Osmosis: bottom peeled but not drying?

[wmartin]

I have an Oyster Lightwave 395 which has a balsa core GRP construction. Showed evidence of osmosis and has been peeled, grit blasted and pressure washed. After six months it still has a moisture reading above and below the waterline of 20 (sovereign meter) as opposed to the required 5. We suspect the balsa core is wet and it has been suggested that we put on another layer of glass followed by epoxy rather than GRP. Does anyone have any experience of this method? Any other ideas?

 

[sarabande]

have you any indication of the mass of the boat, perhaps at the last crane-out? Then you might be able to compare a boat known to be 'dry' with yours

I can't see any other way of getting an indication of the core being wet, unless you drill a few holes. Perhaps someone knows if Oyster used closed cell foam ?

Is there an Oyster Owners club apart from the one under control of the builders themselves ?

 

[oldsaltoz]

Oyster Lightwave 395 which has a balsa core GRP construction. Showed evidence of osmosis and has been peeled, grit blasted and pressure washed. After six months it still has a moisture reading above and below the waterline of 20 (sovereign meter) as opposed to the required 5. We suspect the balsa core is wet and it has been suggested that we put on another layer of glass followed by epoxy rather than GRP.

If you seal it now with an epoxy you will create a bigger and more expensive problem as this will only seal the moisture in.

I would be drilling holes at the lowest point and just above the lower readings on the topsides, the moisture must be exposed in order for it to escape.

Start with a full set of readings and mark them on the hull / topsides, then you can get a picture of what areas are effected and to what extent.

The holes below the waterline need to expose at least 25 square mm, the ones in the topsides can be 6 mm drill holes.

Keep them no more than 300 mm apart.

It will dry but it will take a long time, you might like to look into the heating and vacuum system.

Never seal any moisture in a hull.

Running a heater inside the hull will halp speed up the drying as will heat lamps.

Let us know what you decide on and the outcome, this may help others searching for answers.

Avagoodweekend......

 

[chasroberts]

I have an Oyster Lightwave 395 which has a balsa core GRP construction. Showed evidence of osmosis and has been peeled, grit blasted and pressure washed. After six months it still has a moisture reading above and below the waterline of 20 (sovereign meter) as opposed to the required 5. We suspect the balsa core is wet and it has been suggested that we put on another layer of glass followed by epoxy rather than GRP. Does anyone have any experience of this method? Any other ideas?

Can I suggest that you fill in some of your bio details? It will help us to help you.

If you are UK based then these poeple have, as far as I know, a good reputation for their product.

http://www.hotvac.com/

This will certainly draw out moisture from the hull as opposed to simply letting it dry.

There will be more advise along shortly.

Good luck.

Chas

 

[Manuel]

At this stage I'd contact a good surveyor who is keen on working on boats. A 'sleeves rolled-up' type not an academic. I would expect him to drill a test hole where the electronic instrument registered the highest moisture reading and determine whether the balsa is saturated. Electronic instruments of all kinds only give an indication. Listen to the surveyor's advice. It should not need more than a couple of hours of surveyor's time. The surveyor, if local, is the best person to recommend a suitable yard for the work.

 

[Chris_Robb]

Isn't there another potential problem with Balsa core - delamination of the inner skin from the outer, on which the whole strenght of the boat depends?

 

[wmartin]

Thanks everyone. Sounds like the next step is to drill some holes to ascertain what's happening to the core and see if we can get the moisture out. Does anyone know a good surveyor on the north east essex coast?

 

[oldsaltoz]

Is your Oyster Lightwave 395 which has a balsa core GRP construction balsa below the waterline?

 

[boatmike]

I have an Oyster Lightwave 395 which has a balsa core GRP construction. Showed evidence of osmosis and has been peeled, grit blasted and pressure washed. After six months it still has a moisture reading above and below the waterline of 20 (sovereign meter) as opposed to the required 5. We suspect the balsa core is wet and it has been suggested that we put on another layer of glass followed by epoxy rather than GRP. Does anyone have any experience of this method? Any other ideas?

I am rather suspicious of your results. Usually the different meters used need calibrating and numbers alone are meaningless without. If the boat was very wet I would expect a noticable difference between the reading above the waterline and below it. Also balsa seldom "wicks" to arrive at a uniform reading throughout the structure unless it is severely delaminated from the outer hull skin which seldom happens uniformly as it is "cross cut " and does not have linear fibres.
You have not said who has provided the results but if it is the same party that has recommended plastering up a new layer of GRP over wet laminate I would discount the results as suspect and get an independent survey by a reputable surveyor. Unfortunately not all yards are particularly knowlegable or competent and this sounds rather like a cowboy outfit to me. If in doubt you need to remove a small area of outer skin This is best done carefully with a large diameter hole saw. Drill carefully to penetrate the outer skin only and see if the skin peels easily away from the balsa. If it falls away and is not attached firmly to the balsa core you may have a very serious problem on your hands. If, as I suspect, you find it still bonded to the balsa and needs to be cut away to remove it then test the balsa itself. It should look and feel dry and when cut should look like fresh wood. If it is obviously wet or looks black and soggy lets talk again but my guess is the hull is perfectly OK especially as you are getting the same reading all over. If indeed it needs further drying then vacuum extraction is required as someone else has suggested. Personally I think a good surveyor with detailed knowledge of composite repair is called for before you do anything more.

 

[wmartin]

Yes, balsa core throughout - it was one of the first lightweight displacement boats, built in 1988.

 

[30boat]

My last boat had a balsa core and osmosis.It turned out that it is almost impossible to dry out a balsa core.The outer layer is not very thick in these boats so won't stay wet for very long,it's the core that gives the bad readings.I would give it a fair period to dry,as you have already,and then do as you suggested.A thick epoxy roving coating should insulate the core from the sea water and will eventually dry to the inside providing you keep the bilges dry and airy.It would be a good idea to take a few samples of the core around the hull just to make sure it isn't soaked.That's what I did with my boat.As far as I know it's still out there sailing happily.
This all goes against established practice but balsa cored hulls need special measures.

 

[wmartin]

Thanks Mike, that's really helpful. I thought it odd too the meter reading was consistent throughout. Before the meter was put on my boat it was tested against a boat that had just undergone osmosis treatment and that one was showing 5% across the hull. Agree that the next step is to contact a surveyor.

 

[jason -and the arguenauts]

I have a moisture meter and one thing I have found is that the reading with the probe over timber is always high. Timber has a higher moisture content than dry grp to the point where you can tell exactly the location that timber bulkheads are bonded to the hull with a spike in the moisture meter readings.

On that basis I would expect a balsa cored hull to always have higher readings than a solid grp one, and never to get near 5 even when bone dry. But I am not a surveyor so I might be wrong.

If you really have unacceptable moisture in the balsa, holes and a vaccuum pump is the only way to get it out. But when I had some moisture in the balsa deck of my old Prout I found that it had not travelled far at all because it was end grain. So I would have great suspicion of someone saying there was a uniform moisture reading of 30.

You can hire your own meter from "Passion for Paint". He will also give good advice.

 

[boatmike]

I have a moisture meter and one thing I have found is that the reading with the probe over timber is always high. Timber has a higher moisture content than dry grp to the point where you can tell exactly the location that timber bulkheads are bonded to the hull with a spike in the moisture meter readings.

On that basis I would expect a balsa cored hull to always have higher readings than a solid grp one, and never to get near 5 even when bone dry. But I am not a surveyor so I might be wrong.

No Jason, you are not wrong. Different materials will have different readings, not necessarily because of moisture content though. In fact the only real meaningful readings are comparative ones. Usually to check a solid GRP hull a reading as high as possible just under the gunwale is assumed to be a "dry" reading for the layup of the hull concerned. As the thickness increases towards the keel (usually) the reading will naturally increase marginally even if totally dry, but will increase to a large factor if it's wet down there. Using a different boat with a solid layup to calibrate the instrument and then translating to a sandwich construction is just total balls. It WILL read differently and possibly very markedly so. Thats one reason why I suggested his hull is possibly OK in the first place!

 

[dombuckley]

I'm "in the trade" and am always suspicious when numbers start getting bandied around. The truth is that many people who wield moisture meters do not know how they work (for starters, they do NOT directly measure moisture content!), and often use and interpret their results incorrectly. As has been said, using a solid GRP hull as a reference is a complete non-starter. Furthermore, the fact he told you it was "5%" would be cause for concern, as the manual specifically states that the meter does not give a percentage moisture content.

Before taking anything sharp anywhere near your boat, a proper systematic set of moisture readings should be taken of the entire hull (39fter: approx 200 measurements), using a meter such as the Tramex, capable of reading deep into the laminate. A good surveyor should state what setting the meter was on, and take readings from the correct scale (don't get me started on that one...!), before correcting for thickness and the specfic gravity of the timber species. Statistical analysis will then reveal any "outliers", indicating areas where there may be genuine moisture ingress.

I have also sent a PM.

Dom

 

[sailorman]

I have an Oyster Lightwave 395 which has a balsa core GRP construction. Showed evidence of osmosis and has been peeled, grit blasted and pressure washed. After six months it still has a moisture reading above and below the waterline of 20 (sovereign meter) as opposed to the required 5. We suspect the balsa core is wet and it has been suggested that we put on another layer of glass followed by epoxy rather than GRP. Does anyone have any experience of this method? Any other ideas?

i have seen a Lightwaves bottom outer layer completely stripped EGB removed & replaced with divnycel (spelling ) then outer skin of epoxy. Lotsa £s

 

[Refueler]

I'm "in the trade" and am always suspicious when numbers start getting bandied around. The truth is that many people who wield moisture meters do not know how they work (for starters, they do NOT directly measure moisture content!), and often use and interpret their results incorrectly. As has been said, using a solid GRP hull as a reference is a complete non-starter. Furthermore, the fact he told you it was "5%" would be cause for concern, as the manual specifically states that the meter does not give a percentage moisture content.

Before taking anything sharp anywhere near your boat, a proper systematic set of moisture readings should be taken of the entire hull (39fter: approx 200 measurements), using a meter such as the Tramex, capable of reading deep into the laminate. A good surveyor should state what setting the meter was on, and take readings from the correct scale (don't get me started on that one...!), before correcting for thickness and the specfic gravity of the timber species. Statistical analysis will then reveal any "outliers", indicating areas where there may be genuine moisture ingress.

I have also sent a PM.

Dom

This post and Boatmikes are actually getting nearer the real matter.

I use Protimeter and Tramex meters - each has its specific use and can say that cored sturcture will give markedly different results to a solid layup. Balsa as already stated is cross cut without grain laying along the hull - so moisture travel is limited unless core has separated.

So the question is IMHO - is the hull naturally drying or does it have heat / heatvac / IR focused on the hull to speed drying ? If natural then you will likely wait a long time for any movement of moisture.
Sovereign Meter may be an industry named meter - but IMHO is not much better than a builders stud meter !

As Boatmike says - it is suspicious findings ... needs more investigation by an independent.

 

[Chris_Robb]

I use Protimeter and Tramex meters - each has its specific use and can say that cored sturcture will give markedly different results to a solid layup. Balsa as already stated is cross cut without grain laying along the hull - so moisture travel is limited unless core has separated.

I suppose the really critical thing here is whether or not the core has separated. If it has, then this needs to be determined before deciding on any course of treatment. Who ever though of putting this stuff below the waterline? or am I just a bit conservative on this.

 

[bluedragon]

Just one thought that nobody has mentioned...after stripping the hull was pressure hosed...but was this just a superficial wash or a repeated wash cycle to remove glycols and other solutes in the resin? If not the latter, then you may not be reading "wet" water at all, but just these residual hydrophilic materials in the GRP layup. There's others that know a lot more about this than me, but a lot of people assume that these just "dry" out by the boat sitting in the yard for a few months. They don't.

 

[Refueler]

I use Protimeter and Tramex meters - each has its specific use and can say that cored sturcture will give markedly different results to a solid layup. Balsa as already stated is cross cut without grain laying along the hull - so moisture travel is limited unless core has separated.

I suppose the really critical thing here is whether or not the core has separated. If it has, then this needs to be determined before deciding on any course of treatment. Who ever though of putting this stuff below the waterline? or am I just a bit conservative on this.

There are quite a number of boats with composite structure below waterline. It is not unique to this builder.

Why ? To get strength with reduced weight.

There is another item that I forgot to touch on ... the methods of Gelcoat removal also affect drying. IMHO the blasting of a hull is best as it opens up weak voids, breaks the surface up to give greater surface area to the air / heaters, peeling is not my favourite but is neater. IMHO peeling creates a smooth surface with minimum surface break up, fails to open up the weak voids etc. A poor operator with peeling gear can in effect close up a structure making it extremely difficult to dry out. IMHO of course .....

Having oversee'd, diagnosed, checked many a boat for osmosis work ... I can say that there is far more to the process than just simply open up, dry and coat. How many understand that a hull heated to dry and then heaters taken away can create a "sucking-up" of water vapoure from the surrounding air ? How many understand that a hull can be dried to lower figures, with care, in winter compared to summer ? ....