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Old 01-25-2014
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Drying out holes in fiberglass before filling

Hi there,

I just got hold of a 1980 36' hunter, and there are several holes that I need to fill in the fiberglass. There are about 6 holes in the upper hull where the dodger used to screw in, and two holes below the waterline where a grounding plate used to screw in (it leaked so I've removed it).

My question is, am I good to fill them in with Marine Tex, or should I dry them out? I suspect they got a lot of water in them (through rain/seawater leaking in the respective locations). Both those locations are solid fiberglass, not cored and the boat has been out of the water about two weeks.

If I DO need to dry out the holes, how is the best way to do that? Silica gel?

Thanks for any replies.
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Old 01-25-2014
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Re: Drying out holes in fiberglass before filling

East, Central or Western Canada?

Temperature is going to play a role as to the dry time. Ideally you should grind material around the below-water holes and reglass/epoxy the area. If they are just screw/bolt holes grinding back to dry material and repairing/filling with thickened epoxy should work. Anything larger like an old through hull needs grinding at a shallow angle (12:1) around the hole and building material back up properly with layers of glass and resin. Ideally even with smaller holes this would probably be the 'proper' procedure.

Filling the on-deck holes is cosmetically more challenging, always hard to make the repair 'invisible'.. Will they be covered by a new dodger? Again enlarging the holes to dry material and filling should do, gelcoat matching is always a challenge though.
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Old 01-25-2014
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Re: Drying out holes in fiberglass before filling

West Coast - Victoria Area. It's beautiful here! It's a boat that I got cheap and had sat neglected at a marina for years (freshwater though luckily). I intend to live on it eventually - http://www.tuglife.ca is my blog.

The holes are the top aren't really that visible - the old owner splashed non-matching paint colour over a bunch of the boat as 'repairs' so even if it's not an exact match, it's the least of my worries for a bit.

I was mainly worried about water saturation but drilling out the hole a bit larger should negate that, right?

Last edited by alctel; 01-25-2014 at 12:51 PM.
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Re: Drying out holes in fiberglass before filling

Suggest that you
1. dry out the core by using a sealed 'tent' made of plastic film, containing either a deliquescent salt (Damp Rid) or silica gel (the same stuff used for drying flowers, etc.). If you useSilica Gel ... prepare it by 'roasting' in your home oven for 6-8 hours @ 350°F (let cool then 'seal' it from the atmosphere).
2. When fully dry, Inject a penetrating epoxy (Git Rot, etc.) and then repair the hole with thickened epoxy and then repair the gelcoat. If the core is 'dry', Penetrating epoxy will 'wick' through all the fibrous channels of the wood understructure.
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Re: Drying out holes in fiberglass before filling

Use a heat gun around the area. If there is moisture, you'll see ti come out as you heat the area. You could even make a fixture to direct the heat into the hole.
I will use this method on my S2 with a thru hole for a lifeline post. Unfortunately, I wil have to buy the heat gun in Marsh Harbor Abaco as I dont want to carry it over as baggage.
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Re: Drying out holes in fiberglass before filling

Here is a good guide on repairing holes.
WEST SYSTEM | Projects | Fiberglass Boat Repair & Restoration - Repairing machined holes in fiberglass
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Re: Drying out holes in fiberglass before filling

Follow Faster's method and you'll be fine. There is absolutely no benefit to using epoxy for such small repairs and it will be difficult to gelcoat or paint. Stick with plain ol' polyester. Cheaper, faster, easier.
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Re: Drying out holes in fiberglass before filling

When I am concerned about moisture for a repair or a coating application my last step and sometimes intermediate step is to use acetone to dissolve and evaporate it. If it is a surface alcohol is enough. Both compounds "dissolve" water and evaporate at a much faster rate than the water itself. An acetone "bath" will penetrate and draw moisture out of a laminate in the area of the damage. It is a very powerful solvent and will penetrate skin so use nitrile gloves when handling it. It will dissolve the plastic crystal on your watch and the plastic handle on your knife so be careful with it. It is very volatile too, so good ventilation is a must. No smoking!

A small piece of towel loosely stuffed into a hole to act as a wick that gets soaked with acetone will draw water out as it dries. Repeat as necessary.

Be careful. Use eye and skin protection, ventilation and or organic respirator. Acetone has another insidious quality. It dissolves organics, too and can carry molecules of other materials into your skin that would otherwise not be capable of penetrating. Just handle it with care. It is easily available and can speed up a difficult moisture problem when repairing fg.

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Re: Drying out holes in fiberglass before filling

we just did this on my boat within tide ranges so plus or minus 6 hours...even glass work

polyester resin and talc is the key here...why cause I was under a time constraint

simple and effective

heat gun is key too

around the hole not just in the hole...this will push water out if you will

the acetone or thinner trick works well too

basically just do as best you can...if you are in tides or careened you always have to use the fastest method...if you have time...many methods

notice that EPOXY needs more prepwork and reacts differently to some materials plus ive had it fail more than simple old resin and talc again cause you need more prepwork and perfection for epoxy work

like always horses for courses
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