How to bond plywood edges?

[Rippenlips]

Hi all, I've purchase an old searay that has to have the floor fixed and new engine installed. I've been reading a lot about the floor repair and think I have a good idea on how to repair it. Epoxy the marine plywood on both side before install. Then the glass mat on top. I have cut out the old floor at a 45 degree angle and will do the same when I cut the new wood.

My question is, what do I use to bond the edges together?? Epoxy? Exterior
wood glue? Use some short galvaniezed screws?

Another is, I'm Using a 95 mustang HO motor to replace the 73 289. Everything is the same but the water pump. The new one has a reverse rotation pump and the old one wont bolt up. I was thinking electric?

I'm a little worried that this motor may be a little strong for the Merc outdrive.

I'm more using it because it has a roller cam and will run a little cooler than a flat tappit motor. I can probably retard the timing to reduce the power a little.

Thanks for any input.

Jon

 

[Mark42]

Re: How to bond plywood edges?

Seeing as you cut the edges at a 45* angle, then mix up epoxy with some thickener so it won't run, and epoxy the patch panel in place. Once cured, it won't come out. Might want to put a coat of straight epoxy on the cut edges of both the deck and the patch piece, because the edges tend to soak in the epoxy. Then the thickened epoxy will work better.

Regarding the 5.0 gt motor, all I can say is that the accessories, like starter motor and alternator must be swapped out for marine units. Use the ones off the old motor. This is a safety issue, the marine parts will not ignite gas fumes in the bilge because they are sealed.

If you are using a carburetor , it too must be a marine unit, otherwise the fuel injection should work fine.

 

[Rippenlips]

Re: How to bond plywood edges?

Seeing as you cut the edges at a 45* angle, then mix up epoxy with some thickener so it won't run, and epoxy the patch panel in place. Once cured, it won't come out. Might want to put a coat of straight epoxy on the cut edges of both the deck and the patch piece, because the edges tend to soak in the epoxy. Then the thickened epoxy will work better.

Regarding the 5.0 gt motor, all I can say is that the accessories, like starter motor and alternator must be swapped out for marine units. Use the ones off the old motor. This is a safety issue, the marine parts will not ignite gas fumes in the bilge because they are sealed.

If you are using a carburetor , it too must be a marine unit, otherwise the fuel injection should work fine.

Thats what I was thinking. After I treat the edges should I let it dry? Then glue them together? I was reading something about wax in the epoxy and I need to see if has it or not before I mix it.

I have all the accessories from the old motor. They are all marine grade. The only problem I have to far is the waterpump.

Thanks for the reply.

Jon

 

[ghamby]

Re: How to bond plywood edges?

Let the clear epoxy reach "green" or tacky stage on the edges then glue up
with the thickened epoxy. Other wise you will have to sand the cured epoxy
an wipe it down with thinner.
Shave down the thickened epoxy when it is in it's green state with a shurform
and scrape out the marks with a utility knife blade. This cuts down on sanding
time and dust in the finishing phase. Wear gloves and a mask epoxy's irritating
stuff
On another note: skip the galvanized hardware. Go with stainless
steel. When the galvanized hardware corrodes it will rot the surrounding wood.
Good luck gh

 

[jonesg]

Re: How to bond plywood edges?

Pre-fit the deck, remove it and glass the bottom surface w/ matting.
Seal the edges real good with resin.
Install and seam together with a bead of PL Premium, glass over the whole deck top surface in one shot.
This way theres no need to sand anything except the final top finish .

 

[bananaboater]

Re: How to bond plywood edges?

That 45 degree surface may not be strong enough. I just glued (water proof) up two pieces of 1/4 inch marine ply using a scarf joint to get the 10 feet I need. Google scarf joint and you should find a kayak maker that has a great article on making them. It is not easy and I had to make a jig to cut the shallow 80 degree angle but the results are great. I plan to epoxy the entire sheet with one side fiber glassed for greater strength and longevity.

 

[jonesg]

Re: How to bond plywood edges?

Scarf joints are the best for long joints but he has gravity on his side.

 

[Rippenlips]

Re: How to bond plywood edges?

Thanks all for the input. I will porbably get the chemicals next week since it looks like it will be in the 80's.

Scarfing or not to scarf is the question. I think it would work great. I could just use some blocks of weight to hold it down until it dried. I'm thinking a router with a special bit. Then I could use a nice straight edge to make the line perfect. I did not cut any curves since it will be easier to make the replacement panel. (I grew up building houses)

Thanks again.

 

[Rippenlips]

Re: How to bond plywood edges?

I just called TAP plastice here in Oregon to see if they had all the supplies. They do. Then the guy told me I shouldnt use epoxy with the fiberglass mat. He said it wont break down the fibers like the regular resin. He said it will be OK to adhear to the old fiberglass. He said I can use the epoxy and it will stick to the fiberglass better but is not the correct way to do it.

Any input?

Jon T

 

[ghamby]

Re: How to bond plywood edges?

I have found epoxy works great with fiberglass. It's more water proof. It does,
however, break down in sunlight. Paint it once it is cured and finished.
GH

 

[Mark42]

Re: How to bond plywood edges?

I just called TAP plastice here in Oregon to see if they had all the supplies. They do. Then the guy told me I shouldnt use epoxy with the fiberglass mat. He said it wont break down the fibers like the regular resin. He said it will be OK to adhear to the old fiberglass. He said I can use the epoxy and it will stick to the fiberglass better but is not the correct way to do it.

Any input?

Jon T

What TAP is telling you is the mat they sell is not compatible with epoxy, only poly. This is due to the chemical binders that is used to keep all the glass fibers stuck together otherwise it would just fall apart into a pile of loose fiberglass strands. The binders dissolve in poly resin so the glass is in contact with the resin. With epoxy the binders will not dissolve, and the glass fibers stay coated with a binder that doesn't stick to epoxy well. Makes a weak product. So you need mat that is epoxy compatible. Sometimes its stitched every inch or so to help keep it a mat and not a pile of fibers.

Regardless, just using the epoxy with some thickener in it will make a very strong repair, even without glass fiber.

 

[Rippenlips]

Re: How to bond plywood edges?

What TAP is telling you is the mat they sell is not compatible with epoxy, only poly. This is due to the chemical binders that is used to keep all the glass fibers stuck together otherwise it would just fall apart into a pile of loose fiberglass strands. The binders dissolve in poly resin so the glass is in contact with the resin. With epoxy the binders will not dissolve, and the glass fibers stay coated with a binder that doesn't stick to epoxy well. Makes a weak product. So you need mat that is epoxy compatible. Sometimes its stitched every inch or so to help keep it a mat and not a pile of fibers.

Regardless, just using the epoxy with some thickener in it will make a very strong repair, even without glass fiber.

So Im replacing a 5x8 foot section of floor in my boat. Should I buy the mat that will take the epoxy or just use the poly resin with the regulat mat?

I will be grinding the old fiberglass so that I have a nice transition and will probably go up the sides of the boat a few inches.

Or is there a way to use both?

Thanks for the input guys.

Jon