Flat roof fibreglass resin disaster

18 Mar 2008
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United Kingdom

I suppose I should really post this in the diy disasters forum, but I need a bit of advice/help.

I've replaced my flat garage roof with a warm deck as it was converted (badly) to a habitable room by the previous owner. I decided to fibreglass the roof to finish it and, not having done it before, I've watched countless videos, read lots of advice and so on. Cue roll of eyes from professional roofers...

The deck is 18mm OSB3 (not T&G) - I've left 3mm gaps between boards and 25mm to the wall of the house; I've taped all the joints and began fibreglassing the trim and joins with 75mm bandage. Unfortunately the deck surface temperature was 38 degrees when I started and my resin started to go off incredibly quickly. I was using 1% catalyst and mixing 1 litre at a time; after 25 minutes my roller was unusable - rock hard. The second one barely lasted 20 minutes. By that time my bandage had fully cured and in most cases I couldn't use a consolidating roller by the time I'd finished wetting out the bandage. All in all, a disaster. My question is, can I remedy the situation? I have some lumps of hard resin and bandaged areas that have visible air pockets in, not to mention pin-holes etc. I've not laid the fibgreglass mat yet; I've covered the whole roof with tarpaulin while I consider the next move. Help!

I'll post some photos in due course, just wondered if a thorough sand and start again on a cooler day (or cooler time of day) would be OK.

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You do not get long at those temperatures I would suggest you over board with osb 3 which is t&g and start again on a cooler day, and don't bit of more than you can chew.
The good news- yes knock it back (probably with an angle grinder or a fairly vicious sander), recoat and it'll be fine. You'll have air pockets all the way under your 3mm gaps I expect- they may be more of an issue. Don't get too worked up about pinholes in the bandage- the main mat coat should sort them out- but do grind out any proper bubbles and big lumps.

Questions for you.

What did you tape the joins (on the OSB3) with (or did you just mean you'd bandaged them)

The 3mm gaps between boards- presumably that's on the long edges? Not in my instruction manual but whatever- you don't really need to get too worked up about expansion joints till you're at 4 or 5 metre widths/length)

One big drawback of not using T & G is you have to support the joins on the short edges (ideally a joist, failing that another bit of OSB3 firmly fixed to the deck sections)

When did you buy the resin and hardener? If it was over the winter then you may have winter catalyst (which works a lot faster than summer)- see if the bottle is marked or talk to your supplier. And did you stir the resin properly before you added the catalyst (if its been stored for a while resin can start to stratify- if you only got the top of the tin then you could be in all sorts of bother)

And your going-off time of 20 minutes or so isn't far off the mark- 30 minutes workable is the aim. If you are definitely on summer catalyst then you could try 0.5%- do a very small batch (100ml of resin) to make sure it actually goes off. Rollers are consumables in the world of fibreglass, so are brushes.

Have fun.

Thank-you both for your replies. With the benefit of hindsight and all that I would have waited for more suitable weather, but here we are.

To answer your questions, oldbutnotdead:

I taped over the 3mm gaps with Duct tape and then bandaged over the top

The board size is 8' x 4' and I left a gap for every joint and taped + bandaged every joint. Total deck size is 7.6m x 2.8m

I bought the resin + hardner online just last week, so I'd hope it was summer catalyst. I was very careful about measuring and mixing and was advised never to use less than 1%, but I guess in the temperature it wouldn't have harmed it too much to go less.

When I grind/sand it down to re-do I presume I can leave the bits that came out OK - can I just bandage over those bits again or bandage up to them (slight overlap maybe?). I don't care too much what the actual finish on the roof looks like in terms of edges and seems etc.

I need more rollers to use and dispose of before I try again, though!

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Yes chemically you'll be fine- good sanding/grinding, sweep down, wipe over with acetone, let that dry then off you go. It'll look a bit bumpy but it'll keep the rain out. I'd overlap the bandage rather than butting up- gives you a better chance of getting a full seal.

The duct tape over the joins is a new one on me but it should have retained the resin on the bottom of the bandage so the joint will be up to full strength (problem if you have a large gap is the resin drops out of the mat leaving a weak bit of mat and a puddle of not very strong resin)

My instructions also say never use less than 1%. They also said that winter catalyst at 2% would be fine for October. Was it heck- one batch took about 4 hours to go off, I was dancing about with polythene to keep the rain off it. That was when I started playing with 100ml batches. Oh yes, if you do do some test batches don't mix them in polystyrene throwaway drink cups- they disslove.

For the bandage I used small rollers from Toolstation 81477- think they were about £8 for 10, solvent resistant. Make sure you get solvent resistant ones- the core of the sleeves of non-solvent resists may dissolve in the resin, which is annoying.

Don't bother starting if it looks like rain (unless you can completely waterproof the job without standing on it), do try and get the topcoat on as soon as possible after the mat coat has cured (24 hours is plenty this time of year)

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