Fairing Flat Spot on Glass Hull

[BobBill]

I did broad search and found nothing specific. Most discuss over-wood glassing and fairing.

I have 14 x 16 inch flat spot on bottom of hull that needs to be faired up.

Was going to layer with cloth and fair after cure.

Would micro-balloon epoxy mix or ready made mix like West's be better solution, being lighter, though softer?

Thanks.

[alan white]

Try West Microlight #410 with epoxy, thick like frosting. Use a toothed trowel (tile trowel, groove size to match depth of depression) to apply. Longboard (do you know what this is?) to fair. Fill trowel grooves to flush with sanded surface. Touch up and longboard (lightly) again. Add more Microlight to fill sanding scratches. Coat (paint) with a coat of neat (plain) epoxy, wet sand, and prime/paint

[BobBill]

Thanks Alan.

Yep, know the long board well, but do not think I need for this job.

Going to glass-over the fill material or do the layered glass build-up, over sanded glass hull,

and wondered if the fill versus layered glass approach is advised?

I know the fill approach would be lighter, but the glass is stronger...the areas are small.

[Doug Lord]

Originally Posted by BobBill

Thanks Alan.

Yep, know the long board well, but do not think I need for this job.

Going to glass-over the fill material or do the layered glass build-up, over sanded glass hull,

and wondered if the fill versus layered glass approach is advised?

I know the fill approach would be lighter, but the glass is stronger...the areas are small.

=====================
BobBill, how thick would the spot be when filled properly? Are you going to use polyester gel coat to finish the repair?

[BobBill]

The build would be about 2mm, maybe 3 at center.

No gel coat, just fill, glass (epoxy) and paint.

At one time, was going to use Bondo type filler, as I did on another boat, but decided not to go that route.

[Doug Lord]

I think Alan has it right. I might modify his suggestion by using a smooth metal or glass batten to apply the fill that you could bend as you apply the stuff. This might be better since it would feather the fill with no grooves. The disadvantage might be slightly less control of the application but if done carefully it would work. I don't think a thin epoxy based fill like this needs any glass.

[BobBill]

For reasons not mentioned, I am going to apply a thin layer of glass from near stem to stern, so the question is not using the stick to apply the filler to fair; the question is whether I should use glass (laminated and fair or the softer filler), keeping in mind the sections being faired are where the hull naturally rests, sort of a fulcrum area on each side that gets abused by grounding, beaching and so on.

[alan white]

Glassing the area is going to work to a degree, but it's a lot more itchy to sand.
The glass is set in a resin so sanding is also more rigorous.
Here's the deal though: The area is where the boat rests and it really ought to be reinforced from the inside since adding layers of glass externally will tend to deform the edges of the patch where the hull is only original thickness.
The inside reinforcement should extend well beyond the edges of the deformation, tapering to nothing at the margins.
Fill the depression with filler and seal with epoxy, but glass the inside as described.

[Landlubber]

...I tend to follow the alan white system, overlap the inside layers(s), and you may be able to brace the section (outwards) whilst doing so, thus avoiding the need to fill on the outside anyhow.

[BobBill]

Yes. As you note. I have already ordered some carbon and some cloth for that procedure, but need to keep it light. No way I can reshape the flat spot so will have to do work-a-round and hope the stess is low. Still, I do thing the glass is strong enough as is, but taking no chances on this old dinghy.

Will post pics and progress...

[Landlubber]

I have already ordered some carbon ........


....why....you cannot simply throw carbon around and expect it to do wonders you know....carbon is the strongest of all the materials, it will take the load instead of the glass, as it is the strongest...it will not be enough to handle the full load, so it will fail, then the glass not being strong enough on its own will fail, so the whole job will fail......in theory anyhow.

[BobBill]

The carbon strips, matched with glass on interior will do the trick, carbon is strictly used as stiffener, not as single reinforcement, and the glass, even without the interior backing, is strong enough alone.

Was just wondering about fill application...

Thanks for help, it will be fine either route taken.

[alan white]

Originally Posted by Landlubber

...I tend to follow the alan white system, overlap the inside layers(s), and you may be able to brace the section (outwards) whilst doing so, thus avoiding the need to fill on the outside anyhow.

Good thinking. Maybe a tab can be bonded to the outside that can be used to pull the hull skin outward so no prop gets in the way inside. Later the tab can be cut and gound off.

[BobBill]

Gel coat removed. I doubt anything would force hull back to original shape. As someone noted, matrix in that area is kaput, so the exterior glass seems necessary. Not talking about heavy cloth, and with inside work, should be strong and not excessive weight.

[BobBill]

Originally Posted by alan white

Glassing the area is going to work to a degree, but it's a lot more itchy to sand.
The glass is set in a resin so sanding is also more rigorous.
Here's the deal though: The area is where the boat rests and it really ought to be reinforced from the inside since adding layers of glass externally will tend to deform the edges of the patch where the hull is only original thickness.
The inside reinforcement should extend well beyond the edges of the deformation, tapering to nothing at the margins.
Fill the depression with filler and seal with epoxy, but glass the inside as described.

Alan, took me a bit to get back to this thread. Good advice.

My plan is to lay up the outer glass to just over the area and sand to match hull and fair. This inside should provide the strength, the outside protection and fairness, if that is the best way to put it.

the work for me really is to separate the deck from the hull...pure grunt work to get through the seam gunk etc.