How 'bout that Home Depot (Baltic?) Birch?

Hello everybody. First post. I'm glad I found this forum. Can't believe I didn't find it sooner. I've become a boat nut the last 4 years and now own 3 different boats. Sigh.

Anyway I'm sure I'll be checking out these forums a lot and asking lots of questions in the future. For now, a quick question. I bought a 23' Reinell Bowrider about a year ago and bought it cheap because the gas tank leaked. Just got around to ripping the deck up and sure enough the ~75 gallon tank had crevice corrosion. So now I'm gonna create a hatch about 5' long and 3 feet wide. Going to be bolted down 99.9% of the time so it's really not exactly a hatch. Just want access if the tank ever decides to go south again.

So I called my local lumberyard. They quoted me $66 for a 4'x8' piece of "external" baltic birch. Just happened to be at Home Depot today and noticed that they had the same size birch (didn't say Baltic) for $34. I know some might insist on marine plywood, but looking past that is the Home Depot stuff going to be inferior to the lumberyard stuff? In other words, is it "known" that you shouldn't use Home Depot birch for "external" purposes?

Thanks in Advance!

 

First thing....with a three foot span you're going to need to reinforce that hatch, regardless of the ply you use. Make sure you do this or you'll end up with a spongy hatch. As far as the plywood is concerned.....Birch is NOT a rot resistant species and I believe that ply you're talking about is interior grade. This means, among other things that the glue is not waterproof. Not good. So what might work, and not break the bank.....I'd suggest two types of plywood. First Radiata Pine plywood. I've used this in many places on my boat (in non-structural areas like interiors and on the flybridge) with no issues over the past 5 years. HD carries this in 3/4. See the link here: http://www.araucoply.com/default.asp

You could also use MDO or Medium Density Overlay. Companies make billboards and road signs out of this stuff. You'll find it at good lumberyards.

I've learned from the experts on this site that properly prepping plywood will make it waterproof. First, coat the plywood with three coats of epoxy resin on all 6 sides. Pay particular attention to the edges. Radius your corners a bit so you don't have sharp edges. If you want your hatch to last forever, over drill the places where you're going to place screws. Get a 3/8" Forstner bit. After the ply is coated 3X, and the 3/8" holes are drilled, put some packing tape on the underside of the holes and then fill each hole with epoxy resin. Once the resin is cured you can drill through the center of the 3/8" hole. You now have an epoxy "grommet or doughnut" surrounding your screw and your plywood hatch is never going to rot. Hit it with a sander, put some non-skid and paint on it and you're all set. If you really want it to wear well, put a layer of 4 oz. fiberglass cloth over it.

Good Luck with your boat.

MIA

 

Thanks for the reply. Excellent tips about the the woods. I had never heard of Radiata Pine. Nice to know the alternatives. Also, will definitely use the tip about creating an "epoxy grommet". Brilliant

 

You're welcome, and by the way welcome to the forum. PAR (Paul Riccelli) suggested that epoxy grommet idea to me years ago. It's a little more prep work but if you plan to keep a wooden boat for a long time, I think it's worth the effort. One last thing. You might want to think about paring your boat inventory down. I used to own a couple of boats but soon realized that I could only use on at a time. I saved a lot of money (which made my wife very happy) by making a choice and focusing on just one. Just my 2 cents. Have fun out there.

 

If in the USA and selecting from APA plywood grades, stick with underlayments or exterior, as these will have a waterproof glue. If it doesn't, there's no amount of coating you can apply that will prevent the non-water proof glue veneers from separating. Additionally, instead of using a big, thick hunk of plywood to bridge the gap, consider using two thinner pieces of plywood. So if you need 3/4" stock, use two layers of 3/8". You can orient the grain to add some additional strength, it's easier to handle the smaller sheets and it'll be stronger and stiffer once glued together too. Baltic birch is commonly a "cabinet grade" not an exterior grade, so I'd question the seller about the adhesive used. If they can't answer, go some place else. BTW, a cabinet grade will delaminate if you pee hard on one side of it.

 

Baltic birch has higher sugar content wich nakes it prone for mold and rot so if used it must be properly sealed. See if the ply is made in Finland, if so it's glued with fenol which is weather and water proof. Dunno about Swedish ply but Norwegian ply not necessarily as they use also other glues.

Teddy

 

Birch plywood can be had from certified aircraft grade to rubberstamped junk. No one can tell what your local store sells under the name of "baltic birch ply". All birch ply is heavy compared to ply made from other species.

 

Old saying.
You get what you pay for.

 

Generally, in the big picture of a total project cost, skimping on the quality of the plywood, particularly the hull shell isn't economical. There's plenty of places to save a buck, but the stuff that keeps your socks dry isn't the best place to start.

 

You can tell the difference between cabinet grade birch plywood and Baltic birch with just a casual glance. I mostly shop at Menards rather than Home Depot as its closer but Menards carries both. Baltic birch has many veneers just like BS1088 marine ply and has an exterior glueline, its nice stuff but heavy and non durable but remember, okoume marine ply is also a non durable species, so both require proper epoxy sealing. The most reliable plywood I would buy at a big box is as MIA mentioned MDO plywood, it is much better than the Fir marine ply that Menards sells.

 

In my limited experience I have found that you need to put fiberglass cloth on both the exterior and interior surfaces to seal plywood. Multiple coatings of epoxy never seemed to work for me. I also agree with using multiple layers of plywood. I thicken the epoxy between the layers with cabosil. This will fill any gaps between the layers. Also when gluing the layers together start in the middle and work out to the edges. I screw the layers together. Then remove the screws after the epoxy has cured and fill the holes with thickened epoxy.

 

You don't need to seal plywood, though it can be advantageous in the marine environment. Not just both sides need to be encapsulated, but as the word suggests, every edge, every side, every penetration, notch, cutout, etc. needs a minimum of 10 mils (cured film thickness) to be considered a minimum for waterproofing the stuff. If there's more, such as when sheathing is added, the better. Some species do seem to need a sheathing like Douglas fir, though birch seems to do well with out it. You can thicken epoxy between plywood layers, though a stronger joint can be had if it's straight epoxy. Lastly, as Chuck has mentioned start in the middle of a panel and work to the edges, to help move air gaps and voids. I prefer to "roll" the panel, as I weight it down or screw it together. Just slightly bend the panel as you drive screws from the center to the edges and the air finds the least path of resistance to escape. Birch plywood is a fair bit heavier than the more commonly available okoume, meranti and Douglas fir, so take note on weight sensitive projects.

 

It sounds like you have been using US made fir plywood. I would be inclined to agree with you on both counts if this were the case because Fir has a tendency to check badly although a few coats of a 100% solids epoxy with good elongation should be fine on the inside with cloth on the outside. Also American plywood, even that pretending, i mean proclaiming to be marine plywood does not have enough veneers to be a nice stable stiff panel in thinner sheets. Real imported marine ply manufactured to BS1088 has many more veneers for a given thickness and is stiffer and more stable and you don't need to laminate two together unless you are making a curved panel such as a beamless cabin top in which case, of course you would laminate three or more thinner plies. Also Real marine ply is typically manufactured with hardwood veneers with tight grain with no football repairs or defects and has little tendency to check so it is easy to epoxy seal without cloth. You get what you pay for with plywood but it may save you money in the long run.

 

Steve, you know my level of understanding on plywood, encapsulation and waterproofing with epoxy. You're correct that the Lloyd's certified stuff (well, what used to be) is well regarded and I'd further the BS-6566 stock often rivals the quality of the BS-1088 (meranti). Of course, careful inspection of each sheet is necessary, but I've see rare voids in BS-6566 any only one or two on a BS-1088 sheet. Surface defects are more common in BS-6566, though at nearly half the cost of a Joubert 1088 sheet, you can be more economical. There are a few Asian imports (Aquatech and Hydrotech) that are proving very good substitutions too. I've found the lesser grades of meranti can check pretty badly if well stressed, so I always skin these. Additionally, the filler in these surfaces don't like much stress or bending so sheathing is a good idea. In the end it's what you find and need that'll dictate what you need to do.

On a traditionally built yacht, the planking would typically be some of the finest on the build, for obvious reasons, so short cutting in this area isn't a wise investment in materials and/or labor. More modern build methods can tolerate some adjustment in this regard, but on a small boat not so much, because you just can't amortize the costs in materials and labor.

 

Yes, I agree for many non cosmetic uses the BS 6566 is a good cheaper substitute and in fact my son is looking at buying some ply for some remodeling work on his Simpson 42 cat and is probably going that direction. I always sheath the exterior regardless of what ply I'm using but I don't feel its necessary to use cloth on the inside as Chuck suggested as long as it is properly epoxy encapsulated. I think meranti offers a very good value in marine ply as long as you can tolerate the weight penalty over okoume, its stiffer and more rot resistant. Iv'e been a boatbuilder for over 45 years now in several different countries so have used plywood made in many different countries to British standards and I don't think ive ever seen a void in 1088. I know that Australia and New Zealand have a joint standard of their own that iv'e seen some claim to be better than 1088 but i really can't see how. I have built dinghies many years ago out of luuan underlayment that have lasted 20 years but that stuff just doesn't seem to exist anymore and when a paraplegic friend built a little 12ft tri some years ago and do a nice job only to have it delam before he even got to use it much I
I just stay away from anything without the BS label now for anything that's going to consume much labor.