How strong is fibreglass?

Elessar said:
Paul, my GRP expert, does indeed argue that epoxy is worse. He says that whilst epoxy can have a stronger bond, there are far more ways to get it wrong. So for DIY he strongly advises polyester.
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Ah ha. Now there goes a wise man. As a novice, I'm bound to do this in one of the ways that's wrong and thus screw up my time and money. My mind is clear on this. I'll take my chances with the Greek products available on my little island and do the job 'siga siga' [slowly slowly] as we say in Greek.

Thanks for all the advice guys.
 
I know very little about this sort of thing....you may well ask why if I know nothing am I venturing a few words.
I have spent many years dinghy racing with a crew who was both knowledgable and talented in these matters. We decided the centreboard case was fllexing and he expoxied a couple of pairs of knees to stiffen the c/b case to the floor. Worked a treat and the boat was definitely faster.... until one day we had long hard beat in heavy weather when the performance fell right off. Ashore we found every epoxy joint to the floor had broken. " Ah I was afraid that might happen" my man said and refitted them using polyester.... never a problem again.
I was unable to pluck up courage to ask him why if he expected it might happen he did not use polyester in the first place.... sometimes these craftsmen get a little tempremental when you ask them the bleeding obvious.
 
I would not use polyester resin as this will be weaker and may peel off even new wood reinforcement.
Best use Epoxy resin for assured results.
 
I'd certainly go with polyester resin. I think the hardest part you'll encounter will be applying the glass/resin 'upside down' - the resin will continually try and run out the bottom of your stiffening beam. Don't worry too much about adhesion to any timber former you use, try and get the strength in the new glassfibre rather than the former. (as stated above, the former could even be made of something as weak as foam anyway)

Crucial to getting the new stuff to stick is the way the layers are applied. I'd suggest overlapping first layer 25mm, second layer 50mm, third layer 75 mm etc for a good bond. Don't apply more than three layers at a time else resin seepage will be a serious problem. Grind the old surface well to expose the raw glass strands first and soak well in acetone to soften surface. This is important so that the new resin actually combines with the old and doesn't just stick to the surface. (Left long enough - several months, so don't worry) - acetone will actually render any age resin a pulpy mess!!)

Don't use too heavy a weight glass for best results.
 
As you were. I just re-read the OP and it looks like you're just trying to add 'brackets' to joint area between deck and hull.

My mistake, sorry. The sketch/instructions I just posted refers to stiffening beams right across the deck so may not be what you're after. (even though IMHO it'd be a better job and doesn't lose much headroom)
 
Stick with the polyester resin and plywood method, and you can counter the lack of adhesion to the plywood by priming the plywood with polyester resin thinned with 10% acetone first as this gives better penetration and adhesion. Then stick it in with polyester resin and laminate with several coats of resin and matting.
 
LittleSister said:
Are you sure you don't have a balsa or foam cored deck? I don't know the Colvic, but many boats have deck stiffness provided by having two layers of GRP with a thick layer of end-grain balsa or plastic foam between them.

This 'sandwich' is a very good way of providng stiffness, in terms of cost and weight, but can fail over time. Balsa cored decks in particular are vulnerable to poor maintenance or inappropriate fixings. Unless the top layer and through fittings are kept completely waterproof, water can get into the balsa, it then rots, and the stiffening support to the deck is drastically reduced, resulting in 'springy' decks which flex underfoot.

If you have this sort of construction, adding stiffening beams or boards under the bottom layer is not going to help (the top one will still move). To find out if you have this sort of construction check how deep your deck is, e.g. by checking the thickness aroud a hatch, or if necessary by removing a though bolt. A single layer will probably be less than 1/4 of an inch, a cored deck will be much thicker.

If you do have a cored deck, and a rotten or detached core is the problem, then it is a rather different, and bigger, task - replacing the core, which will involve cutting out the relevant section of grp -either the deck on top or the underside (cabin ceiling) beneath it - clearing out and replacing the core with new balsa, foam or plywood; then glassing the cut out part back in place. There are numerous articles in books, magazines and on the web if you need to go down this route.
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Hit the nail on the head, Colvics have cored decks. The curve of the deck ad the bonded cored structure should be quite stiff, but disbonded and it flexes
 
Hi,

Interesting thread as I'm in the process of replacing floor, stringers, transom and engine bearers in a 21' Fletcher.

My floor was mostly solid but with some flexing in a couple of areas, but this concealed a compost like composition of the plywood within the floor! :eek:

I did quite a bit of research and started a few threads on PBO and other forums on best methods and tips for rebuilding etc before I had even finished cutting out the original. As here, the opinion seemed polarised on the epoxy vs polyester!

Due to quantities required the epoxy route was always going to be prohibitively expensive for me but I obviously don't want to compromise on something so important structurally. There are two things that stood out as significant to me, firstly the boat's original structure was polyester so this seemed a good reason to stick (:o) with this. Secondly, although the original GRP had separated from the timber in some places this has to be put in perspective and it was after 30+ years! When I cut the old capping etc from stringers and ply bulkheads etc the reasons for the separation became apparent. The stringers etc were clearly 'laid out' with framing etc 'tabbed' into place and then the whole lot capped over with layers of matting and polyester resin. The major pitfall with this is that once a later fixing compromised this 'skin' and moisture entered the 'cell', the wood starts to decay and this will be from the outermost layers first. Evidence of this is apparent on the sections of capping as I removed them - fibres of the original wood surface remain in/on the resin cap. Thus the moisture appears to have tracked along under the surface of the wood and rotted the wood away from the GRP. This is further substantiated by the fact that the ends of the stringers or where holes were later drilled were worst affected by rot due presumably to capillary action having drawn in trapped moisture. Had each piece of timber been pre-treated, the rot could not have spread beyond a compromised timber. I guess the epoxy has a small advantage here because it absorbs better into the wood than the polyester - thus a less clearly defined 'bond'. (Much like superglue 'melts' into plastic - or skin :D)

To protect the new timbers as I fit, I aim to follow advice I was given to treat with CPES which will penetrate the timbers and inhibit decay - much like the use of Acetone to dilute the polyester resin.

Everyone I have spoken to says the same however and that is that the cured polyester you are bonding to MUST be clean and as mentioned above, best abraded. I have also been told the same advice about polyester giving much better results for a novice (like me!) and as I'm going to be doing all the work myself, this seems to offer the best chance of success provided preparation is good. As I understand it, the epoxy is a chemical reaction between the resin and hardener so the quantities are critical to success, whereas the additive for the polyester is only a catalyst which triggers the reaction in the already correctly proportioned polyester resin. Thus within limits, more catalyst = faster reaction, less catalyst=more time to work... :)

Will be interested to hear how you get on!

Regards,

Robin
 
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rbcoomer said:
Hi,

Interesting thread as I'm in the process of replacing floor, stringers, transom and engine bearers in a 21' Fletcher.

My floor was mostly solid but with some flexing in a couple of areas, but this concealed a compost like composition of the plywood within the floor! :eek:

I did quite a bit of research and started a few threads on PBO and other forums on best methods and tips for rebuilding etc before I had even finished cutting out the original. As here, the opinion seemed polarised on the epoxy vs polyester!

Due to quantities required the epoxy route was always going to be prohibitively expensive for me but I obviously don't want to compromise on something so important structurally. There are two things that stood out as significant to me, firstly the boat's original structure was polyester so this seemed a good reason to stick (:o) with this. Secondly, although the original GRP had separated from the timber in some places this has to be put in perspective and it was after 30+ years! When I cut the old capping etc from stringers and ply bulkheads etc the reasons for the separation became apparent. The stringers etc were clearly 'laid out' with framing etc 'tabbed' into place and then the whole lot capped over with layers of matting and polyester resin. The major pitfall with this is that once a later fixing compromised this 'skin' and moisture entered the 'cell', the wood starts to decay and this will be from the outermost layers first. Evidence of this is apparent on the sections of capping as I removed them - fibres of the original wood surface remain in/on the resin cap. Thus the moisture appears to have tracked along under the surface of the wood and rotted the wood away from the GRP. This is further substantiated by the fact that the ends of the stringers or where holes were later drilled were worst affected by rot due presumably to capillary action having drawn in trapped moisture. Had each piece of timber been pre-treated, the rot could not have spread beyond a compromised timber. I guess the epoxy has a small advantage here because it absorbs better into the wood than the polyester - thus a less clearly defined 'bond'. (Much like superglue 'melts' into plastic - or skin :D)

To protect the new timbers as I fit, I aim to follow advice I was given to treat with CPES which will penetrate the timbers and inhibit decay - much like the use of Acetone to dilute the polyester resin.

Everyone I have spoken to says the same however and that is that the cured polyester you are bonding to MUST be clean and as mentioned above, best abraded. I have also been told the same advice about polyester giving much better results for a novice (like me!) and as I'm going to be doing all the work myself, this seems to offer the best chance of success provided preparation is good. As I understand it, the epoxy is a chemical reaction between the resin and hardener so the quantities are critical to success, whereas the additive for the polyester is only a catalyst which triggers the reaction in the already correctly proportioned polyester resin. Thus within limits, more catalyst = faster reaction, less catalyst=more time to work... :)

Will be interested to hear how you get on!

Regards,

Robin
Click to expand...

Hi Robin. Thanks for that well-thought-through message. My updated position is that I have now tried to stick three layers of matting [soaked in resin one at a time of course] onto my deck and the result is a disaster. I've got bubbles in places and in other bits I've got some 'dry' matting with no resin etc. How this result happened I don't know as I was as diligent about spreading as I could be. SO I've bolted a solid curved 3" beam to the underside of the deck - but guess what? - I've still got flexing in my foredeck! But oddly - there's more flexing above than below.
Now, I've got limitations on what I can do here. I'm on a tiny Greek island and only have the tins of Greek-made resin and little bottles of hardener sold by the local hardware store - with no instructions - even in Greek. But I was also doing this job in wind and with a little wallpaper scraper to spread my mixed resin.
Those limits notwithstanding, I guess the flexing is due to old ingress of water which has separated the original wood from the original fibreglass.
Solution? I'll live with the flexing until next year and - if it gets worse - then I'll have no option but to cut out the original and replace using all the advice I've had here.
Good luck
 
GreekYiannis said:
Hi Robin. Thanks for that well-thought-through message. My updated position is that I have now tried to stick three layers of matting [soaked in resin one at a time of course] onto my deck and the result is a disaster. I've got bubbles in places and in other bits I've got some 'dry' matting with no resin etc. How this result happened I don't know as I was as diligent about spreading as I could be. SO I've bolted a solid curved 3" beam to the underside of the deck - but guess what? - I've still got flexing in my foredeck! But oddly - there's more flexing above than below.
Now, I've got limitations on what I can do here. I'm on a tiny Greek island and only have the tins of Greek-made resin and little bottles of hardener sold by the local hardware store - with no instructions - even in Greek. But I was also doing this job in wind and with a little wallpaper scraper to spread my mixed resin.
Those limits notwithstanding, I guess the flexing is due to old ingress of water which has separated the original wood from the original fibreglass.
Solution? I'll live with the flexing until next year and - if it gets worse - then I'll have no option but to cut out the original and replace using all the advice I've had here.
Good luck
Click to expand...

Sorry to hear your attempt didn't go to plan, I think I have a link at home for a 'how to' guide that I was kindly sent by someone. I will look when I get home and post here later. I think the idea is that you paint on the resin with a brush and then roll the matting into it using some rollers with 'teeth' (wrong terminology I'm sure, but I'll post a picture later!) this ensures coverage of the resin and removes the air bubbles. You then add more resin and repeat as required to build up layers. I confess that I've not started mine yet, but I have cleaned some of the old bits of fibreglass that I cut out and experimented by sticking them together to check adhesion. Two flat sections stuck together with a 2" wide overlap cannot be separated by hand after a week curing, although I did clamp them which I won't be able to do in the boat! On that basis however I was fairly content that using polyester resin would be ok for what I'm planning. I did find that I could separate some sections with a hammer and screwdriver ( :rolleyes: ) but not without splitting some of the original GRP. Thus I think my bond was mostly as strong as the original fibreglass and provided I clean the hull well where I intend to stick, it should be good... I hope! :D
 
My problem seems to be that air has got stuck between layers. So what I'm going to do is simply take a stanley knife to the air pockets, slice open the 'bubble', and really slosh some new resin on - and rub it well in. I can't think why that wouldn't work. If I get anything like a satisfactory result, I'll just sand it down and paint it. I don't use my foredeck much anyway. Next year i'll maybe cut out the deck and lay a new one in wood.
 
hello there,

Yanni, what LS and BO are saying is that you have most likely a sandwitch of GRP some sort of foam (maybe 10-15mm or more) and then GRP again. Thats what they call cored. Sorry for going through this analytic explanation, as a fellow greek I know that core is not one of the english words we learn at school you have to come across and search for its meaning :D

Structurally, this is one of the best solutions for gaining rigidity. So now what happens is that the two loadbearing skins of GRP (the top and bottom) are disconnected from the inbetween thing and there's no way in hell you're going to obtain the same structural abilities out of laying a couple of layers of glass matt. You'll need to apply lots and lots of layers and then you're going to have a very heavy superstructure as a result. Rigidity will still be less than the original method.
I'm not into GRP stuff, but as I understand it you're in for some "operation" checking what's happening inside and taking action afterwards.

May I suggest you start a photobucket or similar account and start posting pics so the more knowledgeable of the lot can give some help?

Also, where are you based? There are places that will mail order things to you and the prices are not that bad. One such company is in Volos where I am and his prices are indeed amongst the cheaper in europe ;) If you want drop me a pm and we could talk a bit on that.

kalh doylia

B.
 
Epoxy or p[olyester ?

I also have read different reports about the adhesion to plywood.

What is correct?

Will polyester stick as well as epoxy to new plywood?

I have just laminated some plywood beams and used epoxy because of conflicting opinions.

Which would be best for fixing new bulkheads to a GRP hull?

Are there any disadvantages to using epoxy ?
 
mpe said:
I also have read different reports about the adhesion to plywood.

What is correct?

Will polyester stick as well as epoxy to new plywood?

I have just laminated some plywood beams and used epoxy because of conflicting opinions.

Which would be best for fixing new bulkheads to a GRP hull?

Are there any disadvantages to using epoxy ?
Click to expand...

Hi, I think if you look back at the posts to my original question, there are answers to all your questions.
 
Hi GreekYiannis

To explain fully how to use fibreglass would take up pages on this forum. Its more complicated to explain than to do though. These people have been going since the sixties and used to do a really good guide pack. Take a look at their site. (and I'm sure if you emailed them they'd help anyway, used to snail-mail a huge written guide)

http://www.glasplies.co.uk/
 
MPE:

To answer your questions, yes polyester will stick to plywood as well as epoxy, but you can coarsly sand the plywood if you are not sure, then thin polyester resin with 10% acetone and prime the plywood first to give more pepetration and adhesion.
Second, don't store your plywood outside or in damp sheds or garages as the moisture content rises and inhibits the adhesion, particularly at this time of the rear when the air is damp. If you can I would suggest storing it in the house which is centrally heated to reduce this moisture content from about 15-20% outside, to about 3-4% inside. Alternatively you could do the work in the middle of summer and get the sheets out in the sun and turn them to dry them until they are as dry as possible.

With the primed sheets you can cut out the shapes you require and prime the edges, being ply this gives excellent penetration so you may want to do them twice to ensure good penetration and a good build up of priming resin. Coat the edges again and install in position and let it set, coat with matting and overlap by 1" onto the boat hull, stipple well with a stiff paint brush and roller out any air. Once set (15-20 minutes during a hot summer) apply a second coat of polyester and matting, but overlap onto the hull by 1 1/2" with this second mat. Repeat with the third coat of resin and matting and overlap onto the hull 2" and so on. Repeat until you have sufficient coats of resin and matting on and overlapping onto the hull to the ratio of 75% of the thickness of your stringer.

If your stringer is 4" deep your overlap onto the hull must be 3" either side, and stepping the matting with each coat prevents stress lines from forming by spreading the load while maintaining adequate flex to prevent cracking.
 
Epoxy has some disadvantages, these are that it is a different material to GRP and flexes at a different rate and this can induce local stresses and stress cracks. Laminating plywood together with epoxy is fine as most plywood is epoxy laminated when it is manufactured.

When you bond it in use GRP and the method as described above.
 
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