Filling Bolt Holes In Non Cored Deck For Strength

[RunAgroundHard]

I need to fill 4 x M10 holes that are about 2” deep, straight through the deck. The holes may be contaminated with sealant.

New M10 holes will be drilled, different foot print, but close to the old holes, with two very close.

I need to ensure that the filled holes are good strength. New foot blocks will be mounted.

I can clean out the old holes by drilling through and wiping with acetone. Should I rough up the cleaned out holes?

The boat is built from polyester resin and I will use Epoxy to fill the holes. Not sure what filler to use, but I guess there will be structural fillers, or should I use chopped strands of glass cloth?

The filled holes will be covered by a base plate, so will not be exposed to light. I assume there is no point in gellcoating the tops of the holes.

Any advise, tips?

 

[Refueler]

What you need is Chopped Strand Filler such as Devcon or similar ... if you can get to the underneath - I suspect you can from your description ... I would create a countersunk V to the holes above and below ... an old plastic lid pressed up under with 'Devcon' to fill under and to provide a smooth surface ... then filler from top to finish.
Once set - grind off to level / smooth ...

You could use Plastic Metal ... the tubes of two part - you basically kneed to mix ... fill holes ... grind smooth etc.

 

[prestomg27]

Use epoxy with cut up grp fibres mixed in. You can cut up grp mat with electric or manual scissors to get a lot of fine fibres. Add coloidal silica thickener, if needed, to get to a peanut butter texture thickness. Mix the epoxy resin well before adding the glass fibres and then the thickener if needed.

 

[Boathook]

Use epoxy with milled fibre strands and microfibre to thicken. Use a neat epoxy mix to wet out the holes and chamfers

To clean, I would overdrill (to 11mm) the hole plus acetone.

 

[Refueler]

The suggestions to cut up strand / matt ... nice - but what a mess to clear up after ... and the possible health issues of fibres ... its going to be bad enough the sanding / grinding back ... and is why I suggest the plastic lid to flatten the interior side ..

There are many ready made Fibre filled resins out there ... Devcon being a reputable brand as example.

 

[Frayed Knot]

Whatever you use to fill them I would certainly recommend “cleaning” the holes mechanically, either by overdrilling as Boathook suggests or by some other method - rasp, Dremmel etc. which would also roughen the surfaces to provide extra key. Personal experience tells me that chemical contamination can cause epoxy to shrink away from the very surface you want it to seal against.
Although it probably makes no difference to the filling, 2” of solid grp sounds quite unusual - often there is local reinforcement to decks around the mast - possibly plywood which may (should) itself have been overdrilled, filled with grp and redrilled.
If you find that to be the case you should definitely consider doing the same for your new holes.

 

[RunAgroundHard]

… Although it probably makes no difference to the filling, 2” of solid grp sounds quite unusual …

The hull moulding has a shelf running right around, then there is the deck moulding that sits on the shelf. The shelf is relatively thick, as is the deck at these points. Between the two the drawings state “epoxy dough”, and quote an old Epifanes product code. I think by the time the deck was glued to the hull with a dollop of dough, it resulted in quite a thick structure.

 

[RunAgroundHard]

Thanks everyone for the advice, some good takeaways to build into the plan. Appreciated.

 

[Tranona]

All too complicated. Clean the 10mm hole, coat with epoxy using a small bottle brush. Cut pieces of 9mm wooden dowel to length, coat with epoxy thickened with collodial silica, tap into hole, leave to cure. Job done. Even better if you can find fluted dowelling but not sure you can find 9mm*50mm. Cover the bottom end so that epoxy does not dribble out and make a mess.

 

[Trident]

Cant imagine why one would put wood in to a solid GRP deck

Over drill to clean , run through a cloth with acetone. Mix resin with "milled glass" - powdered fibreglass and used for things like the engine beds of MotorTorpedo Boats so very tough and as its a powder a nice easy mix. Personally unless you have epoxy knocking around I'd use normal polyester/vinylester resin - which ever the boat was built from - will be plenty strong enough and much less costly

 

[Tranona]

What is wrong with using wood soaked in epoxy? It is only filling a hole and avoids trying to fill a deep narrow hole with a sloppy mix, which if epoxy will probably have a thermal runaway. The dowel fills the hole and the epoxy seals it. Alternatively as it once had a metal bolt in it (who would put a metal bolt in GRP?) just replace the bolts set in sealant.

 

[Hacker]

As a significant number of decks are cored with end-grain balsa a few wooden plugs won’t make any difference (as long as they are sealed properly). Filling with appropriate thickened epoxy would also work. Choices…….

 

[Refueler]

Sorry but why the hassle ?

Over counter can be bought Chopped Strand Filler that is perfect for this job ...