Moldable/pourable materials that dry hard?

Hey guys,

I'm curious if any of you have used moldable epoxy putty on a rotomolded plastic? (Something like a Quick Fix epoxy surfboard repair stick). Or have another suggestion?

I'm hoping to mount two of these threaded anchor nuts inside the hull of my kayak basically where the two holes are drilled in the second example pic below:



When I reach inside the hull and feel around those locations, I can tell the surface isn't very flat. Instead, it's almost rounded, with a gradual slope around the sides.

I'd like to find a material that a can smoosh into those two locations and smash/sandwich flat with a little cutout of thin Starboard. Basically I'd like to fill in the contours around the two hole locations and end up with flat, sturdy mounting locations.

I guess another option would be to use this Hobie repair kit to lay down some extra LDPE material, but I don't think I could actually reach this location with the soldering iron welder tool.

http://www.austinkayak.com/products/1587/KC-Welder-Pro-with-Hobie-Color-Rod-Stock.html

Any bright ideas?

Thanks in advance.

~Alex

Epoxy putty stick or bondo?

Come to think of it, it's not terribly vital whether the material actually bonds to the kayak. It it doesn't, I can always add a little goop before tightening the threaded inserts into place (two small bolts/nuts/washers per threaded insert).

Hadn't thought of bondo. I wonder if it would stick to the hull?

Don't think it would stick.  Hard to find stuff that really sticks to the hull.  Other alternative, though quite a bit more expensive, is West System resin with a bunch of Collodial Silica thickening agent (about the consistency of peanut butter).  I'd go for the epoxy putty.

Don't think it would stick.  Hard to find stuff that really sticks to the hull.  Other alternative, though quite a bit more expensive, is West System resin with a bunch of Collodial Silica thickening agent (about the consistency of peanut butter).  I'd go for the epoxy putty.

     Bill hit the nail on the head with this one.    Epoxy is slower curing time than a polyester resin.   I've sometimes cut up fibers of fiberglass (or carbon fiber)  to mix in with the resin.   It too thickens it into a mold-able  "hairball".
     Could even make that same thing ( like a molded in insert), using a fender washer ( as backer plate )  with a nut below it.   Goober up the whole mess and hold it in place with a bolt until the resin cures...   just be sure to grease the threads on the bolt ( or screw )  so it can be removed.       If you  need it to stay in place.  After it cures, pop out the molded part, then glue it back in with a dab of Goop. 

From what I think you need it for, any of the above materials should work.  Basically, you are making a molded part to create a 'flat' for the nut/washer to sit on ... a compression flat.  As Jim stated, be sure to wax or lube the bolt so you can get it out later.

That's correct. I basically want to take a concave surface and fill it in so that it's a flat surface. This way I can easily mount my threaded insert.

I think I'm going to give the epoxy putty a try. I already have a stick on hand of surfboard and windsurfer repair.

I'll probably pack a little dab into an inconspicuous spot inside the hull of my old Scrambler XT just to see how it works.

Like I said, it's not vital that it sticks strongly to the hull since these threaded inserts get bolted in anyway. I can always GOOP the hardened "puck" of epoxy back in place before drilling and installing the insert.

Thanks for all the help, guys. I'll create a thread to document this project as it comes together.

Maybe use some really firm rubber - I've seen auto parts in the street that are softer than a rubber mallet, but not as soft as foam. You could saw a slice of it and then use a backing plate of metal that would bend as it compressed the rubber to conform to the curve, and not have to worry that pieces of putty or whatever would crack and fall out of place over time.

That's an interesting idea. I'd be afraid it might have to much flex if I add a layer of flexible rubber? I don't want this thing to move at all. I want to be able to crank the crap out of the downrigger without worrying about bolts wiggling around and expanding the holes drilled in my kayak.

Could you take a piece of thick starboard and file one side to match the contour? If so, then you'd have a flat mounting surface. I did a similar thing when installing a hatch on a rounded surface.

That could definitely work. Might as well give that a shot before I break out the epoxy.

Here's a picture of the spot.

Elevated border( like a piece of wood or PVC tubing) glue it with hot glue.Package tape the area you want molded. You can use window weld(urethane ) shoot it out of a caulk gun. Let it set. Remove plug (working part). And make an external mold with fiberglass.  If you need to make another one. Or just use that working part. For what ever your needs are. TAP Plastics has this epoxy additive in powder form. When you add it too epoxy , it becomes like a putty. Urethane is just cheaper easier to get very inexpensive. I've seen it at auto stores . It's also used for engine motor mounts.

Slack- That could work, but It would be really tough to do precision work like that in a spot that's so awkward to reach. I can't even see the spot without a mirror or camera, and definitely can't see it at the same time I've go my hand in there working.

That's why the putty idea is appealing. Or the sanded/shaped piece of starboard. With either of those, I should be able to feel it well enough without seeing.

Here's my current plan:

Bum some Play-Doh/clay/beeswax from my girlfriend's classroom, wrap it in cling wrap, smash it up into the mounting location, then carefully remove it. This will give me a "working part", as you called it. Then I'll cut out a little piece of 3/8"(ish) thick Starboard to match the outline of the shape and file the edges to match the contour. A little trial and error, and I'll be in business.

From there I'll just need to GOOP the piece in place, drill the three holes, and mount the threaded insert with a couple stainless steel machine screws, washers, and nuts.

Sounds to me like that should work.

I assume you're going to mount your downrigger base on this. Do you plan to use the cup holder to prevent it from rotating?