Newbie Redecking question (Plywood and sealant)

[domwebhost]

Hi all,

I have been reading MANY MANY posts on several different forums about the type of plywood to use, the effects of pressure treated wood on aluminum, and using epoxies to seal the wood. I am still a little bit confused and so I thought that I would ask it on this forum.

So, I get it that Marine grade is the norm and (CCA) (Around here in Indiana / Michigan area it looks like over $100 a sheet (if I am lucky) and I need to do a complete redeck).
However, I have read others that have said that they have used untreated (so as not to corrode the aluminum) CDX since the glue is exterior-friendly and have tried using various sealing/topical solutions to extend the life of the wood.

My questions are:

Could 3/4" CDX untreated be used and then coated with fiberglass resin (such as Bondo Fiberglass resin) on all 6 sides (including pouring/injecting into any voids seen at the edge) to make it water resistant and last considerably longer? (Is this even a thing that people do?)

Should I use slightly thinner plywood and build up both sides with coats of resin to make it 3/4"?

Would it need multiple coats?

Is it a complete waste of time?

Saturate all seams and screw holes with silicone (RTV) to further impede rot..etc?

Will carpet adhesive stick to fiberglass resin (I assume I would have to scuff it?)

If I had the $$$ I would get the best of the best marine grade plywood and do it like the big boys do, but my budget doesn't allow for it; however, I do have time on my hands and can score a decent amount of resin, so I am looking at this solution but I don't wanna throw my $$ down the crapper if it is going to fall apart in 2 seasons and may look into some alternative decking solution.

It is okay to laugh at my idea as I have thick skin and can take a joke

Happy Boating

 

[ondarvr]

You don't want to use polyester resin without glass, it's brittle and weak, so it cracks and peels off rather soon. Epoxy resin will work though.

​MDO ply is another option, it's typically a fairly good grade of ply, and costs less than Marine ply.

​Whatever you do will last 5+ years rather easily, 10 if you take half decent care or it, sitting in the side yard under a tree for several years with no cover doesn't count as good care.

 

[domwebhost]

​MDO ply is another option, it's typically a fairly good grade of ply, and costs less than Marine ply.


Do you still have to seal the MDO ply?

 

[domwebhost]

You don't want to use polyester resin without glass, it's brittle and weak, so it cracks and peels off rather soon. Epoxy resin will work though.

​MDO ply is another option, it's typically a fairly good grade of ply, and costs less than Marine ply.

​Whatever you do will last 5+ years rather easily, 10 if you take half decent care or it, sitting in the side yard under a tree for several years with no cover doesn't count as good care.

Do you still have to seal/treat the MDO? (I don't seem to see the lumber yards in my area carrying MDO in 3/4"...just MDF ) Epoxy? Good to know

 

[Chaser 32]

Question # 1. How long do you plan on keeping the boat? I've used 5/8 Plywood coated 3 or 4 times with good spar varnish and its lasted years without issues. I helped a friend redo the transom of his, we used 3 sheets of 3/4 inch A/B (Making sure the A side faced out) tightly glued together with tightbond III wood glue and coated in fiberglass. Personally I feel that marine grade plywood is over-rated. If your in corrosive salt wter conditions having to deal with barnacles and such, then perhaps it has its uses. If you decide to use fiberglass and resin, I wouldn't skip the glass. It's purpose is to provide strength to the resin and vice versa. They work together. You'll still want to use a urethane top coat over the fiberglass.

 

[ondarvr]

All plywood rots and benefits from being sealed, but even unsealed they will last for many years. Sealing helps, but only if you don't drill holes and leave them unsealed, as soon as water hits the plywood the clock starts ticking.

 

[domwebhost]

Well, the Menards here in my town has 3/4" MDO for $64.99 a sheet (It is a 1989 Starcraft Bass Buggy 20ft that I will be redecking). I am not sure how long I will keep the boat, but I was hoping to keep it for a few years at least and get some enjoyment out of it. So, do you think I should just use that and put a few coats of spar varnish on it (something like Duralux clear spar varnish), silicone the seams and screw holes, carpet and call it a day?

 

[jbcurt00]

How about we back up a bit and find out what boat you're working on and see some pix of it.

1st question, why do you think you need a 3/4in thick deck? Many tin boats have 1/2 or maybe 5/8ths, and its normally sufficient.

2nd question, unless its a pontoon, which may need a replacement too, have you checked the transom? Often what looks good on its face, isnt, and sometines it looks near perfect and is actually closer to mulch then plywood.

Sounds like you are confusing Marine and CCA plywood, they are not the same.

As mentioned, dont use bondo resin alone.

IMO, you dont want to use CDX, its C graded face isnt ideal, BCX at a minimum. ACX would be a much better choice. Its about voids in the layers, esp those you cant see because they arent at the edge, and the quality of the outer veneers.

As mentioned, MDO is also a great choice. Its used for highway signs and concrete forms. Great to work with.

Regardless of which thickness ply you buy, no need to try and thicken it to reach the nominal dimension, whatever it is, is likely what it was when the boat was built (guessing it had a deck originally from the factory because you said re-deck). So if its really 23/32in ply (its whats called 3/4), that will be fine.

No silly-cone on a boat. There are better choices that wont upset your budget. And you'll be sealing the plywood on all the edges everytime you seal 1 face or the other, so the edges get twice as much of whatever sealer you pick. But it shouldnt be silly-cone.

There is a lot of choices of how to do a lot of what you need to do. You'll have to decide which best suits your timeline, budget and skillset.

It will be a trade off: expense now vs putting off another redo when low cost choices dont last.

Time and money now vs how long you're willing to wait for various parts and pieces to be finished and ready for install. Which then feeds back into expense now vs longevity.....

Good luck w your project and let us see what you're working on.

 

[jbcurt00]

You posted while I was typing. So its a toon?

Yes to 3/4 then

 

[MH Hawker]

one of several reasons for marine plywood is its 7 plys, it is considerable stiffer, it is the spine of the boat, how ever if you want to ride around on a wet noodle go for it

 

[domwebhost]

Yes, it is a pontoon boat. I was under the impression that 3/4" was standard for a pontoon deck, but am open to suggestions. I was looking at MDO as suggested (as my local Menards has it) and was thinking about using Duralux or Helmsman (spar finish) as suggested for sealing. I will run out and take some pics of the boat. The deck is in pretty bad shape with decent sized holes in it and I am not sure I would even deem it safe to walk on in a lot of spots. I'll run down to the boat (a couple of miles away) snap some pics and show ya guys the turd I wanna polish

 

[ondarvr]

Spar varnish isn't a great waterproof finish, it needs to be reapplied fairly often for it to retain any amount of it's water resistants'. If there's going to be carpet over it, spar varnish won't help much at all.

​Check the online pontoon boat sites for ply designed for this purpose.

 

[domwebhost]

Spar varnish isn't a great waterproof finish, it needs to be reapplied fairly often for it to retain any amount of it's water resistants'. If there's going to be carpet over it, spar varnish won't help much at all.

​Check the online pontoon boat sites for ply designed for this purpose.

I was planning on at least 4 coats of varnish and Marine ply is 1) not available in my area and 2) not in my budget

 

[ondarvr]

4 coats are of little value, it just isn't that waterproof.

 

[domwebhost]

No Title

How about we back up a bit and find out what boat you're working on and see some pix of it.

1st question, why do you think you need a 3/4in thick deck? Many tin boats have 1/2 or maybe 5/8ths, and its normally sufficient.

2nd question, unless its a pontoon, which may need a replacement too, have you checked the transom? Often what looks good on its face, isnt, and sometines it looks near perfect and is actually closer to mulch then plywood.

Sounds like you are confusing Marine and CCA plywood, they are not the same.

As mentioned, dont use bondo resin alone.

IMO, you dont want to use CDX, its C graded face isnt ideal, BCX at a minimum. ACX would be a much better choice. Its about voids in the layers, esp those you cant see because they arent at the edge, and the quality of the outer veneers.

As mentioned, MDO is also a great choice. Its used for highway signs and concrete forms. Great to work with.

Regardless of which thickness ply you buy, no need to try and thicken it to reach the nominal dimension, whatever it is, is likely what it was when the boat was built (guessing it had a deck originally from the factory because you said re-deck). So if its really 23/32in ply (its whats called 3/4), that will be fine.

No silly-cone on a boat. There are better choices that wont upset your budget. And you'll be sealing the plywood on all the edges everytime you seal 1 face or the other, so the edges get twice as much of whatever sealer you pick. But it shouldnt be silly-cone.

There is a lot of choices of how to do a lot of what you need to do. You'll have to decide which best suits your timeline, budget and skillset.

It will be a trade off: expense now vs putting off another redo when low cost choices dont last.

Time and money now vs how long you're willing to wait for various parts and pieces to be finished and ready for install. Which then feeds back into expense now vs longevity.....

Good luck w your project and let us see what you're working on.

Here are the pics that I took.

I measured the thickness of the ply and it looks to be 3/4"

Yes, I know that the 'toons are on the ground but I was renting a trailer by the hour and I plan on putting them on PVC rollers this Saturday.

 

[domwebhost]

Marine ply is NOT available in my area so that is why I started this post; to find alternative solutions. So far an alternative solution is to go with the MDO (even if it is only 5 ply) and seal it either with epoxy or some kind of varnish. Feel free to give me any advice that doesn't include MP and excessive shipping costs since it is not readily available anywhere around here that I have looked, nor do I have the budget for $120 a sheet + shipping.

 

[domwebhost]

No Title

You don't want to use polyester resin without glass, it's brittle and weak, so it cracks and peels off rather soon. Epoxy resin will work though.

​MDO ply is another option, it's typically a fairly good grade of ply, and costs less than Marine ply.

​Whatever you do will last 5+ years rather easily, 10 if you take half decent care or it, sitting in the side yard under a tree for several years with no cover doesn't count as good care.

I was looking at this after your advice BTW

 

[jbcurt00]

Just make sure you're getting MDO not MDF.

 

[domwebhost]

Also, when I lay the ply should I stagger the vertical seams (the ones going from bow to stern)?

 

[domwebhost]

Just make sure you're getting MDO not MDF.

Will do for sure. Thank you and everyone for your suggestions so far . Oh, and I forgot to mention that this boat will only be on fresh water.