fibreglass hull treatment

[Frank mellin]

i have a westerley centaur which I recently removed from water in order to have bottom cleaned and all old anti foul removed.
I had the hull blasted by a specialist firm resulting in a very clean job but unfortunately this uncovered some osmosis on one side of the boat.
Not serious but needs attention
The boat had been treated for osmosis several years ago at a cost of £3000,before I bought it fortunately.
the problem I have is that having sanded the offending areas and removed all the blisters I want to go over these areas with a two pack filler before priming and re anti fouling.
I was recommended to use a two pack filler made by Hempel but have found it very difficult to apply,its like trying to spread putty.It is also not very easy to sand smooth .
As I have some areas still to fill can anyone recommend a 2 part filler which is easy to mix,apply and sand.
As I am a builder by trade I have been used to plastering small areas and know how to use a trowel but i am finding the task very difficult with the product i have.
Any advice appreciated

 

[Bobc]

Grind all the bad bit out, and then use Isopon P40 to get it roughly up to level, then a gelcoat filler over the top.

Use a disc sander to cut back the P40 to level (you'll be there all week with a normal sander)

 

[Concerto]

How large are the bubbles? If they are only 2 - 3 mm in diameter, this is not osmosis but air bubbles in the gel coat. This is a common fault in a lot of Westerlys including my Fulmar. Osmosis bubbles can easily be 10mm or larger in diameter and be very raised by 3 - 5mm and when broken have a vinegar smell.

If your problem if just air bubbles then just fill with Plastic Padding Gel Coat Filler and sand smooth. This is an epoxy based filler and you can then paint over. This process may need repeating every time you are lifted out, but eventually they will all become filled.

For osmosis I would recommend grinding out the blisters and laying in discs of glassfibre using epoxy. See this West manual for detailed instructions. https://www.westsystem.com/wp-content/uploads/Gelcoat-Blisters-Diagnosis-Repair-and-Prevention.pdf

 

[LoneHort]

Frank I suspect a large part of your problem is ambient temperature or lack of it. If you can wait until the weather gets warmer it will be a lot easier to apply.