To paint or Not to paint that is the ?

[ezrollin]

I've asked this question on other sites with mixed response so I thought I'd get your input.I'm re-decking a 24" pontoon boat with 3/4" marine grade AB pt/kiln dried plywood, with A side up I'm using Marideck vinyl and MD 101 adhesive .On other pontoon boats that I've looked at the underside is never painted but actually seems to hold up better than the carpeted side,due to carpet holding moisture.My question is do you think that a coat of deck paint on the underside [b]would prolong the life of the deck?The difference of opinion is,"don't paint it,it needs to breathe,paint will trap moist in" and the other is " good deck paint will keep out moisture and ward off fungus".Does anyone know for a fact that wood should be left open on one side so it can "breathe"? It's my personal belief that a good coat of latex deck paint would keep out more moisture than it keeps in but I could be wrong.

[gonzo]

Wood "breathing" is one of those old wives' tales. The cycle of wet and dry checks the wood which eventually allows moisture, bacteria and fungus to penetrate and deteriorate the wood. A paint with fungicide will help prevent organisms from thriving and will stabilize the moisture content in the wood.

[judgegage]

EZ, let me confuse you more or it might just what you are looking for. COP-R-TOX, look at the link below.

http://www.blpmobilepaint.com/arch_p...reatments.html

COP-R-TOX is not a new product, but it still works. My family has used it for building (boats, houses or anything where wood meets water) for as long as I can remember. I know some other boat builders that use it as well.

[judgegage]

Sorry EZ this was removed from above.

A pontoon boat deck gets wet 2 ways, from spray and splash from the bottom or on top from washing, rain...etc. Should you coat it...Yes. What you coat it with is your choice.

[PAR]

Cop-R-Tox is a copper naphthenic product and quite toxic as you might expect. It's a common wood preservative and was once used in pressure treated wood. It will color the wood green initially, though with UV exposure and salt degradation will turn brown in time. It's not something I would recommend just because you can't get it deep enough to be really effective on plywood without an autoclave.

Paint will let wood "breath", though plywood is a wood product and doesn't act like solid wood at all, so shouldn't be treated as such. Plywood is dimensionally stable, so sealing the surface is a good idea. Epoxy is the usual choice if water proofness is truly desired. If you want something less then water proof, then use paints, polyurethane coatings or preservatives. These will offer some protection, but it'll still get wet and eventually have issues as a result.

In most cases pontoon decks fail because they've been covered with something that traps moisture against it. Vinyl and carpet are the big culprits and should be avoided if possible, unless you've encapsulated with epoxy. If you encapsulate, then the vinyl or carpet can't get at the plywood below so it lasts a long time.

[ezrollin]

I just found an informative article on wood finishes that in quite informative.Read the section starting on 15-11 [effects of finishes on water and vapor adsorption] actually read the whole article for a better understanding wood and finishes.I would like to see what conclusion you drew from it.http://www.toolbase.org/PDF/DesignGu...shing_Wood.pdf

[judgegage]

Cop-R-Tox is a penetrate and will penetrate better than most paints. As stated off the BLP information sheet: Recommended Film Thickness - This product is designed as a penetrating finish and film thickness cannot be accurately measured.

Cop-R-Tox is toxic until dry or if it is an enclosed area, most paint and all epoxy is toxic as well until dry. Titanium dioxide is also very toxic, it's used in paints, printer toner and ink cartridges, Oh and your toothpaste. http://www.sciencelab.com/msds.php?msdsId=9925268 And the floride in your toothpaste. http://www.sciencelab.com/msds.php?msdsId=9927595

Cop-R-Tox is still widely used, that's why they still sell it. It is also widely used on bee hives for honey bees, can't be that toxic when dry (a bee keepers job is not to kill his bees). Cop-R-Tox dries in about 24 hour and the toxicity drops as the mineral spirits evaporate.

The cases of copper poison are from prolonged exposure, Sprayed inside a house and the people making copper naphthenic.

You know to think about it, copper naphthenic may kill you. A good friend of mine and wood boat builder (one of the people that taught me) might have died from using copper naphthenic. I think he used it on every boat he built. He was over 90 when he died.

[keysdisease]

If you want your great grandchildren to deal with this deck the next time it needs work, coat it with epoxy and take care to also seal all the fastener holes.

Everything else is scaled down in lifespan from that, and at the bottom of the scale is "no coating."

As you are using marine plywood, and it seems this is a lake use boat from your location, coating it with just about anything will probably help the deck outlast the engine.

Steve

[Dirteater]

Hi ezrollin,
good question,
I've was pondering this one myself a few weeks ago.
I am currently working on a small plywood dory. I am using 1/4" and
3/8" marine plywood. From what I have found, most suggest to seal it
with a few layers of epoxy. (and I did fibre the hull as well). so far I have rolled on about 4 coats of epoxy and I believe that will be enough as I do
still want to paint it. which is the next question...

I plan on using exterior enamel deck paint.
my understanding here is it will do just fine as long as the boat
is not permanently in the water. and will require some touch up year to year.

this is my first build, so I may get corrected here (which is always a good
thing around these parts .) . of course any thoughts are always welcome.
happy building ez.

DE

[PAR]

Ezrollin, the PDF you list as representative and "informative" has the word epoxy is it exactly once, suggesting it is far less informative then you might imagine.

Dirt, once a surface is coated with epoxy, it can be painted without regard for the moisture resistance of the top coats (type of paint). Using house paint is just fine, as the real protection is coming from the epoxy.

[ezrollin]

Discussion is good,we can all learn from it but some of the replies go beyond what I was asking.My post wasn't as clear as it could be so here's a simplified version.Using 3/4 marine plywood [pressure treated / kiln dried]the type which is normally used for pontoon decks.Top side would be covered with Marideck Vinyl and MD water based glue[which they recommend].Would painting the bottom with deck paint only prolong life of the wood or cause premature decay?What I get from reading the article is that if wood is painted on both sides it will protect the wood until the paint barrier is broken,then if water enters the wood it will be retained longer and can lead to decay.I'm not sure vinyl and glue on top would act like another coat of paint.

[PAR]

Paint will not seal the wood unless it's a true epoxy, at which point it will seal better then the average paint, but the wood will still be able to breath, not that this is necessary for plywood. Paint protects the wood from UV and intermittent splashes, but not the soaking it'll get on the bottom of a pontoon deck. Vinyl will not act like paint, but more like a plastic coating, trapping moisture vapor between it and the plywood. I've replaced many decks as a result of vinyl and carpet overlays.

In short, the best protection you can provide the plywood is epoxy encapsulation before anything else (paint, vinyl, etc.). Paint will make it pretty, but that's about it, unless it has a fairly high lead or other "killing agent" content.

[pauloman]

seal with a solvent thinned epoxy like ESP 155
or a moisture cured urethane (probably better as it includes pigment) like Aluthane

paul

[Ike]

Dirt: I have just finished building a wood dinghy with marine ply. It has three layers of epoxy and that is by far enough. I am going to leave it bright. no paint.



Three years ago I built a 12 foot boat using exterior grade plywood and I put on four coats of epoxy and then painted it with Interlux Brightside marine paint. Three years later it looks like new. But as PAR said any exterior grade paint will do.

[Dirteater]

Hi Par,
thanks very much for the follow-up and confirmation.
good advise as always
Her kodak moment should be soon.

Ike,
Good pics! perfect examples of (our friend) epoxy at work, and as you mentioned, they look as good as new.
I truly hope mine should fair as well.
(and by all accounts it should).

thanks again for the help,
I will forge on...

DE