GRP roof

[nod]

Im now going to tackle the orangery roof 5m x 4m with 2mtr x 1.5 lantern central

ill form the slopes and board with OSB3 Close the cavity with OSB and return the fibreglass over the cavity and finish with copings

Ive a drain at either corner to run into two hoppers

I have done most the work myself but had allowed to bring someone in for the GRP

The quote is more than expected £1600 Ive priced all materials 400 including vat

Price seems a bit steep?

My question is GRP so specialist Or is it something I can tackle myself

 

As previously stated We had a quote of 8500 for slating the main house But found it very easy with no experience of slating

Any advice on this would be appreciated

[Ferdinand]

I think it is something you can tackle yourself once you have learnt the skills.

 

Perhaps do a roof for a garden shed or a gazebo or similar first as a trial.

 

@SteamyTea has much more personal experience than me; we had a family business in fibreglass specials that I watched.

 

Ferdinand

[SteamyTea]

I worked in the composite plastics industry for over 25 years, so feel qualified to say a few things.

 

It is not difficult, I can teach you in about 2 hours what to do.  After that, it is just practice.

 

There are a few rules to stick to (pun intended).

Everything needs to be dry, totally dry.  Even damp can adversely affect the chemical structure of polyester resin.

Even your chopped strand mat needs to be kept dry, so no keeping it in a damp garage/shed.  It will cause you problems.

UV light causes the polyester resin to cure faster, as does excessive temperature. So you have to pick a warm, but not hot, a dry, but not a sunny week to do it. 

Then it is a matter of starting with a small area and working from there, don't be tempted to do more than 10 minutes work at a time.  The OSB will absorb a lot of resin, so make sure it is well 'wetted out' before you put any dry matt on it.  Then wet out the mat with a brush or roller.  Don't be tempted to use a large brush or roller.

The mat takes a couple of minutes or so to absorb the resin, don't be tempted to try rollering (consolidating) it too soon, it will just not work.  You can tell when it is working right at it goes almost transparent, rather than white, the noise changes as well, it sounds 'soggy'.  Don't push too hard with the consolidating roller, that will just pucker it up.

Once the area is covered in GRP, you will have to sand it down and put a top coat/flow coat on it.

Sanding is a horrible job as it is itchy and makes your arms ache, but it has to be done right.  Probably best to leave it a day to fully cure before sanding.

Then, when you paint on the top coat/flow coat, you have to make sure that it is adhering properly.  You can tell when it isn't right as you will see tiny little pin holes.  If that happens you have to let it fully cure, sand again, then reapply.  All a pain in the behind, but it is what really makes a good weather tight finish.

 

Choice of materials is a hard one.  I had my favourite mat 450gm CSM from Saint-Gobain, polyester lay up resin from Cray Valley and gelcoat (to make a top coat/flow coat) from either Norpol or Llewellyn Ryland.  Pigments I usually got from Llewellyn Ryland too.

Hardener I was easy about, it is the same stuff generally.

Who you buy it off is up to you, but probably easier to find a local GRP place and see if they can get it for you, may work out cheaper.

 

Did I mention that everything must be dry, really dry.

 

If you are in an area that has a boat building industry, you may be able to 'find a couple of lads' that are willing to do the job.

I would charge more that £100/m² so the price don't seem too bad to me.

 

 

Edited May 8, 2017 by SteamyTea

[Onoff]

My nephew GRP'd his large, porch flat roof. First attempt and I don't think he'd mind me saying.....made a complete ****of it!

Edited May 8, 2017 by Nickfromwales

[jamiehamy]

GRP was an option for us,  but the chances of getting the right weather conditions for enough time to do 270m2 were slim to none! The last week and a half has been blazing sunshine every day and will doubtless change to howling gale next week with rain for a fortnight. EPDM gave us lots of flexibility and bar one area,  we're happy with the result. Would be keen to try GRP one day tho. 

[Ferdinand]

The one thing I would add is that GRP is an extraordinarily useful skill to have for any number of jobs that you do not expect, since it is a waterproof robust surface which can adapt to any shape, and can be eg translucent or fire resistant etc with the correct materials.

 

One technique is to make a pattern in a controlled environment and then fix it afterwards.

 

At one time we did an entire roof from sections of GRP pantile like surface made by building a section of roof in the factory, or slate looking translucent panels used to provide light into traditional roofs. Worked a treat.

Edited May 8, 2017 by Ferdinand

[SteamyTea]

One way around the weather problem is to sheath the OSB before it is put in place.  Then all that needs to be done is the joints over laminated and then sealed with the topcoat.

I am surprised that this is not done more often.

 

Laying up in a temperature controlled workshop makes the job easy.

Edited May 8, 2017 by SteamyTea

[nod]

18 minutes ago, SteamyTea said:

One way around the weather problem is to sheath the OSB before it is put in place.  Then all that needs to be done is the joints over laminated and then sealed with the topcoat.

I am surprised that this is not done more often.

 

Laying up in a temperature controlled workshop makes the job easy.

Thank you for all the pointers and suggestion

As always a great help

      Gary 

[Ferdinand]

As an example of what you can do with GRP, this is an example of an experimental GRP pantile-like roof made from approx 8x4 workshop made GRP panels. They built a section of roof in the factory. This is an example of one of my father's (architect turned GRP specials manufacturer) projects.

 

This is a 2009 (ish) photo of a roof installed in the early 1980s.

 

As you can see the individual panels work well, but the connections - while being acceptable in practice (it was a pitched roof on a previous flat roof so there was a waterproof layer underneath) - are not good enough aesthetically after the time. To work long term it would require better waterproofing and better attachment to a structure.

 

The issue is resilience of the shape under environmental influences.

 

The individual panels are ideal for eg porch canopies, cost considerations aside - would be a good solution where you need a lightweight roof section which would be suitable for a conservation area or similar, if you can get the Conservation Officer out of the coma they may enter when you suggest GRP.

 

This bungalow was completely renovated in about 2011 with the roof off, with the roof being taken to traditional pantiles. I wrote a blog about that here back in 2014.

 

I would be interested in @SteamyTea thoughts, but if no one ever tried this kind of thing, we would lose some of our innovative new ideas.

 

 

 

Edited May 8, 2017 by Ferdinand

[MarkH]

13 hours ago, SteamyTea said:

 

Sanding is a horrible job as it is itchy and makes your arms ache,

 

 

SteamyTea has told most of what you need to know there. As with most things, maybe slightly more so, working with GRP is all about good preparation. Otherwise not trying to do too much and working clean are very important.

 

Concerning the above-mentioned itchyness, here follows what will undoubtedly be my greatest contribution to this forum, maybe even to humanity:

 

 

[SteamyTea]

16 hours ago, Ferdinand said:

I would be interested in @SteamyTea thoughts, but if no one ever tried this kind of thing, we would lose some of our innovative new ideas.

The main problem is that GRP is a laminate of 3 different materials.

There is the glass/resin matrix and then the gelcoat.

This acts like a bimetallic strip and when heated or cooled it will bow.  One way to minimize this is to paint a top coat (really just a 50:50 mix of resin and gelcoat with a bit of wax in it) onto the back of the lamination.

Then it needs to be fixed down securely.

Shrinkage is on of the main problems with GRP and needs to be thought about when designing.  Not really an issue when just sheathing OSB, so not a problem when making a water tight flat roof.

Edited May 9, 2017 by SteamyTea