Repairing Fibreglass Greenhouse

doxford jim · Sep 26, 2014

Hi Guys,

I am wondering if any of you have done much fibreglass repair work and would appreciate some advice.
I have a fibreglass greenhouse that collapsed under a snow load last winter. The green house is around 25 yrs old and has suffered from UV and weathering, but it did survive that time without any supports etc.

I have managed to get the outside to close to where it was before collapsing and am wanting to repair the fibreglass for the coming winter. I have been told the epoxy resin will work in temperatures around 55F and extra catalyst/hardener would accelerate hardening time (offset the lower temps).
Providing I sand and clean with acetone, I am assured the repair will work fine and might take a little longer to cure.

I have attached some pictures so you can see what I am talking about regarding repairs needed. I believe the woven cloth cut to required sizes (strips) with the resin would do the job. I would appreciate any tips regarding the repairs to the fibreglass as I am a novice regarding fibreglass repair work. I believe ambient temperature and humidity play a major role - along with cleanliness and proper preparation. Once completed, the greenhouse will have "winter props" come winter time to prevent ay further collapsing.

Thanks in advance.

Jim

Pipestone Kid · Sep 26, 2014

The repair should be fine. If you can get the temp warmer it would be better. I prefer the mat type cloth versus the woven type, but either will do. Good luck.

quicksandfarmer · Sep 26, 2014

Fiberglass is pretty easy. The key is to be all prepared, because once you mix the resin you only have about 20 minutes before it hardens.

Most fiberglass uses polyester resin, not epoxy. It's also a good deal cheaper. It does have trouble catalyzing below about 60F, if you can put a halogen light on it for a little while that will help tremendously. If the resin is at room temperature when you start it will generate heat in the pot as it hardens, which helps too. With proper temperature it will harden in a few minutes. Without it will eventually harden, but will never be very strong.

You're right that sanding and cleaning the existing fiberglass will make it adhere. The other thing to worry about is that if fiberglass changes thickness too radically it creates a spot that will crack if flexed. So you want to feather the edges of the old material before patching, and feather the edges of the patch after it hardens.

The resin is really soupy and has no strength before it hardens, so you want to back a crack with masking tape so it can't move while it hardens. A hole you want to back with tape or cardboard.

jaotguy · Sep 27, 2014

basically 2 types of fiberglass resin ... one for cars and one for marine ( will not de-laminate in water ) ... also has 3 different bases or mixes ... polyester based, vinyl ester based and epoxy ...

resin has no strength by itself (must use cloth to cover large ares )

old surface must be cleaned well , then sanded lightly to give some tooth to bond to , then wiped again to remove any remaining "oils" ( that may be present in the fiberglass )

fiber glass cures with heat ... low temps give a soft cure ... when the temp rises , the glass softens ( becomes more plastic ) and re-cures at the higher temp .. if the temp goes too high before it re-cures , the fiberglass can return to the fluid state and deform ( ask any composite plane builder about it happening on runways on hot days )

fiberglass is also affected by UV ... so most mfrs cover the final product with a UV paint or varnish ....

doxford jim · Sep 27, 2014

Hi Guys,

Thanks for the comments.

I have done a quite a bit more reading and it looks like I might just have to wait until the spring before I try to do the patching with fibreglass. It currently is foggy and around 40F here but supposed to warm up to around 60F. I guess it would be borderline regarding proper repairs at these temperatures and humidity. Might be worth waiting until the spring to get a better repair. Too bad as I have just bought the resin (polyester) and hardener etc. Seems that the polyester is the most common type used for boat repairs and also the cheaper of the types.
I really don't want to go through all that work to make a faux pas, so I guess it will be put on hold for now. The weather forecast around here is about the same conditions for two weeks, with night time temperatures dropping below freezing - my how the weather forecast changes so quickly when you least want it eh ! No way do I want to waste time and money on an iffy repairs, so next spring is probably a better choice. Guess I need to be better organized to do the job properly as the greenhouse is 20ft long, 8ft wide and 9ft tall and will be quite a bit if work to do properly.

Oh well, worst things can happen and there is no way the greenhouse will collapse again after having centreline props installed for support.

Thanks for your interest - much appreciated.