Blow torch - Osmosis treatment

[SailingEcosse]

Final (ish ) update on this thread for anyone thinking about doing the same thing, parts required and money spent.

Hopefully this will save others some time and money if going down the same route


Pics of equipment used:
Vacuum pump - small twostage, 3cfm pump
Silicon heat mat - Gotherm 2kw mat approx 1000x600mm
Flexelec 16a temperature controller (capilliary thermostat)
Rubber pad - slightly larger than the heat mat and approx 1mm thick
Bulkhead style fitting to connect the vacuum hose through the rubber pad
All assembled and working.

Costs:

Equipment
Vac pump - £150 (used)
Heat mat - £125 (unused from ebay)
Temp controller - £25 (new)
Rubber pad - £10
Vac fittings - £20
Mastic tape - £16

Total = £346

Epoxy
5kg High viscosity primer
12kg epoxy
5kg epoxy filler (fairing the hull)
Rollers, brushes, sanding pads etc

Total £520

Labour
Gelpeel - £450
Labour (mine) - 50-60hrs

Total costs to peel, dry and epoxy - £1316

 

[KevB]

Hotvac I have seen and had priced but the boat just isn't worth the cost i.e. £4k (although this did include the epoxy treatment as well) but it's twice what I paid for the boat (26ft colvic).

Why bother with the hassle of trying to get rid of the osmosis? The boat's not going to sink is it.

 

[pelissima]

Final (ish ) update on this thread for anyone thinking about doing the same thing, parts required and money spent.

Hopefully this will save others some time and money if going down the same route


Pics of equipment used:
Vacuum etc

Costs:



Total costs to peel, dry and epoxy - £1316

True, this is great help at least for me.

OK, Vacuum I managed to get one.
For the sillicon heat map how long were you hunting one, as none now on ebay?
Am I assuming correctly in that temp controler turns off the mat once the required temp was reached ?

 

[SHUG]

Osmosis is a slow diffusion -based process and reversing it is also a slow diffusion based process which can be speeded up a bit by heat and vacuum bagging. If its taken 5years to establish ,its not going to be fixed in 5minutes with a blowtorch.

 

[Sniper]

Osmosis is a slow diffusion -based process and reversing it is also a slow diffusion based process which can be speeded up a bit by heat and vacuum bagging. If its taken 5years to establish ,its not going to be fixed in 5minutes with a blowtorch.

Osmosis is not diffusion. Diffusion is the movement of a substance down a concentration gradient to establish equilibrium. Osmosis is the movement of water across a semi-permeable membrane, in this case the gelcoat, drawn by hydrophilic substances in the substrate. Therefore, there is no reason why the elimination of the water and gloop-filled blisters should not be substantially accelerated once the osmotic process is stopped.

 

[SailingEcosse]

The boat's not going to sink is it.

Thats open for debate

I've had lots of conversations with lots of different people on this subject and while the usual comment goes along the lines of "I've never heard of a boat sinking because it had osmosis" I'm not so sure, I mean, how would you actually know?
Seems to me that a hull suffering from an advanced level of hydrolysis/osmosis is going to be substantially weakened at the least, and if left unrepaired I don't see why eventual sinking wouldn't just be a matter of course

The reality probably is that mine wouldn't have sunk anytime soon though, but after seeing the damage to the layup underneath the gelcoat I'm glad I did the gelpeel, dry out and epoxy coat, as it's not a huge cost in the grand scheme of things, it should extend the life of the boat, and brings some piece of mind

 

[SailingEcosse]

True, this is great help at least for me.

OK, Vacuum I managed to get one.
For the sillicon heat map how long were you hunting one, as none now on ebay?
Am I assuming correctly in that temp controler turns off the mat once the required temp was reached ?

The heat mats seem to be few and far between unfortunately and new ones are quite expensive, the only alternative I came up with was to use a heated blanket (the ones used for heating your bed) but the lower temps they generate would mean a longer treatment of heat and vac, might be worth thinking about though as they are cheap enough, and you could do bigger (double bed sized?) areas, or more areas to speed the process up?

The temp controller does exactly that

 

[penfold]

I recall reading the obituary of the guy who patented the Corby heated trouser press; he was able to take the trouser press as it existed and combined it with the flexible heat pad technology he had been involved in the development of. The technology was developed to provide de-icing for the leading edges of aircraft wings.

Which is a longwinded way of saying perhaps if you gutted a Corby trouser press, you might find a thin flexible heating pad and a thermostatic control to run it off...

 

[Ardenfour]

Might be a daft question but how is moisture going to dry off when the surface being treated has a plastic / rubber sheet clamped onto it? And, seeing as osmosis blisters are a combination of fluid pressure and a chemical reaction between water and uncured resin/styrene or whatever, surely increasing the temp while the reactants are still present will drive the reaction faster, resulting in the opposite to the desired effect?

 

[SailingEcosse]

Might be a daft question but how is moisture going to dry off when the surface being treated has a plastic / rubber sheet clamped onto it? And, seeing as osmosis blisters are a combination of fluid pressure and a chemical reaction between water and uncured resin/styrene or whatever, surely increasing the temp while the reactants are still present will drive the reaction faster, resulting in the opposite to the desired effect?

The moisture is removed from the laminate in the same way that a kettle runs dry if left on i.e. the water just boils off.
The rubber sheet is there to allow the vacuum to form (polythene sheet works as well, although tends not to like the heat generated)
The pump as well as creating the vacuum, lowers the boiling point of water and thereby allows the heat to be kept low enough so as not to damage the laminate.
It also has a secondary (but very important) effect where it will, to an extent, cause a post cure to happen, which removes (or should as I understand it) any remaining uncured resin/styrene/glycol which as you rightly say, is what causes the reaction in the first place, and this is the critical part, as they need to be removed for a successful treatment, because you will never stop the water/osmosis, but remove the others from the mix and the water can have no effect!

 

[pelissima]

Lower - higher temps

The heat mats seem to be few and far between unfortunately and new ones are quite expensive, the only alternative I came up with was to use a heated blanket (the ones used for heating your bed) but the lower temps they generate would mean a longer treatment of heat and vac, might be worth thinking about though as they are cheap enough, and you could do bigger (double bed sized?) areas, or more areas to speed the process up?

The temp controller does exactly that

Could you repeat just how long was required the mat to be in place before moisture descended to low green areas ?? (at the temperatures you say 190 degrees)
(Trying to do the maths for my 38ft -30m2 below waterline)
I 'm afraid the process with a blanket (40 degrees ??) will never end.

 

[SailingEcosse]

Could you repeat just how long was required the mat to be in place before moisture descended to low green areas ?? (at the temperatures you say 190 degrees)
(Trying to do the maths for my 38ft -30m2 below waterline)
I 'm afraid the process with a blanket (40 degrees ??) will never end.

The time required to dry each section varied dependant on the moisture levels in that particular area, I had a couple of patches that took approx 6hrs on what I regarded as high heat, which was approx 100degrees at 28hg of vacuum.
The heat mat is capable of about twice that but from what I could determine, taking polyester laminate to those temperatures for extended periods isn't recomended, so I preferred to play it safe, keep the temps lower and leave it on a bit longer.

But the majority of the hull only needed 1-2hrs at 80-90 degrees to reach low moisture levels (scale 2 - tramex skipper).

If it helps any it took me about 4 weeks to do the full hull (approx 20sq meters) to the point where I was happy with the readings, although the majority of this was weekends, and if doing it every day would have been done in a week easily I think.

 

[SailingEcosse]

Hi Folks
Another update on this for you, with some important and detailed info on the hotvac process, supplied courtesy of another forumite, George Natsis, who was following the thread and managed to get communications going with Bengt Bloomberg, author of the Osmosis handbook (and pretty much the authority on this IMO)

Anyway I've edited most of this down to show pretty much only the parts that relate to this thread and the "DIY hot vac" process, and I hope it is helpful to those going down the same path.

Alex
PS
Both George and Bengt have given their approval for this being posted, so many thanks to the both of them for the info



Questions From: George Natsis

Please advise on how I can I get a copy or download of your book on Osmosis repair


Reply from Bengt Bloomberg

Go to osmosisinfo.com there is a link for free download of the book.


Questions From: George Natsis

Within this book another book is mentioned, the "Osmosis" How to repair hydrolysis damage using the
HYAB Osmocure technique".
Could you provide a link for that one as well


Reply from Bengt

George, The Osmocure became forbidden in both EU and USA in 1999 because the fumes from the treatment were decided dangerous. Instead I helped to form another vacuum based technique in a way that made it even better than the Osmocure and that is the hotvac process. You can get all info from www.hotvac.com
Just remember that the operator must keep the equipment at a temperature above 105 degrees C.
Some operators are afraid that will harm the laminate. It will not as all below 130C is safe and at temperatures below 105C some harmful acids will remain in the laminate and cause re-occurances.
Regards Bengt


Questions From: George Natsis

Once the required temp say 120 degrees C is reached, for how long the process need to stay in place so that results are achieved and no harm is done ?


Reply from Bengt

George, whatever the temp of the mats, the laminate never becomes hotter than the boiling point of the fluids remaining in the laminate most of which does not exceed about 70 degrees at the vacuum used during the process. That is why the earlier versions of the hotvac machine were maximated to 90 degrees which was enough to create dry measurements after a few hours. However the the acid that is produced by the hydrolysis is crystallic and must be melted before it can be boiled and sucked out. to achieve that, the laminate must reach 90-100 degrees depending on actual vacuum level. As the acid is crystallic it does not show up on the moisture meters and within short time causes the hydrolysis to start up again. Therefore the 105 degrees mat temperature is needed and the treatment must proceed a few hours after the laminate is dry because the laminate will not reach that temperature before it is dry. To be sure about the time needed, the temp on the inside of the hull beneath the mat should be checked hourly and the treatment not be stopped until the temp has stayed around 100 degrees for a couple of hours.
Regards Bengt


Questions From: George Natsis

So the vacuum level initially helps the mat to stay in place but the actual sucking takes place only after the acid becomes fluid at the temps you mentioned. Just wondering, if someone could drill 1-2 mm small holes close to one another before the process, would that facilitate the acid sucking ?
Regards George


Reply from Bengt

George the vacuum is not to keep the mat in place. It is for creating suction and to minimize the boiling temperature of all the fluids because gases only can be sucked out. The mats are fixed with tape to the hull. The gases from boiling water and glycols are leaving long before the temperature of the hull reaches 100 degrees. It is of great importance to drill some 4-5 mm holes in top and bottom of all areas with high moisture readings before the process. Such areas might be delaminations filled with hydolysis fluids parts of which might just flow out during the drilling already. Then after the Hotvac treatment one can inject epoxy through the lower holes until it comes out of the upper ones in order to repair the delamination. Just be sure that you don´t drill more than max 3/4 through the laminate. Just one small hole through the laminate and there will be no vacuum under the mat. Also never drill larger areas than are fully covered by the mat.


Questions From: George Natsis

Can I ask what you mean by "never drill larger areas than are fully covered by the mat"


Reply from Bengt

George, if you happens to drill holes in a delamination which are not covered by the mat, the vacuum pump will suck air through them and there will be no vacuum. If the delamination is larger than the mat surface, the first holes must be closed with epoxy filler and new holes be drilled in the next area that will be covered when the mat is moved.


Questions From: George Natsis

Out of curiosity, is the styrene in crystal formations or liquid and at what state of the process is it sucked?
But even more important, I would like to understand better the idea of the glass (roving) getting in a higher bond with the plastic.
Could you elaborate a bit?
The reason I am asking is that a surveyor had checked with a meter (cannot remember the maker) my 1984 First38, and claimed that apart from moisture, my hull was “rotten” or softer or more fragile than it should be. So am I anxious if this state is reversible.
Regards George


Reply from Bengt

The styrene has the lowest boiling point and is the first to leave. Regarding bond, the hydrolysis totally dissolves the polyester into fluids and the crystallic phthallic acid. In early stages of the process this causes just small 2-10mm cavities between the two outer laminates. Then it can be fast and easily repaired by peeling of the gelcoat and first laminate layer followed by a Hotvac treatment and relaminating with epoxy resin and a light fibreglass mat. If the hydrolysis has been allowed to proceed for 3 years or more or started again after a bad treatment, it will very fast spread over larger areas between 2 or more laminate layers and cause all polyester to be dissolved in those areras. This means that there is no longer any bond between the fibreglass mats in those areas. This is called delamination and can not be restored by Hotvac or any other drying technique! After a Hotvac treatment such delaminations will be dry and not show up on the moisture meter but the hull will have much less strength and the delaminations will be filled with water a few weeks after launching. After a proper Hotvac treatment there is practically no risk for further hydrolysis as the other elements needed have been removed but the hull strength can be very inferior.
In your case, what I can understand from your surweyors wording, you have quite severe delaminations already. Before the Osmocure and Hotvac techniques a hull like that was practically doomed because even remowing all of the bad laminates and complete relaminations, hydrolysis would start immediately under the new laminate and make it loose from the hull like an eggshell. Now after a Hotvac treatment one can either cut away all the affected laminate areas and relaminate each area, or which is easier and still safe, drill them as I explained before and fill them with epoxy resin. Just remember to mark them out on the hull after the peeling but before the Hotvac when you still can get the moisture readings. Or drill them before the treatment. Then you must close the holes when the mats are moved but you will know the locations and open up a few afterwards for the injection.
Regards Bengt