Poignard
Well-Known Member
They didn't when they fitted through-hulls in my boat.
A survey made 30 years after she was built showed higher moisture reading in those areas than in the rest of the hull.
Sealing the cut edge of GRP
- Thread starter Gixer
- Start date
A survey made 30 years after she was built showed higher moisture reading in those areas than in the rest of the hull.
PaulRainbow
Well-Known Member
How are you going "saturate the exposed GRP" ?
If that was possible a chip in the gelcoat and the hull would saturate with water and sink
ducked
Well-Known Member
A GRP hull saturated with water would be heavier, but it wouldn't sink unless very advanced osmosis very rarely put a hole in itHow are you going "saturate the exposed GRP" ?
If that was possible a chip in the gelcoat and the hull would saturate with water and sink
Just as a wood hull saturated with water doesnt sink unless rot puts a hole in it
Just as a steel boat, saturated with ...er...steel, doesnt sink unless rust puts a hole in it
Eureka stylee
But you knew that, didn't you?
Moodysailor
Well-Known Member
Sorry, a strong opinion from me, but this sounds like poor advice. Sealing the ends of a GRP hole makes no sense unless it is a cored structure, it is so far up on the diminishing returns list it doesn't warrant further review IMO. If you are putting a skin fitting in and use an appropriate sealant then it's job done. The reason most skin fittings need to be cut out is because the right sealant was used and it holds well.
PaulRainbow
Well-Known Member
You completely missed the point
mjcp
Well-Known Member
If GRP layers were *ALWAYS* water tight, osmosis wouldn't be an issue would it ? Granted, the likelihood is low, but for the sake of £20 in epoxy and an few hours effort once every 5-10 years why not? You'd be smug with yourself with never having an issue if you do it and annoyed that you were the one who didn't and then had a duff survey result later on... All for £20 and 2 hours effort.How are you going "saturate the exposed GRP" ?
If that was possible a chip in the gelcoat and the hull would saturate with water and sink
PaulRainbow
Well-Known Member
Perhaps you should have a read of what osmosis is.
Virtually every GRP boat in existence has various through hulls which would have simply been cut out and the fittings installed with sealant, manufacturers do not epoxy the edges of the holes.
It's a pointless waste of time and money.
Tranona
Well-Known Member
The likelihood is non existent if you seal the fitting properly. Osmosis does not start from water entering via "unsealed" edges of a hole. In fact if the laminate is properly wetted out with resin it is sealed anyway. The OP and anyone else in the same position can check the hole they are enlarging for any sign of water entry or delamination. Chances are they will have to remove a layer of cured sealant before they even find the GRP - and it will be dry.
So complete waste of time to add anything other than the sealant required for the fitting.
ducked
Well-Known Member
I think I picked the part of the point that had the hole in it.You completely missed the point
PaulRainbow
Well-Known Member
If i have to explain it, i don't think you'll ever grasp it.
I'll try one last time, keeping it nice and simple (hopefully). If it was possible to saturate the GRP layup with resin, it would be extremely porous, ergo, not waterproof. Most of us here know that's not the case.
ducked
Well-Known Member
"In fact if the laminate is properly wetted out with resin it is sealed anyway." seems to assume perfection. 100% wetting. no voids. no wicking/ tracking along fibre bundles, no contamination, consistent resin catalyst mix, etc. Yet one hears of sub-perfect construction happening.
"Du Plessis, author of the most definitive work on GRP construction, lays the blame for blisters primarily on bad moulding, and as this work is normally done by error-prone/hangover/angry/about to be fired humans, it is both common and random, hence some twenty year old Seabasher 40s getting "osmosis" and some not."
GRP Osmosis|Boat Surveys|European Marine Surveys | European Marine Services Ltd
Wicking: Wicking is where the individual strands of the fibreglass mat behave like straws and draw water along their length, in doing so they swell in size and wicking will quite commonly be identified by a very slight raised pattern of the original matting visible on the gel coat.
Or less anecdotally
https://www.researchgate.net/public..._fibre_reinforced_vinylester_resin_composites
All stuff that never happens?
Maybe the OP isnt such an optimist
ducked
Well-Known Member
Yeh, you are right. I dont think that makes sense.
This is because it doesný.
Maybe you were trying too hard to keep it simple.
My simple understanding is that saturating the GRP layup (actually the glass in the GRP layup, otherwise it becomes logically circular) with resin is the objective, and the hope is that this will make it relatively impermeable to water and relatively strong.
Failure to achieve this makes the hull more vulnerable to wicking and osmosis, as noted in the reply to Tranona above.
Saturation with water, which is probably what you meant to say, probably isnt technically appicable as a term to a composite solid structure, since it seems to imply there is some maximum water content, which probably isnt the case. In the limit the hull material would simply dissolve and disintegrate.
PaulRainbow
Well-Known Member
Do you not think they saturated the layup when the boat was build !
A reply which is largely irrelevant drivel, much of which looks like AI.
Not sure if you are trolling, being deliberately argumentative, or just not capable of simple understanding.
Tranona
Well-Known Member
They are talking about a very different scenario where the laminate is already contaminated with typically styrene from the original layup where often there are dry patches with exposed fibres and the moisture is migrating through the layup.
The OP wants to cut a larger hole through a solid layup which is dry and will forever remain dry if the fitting is well bedded in sealant. The "exposed" are of laminate is tiny in area and not exposed to water - so how can any wicking occur? A typical modern boat has anything up to 15 holes cut below the waterline with a CNC controlled drill and never coated with anything except sealant. That has been so since GRP was introduced (although mostly manually drilled!). i have never heard of this being an issue until this doom laden thread .
ducked
Well-Known Member
RE Do you not think they saturated the layup when the boat was build ! Tis you who posted "If it was possible to saturate the GRP layup with resin, it would be extremely porous" which, as well as not making sense, means that you dont think they saturated the layup when the boat was build (sic). WORDS HAVE MEANING.
I said they might not have, because they might not have. I see little point in repeating mayself. You can flog a dead horse underwater but you cant make it drink.
Enough already. You originally posted a strawman. Then you posted something which can only be a mistake on your part, which you didnt acknowledge, and you continue to be gratuitously insulting. Enjoy your last word, even if it also turns out to be nonsense.
PaulRainbow
Well-Known Member
Incapable of understanding.....
I said "If it was possible to saturate the GRP layup with resin, it would be extremely porous". Note the use of the word IF. How does that mean i think it wasn't ? On the contrary, it means that i believe it WAS. Therefore, trying to further saturated it with additional resin is totally pointless.
Let's do it like the manufacturers do, cut the hole, apply sealant, fit through hull and go sailing. (Unless it's a cored hull, which the OPs isn't).
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Tranona
Well-Known Member
Even if the hull is cored as my Bavaria was (and HRs are) where some through hulls are it is normal to ramp down locally to solid layup. But a 30 year old Hunter is solid.
Gixer
Well-Known Member
Incase you’re interested, I just used Sikaflex 291i
Tranona
Well-Known Member
Well done. You can now forget about it!
Worth raising it though as it elicited some very interesting perspectives on the topic
Worth raising it though as it elicited some very interesting perspectives on the topic
