High Moisture Reading - Epoxy Barrier or not?

[rajjes]

I have soda blasted my hull back to gelcoat which revealed many very small blisters which I sanded down and a few larger blisters which I grinded back to laminate and filled back after pressure washing regularly for 7 weeks.

Despite 7 weeks since blasting the moisture readings are very high all over (70-90) and the yard guys are telling me absolutely not to gel shield as it will make the blisters return more aggressively.

They are suggesting applying a couple of coats of Primocon and antifoul to allow the hull to 'breathe'.

On the other hand, chatgpt says that in practice even on a wet hull, Gelshield would still improve the situation and slow down osmosis as the hull will not absorb more moisture.

Is this a case of AI hallucinating or should I really consider Gelshield on a wet hull?

Are there any real experiences of an epoxy barrier doing rapid damage on a wet hull?

I understand the 'no boat' ever sunk from Osmosis but I would like to do the best I can in the situation while I am back to a bare hull.

Boat is a 1984 Moody 36.

Appreciate any feedback!

D

 

[Plum]

I have soda blasted my hull back to gelcoat which revealed many very small blisters which I sanded down and a few larger blisters which I grinded back to laminate and filled back after pressure washing regularly for 7 weeks.

Despite 7 weeks since blasting the moisture readings are very high all over (70-90) and the yard guys are telling me absolutely not to gel shield as it will make the blisters return more aggressively.

They are suggesting applying a couple of coats of Primocon and antifoul to allow the hull to 'breathe'.

On the other hand, chatgpt says that in practice even on a wet hull, Gelshield would still improve the situation and slow down osmosis as the hull will not absorb more moisture.

Is this a case of AI hallucinating or should I really consider Gelshield on a wet hull?

Are there any real experiences of an epoxy barrier doing rapid damage on a wet hull?

I understand the 'no boat' ever sunk from Osmosis but I would like to do the best I can in the situation while I am back to a bare hull.

Boat is a 1984 Moody 36.

Appreciate any feedback!

D

What is the moisture reading above the waterline?

 

[rajjes]

Moisture Reading above waterline is around 50

 

[Malish]

sounds like you need to leave out of the water for a month or three (without further jet washing) and monitor whether the moisture levels drop

 

[rajjes]

I have pressured washed the hull 40 hours before the readings were taken. It was dry and breezy so should not have affected the readings? It has been out of the water since 23 Feb so more than 7 weeks.

 

[neilf39]

Professional osmosis fixers used heated pads for weeks at a time to dry out a hull so 7 weeks is not alot. Probably 3 months over summer with gel coat stripped would be required without heat pads. We gelshielded a damp hull and in some spots bubbles have appeared over 5 years but we just now treat as they appear.

 

[[208637]]

Jet washing the hull it what has caused it. The damage needs to be thoroughly dried out and have multiple Acetone cleans before repair. I would then repair as normal; gelcoat damage, resin and filler as required or laying up if the damage goes deeper, before repairing the finish with flowcoat.

 

[jwilson]

The water has taken 40 years to get through gelcoat and into laminate, so without agressive intervention (peeling/very long drying/heated pads etc) it won't leave in a matter of weeks, though the close to surface moisture level may improve a bit. The gelcoat is fairly effectively stopping wet laminate drying out, just as it has stopped lots of water getting in over 40 years. What meter, what settings?

Personally I am not a believer in "sealing in" moisture with epoxy, but the choice is more related to religious belief than scientific fact. If you do gelshield, there will still be some drying through the inner skin as long as the interior is dry.

I am a believer in ashore over winter, with a dehumidifier inside. It may not ever totally defeat osmosis but the boat only has 8/12ths time afloat and some moisture must diffuse through both extenal and internal hull. The inside only usually has flowcoat (not any epoxy). I did have severe osmosis on a boat kept 364.5 days a year afloat in Hong Kong. Didn't sink though - most boats there had osmosis.

 

[RunAgroundHard]

Lots has been written about moisture readings in GRP never reducing despite the boat being indoors and drying with heat, infrared lamps. The reason given is that the water molecules (its not pockets of water) have reacted with chemicals in the resin that failed to cure for various reasons. The new molecules are larger and can't move through the GRP hence they always show as high moisture readings. The only way to deal with it, if this is what is found after trying to air dry, is through hot vacuum process after a gel coat peel. You probably do not need to do that.

Other reasons for high moisture content not reducing is water in the bilges, water in tanks touching the hull and condensation inside. It is easy to test. On a GRP coaming where you can access each side, place your moisture meter, then place a water bottle, 0.5 litre size, on the other side of the laminate, the moisture reading will rise as a result and drop when you remove the water bottle. The point is, make sure that the inside is bone dry.

This book is worth saving and reading before you do anything https://montymariner.co.uk/wp-content/uploads/2014/02/Osmosis-handbook-9a.pdf

In my opinion, as an owner of an old GRP hull, with high moisture reading and no blisters, don't bother doing anything beyond what you have already done, remove blisters and treat. Antifoul the hull and go sailing, don't spend a lot of money unless you are flush with cash and the boat value is very high, which I don't think it is (realistic, not being cheeky).

As for slowing down hydrolysis (it is not osmosis) you can't, it has already happened, the water molecules have reacted with the chemicals. If the GRP was perfectly cured, the water molecules would pass through the hull and disperse without anyone being any the wiser. In the book referenced earlier, it claims that adding an Epoxy barrier could make blistering worse.

 

[Flynnbarr]

Do not epoxy.
The yard guys are correct.

I have had experience of this due to a muppet previous owner.
It was very painful,time consuming and expensive to rectify.
If you epoxy over a ‘wet hull’ it will end up eventually looking absolutely dreadful…bit like the surface of the moon and the only way to get it off was a gel peel…..then it had to have heat pads as being on the land for the whole of a very hot summer didn’t get it dry.

 

[steve yates]

I have soda blasted my hull back to gelcoat which revealed many very small blisters which I sanded down and a few larger blisters which I grinded back to laminate and filled back after pressure washing regularly for 7 weeks.

Despite 7 weeks since blasting the moisture readings are very high all over (70-90) and the yard guys are telling me absolutely not to gel shield as it will make the blisters return more aggressively.

They are suggesting applying a couple of coats of Primocon and antifoul to allow the hull to 'breathe'.

On the other hand, chatgpt says that in practice even on a wet hull, Gelshield would still improve the situation and slow down osmosis as the hull will not absorb more moisture.

Is this a case of AI hallucinating or should I really consider Gelshield on a wet hull?

Are there any real experiences of an epoxy barrier doing rapid damage on a wet hull?

I understand the 'no boat' ever sunk from Osmosis but I would like to do the best I can in the situation while I am back to a bare hull.

Boat is a 1984 Moody 36.

Appreciate any feedback!

D

Whatever else you do ignore what chat gbt tells you, I have tried it several times for various boat stuff and conveyancing stuff and it has been badly wrong on several occasions, and sometimes been quite adamant that it was right. It cannot be trusted.

 

[Boathook]

7 weeks to dry out a hull isn't long. Ideally require a minimum of 6 months.

 

[elenya]

Personally I believe the boat yard staff are spot on. Leave it until you want to commit to doing a good job rather than a half assed one. Enjoy the summer sailing and haul out early to get it stripped and drying before winter.

 

[Jim@sea]

I have soda blasted my hull back to gelcoat which revealed many very small blisters which I sanded down and a few larger blisters which I grinded back to laminate and filled back after pressure washing regularly for 7 weeks.

Despite 7 weeks since blasting the moisture readings are very high all over (70-90) and the yard guys are telling me absolutely not to gel shield as it will make the blisters return more aggressively.

They are suggesting applying a couple of coats of Primocon and antifoul to allow the hull to 'breathe'.

On the other hand, chatgpt says that in practice even on a wet hull, Gelshield would still improve the situation and slow down osmosis as the hull will not absorb more moisture.

Is this a case of AI hallucinating or should I really consider Gelshield on a wet hull?

Are there any real experiences of an epoxy barrier doing rapid damage on a wet hull?

I understand the 'no boat' ever sunk from Osmosis but I would like to do the best I can in the situation while I am back to a bare hull.

Boat is a 1984 Moody 36.

Appreciate any feedback!

D

If you don't mind me making a stupid suggestion, years ago I sold Vans and at my bodyshop I would hand paint a Transit Van, (3.5 hours) I found that in the winter I needed to not only warm the paint up to stop runs, I would put a fan heater in the van, leave it for 15 minutes and then the bodywork was warm to the touch which also gave the advantage that any small brush marks would shrink as the paint dried quickly. (not that you can buy that sort of paint any more) So I would consider having a fan in the boat and see if the heated hull helps to dry out the hull. I have also done repairs on fibreglass hulls. On the last boat I had there were blisters. I dug out the blisters and used a heat gun in the area to dry it out properly then filled it with the filler suitable for underwater use, One was that bad that the blister came back, fortunately it was in an area where the hull was quite thick so I mase a hole where the blister was, screwed in a stainless steel screw with the head just below the hull surface, then filled it with filler the idea being that the filler underneath the screw head would not move as it would be trapped.
I also used a similar product as Gel Shield and did 6 coats with a roller.

 

[vyv_cox]

These photos taken in Greece show the hull of a boat that had been sailed to Türkiye to be epoxied and Coppercoated. The treatment was only a few months prior to the photos. The yard found the hull water content to be high. The boat was about to be taken back to Türkiye to have the job redone after drying. Cost was expected to be about €10,000

 

[Graham376]

Our first boat had been epoxied by or on behalf of seller, IIRC a year or so before we bought it. After a couple of years, large blisters appeared so arranged treatment. On stripping, it looked like craters on the moon and took months to dry out. Obviously had not been dried out before previous treatment.