# How to protect plywood floor in a jon



## grover (Oct 25, 2016)

I've read and read and now I'd like to ask. I'm replacing the floor in my 1448 jon with 1/2 plywood. I think it's CDX. Smooth one side and exterior glue. I've read differing opinions about how to protect it. Old timers formula and epoxy resin are two of my top choices. With old timers formula does it need to be spar varnish or does spar urethane work as well? 
So of the two, old timers and epoxy resin, which would protect best? Any other suggestions? As of now I'm planning to finish it off with the deck restorer product by rustoleum instead of carpet.

Another question, how much product to cover about 1 1/2 pieces of plywood front and back?

Thanks for your help


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## Johnny (Oct 26, 2016)

start with the mindset that your boat may be exposed to the weather and elements 24/7/365.
the general concensus is to preserve the plywood, apply paint, then glue the carpet.
plywood is the most flexible of all wood - meaning it expands and contracts severely with the weather.
with this being understood, it is IMPERATIVE that whatever sealer you use, it must penetrate 
to the deepest depth possible in order to do its job. then, after that application,
more layers of straight varnish or paint for more sealant protection.
personally, I am not a fan of "urethanes" on boats - it is designed for cabinets, furniture and floors.

now, to your question - - - - 

you can adjust the blend ratio of the varnish to suit your needs. 
Once an additive is added to the mix, it is then called “modified”. 
DO NOT return any modified product back to the original can or else 
it will spoil the whole can. Which could be costly in the higher priced coatings.
One of many blends of a home-made penetrating sealer is to add the following products together:
*1 part varnish
1 part boiled linseed oil
1 part (or a little more) of mineral spirits.* Don’t use naphtha.

One note that I read is if you are in a really humid area where mildew is frequent, 
skip the addition of linseed or tung oil and use a straight mix of 50/50 plain mineral spirits 
and your varnish for a penetrating sealer. 
The reason is that the long oils actually “may” promote mildew and mold 
within the wood which contradicts all that I have read on organic oils. (not a good thing).
(sort of like cooking oil going rancid when exposed to the air - it promotes bacterial infection).
Adjust the mix to suit your application and environment.
Apply liberally with brush, roller, spray or rag and wipe off the excess when the surface appears 
to be fully saturated. Let dry for a minimum of 48 hours before applying additional coats. 
Two or more coats of straight varnish applied 24 hours apart will seal the wood quite well…..
Varying climatic conditions and time of day can affect the drying times. so adjust accordingly.
surface coverage varies by product and method of application, but the average is 100-125 square feet 
per quart. then 1/3 of that for each additional coat.
so figure out how many square feet of board you have and guestimate it from there.
and yes, both front, back and edges require the same number of coats.
and personally, I do not use epoxy - but many members here swear by it...... your boat = your call.

as for the Rust-Oleum Deck Restore: it is new on the market and not enough
feedback and reviews have been submitted for me to form an educated opinion.
Google it - do your own research by reading the reviews - make your own decision on this one.

this is strictly jus my Dos Centavos.

*Read, Understand and Follow the directions on the label of all products you may use.*


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## lckstckn2smknbrls (Oct 26, 2016)

I like the old timers formula. I mixed one part of Boiled Linseed oil, One part Spar Varnish or Spar Urethane and two parts Mineral Spirts.
The terms Urethane and Varnish are somewhat interchangeable depending on the manufacturer.
My transom is 5' long 16' tall and 1.5 inch thick. I mixed 32 ounces of the old timers formula and had about 8 ounces left over.


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## water bouy (Oct 26, 2016)

Here's what I'm doing which may or may not work: on the trolling motor bow plate I used two coats of Titebond Ultimate, a wood glue, and covered with quality vinyl. It made the 3/4" plywood feel like hard plastic. On the floor at front I'm trying Thomspon's Water Seal and when it dries, two coats of Titebond and covered with vinyl. I'll know in a couple of years how they perform. Replacing them won't be much of a chore. The factory had installed a wood shelf covered with vinyl 12" below the top of the bow and it appears to be rotting and this boat was made in 1997.

On the wood holding a seat across one bench I'm trying two coats Rustoleum Restore 10X. It says it's 10x thicker than paint and I believe it. They will mix it any color you like. I spread it with cheap foam brushes and the surface feels like very rough sandpaper which may be hard to clean. We'll see. I could not get it smooth at all so I'll probably cover it with vinyl some day.

Just found out the Rustoleum will eventually peel and flake off. It would have been nice if the person at Home Depot had mentioned the class action lawsuit.


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## richg99 (Oct 26, 2016)

*"plywood is the most flexible of all wood - meaning it expands and contracts severely with the weather"*

This statement says to me....DON'T fit your plywood too tight. Give it a little room around the edges and where 2 sheets abut. 

richg99


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## Lonedrake (Oct 26, 2016)

I was lazy and did a temporary floor in my duck boat. Put 3/4 regular non treated plywood in it 3 years ago. I use the boat almost every weekend. It does stay covered when not in use though.


Sent from my iPhone using Tapatalk


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## Shaugh (Oct 27, 2016)

One bit of advice that you almost never hear is to design your flooring to be "modular" or more easily understood... make it in pieces that can be easily removed and serviced. Don't make one giant floor. Break it up into sections that can be easily serviced and replaced.... then you don't have to sweat bullets over whether your plywood lasts "forever".... If a part gets soft just pop out a few screws and replace it.... make whatever you do with that mindset and you'll worry a lot less....


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## richg99 (Oct 27, 2016)

Great advice from Shaugh. I put my floor in in two pieces, for that very reason. Much easier to install, too. 
richg99


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## CedarRiverScooter (Oct 27, 2016)

Epoxy sealer will cost as much as the plywood itself. Go with the varnish mix. So what if it only lasts 25 years . . .


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## LDUBS (Oct 27, 2016)

Huh, reading here that plywood is not dimensionally stable? I've learned just the opposite to be the case (when compared to solid wood boards/lumber). I might be misunderstanding something here.


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## Johnny (Oct 27, 2016)

Lay some dimensional lumber out in the weather
lay some 1/2" untreated/unpainted CDX plywood beside it and see what happens.
smaller scrap pieces will not warp too bad because of the light stress within the plies.
half to full sheets will be worthless in a week (or less).
CDX is an exterior grade plywood - - - pine veneers with waterproof glue.
BUT-it will still warp and twist if not installed on a rigid frame, such as a deck.
T1-11 house siding is a prime example of CDX plywood.
look at any building with T1-11 siding and you will see vertical stress cracks all over it.
and if it was not properly primed and painted, it may experience "dry rot"
even with the exterior glues in the laminations.

yes, on the other end of the spectrum is that furniture grade plywood used
for interior projects, cabinets, furniture, etc is very stable.
if screwed to a rigid frame, CDX will remain "mostly" flat, but still moves within.
during my sign making career, I have used hundreds of 4x8 sheets of 
MDO (medium density overlay) plywood for roadside signs.
some have been in the elements for over 15 years and still as flat as when I put them up.
unpreserved wood is like a sponge - it will absorb moisture and react accordingly.
The preventative measure is to protect it from within with primer, paint or varnish.
anything reduced will soak deeper into the wood fibers thus providing a moisture barrier
with subsequent coatings applied to both sides and all edges.
the reducer will allow the mixture to soak deep into the wood, when the reducer evaporates,
the varnish (or primer) is left behind . . . . then, the wood will be a little more stable.
and like said above, avoid large panels when possible.
-or- use a higher grade of plywood; such as marine grade or MDO signboard material.
many of the Big Box Stores carry the MDO signboards for about $48.00 a 4x8 sheet of 1/2".
MDO is already sealed both sides at the factory - and is strongly recommended on tin boats
for transoms, decks and hatch covers.
does that make sense ?












.


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## LDUBS (Oct 28, 2016)

Johnny said:


> Lay some dimensional lumber out in the weather
> lay some 1/2" untreated/unpainted CDX plywood beside it and see what happens.
> smaller scrap pieces will not warp too bad because of the light stress in the plies.
> half to full sheets will be worthless in a week (or less).
> ...



Yep, makes a lot of sense - thanks. CDX is far from "waterproof". I've spent 30+ years doing all kinds of woodworking (mostly cabinets/furniture) but other than a mahogany deck on a small sailboat back in the late 70's, I'm not a boat builder. From what you say about MDO, it would be a great choice. I assume much more expensive than exterior ply but much cheaper than marine grade and I see that it may have an added advantage of weighing less than other plywoods, especially marine grade.


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## surfman (Oct 28, 2016)

LDUBS said:


> Huh, reading here that plywood is not dimensionally stable? I've learned just the opposite to be the case (when compared to solid wood boards/lumber). I might be misunderstanding something here.



I have always heard the same thing in fact I used to work in the cabinet business years ago and Formica would no guarantee their product if used on plywood because the ply wood was much more stable and did not expand and contract due to temperature and humidity due to the fact that the grain is laid up in opposite directions, particle board would basically expand and contract at the same rate as the Formica and would prevent edge chipping, plus it is less dense than particle board and will suffer denting a lot easier. I also don't buy the statement about using 3 sheets of 1/2 inch is stronger than 2 sheets of 3/4, the end result is exactly the same. Sure if you leave it out in the rain unprotected it will go bad. there are many reasons some plywood is better than others and usually 1/2" CDX only consists of 3 plys therefore it is no where near as "stable" as 5 ply plywood. CDX is not intended for outdoor use with no protection from the elements. It is intended as an underlayment for roofing and that is it.

I don't recommend it but, I also don't have a problem with using pressure treated plywood as long as it is sealed to prevent the copper in the wood from coming in contact with the aluminum. It is used on may pontoon boats but, they usually add an insulator tape of some sort between the wood and the metal. Coating the wood with many coats of varnish or a couple coats of epoxy would also help. There is a marine grade PT Ply that is made the old way with arsenic and less copper, it has more plys and is a high grade and expensive. Basic PT ply that you get at the lumber yard today has a much higher concentration of copper and is soaking wet as well. If you use it allow it to dry stacked in a way to allow air to circulate around it for at least a month. It will be warped but it does not matter since you are going to screw it down anyway. select the best pieces and cut your shapes, then clean and sand it using a belt sander before painting. It will last forever. But, the easiest, cheapest and still a very good way is to just use good old CDX and seal it well with varnish or epoxy. Do not use polyester type resins, they will not hold up without glass!!


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## LDUBS (Oct 30, 2016)

surfman said:


> LDUBS said:
> 
> 
> > Huh, reading here that plywood is not dimensionally stable? I've learned just the opposite to be the case (when compared to solid wood boards/lumber). I might be misunderstanding something here.
> ...



Thinking about how it is manufactured, it has always been kind of surprising to me that any movement occurs with particle board or MDF. Though for cabinet cases, MDF is considered very stable, especially when compared to glued up panels. I think what caused my original head-scratching was that I was thinking of dimensional stability as opposed to warping/de-lamination of exposed plywood. The point you guys make that protection is required is well made and should probably apply to any wood product used on a boat.


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