f'glass advice needed-filling a gap?

[John F.]

The overlay is on, and I have a 1/4" gap on each side that I'd like to fill and blend in. Grind, a few layers of f'glass tape with a radius, and fair? Not sure how to do this. Thanks.

[CaptPatrick]

John,

Go to your local plant nursery and get a bag of vermiculite. Mix your epoxy with cabosil until it's the consistancy of ketsup, (a little runny), then add the vermiculite to the point that the mix is like grainy peanut butter. Pack the gaps with that mix, let it harden for a few days before adding glass. On all epoxy work, especially heavy fills, hold off final fairing and give the epoxy the most time you can to shrink down. Epoxy never fully cures 100%, but the 98% point is reached in about 30 days...

[CamB25]

The Cap't is the expert and I will never be confused with an expert, but I would try to glass on the back side as much as possible to keep the two parts from moving relative to each other. You're likely to get a lot of twisting type motion up there. Then fill most of the void with foam sheet or a piece of wood...somthing with some shear strength...glued to each surface and the backing glass. Try to leave just enough "space" to pull a nice finishing filet to cosemtically finsh the joint. The back glass and the void filler provide the joint strength.

another idea:

If you can't effectively glass behind the joint, try to secure a backing block to cover most of the rear and bottom areas of the joint. Wrap a piece of wood with Saran Wrap to keep the epoxy from sticking. prep the mating surfaces. Glob in some thickened epoxy. Take 45/45 tabbing, wet it out and cram it in the open joint, filling the void. Clamp another wrapped block in to the joint until the epoxy hardens. Now you have a semi-structural repair that will carry shear loads. Pull a fillet to finsh the joint cosmetically.

My ideas are trying isolate the structural "repair" from the cosemetic "finish". Cosemtic repair of structural joint is a PITA. I would not use glass on the facing surfaces for this reason. All the strength should be behind the scenes.

just my thoughts

[CaptPatrick]

No matter what filler is used to pack a gap, fillers have next to no structural strength. Filled epoxy does come closer than most other resins, but as it continues to cure and shrink, unglassed fillers are going to crack, if for no other reason than from shrinkage.

It's necessary, always, to glass over gaps and joints. It's the glass that prevents any cracks from developing on the surface. The more glass over the joint, the stronger it is.

[John F.]

Thanks for the advice. Much appreciated.

[CamB25]

i think we are saying the same thing. This joint has depth and the joint strength can be developed behind the facing surfaces, thus eliminating the need for fiberglass on the faces and the associated finishing chores. In fact, unless you are going for a yacht grade finsih, just use some 4000 UV for the filet after you paint.

have fun! It's hot this weekend....be quick with the epoxy!

Cam

[CaptPatrick]

thus eliminating the need for fiberglass on the faces

Nope, the exterior face is exactly where the glass needs to be, unless you want an eventual crack to show up in your expensive paint job...

[Yannis]

A nicely cut and rounded teak, that may go elsewhere too.
Fills crevices the most 31ish way.

[Marlin]

I agree with the cap, u have lots of round stuff up there already , filled in as he says with some biax and a large radius would blend in and never be noticeable, the square corner isn't Bertram , the teak trim is not the Bertram image, I have always felt that molding in non molding areas are kinda the DIY approach and constant maintenance, either varnish teak oil, teak brightener,my opinion

[Rawleigh]

Could you layup a fiberglass strip about the thickness of the crack on a flat surface and them cut it to width and epoxy it to either the bridge or the cap to reduce the amount of filler you have to gob in there? Or cut a rectangular strip out of a scrap boat to fill it. Or is it better to have a big gap when you have to fill it??

[CaptPatrick]

Rawleigh,

Yup, that'd work too... The key is to fill the gap with something that has as little or no shrinkage as possible to glass over. That's the beauty of the vermiculite mix, very little shrinkage due to the high light weight volume of the material and low volume of epoxy.

When I started using vermiculite as a bulk filler, I did a few experiments with it to determine the practicality. One was several linear strips cast into 12" x 1/2"x 2" molds. The linear shrinkage on the 12" length was less than 1/8" after a 90 day cure and only 1/8" after a year. Lateral and depth shrinkage was almost nil for the same periods.

Vermiculite is fairly absorbant to moisture, but once encapsulated with resin, especially epoxy, it's water proof. Another close runner up for a bulk filler is saw dust. I even, in a boatyard pinch, used plain dry dirt. The third runner up was shreaded paper. Basically, anything will work as long as it's reasonably dry...