service. They did a flat roof for us, some lead work and a variety of other external work, all of the highest quality. If Jim provides the service, you need look nowhere else. We’d trust him with any job, large or small.
arron weaver
arron weaver
15:01 28 Oct 16
Great price, no hidden costs, professional and friendly service, the results were simply stunning. would recommend to anyone. Thank you to all the team. Great work!
Katherine Massey
Katherine Massey
14:11 26 Mar 15
Jim and Chris recently carried out outstanding work to our fibreglass roof on a listed building. We were delighted with the standard of workmanship, service, communication and the 25 year guarantee. The work was carried out in a timely and professional manner and was also reasonable in terms of cost. We were lucky to get some dry weather and guys that really know what they are doing. Thanks Jim, much appreciated! I will recommend you to family, friends and anyone I come across!
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