Why is my Hull not drying out?

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Vertor

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Hello Members, I am mid way through a total re-fit including treating osmosis on my Nicholson 40DS and am seeking some advice. The GRP on her is around 1inch thick, it's a solid Hull.

She is on the hard under cover in East Yorkshire UK since October 2017 - weather has been temperate.

- The vessel has been out of the water on the hard for 6 Months;
- Under cover as we are also replacing the teak deck;
- Gelcoat has been professionally peeled - not shot blasted;
- Hull has been steamed some 20 times using an industrial pressure steamer;
- The exposed GRP has turned white on the surface as opposed to its original yellow when we first peeled the Hull;
- Just started using an IR short wave heater which, after the first few sessions seems to have made no difference.

According to my Tramex meter the high readings have remained constant - not come down. In order to get a quick manual indication of damp, I have sealed with tape a small clear plastic patch on the hull, thinking it might steam up, there is no sign of condensation at all on the clear plastic bag.

Any guidance gladly listened to.

Thank you in advance.
 
There are two main reasons the moisture meter gives high readings generally. The first one is that after a vessel is removed from the water there will almost certainly be retained water moisture in the gel coat and possibly the laminate. This generally has no structural effect and will dry out reasonably quickly, sometimes within a few days of being ashore. Hence the reason that a suggestion to not do moisure meter readings of a vessel for survey for instance for a few days following lift out. This initial drying happens quite fast and generally does not need forcing. The other reason is that the chemical change that causes blistering is due to a new chemical being created within the laminate. This chemical is identified by the moisture meter as being water. The meter cannot differentiate between either. This chemical does not naturally dry out in the same way water does and remains intact within the laminate. Similar to waiting for a spot of glycol antifreeze to dry out on a saucer alongside a saucer of water. The water evaporates, the glycol does not. Hence the reason that steam cleaning is used to flush out this chemical. Infra red heaters do not significantly help in isolation as all you can do is heat the chemical but not remove it..
Sometimes the older hulls might give very high readings but never go on to develop delamination or blistering. Possibly need more information on the hull condition other than moisture readings to comment further. Of course, also bear in mind that most moisure meters will register damp linings internally as well as plywood and timber structure and give misleading reading.
 
It took me best part of 18 months to get my hull from off-the-scale on the tramex to in the green / yellow part of the scale. I hot washed my hull daily before before going to work, heat helps but in my experience hot pressure washing and leaving it to air dry does most of the work.
 
When we had our boat treated for osmosis in windy SW France the drying time was quoted as "typically" 9 months for a simple gelcoat strip and 6 months for a deeper strip of the laminate. We opted for the latter as it involves applying an additional layer of robust fibre glass mat and waterproof resin. These times include a regular hot wash with caustic soda.

I would think you might expect the drying time in E Yorks to be double these?
 
At least 2 possible reasons, might be more:

1) Assuming that your boat is something like 30-odd years old it's taken that long for the water to get into the depths of the quite thick laminate: it won't come out again very fast.

2) Some laminates contain materials (other than water) that "fool" moisture meters - "moisture meters" don't actually measure water content, just conductivity. Occasionally perfectly good hulls get "osmosis treated" at considerable extent when there was nothing wrong with them.

So it could still be damp or it might be quite dry. A core sample weighed on a really accurate scale and then again after baking in an electric oven is one way to decide.
 
Hoolie said:
When we had our boat treated for osmosis in windy SW France the drying time was quoted as "typically" 9 months for a simple gelcoat strip and 6 months for a deeper strip of the laminate. We opted for the latter as it involves applying an additional layer of robust fibre glass mat and waterproof resin. These times include a regular hot wash with caustic soda.

I would think you might expect the drying time in E Yorks to be double these?
Click to expand...

A good bit warmer there than in a shed in Yorkshire I would imagine.
 
Hoolie said:
When we had our boat treated for osmosis in windy SW France the drying time was quoted as "typically" 9 months for a simple gelcoat strip and 6 months for a deeper strip of the laminate. We opted for the latter as it involves applying an additional layer of robust fibre glass mat and waterproof resin. These times include a regular hot wash with caustic soda.

I would think you might expect the drying time in E Yorks to be double these?
Click to expand...

Indeed much warmer in France, which is why I thought the IR heater might help. Caustic Soda is intertesting Hoolie, did you put the soda into the resevoir on the washer or apply by hand?
 
jwilson said:
At least 2 possible reasons, might be more:

1) Assuming that your boat is something like 30-odd years old it's taken that long for the water to get into the depths of the quite thick laminate: it won't come out again very fast.

2) Some laminates contain materials (other than water) that "fool" moisture meters - "moisture meters" don't actually measure water content, just conductivity. Occasionally perfectly good hulls get "osmosis treated" at considerable extent when there was nothing wrong with them.

So it could still be damp or it might be quite dry. A core sample weighed on a really accurate scale and then again after baking in an electric oven is one way to decide.
Click to expand...

Thank you. Perhaps a core sample after another good spell of time and hot wash might be sensible, should I not see any results
 
Vertor said:
Indeed much warmer in France, which is why I thought the IR heater might help. Caustic Soda is intertesting Hoolie, did you put the soda into the resevoir on the washer or apply by hand?
Click to expand...
Obviously the caustic soda is to neutralise the acid in the laminate and it was applied by the yard operative using a hot water reservoir with the caustic dissolved in it. I only saw him do it a couple of times but was told to stand well clear! The yard was actually gravel on sand so it was relatively easy to rinse away. Not so easy if your boat is on a hard base.

Of course it's warmer in summer down there but our boat overwintered when it can be quite cold. Dry winds from the Pyrenees helps drying.
 
Vertor said:
Hello Members, I am mid way through a total re-fit including treating osmosis on my Nicholson 40DS and am seeking some advice. The GRP on her is around 1inch thick, it's a solid Hull.

She is on the hard under cover in East Yorkshire UK since October 2017 - weather has been temperate.

- The vessel has been out of the water on the hard for 6 Months;
- Under cover as we are also replacing the teak deck;
- Gelcoat has been professionally peeled - not shot blasted;
- Hull has been steamed some 20 times using an industrial pressure steamer;
- The exposed GRP has turned white on the surface as opposed to its original yellow when we first peeled the Hull;
- Just started using an IR short wave heater which, after the first few sessions seems to have made no difference.

According to my Tramex meter the high readings have remained constant - not come down. In order to get a quick manual indication of damp, I have sealed with tape a small clear plastic patch on the hull, thinking it might steam up, there is no sign of condensation at all on the clear plastic bag.

Any guidance gladly listened to.

Thank you in advance.
Click to expand...

The IR by itself, will not be able to heat any compound trapped in your hull to boiling point. It would need to reach boiling point to turn into steam and expand enough to escape the hull. As it goes the only good solution seems to be to lower the boiling point of the liquid by using a vacuum and heat it up to above that value to volatise any compound and having the vacuum “suck it “out. Air drying will not dry any of the compounds created inside the hull and any water trapped there will remain trapped as well. There may be a marginal improvement but only marginal. Your options would be to seek professional treatment for the drying with a vacuum heating system. Or doing it DIY by buying a small vacuum pump and a silicone heated mat.
There is a channel on YouTube were a DiY’er is doing that to his boat, “sail Life” that is the option he ended up using and its much more cost effective. I believe £ 200 ish for the pump and £250 for silicone heated pad.
https://www.youtube.com/watch?v=OXrCBKSAlqM Description of the osmosis

DIY Osmosis VAC System
https://www.youtube.com/watch?v=SfLZEiBiDU4&index=40&list=UU5xDht2blPNWdVtl9PkDmgA
 
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All the osmosis treatment cases I know of used dehumidifiers. In one case a boat went ashore and the side was destroyed. Set out a sheet of plastic under the boat. tape plastic to the hull above the waterline, and to the floor plastic. Put two or three dehumidifiers inside the tent, and tape up the 'full container' switch, put hoses on the outlets, to the outsode world. In the case of the damaged 32ft FV I think it took three months, then they moulded a new side and glassed it in. Boat still 100% thirty years on.
 
fisherman said:
All the osmosis treatment cases I know of used dehumidifiers. In one case a boat went ashore and the side was destroyed. Set out a sheet of plastic under the boat. tape plastic to the hull above the waterline, and to the floor plastic. Put two or three dehumidifiers inside the tent, and tape up the 'full container' switch, put hoses on the outlets, to the outsode world. In the case of the damaged 32ft FV I think it took three months, then they moulded a new side and glassed it in. Boat still 100% thirty years on.
Click to expand...

Dehumidifiers sadly work only with atmospheric humidity. As the “wetness” of the hull is trapped inside the hull and in liquid form it is a pointless exercise to add dehumidifiers.
The moisture must be suspended on air to be able to be trapped by a dehumidifier, you would need to heat the all hull to above boiling point and reach the steam phase for the trapped steam to escape and be suspended in the air inside. Having said that should you close the all boat the steam would actually escape the other way (pressure thing.. ) or even blow the plastic covering like a pot on a stove.
 
Hoolie said:
Obviously the caustic soda is to neutralise the acid in the laminate and it was applied by the yard operative using a hot water reservoir with the caustic dissolved in it. I only saw him do it a couple of times but was told to stand well clear! The yard was actually gravel on sand so it was relatively easy to rinse away. Not so easy if your boat is on a hard base.

Of course it's warmer in summer down there but our boat overwintered when it can be quite cold. Dry winds from the Pyrenees helps drying.
Click to expand...

Thanks for that Hoolie, I will give that a try.
 
GregOddity said:
Dehumidifiers sadly work only with atmospheric humidity. As the “wetness” of the hull is trapped inside the hull and in liquid form it is a pointless exercise to add dehumidifiers.
The moisture must be suspended on air to be able to be trapped by a dehumidifier, you would need to heat the all hull to above boiling point and reach the steam phase for the trapped steam to escape and be suspended in the air inside. Having said that should you close the all boat the steam would actually escape the other way (pressure thing.. ) or even blow the plastic covering like a pot on a stove.
Click to expand...

I really think you are wrong. If you dry the atmosphere the hull is enclosed in the moisture will migrate from the hull. Otherwise how could you air dry timber, it would stay wet by your measure?
 
My wife just came in, she is a scientist, I told her your view and she was quite uncomplimentary, but asked 'did he miss thepoint about a closed atmosphere?'
 
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