How practical is it to DIY fibreglass on a new boarded flat roof of 50 sq. m., and how much would one save over getting some chaps in? I've done a bit of small-scale fibreglassing in the past, and am concerned I'd end up stuck to the roof. Experiences, anyone?
Cheers Richard
If you just use cloth (not mat) and don't care what sort of finish you have its easy enough to do one half,. let it go off and then kneel on that to do the other.
Some sort of hard roller will get air bubbles out and spread the resin around.
Another trick is to cover the thing with polythene sheet and roll that..makes for a good shiny finish if you use a bit more resin
Not personally, but when I had contractors in to lay an epoxy floor they wore things like this to walk over the wet resin:
Ask "Cure It" GRP Waterproofing System 01942 518150 for their how to do it dvd. Having watched it theres nothing an average human can't cope with.
I did one about 20 sq m as a base for a green roof on a workshop a few years back but even with one person mixing and two laminating (and having seen a professional do a similar job beforehand) it was a less than relaxing affair. We wore old boots, poured on the first coat in large self spreading blobs then rolled out the mat, using metal fin rollers on broom handles to consolidate, substrate was 18mm OSB and layup was 2 layers of 450g CSM. Despite walking on the layup on a few occasions we didn't get stuck.
So I'd recommend you get someone in, the quantities of resin being used are huge and you need to work quickly even with a slow catalyst. Learning 'on the job' with a roof that size IS going to be a problem.
Method
Thanks, and to everyobe who has replied. The prices for materials don't look that astronomical. I'm tempted to have a go, maybe a small section at a time until it's done. I've not built the roof yet ...
Cheers Richard
Quite easy in my experience. It requires a modicum of organisation as once you start you have to complete the run you are doing. Spreading resin using a wool roller and working chopped strand mat in with an aluminium one worked well . Ideally have one person cutting and one spreading. If the roof substrate is already prepared the actual fibreglass part goes quite quickly.
You don't need woven mat apart from a bit for some detailed areas, the heavy chopped strand from most suppliers saturates well. You can finish with a wax included gel coat to give colour or a shiny surface.
Most of the suppliers web sites have quite good guides, eg
Its not something easily done piecemeal , trapped moisture could become a problem, another supplier
Follow-up question: how to attend to the detail where roof join?
The flat- roofed extension in question will be attached to a dormer bungalow. The joists for the flat roof will share the wall plate with the first floor joists of the dormer bungalow. The top one or two rows of tiles will need to be removed.
How to join the roofs? A neighbour (who has built his own house) suggested taking the flat boarding up to the existing rafters, then removing the bottom row of (large, interlocking conrete) tiles to be retained, continuing to board up the rafters for a foot or so, fibreglassing the lot, then putting the edge of the roof underdrawing back over the sloping bit of the glassed board, and replacing the bottom row of tiles. That is, no separate flashing material but continuous fibreglassed board. Does the team agree, or have alternatives?
Regards Richard
"The top one or two rows of tiles will need to be removed".
when what I meant was:
"The bottom one or two rows of tiles will need to be removed".
Sigh
Richard
Seems reasonable but think about the thickness of the board and battens that the tiles rest on. I think the board would have to go between the rafters rather than on top or the bottom row(s) of tiles will "kick out". How far up depends on the pitch of the roof, I think I'd like to see at least a vertical foot from the flat roof to the top of the sloping boarding so 18" or maybe 2' along the hypotenuse.
Seems reasonable I'd pay attention to the transition from flat roof boards to the ones going up the roof. If anything is going to move it will be there. Perhaps put an extra 12 " wide strip of glass along the join before taking the main roof matting up the sloping boards.
Underdrawing, I assume you mean the sarking. Yes that needs to come down the roof and over the glassed board but under the battens. Sarking isn't very robust, the bottom 12 to 18" may well be better done with DPM. The sarking coming down and on top of the DPM of course with a good overlap.
Thanks Dave, that's very helpful.
Cheers Richard
You can buy rolls of pre-made fibreglass. When I did my flat roof, I placed some under the tiles and felt, fibreglassed the flat roof and ran the mat and resin up onto the pre-made piece. It's thin enough not to give any problems with the tiles and thick enough not to sag significantly.
SteveW
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