Time required for drying hull

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eddystone

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Think next winter I need to get someone to sand/soda/coconut blast all the layers of anti fouling and primer back to epoxy paint. Any idea minimum period for hull to dry out sufficiently to apply couple more coats epoxy a) in the open, b) in a shed?
 
Having looked into this with boatbuilders it appears that hulls don’t really dry out when left out for the winter and the only effective way to do so is to have the gel coat peeled off and the boat left for several months with regular jet wash cleaning of the hull.

Noting that your boat already had an epoxy coating then assuming this was from new it should have prevented / significantly restricted water ingress so my suggestion would be to have moisture readings taken after the boat has been out for a while and if happy then just apply new epoxy once the old anti-foul has been removed.

Also worth noting that the existing epoxy layer would likely further prevent any drying out and would need to be removed if the moisture readings are considered to be too high.
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If lifted annually, then six weeks is considered sufficient to reduce moisture levels. If not then it depends on the moisture levels found with a meter. Obviously ensure bilge is perfectly dry before measuring.
 
If she was already Epoxy treated - then she will not dry easily if moisture has permeated - which unless layer is damaged - is unlikely..

Unless the epoxy layer is damaged / weakened - why add to it ?

Boat without such layer - can be any length of time - its impossible to say as it depends on Temp - Humidity etc ... as well as how well the 'paint layers' have been removed.

Metering an Epoxied hull can produce different results than a non-epoxied hull .... depends on the treatment conducted.
 
I believe the hull was epoxied around 20 years ago so not when boat was new by any means. I have in the past made good some very small gaps, mainly on the rudder.
 
The question is : Is it really needed to add more layers of Epoxy ? My 'gut feeling' is no.

Personally ..... if the hull has a build up of antifoul layers - that can be holding moisture and also adds weight to the hull. Maybe not much - but think of all those tins of AF over the years and they are now on the hull.
The 38 I bought last year ... I had yard take her back to hull .... the depth of AF was easily seen as the removal progressed. She then received a High Copper content VC 17 two coats and the hull was beautifully smooth ... Lifted out and she was clean ... yard will be applying another coat for this season after a light sanding ...

Drying out ? Given the time between removing the old AF and then waiting suitable weather and temperature - she was good to coat. The primer for the VC17 is epoxy based .... so that served well - BUT if the primer was no epoxy based - I would not be concerned at all ...

My 38 is 1986 build.
 
If the hull was epoxied previously you don’t need any time to dry out. I’ve just removed years of very thick anti fouling on my Westerly to reveal the epoxy layers from a gel coat peel and fill done about 20 years ago. I sanded the surface flat, then applied 2 layers of Hempel High Protect 2, then Hempel underwater primer, now ready for anti fouling. The High Protect says conditions need to be above 10 degrees and dry. I was told it should be OK down to 5 degrees and I applied each coat at about 6 degrees and it’s cured fine. The moisture readings were all low at a survey a couple of years ago and there was no reoccurrence of any osmosis after the original treatment.
 
Drying out ....

The use of Heat Lamps is debatable as they do cause hull to increase temp and should cause moisture to reduce - but its not impossible for such heat to drive the moisture deeper. It also creates a higher humidity capability - that when heat is taken away - the extra humidity that has been as a result of the hotter air - can drop out and as hull cools - draw it in.

It may surprise some - but a cold winter can in fact dry a hull - by way of the air and structure unable to retain the levels of moisture of higher temps. A dry winter is actually a good way to dry out a hull without the humidity factor of applying heat.

Again I will say - there is no way to determine how long a hull will take to dry out - it depends on how the moisture got in ... how much the desnity of the moisture has increased once in ... how well you scrape back the hull to allow it to 'breathe' .. but that word should tell you - it can be a two way process ... given wrong conditions - you could prevent drying or even add to the moisture.

It is not a simple process. And the evidence to back that statement ? The number of failed 'Osmosis' treatments back in the heyday of the 80's - 90's .. when not so knowledgeable people thought it was a business they could do.

My honest suggestion to OP .... get the old Antifouling removed ... let her stand ... and then prime + antifoul to put back in the water ...
 
Refueler said:
If she was already Epoxy treated - then she will not dry easily if moisture has permeated - which unless layer is damaged - is unlikely..

Unless the epoxy layer is damaged / weakened - why add to it ?

Boat without such layer - can be any length of time - its impossible to say as it depends on Temp - Humidity etc ... as well as how well the 'paint layers' have been removed.

Metering an Epoxied hull can produce different results than a non-epoxied hull .... depends on the treatment conducted.
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I agree with you about putting a moisture meter on epoxy ,I made a 12mm solid backing plate for my winch out of biax cloth with the csm stitched to the back used about 12 layers all fiberglass cloth was bone dry And I used and west system epoxy , after it was cured i used my tramex and to my surprise was quite high , it was in the green but only just and even after 13 months sitting in my spare bedroom still shows same reading, in comparison most of my topsides of my 50 year old boat read zero , I’ve also done some repairs on the top sides making sure the before doing the laminating that the reading was as close to zero as possible, now after using epoxy it has similar elevated moisture level not quite so high maybee because the laminate isn’t as thick but still higher that before I did the repair , why would this be ????
 
PCUK said:
If lifted annually, then six weeks is considered sufficient to reduce moisture levels. If not then it depends on the moisture levels found with a meter. Obviously ensure bilge is perfectly dry before measuring.
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Thank you. Boatfolk berth holders who get six weeks ashore included in their annual contract can breathe a sigh of relief.
 
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