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Old 05-12-2017, 22:48   #1
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Sealing plywood fit out.

Will be doing some fitting out inside our steel yacht using structural plywood. It stays mostly dry inside.
It needs to last about ten years.
Do I need to seal the ply with one of the expensive two pack products, or will a coat of latex house paint do the job?

Regards,
Richard.
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Old 05-12-2017, 23:05   #2
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Re: Sealing plywood fit out.

Well you might get 10 years by doing nothing more than edge sealing the plywood with a latex timber primer but the next owner won't like you...
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Old 06-12-2017, 12:44   #3
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Re: Sealing plywood fit out.

Thanks for your response Wotname.
Was intending to paint the complete sheet, not just the edges.

Regards,

Richard
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Old 06-12-2017, 15:50   #4
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Re: Sealing plywood fit out.

Richard, allow me to assume that you are wishing to use structural ply without a epoxy barrier for cost reasons (and perhaps for time constraints). I note you only need a 10 year life and I also assume it doesn't matter what happens after that.

The achilles heel of all plywoods is the multiple exposed end grains on the edges. I think you might get 10 years from Aussie manufactured structural ply with just sealing (two coats minimum, three better) the end grain with acrylic wood primer but don't use an exterior product as they need UV for full curing i.e don't use Dulux Weathershield or similar

Coating the flat surfaces (in your instance) probably won't increase life all that much and would only add to time and cost considerations. However it won't hurt and perhaps is needed for ascetic reasons.

If it was me and if I was subject to the same constraints (time & money), I would almost always coat the end grain with an 100% solids epoxy (e.g. Bote Cote or similar). If I was really pushed for money, I would use an industrial equivalent of Everdure (which is not 100% solids but is a reasonable epoxy product).

Watyl make one but I can't recall its name ATM. It is about half the price (or less) of Everdure and comes in a 4 litre pack (2 l of part A plus 2 l of part B). It is used exactly the same way as Everdure i.e. 4 coats wet on wet with the first 2 coats well thinned. Goes on pretty quickly and much faster curing than a 100% solids epoxy. While it is no where as good as say Bote Cote, it would be way better than acrylic wood primer.

I would only coat the flat surfaces with acyclic paint for appearance purposes.

Sealing the edges with a 2 pack epoxy (of any sort) would pretty much guarantee your 10 year requirement in a relatively dry area.

Note I have used some brand names but similar products from other manufacturers would suffice.

FWIW, my now 40+ year all plywood boat (31') is still as good (or perhaps better) than when launched (but it isn't structural ply ).
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Old 06-12-2017, 19:07   #5
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Re: Sealing plywood fit out.

I agree. At least you have to seal the end grain with some sort of epoxy even if it the stuff that you buy in the double syringe from the hardware store. If you can heat up the edge with a heat gun (or even in the sun) first then it will work even better.
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Old 07-12-2017, 01:34   #6
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Re: Sealing plywood fit out.

Don't know what the EPA or the Australian equivalent have to say about it, but regular treated plywood lasts at least about ten times longer than untreated. Big box store treated ply is pretty rough, but smoother grades may be available; I've never looked, I just pick the best sheets and dress the individual panels accordingly after cutting them out.

There are several different types of 'treatment' a little research goes a long way toward finding the proper one for your application.

The sheets must be properly dried before use, and dust masks are best worn when cutting and sanding.

Technically you wouldn't have to seal it at all, but to avoid problems with distortion induced by differential water absorption (as with any wood construction), all surfaces should be painted or sealed. For interior work the choices could run from latex house paint to west system epoxy.

You may not want to make a galley table out of it though...
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Old 07-12-2017, 02:49   #7
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Re: Sealing plywood fit out.

The CCA or ACQ treated plywood may not fit well if the OP has a steel boat.
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Old 07-12-2017, 03:20   #8
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Re: Sealing plywood fit out.

when i fitted out our 63 ft alloy boat i set up a pvc plastic lean too spray shed under the boat ,used planks and oil drums as trestles.

all the precut panels,floor undersides, lockers,etc got 2 coats of an industrial epoxy primer either sprayed or rollered on.

high gloss ,high wear surfaces would then get a quick sand and 1-2 coats of 2 pack polyeurathane.
other surfaces that needed a top coat would get a coat of epoxy enamel

doors and floors were first stained,then sprayed or brushed with isocyanate floor varnish,2 coats.

interiour battening we used tanalised pine strips attached to the alloy framing,un painted.

head liners we used gel coated GRP panels,these we used a 4x8 formica covered table for the lay up using either 2 coats of gelcoat and one layer of 450g/sm or 2 layers 300g/sm chopped strand mat.

for finishing trim we used 8mm x 1 or 2 inch iroko strips sprayed with isocyanate varnish.

after 18 years i have only had to replace 1 floor panel in the shower,that was constantly getting damp.
plywood is all reasonable quality interiour/exteriour grade plywood,but not marine grade

the epoxy enamel has some yellowing,but otherwise easy to clean and servicable.

in total we probably used about 20 gallons of paint
and about 100kg resin and gelcoat.

lower quality paints start looking tatty after about 5 years.
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Old 07-12-2017, 14:04   #9
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Re: Sealing plywood fit out.

Thanks everyone - I value your input.
Seems like using latex paint will be a false economy, so will go with a high build epoxy, especially around the edges.

Regards,
Richard.
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Old 07-12-2017, 22:31   #10
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Re: Sealing plywood fit out.

Quote:
Originally Posted by boden36 View Post
Thanks everyone - I value your input.
Seems like using latex paint will be a false economy, so will go with a high build epoxy, especially around the edges.

Regards,
Richard.
If money is tight, consider using the industrial equivalent of Everdure as mentioned above. It is a first generation epoxy, considerably cheaper a high build epoxy and way faster to use.

A high build epoxy will give you many many decades of life, Everdure equivalents will give at least 1 decade (IMO / IME).
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