Stopping Checking w/out Epoxy

[TomMcKinney]

Is there a way to stop checking of fir plywood without using CPES or epoxy and glass? Has anyone had success with linseed oil/turpentine combos? Can you paint over that?--I have already looked through a number of threads on checking and did not see this approach thouroughly discussed--I'm building an OldWharf Dory Co. Lumber Yard Skiff, ts o the goal is to keep it low cost,, hence no epoxy. I was thinking of using the oil, priming, and painting with the best latex I can find.
I look forward to everyones comments. smile.gif

[imported_Conrad]

Many years ago we used to use a sealer called "Rez". Don't know if it's still available, perhaps some similar product is. That and some regular enamel used to get us a couple of years before the checking would start to appear, it definitely helped. After that, just sand and repaint.

I've seen ply that was just oiled (a friends Swampscott dory) and it held up well with regard to the checking issue, but was ugly. It got dark and stained as it aged, but he didn't care- used it to run rivers here in the NW, so it had a rough life anyway.

[Pekka Huhta]

Plywood isn't a particularly good candidate for linseed oil impregnation, since the oil doesn't go any further than to the outermost ply. Benefits of a combination of oil and a soft oil-based paint is to let a massive piece of wood live and breathe, but plywood can be finished with a tougher paint system.

If the boat stays out of water most of the time, you will be OK by using oil and an oil-based enamel paint. Using water-based latex paints is not a very bright idea over an oiled surface if you think about it for a while.

A problem with linseed oil is that you should allow it to dry for at least week and a half before even thinking of painting. With some paints and varnishes you are able to start the paint job straight over a freshly oiled surface wet-to-wet, but as this doesn't work with many paints I wouldn't encourage to do it that way. If you are not ready to wait a couple of weeks, you'll have to thin the first two layers of paint to get it in the wood.

Pay special attention to the plywood edges: use the oil liberally and apply several layers of 50/50 thinned paint to them before starting with the whole hull.

I'm a bloody traditionalist anyway, but plywood is about the only place where I would suggest using epoxy as a finish. Thousands of plywood boats have been built without it, but it definitely has its advantages on plywood.

And I'm not saying anything about epoxy on timber, most would consider that a troll smile.gif

Pekka

[NormMessinger]

Or, live with the possibility of checks and fix them when they occur.

I'd question your desire not to use epoxy but that was not part of your query.

I've experienced two types of checking. In the marine grade fir plywood, pretty nice stuff actually, the checks were cracks three to ten inches long that occured apparently when the spring wood shrunk. These can be filled and painted over. The second type was in BC exterior ply used on a six-hour canoe. We were building outdoors in bright august sun. The outer ply actually expanded, delaminated and buckled out. I judged the cause was plywood that was not dry and could not take the heat.

In both cases checking has not continued. So, while my experience is with only two boats which are stored inside it looks as if checking will occur early on and can be repaired. The third boat, also a six-hour canoe was saturated with CPES and painted with latex house paint. I have not seen seen checking in it.

Best to ya....

--Norm

[Wayne Jeffers]

Tom,

About a year and a half ago, Ken Swan, a builder from the Pacific Northwest, had a sidebar on this topic with an article in Boatbuilder magazine. He said that linseed oil will keep fir plywood from checking and that there is no need for glassing. (CPES and/or epoxy without glass will not slow down checking.)

I tried Swan's approach on a boat I built last fall. I'll report the results when it has had a fair test.

Swan's method: Give the plywood a generous coat of RAW, not boiled, linseed oil. I paid $10 for a gallon at the local hardware store and used less than half. Apply the oil after assembly, as epoxy glue will not stick to wood that is already oiled. Next day, wipe off all the excess oil on the surface and paint with an oil-based primer. After the appropriate drying interval for the primer, apply the topcoat of your choice. I used Sherwin Williams best acrylic latex.

Norm,

Was boat #3 built with fir ply? Most BC ply available at lumberyards the last several years is yellow pine, not fir. Yellow pine does not check anyway, and would not be a fair test.

Wayne

[blisspacket]

Elastomeric paints. These are the rubberized coatings used on roofs of mobile homes. I used them on a ply boat about ten years ago, but can't give an update as the boat was sold and I have no record of the buyer. I do remember the stuff is soft, picks up and retains scuffs. But it does penetrate, seal, and gives and takes with the weather.

[NormMessinger]

Well, I am pretty sure I can tell fir plywood when I see it. On the other hand I've not actually seen any decent pine ply. If they are hard to tell apart I wouldn't fight about it.

You should have seen my reaction when my daughter in law questioned my identification of a male Ring-necked Pheasant. Phyllis is still laughing about that.

--Norm

[Wayne Jeffers]

Norm,

Visually, they're not necessarily easy to tell apart. Slight difference in color, maybe, with pine being a shade more yellow. The pine is a good bit heavier than fir per cubic foot, but on a quarter-inch sheet, it wouldn’t amount to much. It is possible the stamp could provide insight. Anything from a mill in the Northwest would be fir. If from the Southeast, or with mention of SPIB, would be pine.

Any kind of fir ply has been nearly impossible to find for a while at any building supply outlet around here.

I won't ask about the pheasant . . . ;)

Wayne

[Dave Carnell]

Try Kilz®.

[NormMessinger]

Thanks, Wayne. I have never and never will buy lumber from Lowes or Home Despot if there is an alternative. The little lumber yard I used folded, unable to compete. Bigger outfits have closed, as well. :mad:

However, that begs the question. One of these days I'll go to the large local independent lumber yard and see if I am as smart as I think :rolleyes: I am when it comes to identifying plywood. In the mean time I will continue to beleive the #3 above is fir and that maybe CPES (or perhaps as likely, lack of exposure) prevented checking. tongue.gif

--Norm

[NormMessinger]

Oh, and another thing.... Ya know, I'm inclined to think the idea that treating plywood with a penetrating substance, CPES, raw linseed oil, WEST, et.al., might stop checking even though the glue line stops deap penetration. It is only the outer layer that checks so it is only this layer that needs protection. Right?

Um, Dave? Does Kilz penetrate any more than "regular" paint undercoats or is it primarily a sealer? I've only used it on top of System Three but wouldn't have thought it would do anything to stop checking.

--Norm

[Mr. Know It All]

Never considered using Kilz on a wooden boat. It's a great sealing paint though and I've used it on my house with good results. Tell us more Dave. How did you apply it and what were the results.
Kevin in Ohio