Interior plywood

[cdawgs65]

What is the best plywood to use for interior work, bulkheads/v-berth ? thanks

[Hirilondë]

Any answer to this would be subjective in many respects. It is all a matter of what characteristics are required of the plywood. There are applications on the interior of a plastic boat where plain old fir plywood would work just fine. There are other applications where the benefits of BS 1088 okoume marine plywood might justify the expense.

If it was a structural bulkhead, that was tabbed to the hull one might easily justify the integrity, rot resistance and expense of the BS 1088 graded material. If it were the painted tops of a berth, the cost savings of the fir plywood might be very appealing. The word "best" is very subjective. There is no carte blanche answer.

[mitiempo]

At least exterior grade made with waterproof glues. BS1088 ply is best but pricy. If it is going to be covered with laminate or will not be visibls as for berth tops fir exterior is fine. But if it will be visible I'd use okoume or meranti as they will take a paint finish much better than fir.

[cdawgs65]

How about luaun is this suitable, it does have a finished side and seems pretty good grade? 3/4", 1/2"?

[mitiempo]

As long as it is "exterior grade", in other words uses water proof glue, not just water resistant. I treat the interior as a place where dampness can be expected. How are you finishing it?

[Quetzalsailor]

Ditto the previous post (his post hit as I was logging on(!)). It's a boat; it's exterior.

Luan's pretty lousy stuff in general, that's one reason it's cheap and used for underlayment. It's often not well glued nor made with watertight glue. There are lots of Southeast Asian species which are related to Luan; some are much better than others. Google 'Luan, Meranti, Philippine Mahogany, etc.' for more than you'd want to know or could use.

I think you can get away with using Luan if you're careful and free with the use of epoxy coatings to keep it dry, encapsulated. Of course, the epoxy will run the as-built cost up. The previously mentioned B1088 grade Okume is rated for quality and good glues. Okume is not naturally rot resistant, like Mahogany, but it's supposed to be treated for that lack. I'd be sure to coat it out as well.

I've used Home Despot-quality Red Chinese plywood for utility uses in Quetzal. I coated it out and I have several years in service for the components. Quetzal has marine plywood of unknown core species for bulkheads and backup work (see my posts on Ports); I think the glue is Urea Resin, and as such is susceptable to delamination with long enough exposure to varying amounts of water. Where possible and where necessary, I relaminate the parts and coat them out in epoxy. I'm in the process of doing that sort of repair and will post.

[cdawgs65]

Thanks, I had Googled it right before posting, so thanks for backing my thoughts up!

[David VanDenburgh]

Does anyone have experience with Lowe's marine-grade plywood? It's the only local source of reportedly marine-grade plywood, and it's only 66.00 for a 3/4" sheet. Would it be false economy to use something like that for the interior reconstruction of the Ensign my students are restoring? We are on a very tight budget, but I'm not willing to compromise the value of the boat by installing inferior plywood. If we *ought* (omit: "have") to go the Meranti BS 1088 route, we will, but OUCH.

Thanks.

[Hirilondë]

According to Lowes' web site they don't carry any marine plywood. So I can't find out what it is. I can't imagine that what ever this plywood is that your local Lowes is carrying is any more than fir plywood with a waterproof glue that they are calling marine grade for the sake of marketing. Ask them who gave the plywood the grade marine. I doubt you will get a straight answer, the salesman probably won't know and likely doesn't even know what the standards supposedly are to make it marine grade. Lumber and lumber products grading these days can be a very deceptive representation. There are so many organizations that perform this service that it is becoming more and more meaningless. In the end, no one is guaranteeing you anything. Lloyds of London is no longer certifying plywood. The use of the grade BS 1088 is a standard they set up, but there are manufacturers today who market their material as meeting this standard when in fact it does not. Some of the plywood boat builders I know have found some brands to delaminate before or during construction. Two of the few brands that still seems to manufacture to the standard originally set by Lloyds are Joubert and Bruynzeel.

But again I suggest that every application within a boat requires different characteristics, so I don't see how anyone can give one answer that would be definitive for all applications. And I am not even sure what you mean by you are not willing to compromise the value. Value is in the eyes of the beholder and most people won't have a clue what you used in the restoration. And those few who might know and care will certainly consider the use of a fir plywood for bulkheads a serious compromise in value.

1. Are you making the decisions regarding which plywood to use on perceived value by a prospective buyer of the boat?
2. Are you trying to teach your students to evaluate value based on the wise choice of materials?
3. Are you evaluating value based on the choice of materials that will meet the requirements of the application yet keep costs as reasonable as possible?
4. Do you evaluate value based on using the highest standards everywhere regardless of cost?

I don't direct these 4 questions necessarily at you David, but the reader of this thread in general. Everyone has to decide for themselves what value means. I think value requires an understanding of the item one wishes to evaluate for this value.

The bottom line to this whole issue of choosing plywood is that there is no answer for all applications unless money is no object. And since for most of us money is a rather large object the choice for any application has to factor this in. Paying $300 a sheet for BS 1088 okoume marine plywood for the removable covers for setee compartments is a waste in my opinion. Purchasing cheap pretend to be marine plywood from Lowes for a tabbed in structural bulkhead is a waste of the effort of the work in my opinion as well.

I'm sorry if this "answer" just complicates the situation, but anyone who thinks any simple answer to this question has any value is sadly mistaken.

[David VanDenburgh]

Purchasing cheap pretend to be marine plywood from Lowes for a tabbed in structural bulkhead is a waste of the effort of the work in my opinion as well.

That's what I wanted to know. Thanks for a thorough response.

Regarding value, I understand your points, but I think that there are, in fact, a few standards (i.e., quality work, quality materials) that apply to boat value in an objective sense, especially given the milieu of the Plastic Classic Forum. I know that there is a certain amount of relativity - all that beauty in the eye of the beholder stuff - but I would also expect that there are certain criteria that comprise quality, mediocrity, or inferiority when it comes to boat maintenance and repair. That seems to be where your reply concluded. I appreciate your thoughts.