Repair & maintenance: waterproof Plywood

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waterproof Plywood

Printed From: Yachts and Yachting Online
Category: General
Forum Name: Repair & maintenance
Forum Discription: Questions & tips on the subject
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=13281
Printed Date: 10 May 25 at 3:21pm
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Topic: waterproof Plywood

Posted By: pij27
Subject: waterproof Plywood
Date Posted: 11 Mar 19 at 8:48am

I am looking to replace some plywood deck panels on a dayboat. Does anyone know of a good method of waterproofing or sealing these panels. They will be placed over the hull to give a level floor and if the bilge fills up with water then will be in contact with it.
Any help or suggestions please?

Replies:

Posted By: JimC
Date Posted: 11 Mar 19 at 9:57am

Not much is really waterproof for ever. Will they just get wet or will they stay wet? If they'll be normally dry then any good paint system will do the job.

Posted By: pij27
Date Posted: 11 Mar 19 at 10:17am

This is decking planks around the centreplate, so underside will be in contact with bilge if boat left unattended for a while. otherwise just from spray or rain. Did wonder whether to use a wood hardener on the edges first and then a few coats of gloss paint?

Posted By: Sam.Spoons
Date Posted: 11 Mar 19 at 11:34am

Is this the cockpit floor, Is weight an issue, if not what about fabricating floorboards from recycled plastic decking boards? https://www.kedel.co.uk/recycled-plastic-decking.html

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"

Posted By: pij27
Date Posted: 11 Mar 19 at 12:24pm

original planks only 10mm thick. use a movable small bar to hold in place.

Posted By: JimC
Date Posted: 11 Mar 19 at 1:05pm

TBH, assuming its not a racing boat and you're concerned about budget I'd be inclined to use exterior grade ply, reasonable paint, and make up some templates so I can make new ones easily. Yes you could get into wrapping them in glass/epoxy and they'd cost 4 times as much and last 3 times as long. Sometimes you can overthink!

Posted By: Rusty69
Date Posted: 11 Mar 19 at 2:04pm

Coat with epoxy resin.

Posted By: pij27
Date Posted: 11 Mar 19 at 2:26pm

Thanks Jim, sounds like an easier plan. cut to size and a few coats of gloss?

Posted By: jeffers
Date Posted: 11 Mar 19 at 3:11pm

Originally posted by pij27

Thanks Jim, sounds like an easier plan. cut to size and a few coats of gloss?

Possibly some really thinned out varnish first too might help. Just to help seal the surface and the ends before you top coat. I did this on a boat I took back to wood. it really soaked in and where the paint has had a few knocks there is no sign of water ingress.

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Paul
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D-Zero GBR 74

Posted By: Sam.Spoons
Date Posted: 11 Mar 19 at 4:14pm

Originally posted by pij27

original planks only 10mm thick. use a movable small bar to hold in place.

Thinest I found in plastic 20mm but there may be thinner out there, and they would last forever without any maintenance.

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"

Posted By: Riv
Date Posted: 15 Mar 19 at 5:11pm

Our club Wayfarer needed new bottom boards. It's on a drying mooring on a slope so the aft end of the boards are often wet and also when we don't pump it out.

We brought 10mm ply from local builders merchant and coated it with 4 coats of this:

https://www.screwfix.com/p/no-nonsense-water-repellent-seal-clear-5ltr/57474

They had an extra coat each year and apart from looking rough there is no delamination.

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Mistral Div II prototype board, Original Windsurfer, Hornet built'74.

Posted By: ColPrice2002
Date Posted: 15 Mar 19 at 7:47pm

A couple of coats of epoxy resin, couple of coats of good varnish, last coat sprinkled with granular sugar.
Allow to set/dry between coats, then wash the sugar off.
You'll have a non-slip coating, and it will last - it's worked on our Wanderer floor boards for many years.

Colin

Posted By: davidyacht
Date Posted: 15 Mar 19 at 9:55pm

Robbins Timber for marine ply. On a previous boat I edge sealed with epoxy, then coated with Deks Olje which worked fine.

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Happily living in the past

Posted By: pij27
Date Posted: 18 Mar 19 at 8:55am

Thanks, will look into the sealant from Screwfix. Sounds like sensible thing to do first is to seal the edges and then either paint and varnish or epoxy then paint.

Posted By: snowleopard
Date Posted: 18 Mar 19 at 10:30am

The big problem with ply these days is it's hard to know what you're getting. Cheap ply with inferior glue, made in China, has flooded the market. It disintegrates in a year or two. It is often marketed as 'waterproof', 'exterior' or 'marine' but is all the same stuff and it doesn't match up to the old BS1088 standard.

Don't touch 'exterior' ply from builders' merchants. Go to a reputable supplier of marine ply such as Robbins and ask them to guarantee that it meets BS1088.

In order of quality/durability, varnishes are :

Epoxy

2-pack polyurethane

1-pack polyurethane

Genuine marine varnish

DIY store varnish.

The big joke these days is stuff bought in DIY retailers labelled 'Yacht Varnish' with small print saying 'not suitable for marine use'!

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One hull good, two hulls better.

Posted By: pij27
Date Posted: 19 Mar 19 at 7:54am

Thanks for the advice, will look at the ply and if not right will change it, looks like seal it with epoxy and then use a decent yacht paint, maybe bilge/locker paint?