Osmosis drying and infrared heaters

[pappaecho]

Has anybody used infrared heaters to dry out a boat's layup after the osmotic patched have been ground out. Any idea of how hot the hull can be allowed to get?

 

[JonJon]

The problem with the products of osmosis is they don't evaporate easily, heating alone does not appear to be the answer. You have to continually wash the hul to remove these products as well as heat. You can also reduce the ambient air pressure by vacuum which helps. The same reason why kettles boil on the top of mount everest at a temperature no good for tea making. Very good for evaporating the products of osmosis if you could get the yacht up there. Am I making sense - no I'll shut up.

 

[Alrob]

Does anyone know if cleaning with steam would speed the process up ???

 

[sarabande]

I've seen various boats wrapped in plastic for delivery. Would it not be possible to put a powerful air pump into one of these 'bubbles' and reduce the air pressure quite a bit - thus simulating the "up a mountain" scenario ?

 

[JonJon]

This is effectively what the "Hot Vac" system does. I have no connection with the company.

 

[carrswood]

Rampion has just had a full Osmosis treatment by a yard in Hamble. They used infrared lamps (as many as 6) but only just to remove the final remnants of any moisture. As someone has mentioned above, the yard told me the salts from the moisture combined with the acidic remnants from the blisters do not necesarily react too well to raw heat. For this reason Rampion was steam cleaned and washed up to 3 times to disolve and draw out the salts and nasties. Prior to all of this the hull was gel stripped in November and then left to the outside elements in the yard. The combination of wind under the hull, snow and you name it soon dried the matting out. In February she was steam cleaned then moved into the sheds for a weeks heat treatment. By the time the full osmosis treatment began the hull was down from moisture reading of 16-19 (in October) to as low as 3-5 on the sovreign meter in March.


It also helped that the Southern Ocean Shipyard layup for the Pioneer 10 was very thick (up to 15mm in the hull) so this allowed the gel stripping company to remove 4mm of matting and basically go behind all of the blisters. Don't know what boat you have but more recent layups wouldn't allow you to do this

I should point out a layer of very strong multi directional matting was applied to replace what was removed. Beautiful job when finished but quite a process to do a proper professional job.

You can't rush the drying process!

 

[pappaecho]

I forgot to mention the whole boat will be acetone cleaned and then steam cleaned, to get rid of the breakdown products of polyester resins. As undertand it, the moisture levels of the layup layer must be reduced so that the epoxy filler does not sweat due to bound in moisture in the layup. Still interested in knowing how hot the hull can get locally in the IR heaters

 

[Boo2]

Rampion has just had a full Osmosis treatment by a yard in Hamble.

...snip...

I know a gentleman doesn't, but may I ask how much that cost ?

Thanks,

Boo2

 

[VicS]

Has anybody used infrared heaters to dry out a boat's layup after the osmotic patched have been ground out

I have seen it done. Boat surrounded by infrared heaters powered by a couple of diesel generators. Dont know how long it took ... several days I think.

 

[carrswood]

I wouldn't rely on lamps alone to force dry the hull dry - you are simply drying/cristalising the salts and acids not removing them. As I said before it takes time so don't force the process.

Boo2 - the full job on a 32ft yacht is £6-7 k

 

[oldsaltoz]

The drying times can be reduced by grinding out past the effected areas.

I have done a few hulls and found that using a concrete grinding disk gives rapid removal and because the finish is well keyed it also helps you spot the lines the chemicals have taken.

This means you can follow them and remove most if not all the bad areas. Look for light brown to yellow lines and follow grinding them out, also look for lighter colours areas they were not fully wetted out during construction.

The above removes most of the residues and reduces drying times because any remaining contamination is closer to the surface.

Lamps can be inside (my preferred method) or outside the hull. as for temperature, epoxy will start to soften at 95 degrees, poly resin will tale a bit more but there is no way of knowing that there is no epoxy in the lay-up so avoid higher temps.

Washing should be done frequently rather than baking it and then trying to rinse it, one reason the Hot-Vac works is it not only brings heat but retains a moist environment longer.

Hope this helps.

Good luck

 

[status]

Still interested in knowing how hot the hull can get locally in the IR heaters

Lamps can be inside (my preferred method) or outside the hull. as for temperature, epoxy will start to soften at 95 degrees, poly resin will tale a bit more but there is no way of knowing that there is no epoxy in the lay-up so avoid higher temps.

Coming from and industrial viewpoint (we do a lot of GRP Lamination) the manufacturers recomendations for retention of structural strength for a bog standard polyester resin we use is arround 60C, this is for continuous use. Obviously you can get hotter than this but the strength drops off rapidly.

Stuart