Fibre glass repair..thoughts

William_H said:
PaulRainbow said:
in my experience long term it is hopeless on wood. olewill
Click to expand...
I also contest that. A FV I built in 1983 still has all its GRP/ply intact. The bond between the (ply) deck and (ply) wheelhouse of my current FV which I did 20 years ago is absolutely sound. If you just apply resin and mat it will fail, the resin migrates into the wood leaving the mat unsaturated. The trick is to get the resin into the wood first. Accelerator used to be termed 'sheathing primer', painted on first it encouraged the resin to cure quickly where it contacted the wood. Better is to paint the ply/wood with a fairly hot resin mix first then apply saturated mat, preferably wetted out away from the work. I always tear the surface of the wood or ply up first with a grinder or circular saw to get mechanical adherence as well.
A local GRP fabricator, car panels etc, has been doing it for many years. Above his workbench he had a chart of ambient temperature against percentages of accelerator and catalyst, the latter never above 2%.
Click to expand...
 
macd said:
They are very expensive, especially if bought from marine outlets.
Compare microfibres (which is what you'd use for the highest strength fillet):
West, £12 for 150g (£80 per kg): https://www.amazon.co.uk/West-System-403-Microfibres-150g/dp/B00G5Q8O10
SP, £15 for 500g (£30 per kg): http://www.mbfg.co.uk/epoxy-resins/microfibres-filler.html

I suspect this is precisely why Force4, for instance, stock the SP version. West is very convenient, mainly because it has excellent distribution in the marine trade and excellent 'how to' information. But it's a rip-off.
Click to expand...

Couldnt agree more. West epoxy is also the poorest quality on the market. The better structual epoxy systems are one to one mix. All the money is in the hardener which is why West use hardly any! SIP resins are far superior but there are many out there just as good
 
geem said:
Couldnt agree more. West epoxy is also the poorest quality on the market. The better structual epoxy systems are one to one mix. All the money is in the hardener which is why West use hardly any! SIP resins are far superior but there are many out there just as good
Click to expand...

This is interesting! I have an outstanding task to glass in a large hole in the binnacle where a plotter was fitted and then cut out a new hole to take a new plotter. I intended to do this with West Epoxy and fibreglass cloth, finishing off with flowcoat before fitting the new plotter - are you suggesting that standard West Epoxy is not up to this?
 
geem said:
Couldnt agree more. West epoxy is also the poorest quality on the market. The better structual epoxy systems are one to one mix. All the money is in the hardener which is why West use hardly any! SIP resins are far superior but there are many out there just as good
Click to expand...

Yet if you read any GRP threads on here people are of the belief that West is best, their guides and advice is gospel and all repairs must be done using West epoxy.

People with polyester boats insist on repairs being made with epoxy, because companies such as West have said so. Even if we accept that epoxy has a stronger mechanical bond than polyester to polyester, the rest of the boat is poly to poly bonded and it hasn't fallen apart.
 
maby said:
This is interesting! I have an outstanding task to glass in a large hole in the binnacle where a plotter was fitted and then cut out a new hole to take a new plotter. I intended to do this with West Epoxy and fibreglass cloth, finishing off with flowcoat before fitting the new plotter - are you suggesting that standard West Epoxy is not up to this?
Click to expand...


If you have access to the inside of the binnacle you could tape a piece of waxed glass over the hole, paint it with poly gelcoat, then use poly mat and resin, not allowing any layer to fully cure before applying the next. The finish would be perfect apart from a very thin line that would polish out.
 
PaulRainbow said:
If you have access to the inside of the binnacle you could tape a piece of waxed glass over the hole, paint it with poly gelcoat, then use poly mat and resin, not allowing any layer to fully cure before applying the next. The finish would be perfect apart from a very thin line that would polish out.
Click to expand...

That is pretty much what I have in mind, but using West epoxy and finishing off with the best colour match flowcoat I can find. I was concerned by the statement that West is "the worst epoxy around" or words to that effect!
 
maby said:
That is pretty much what I have in mind, but using West epoxy and finishing off with the best colour match flowcoat I can find. I was concerned by the statement that West is "the worst epoxy around" or words to that effect!
Click to expand...

There is no benefit in using epoxy for this job though.
 
You get a far superior repair using epoxy on polyester rather than polyester on old polyester. Not important on non-structural elements but far more important below the waterline. Why give West your hard earned cash for a poor quality product? They do however proved the best instruction manuals on how to use their product and they do have superb marketing. It really doesnt make the product any good. If you don't believe me do use Mr Google. The information is out there.
We recently purchased all the materials to replace our teak decks. A good 1:1 epoxy worked out at £18/litre. This is comparable with what we used to pay in the UK for Thistlebond now a 3M product.
We always use cloth not mat for any jobs we do. More time consuming but far stronger construction and easier to go around corners if you use many layers of lightweight cloth. In my opinion mat just soaks up resin amd doesnt form a strong repair.
We have done so much grp work in epoxy we rarely use polyester any more
 
All understood - but you must bear in mind that I'm talking about less than two square feet of non-structural panel. West was readily available and cost around £20 - if it is good enough, then I'm happy - I just want to understand the implications of it being a "poor quality product" - I've never used it before. Is it going to be inadequate to glass in about a square foot of hole in a binnacle which is about three or four mm thick and carry a layer of flowcoat?
 
maby said:
Only ease of availability - I already have it! Are there significant disbenefits (is that even a word???)?
Click to expand...

Polyester would provide a perfectly good enough repair in terms of strength for this job and as you are using polyester gel the finish will be the same either way. As you already have the epoxy, you may as well use it, IMO. West may not be the best, but again, it's good enough for this job. Let's face it, paper mache would do this if it was waterproof :)
 
PaulRainbow said:
Polyester would provide a perfectly good enough repair in terms of strength for this job and as you are using polyester gel the finish will be the same either way. As you already have the epoxy, you may as well use it, IMO. West may not be the best, but again, it's good enough for this job. Let's face it, paper mache would do this if it was waterproof :)
Click to expand...

Excellent - that is what I was hoping to hear!
 
PaulRainbow said:
Yet if you read any GRP threads on here people are of the belief that West is best, their guides and advice is gospel and all repairs must be done using West epoxy.

People with polyester boats insist on repairs being made with epoxy, because companies such as West have said so. Even if we accept that epoxy has a stronger mechanical bond than polyester to polyester, the rest of the boat is poly to poly bonded and it hasn't fallen apart.
Click to expand...

The polyester to polyester structure of the boat is strong because it is done with the polyester not fully hardened so you get the chemical bond. Often also if it done when parts are hardened as in deck to hull join then the huge area of bonding plus fasteners makes polyester to polyester adequate. olewill
 
I have a 2m x 1m polyester to polyester sacrificial patch on my hull, underwater. Applied over a low water in 2001 as a stopgap until lift out. Still there. Of course, not subject to any stresses as internal structure might be.
 
William_H said:
The polyester to polyester structure of the boat is strong because it is done with the polyester not fully hardened so you get the chemical bond. Often also if it done when parts are hardened as in deck to hull join then the huge area of bonding plus fasteners makes polyester to polyester adequate. olewill
Click to expand...

But they don't build whole boats in the time it takes for the hull to cure. Hand built and older, pre-mass production boats, will have all manner of structural layup applied after the hull has cured. We don't see these boats coming apart at the seams.

It is true that poly over cured poly is a mechanical only bond, but epoxy to poly is also mechanical only, no matter when it is applied. Epoxy over fully cured poly may be technically stronger (may), but there is no need for any strength above and beyond that which can be achieved with a good poly to poly process.
 
PaulRainbow said:
But they don't build whole boats in the time it takes for the hull to cure. Hand built and older, pre-mass production boats, will have all manner of structural layup applied after the hull has cured. We don't see these boats coming apart at the seams.

It is true that poly over cured poly is a mechanical only bond, but epoxy to poly is also mechanical only, no matter when it is applied. Epoxy over fully cured poly may be technically stronger (may), but there is no need for any strength above and beyond that which can be achieved with a good poly to poly process.
Click to expand...

Nope, it takes a verylong time for PE to finally cure (as opposed to harden), otherwise you wouldn't have that distinctive acetone fragrance on a brand new boat... I have numerous examples on Gladys (mainly floor bearers) where the poly-poly "bond" has come away - although that may be due to workmanship as well...
 
Gladys said:
Nope, it takes a verylong time for PE to finally cure (as opposed to harden), otherwise you wouldn't have that distinctive acetone fragrance on a brand new boat... I have numerous examples on Gladys (mainly floor bearers) where the poly-poly "bond" has come away - although that may be due to workmanship as well...
Click to expand...

Polyester resin is fully cured in 4 to 6 hours. Any layup applied after this time will only have a mechanical bond. Bonding to wood requires correct resin, correct preparation and does not work with all woods. I have lots of GRP to wood layup and none of it is coming apart. Some bearers that have been added much later than the boat was built (holding tank and additional potable water tank) have adhered well, apart from some they put on the stainless tanks, though that is to be expected.
 
I had to do similar at join of hull mould and sugar scoop so not much room to get in we made up a type of poultice on a plastic bag 4 wetted layers - sounds similar to fishermans solution - away from area then whacked it in not the tidiest but strong and worked
 
You must log in or register to reply here.

Share this page

Top