filling 4" deck hole - epoxy/fiberglass question

[stantale]

Hi,

have a non-cored deck, probably 1/4" - 1/2" thick depending on whether it's a reenforced section.

I need to fill a 4" hole that used to have an air vent in it. It's on the cabin top near the mast, and will be walked on.

Question: can I get by with using epoxy and structural filler, or should use fiberglass cloth?

I have "this old boat", and the west system guides, but they don't quite make the distinction as to when a hole becomes too big to fill with epoxy and filler alone, or what the advantages/disadvantages might be.

Thanks!

[celenoglu]

Use fiberglass cloth. Although the hole is not large enough to hurt you if it fails, most probably you can rehole it if you use other fillers..

[deniseO30]

Why not get a new air vent or solar fan? Not like you don't need one. Boats need some air movement when closed up for long periods. But, yes you would need to use cloth and some sort or backup like plywood or foamcoring. the edges would have to be feather edged for the glass cloth to lay over. Epoxy has to be painted or the sun will destroy it.

[treilley]

Or just use a standard Beckson access port.

Photo courtesy Defender.com

[LookingForCruiser]

Originally Posted by stantale

I have "this old boat", and the west system guides, but they don't quite make the distinction as to when a hole becomes too big to fill with epoxy and filler alone, or what the advantages/disadvantages might be.

Old screw holes are what you fill with thickened epoxy. For bigger holes you want to grind out the edges to a 12:1 taper and use fiberglass cloth. You'll probably need to rig up something underneath to support the glass so it doesn't sag (and doesn't stick to the epoxy of course). Duct tape might do the trick.

[stantale]

thanks for the answers, if I could re-use the hole I would... we're actually putting in bigger vents, but the existing holes can't be made bigger due to the bulkhead.

Another question: can I use filler with cloth to build up the layers more quickly, or is that not done?

planning on using a waxed plastic sheet as a backing plate.

[Beersmith]

Originally Posted by stantale

thanks for the answers, if I could re-use the hole I would... we're actually putting in bigger vents, but the existing holes can't be made bigger due to the bulkhead.

Another question: can I use filler with cloth to build up the layers more quickly, or is that not done?

planning on using a waxed plastic sheet as a backing plate.

To get thicker, quicker, use biaxial cloth. It has cloth and mat woven together and is safe to use with epoxy. Otherwise, you don't need to pile on cloth ALL the way to complete thickness. You need to leave a little bit of space on top for fairing filler. I wouldn't use thickened epoxy to thicken in between layers.

[celenoglu]

Use cloth and epoxy for nearly all the hole. You can use some filler just to smooth the surface. The real force comes from the cloth, epoxy is there, just to keep everything together. If you use filler that means you give up some cloth for hat space ehich is not strong enough.

[mitiempo]

I wouldn't use fillers. I would use biaxial roving 1708 which is stitches with epoxy compatible mat on one side. It will build up the thickness faster than lighter cloth and is very strong. 12-1 taper meaning if the cabintop is 1/4" thick the taper should extend 3" out on all sides. Grind inside as well, but not as far. Tghe first application should be underneath. Cut the biax to size, wet it out on a piece of plastic covered cardboard and press it in place. Duct tape and/or a support will keep it in place until it cures. The rest is easier as gravity is on your side. Solid thickened epoxy can be used in the middle section as shown below. Largest piece of biax first working to smallest as shown so any sanding doesn't weaken it.

[LookingForCruiser]

Using filler to thicken is bad - that has no structural strength. I use woven roving, that's fairly thick to begin with, and then after everything is cured I sand down the high spots, fill with fairing compound (epoxy + microballoons), wait for cure, sand & fill with fairing compound a second time, and then after that cures I paint the whole thing with epoxy, feathering with the brush at the edges (since microballoons will absorb water it's best to seal it). Then a final light sand & paint. If you use West system, you have to wash away the amine blush between each step too, but I use no-blush epoxies.