Fiberglass and epoxy compatability

[firstascent2002]

Hi all,

I am trying to put an outbord well into my seal 22. Have bonded in marine ply laterat walls and a back wall in to the lazarette, presuming that the front bulkhead would be waterproof. Just thought I'd fill the outboard well with water before finally comitting and cutting the bottom and found to my horror that over night about halt a bucket had worked its way into the bilge. GREAT. Next plan is to put three or four layers of chopped mat fiberglass in to the outboard well to strengthen / waterproof it.

my questions are

1) will fiberglass bond to the epoxy if I key it well?
2) Should I a big single peace of mat and conform it to the inside of the well or multiple strips ( easier for complex courners)
3) how fong does fiberglass take to go off?

I really am in some need of help as I've not worken fiberglass before and this well really does need to be watertight or she'll end up on the bottom!!!

help

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[snowleopard]

epoxy is a glue and will stick to almost anything it touches as it sets. polyester resin on the other hand is not a glue. it will stick to previously set polyester as long as it's abraded but less well to epoxy. in your situation you would be better off using epoxy and glass cloth.

when applying chopped strand mat, it doesn't matter whether you use one piece or bits as long as they overlap and are well worked in- the binder that holds the fibres together dissolves in contact with resin so you end up with a mass of loose strands anyway. big areas of mat, especially bent to awkward shapes, are a pain to work with.

if you want advice on working with the various resins, PM me.

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[boatmike]

There is no problem with compatability between what you are calling "fibreglass" and epoxy. Epoxy resin and Polyester resin are both OK to use in bonding to an existing polyester hull. All "composite" materials are simply resin reinforced with glass, carbon fibre, kevlar or what have you. However there are some basic rules to follow. If doing a structural repair or modification NEVER bond over the gel coat. If you already have, tear it out and start again. Abrade the gel coat to expose the laminate underneath first. Gel coat is a resin without reinforcement and has little structural strength. If you bond to this the bond can fail through the gel coat layer. Secondly. ALWAYS abrade the surface lightly anyway and clean thoroughly. NEVER use white spirit or oil based cleaner. Apply resin to the surface liberally BEFORE laying down the glass mat or weave and roll the glass into the resin so that it wets out thoroughly from bottom to top. Repeat for up to 3 or 4 layers maximum and let that cure before building up further if required. Make sure you don't deviate too much from the resin/catalyst ratio. Too much and it will get very hot and cure very quickly. Too little and it will not cure properly and have low strength. Epoxy has better mechanical properties than Polyester and has better adhesive properties but as the rest of your boat is polyester there is little point in using Epoxy as is is more difficult to use and has health risks not associated with polyester. A middle road resin is Vinylester that is easier to use than epoxy but also unnecessary. I would use a good grade polyester but ensure the bond areas are scrupulously cleaned and abraded first. To finish off you can use a gel coat but if you have never done it before it is easier to apply an Epoxy like Gelshield 200 to all outside areas that are in the water. Follow the directions on the tin and apply 6 coats. Only two other rules. ALWAYS make sure surfaces are perfectly dry before starting and the ambient temperature is 16 degrees or above. Work fast as the resins pot life (time to start to harden) will probably be less than 30 minutes and could be down to 15 or so. Practice off the boat first. It's not difficult but there are knacks to master. Oh and wear disposable rubber gloves!!
Hope this helps. Happy laminating!!!!

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[boatmike]

Sorry, missed your other questions. Ok to use multiple strips if the strips overlap by 2 ins or so. Stagger the overlaps in alternate layers though.

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[chriscallender]

Maybe this is teaching granny to suck eggs ... but you also need to think about how the outboard transmits its thrust through to the hull, and make sure the well is strong enough for the job....

Chris

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[Birdseye]

The usual advice is that new polyester resin does not adhere to old polyester terribly well, and that you are better off using epoxy to bond to old poly. Having said that, loads of repairs are done using polyester on polyester without probs in lower stress areas and after carefully prepping the surface. Dont just sand it off - that can be too smooth. Without going so far as to damage the integrity of the old surface you are attaching to, use the tang of a file or something similar to really roughen up the surface.

If you do go the epoxy route, get some woven glass cloth for epoxy. It uses a different binder to cloth for polyester. Chopped strand mat is a nightmare to use with epoxy resin which is generally much more treacle like than poly resing and pulls the matt to bits. Get yourself lots of protective gloves (garage trade suppliers) a decent supply of acetone, brushes and a roller. Keep epoxy off the skin - lots of people have an allergic reaction to it.

Also, if you do use epoxy, it degrades in sunlight so needs some sort of surface coating. A gelcoat will do once the epoxy has cured properly. So will decent paint.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[maxi]

I'm with birdseye on this one. Epoxy does not react well with chopped strand mat - go with woven rovings right from the start.

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[30boat]

You can use polyester for repairs in highly stressed areas it's just more difficult than with epoxy.As long as you abrade a large area and go deep enough the mechanical bond obtained with proper laminating techniques can be perfectly satisfactory.However I would advise the use of epoxy whenever possible as IMHO it's not more difficult to apply than polyester and less material is needed for the same final strength.

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[clio]

do not use epoxy with mat, the binder used in the mat will react with the epoxy,causing loss of strength,sometimes total failure.

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[firstascent2002]

Thanks for all the help. I think in the light of this I am going to take a belt sander with a rough belt and cut deep in to the epoxy I've spilt and the composit. Will epoxy the whole well then using 15 cm tape from uk epoxys . 6 layers in total.

that done I'm going to put the outboard bracket back on and have a really hard 2 weeks sailing and then trail the boat home. Then I'll full up the outboard well with water and see if any water leaks into the bilges... Only when truly happy should you cut an irreversible hole in the bottom of your boat!!!!!!!!!

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[Avocet]

I'd go for epoxy. No matter how well you abrade the polyester and even if you do go down far enough to expose the fibres, you will still have a continuous plane where there are no fibres running through it. It's hard to describe but in a laminate, the fibres run in all directions (including, to an extent, above and below the surface you are looking at). When you lay more GRP on top of the surface, although it will "stick" to an extent, you will always have a "fault" line between the old and the new which the fibres can't cross. The fact that epoxies are better adhesives tends to make up for this.

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[BrendanChandler]

Only when truly happy should you cut an irreversib

Only when truly UNhappy should you cut an irreversible hole in the bottom of your boat!!!!!!!!!


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