MRB Home   -- Flies forum   -- Boats forum

Bottom glued on, now what?
Bottom glued on, now what?
April 19, 2017 10:21PM
Ok so the bottom is glued on to the boat, but now i have a hard edge at the chine. Do i need to remove this hard edge before glassing the chines and outside of the boat?

I used a sander and beveled off a piece of scrap plascore, worked pretty good, just curious if there is a right way to do this.
Re: Bottom glued on, now what?
April 19, 2017 11:17PM
When I glue a Plascore (or in the old days plywood) bottom onto side panels I use epoxy putty but I have a hunch 3M 5200 would also work. I make the bottom panel about 1/4" inch too big all around so slight mis-alignment problems aren't problems.

Then i slowly, carefully stroke the edge with a big right angle grinder, with an extra extra course 40 or 60 grit disk. Use that tool carefully and gingerly. Round off bottom edge ever so slightly. Slower and more laborious but less dangerous than a right angle grinder is the course side of a horse shoer's rasp.

When I glass over top of that I trowel some putty onto the slanted 3/4" inch edge of exposed Plascore cells. I know others who don't (Jeremy and Larry, who sometimes visit this forum). So I know the putty isn't necessary. Still. I do it. But I don't use much putty.

Glass over the entire outside of the boat, sides first with only one layer, overlapping the chine by an inch or two. Now the bottom with three layers, also overlapping the chine by an inch or two. You might have to slit the 1" overlap in a few places, so it doesn't form wrinkles.

Actually layup details vary considerably. I usually start with one layer of 3.5" inch tape over the chine. Then 6" tape. Then fabric over the whole side, overlapping the chine. Then a glass over the bottom, also overlapping the chine. Now add a few more layers of tape, so you have 7 or 8 layers over the chine. Figuring out how to use bi-axial tape is even better, and more sophisticated. I don't want to specify that sequence here.
Re: Bottom glued on, now what?
April 20, 2017 01:13AM
Thanks Sandy, I've got a belt sander. Would that work?

The way i did it, the edge of the bottom panel sits in from the outside edge of the side panel by 1/4", i filled this and glued down with thickened epoxy after wetting out the edge.
Re: Bottom glued on, now what?
April 20, 2017 02:36AM
Interesting. Sure what you did is fine. A belt sander will work just fine.

By the way I mentioned bi-axial tape above and then artfully dodged talking about it. I don't like biaxial tape. It's strong stuff but it's hard to work with. It's hard to wet out. You really need an additional tool: a layout roller, which you can buy at Raka and other such places, like Fiberglass Supply.

But you also need to mix up putty. The edges of biaxial tape are too abrupt to glass over. You need to putty the edges before going over top with a smoothing layer of glass.

And it isn't necessary. Biaxial tape was useful in the ancient days of plywood bottoms. With Plascore bottoms you don't need it. Without that extra glass layer a simple chine of 7 or 8 layers of fabric over the chine will get dinged. It will split eventually, by impacts with a thousand rocks. But so what?

I just recently patched a Plascore chine that was ten years old. TEN YEARS! it was split for several feet on both sides. It caused no additional damage because water doesn't soak into Plascore. I sanded out the split ever so slightly and let id dry for two days, which I don't think it needed but I did it anyway. Then I glassed over it.

Biaxial tape was supposed to make a bomb-proof chine over top of plywood, strong enough that splits in the glass covering would not happen, so moisture could not soak into the plywood. Plascore makes that tits on bull. You don't need no biaxial tape over a chine where the bottom is 3/4" inch or 1" inch Plascore.
Re: Bottom glued on, now what?
April 20, 2017 03:31AM
Well, biaxial is what I've got. Was on sale at Raka. It lays down really nice, not that I know the difference. First boat. I've got a couple of those slotted rollers you mentioned. Is the puttying on the finish layer or between layers. Was gonna do 2 layers inside and 3 outside. I'm not to worried about how polished the boat is going to look. Just want to get on the water.
Re: Bottom glued on, now what?
April 20, 2017 03:32AM
Biaxial is good stuff. There are no negatives other than it's hard to work with. I was only arguing you can skip it--if and only if you use a Plascore bottom instead of plywood.
Re: Bottom glued on, now what?
April 20, 2017 01:01PM
....thinking out loud.........

RE> "that belt sander"
Be careful with that belt sander. They can do a lot of damage. Do you have Plascore sides? Are you building an all Placore boat or do you have plywood sides?

If all Plascore I'd recommend NOT using that belt sander. Not unless you have a practiced light touch with it. And know what you're doing.
Re: Bottom glued on, now what?
April 20, 2017 08:29PM
Yes, all plascore. I'm pretty good with the belt sander I have made alot of furniture, use it often on table tops. So just to make sure, im gonna use it to break the edge on the plascore and smooth out the putty? Concerned that I'm not supposed to sand and round off the plascore. Maybe I'll just use a rasp/file. Just concerned about the plascore.
Re: Bottom glued on, now what?
April 20, 2017 09:22PM
OK you're probably fine. Belt sanders can dig quickly on something as soft as plascore. But it sounds like you have the skills.

Break the edge and smooth putty? The flat surface of the Plascore has a matt layer heat melted into the plastic cells. Don't let the belt sander remove that matt so the tops of any cells are exposed. Keep it to a minimum anyway. You will do a little of that as you round off the edge. Make the radius just wide enough you can wrap it with glass.
Re: Bottom glued on, now what?
April 21, 2017 04:07PM
I round the edge with an angle grinder and an 80 grit disk. In the past I filled the cores in the honeycomb. I think from now on I will just add more glass. It's a faster process.

As for 5200, that would be expansive. Many places sell that for 30 dollars a tube. Home depot has had if for the best price I have ever found. It will bond anything but it also take a week to cure.
Re: Bottom glued on, now what?
April 21, 2017 04:20PM
I've never used that 3M 5200. I like the idea of glue coming out of a caulking gun but......that is expensive.
Sorry, only registered users may post in this forum.

Click here to login