PDA

View Full Version : Attaching plywood to new deck beams



ron ll
03-28-2015, 09:30 PM
I've got the new purpleheart deck beams in place and faired on Snoose's rear deck. I'm going to apply two layers of 3/8" marine ply (liberally CPES'd), then glass cloth and epoxy. The second layer of ply will be bonded to the first with thickened epoxy, but my question is about attaching the first layer of ply to the deck beams. Should it be epoxied to the beams? Or should it be just bedded and screwed down. If bedded, what compound? Should I paint the underside of the plywood and the tops of the beams and then use Dolphinite? How would you do it?

chas
03-28-2015, 11:29 PM
I wish I had the answer to that question. If I was to use epoxy between layers I might consider the sealing of the first layer carefully. Why not just one layer of 3/4", or less? / Jim

shade of knucklehead
03-28-2015, 11:49 PM
I would bed the first layer down with something like lifecaulk or even aquacaulk by dap. I recently made a deck out of plywood for an 82 foot Burger and I bedded the first layer of ply in lifecaulk. All the rest of the layers were bedded in epoxy. It was a big project, three layers in order to come up to the height required to have the last layer be over the aluminum lip at the edge.

I used the lifecaulk because the aluminum and the wood will expand at a different rate, just like your purple heart and the plywood.

If you are having a painted interior its always best to prepaint the underside of the deck, painting overheads sucks

slug
03-29-2015, 01:23 AM
Yah..complety prepare and paint all interior pieces before assembly . You will save very much time.

as for the bonding to frames. Dont know.

Caulking like Sika or 3m will work but iits messy to use ,cleanup and requires substanial clamping pressure to create the bond . Countersunk screws and plywood are not friends

i don't see any reason why you cant epoxy to the frames.

if scarfing the joints is not possible, use butt joints , hollow out the joint on the top, visable layer , then lay a layer of eglass tape across. This will prevent print thru of the joint.

Peerie Maa
03-29-2015, 04:26 AM
I would screw them down and use some form of caulk, or thick old paint to bed them. The screws are the structural strength, so the bedding only needs to prevent damp condensing in there. Dunno why slug mentioned counter sinking, there is no need to countersink the screws because the second layer of ply will cover the heads, just don't use round head screws ;)

Mikey Floyd
03-29-2015, 04:26 AM
I would glue and screw it to the deckbeams unless you are planning on pulling it all off for some reason in the near future. (with epoxy)

Your beams are purpleheart!?

Mikey Floyd
03-29-2015, 04:29 AM
Well, concurrent and conflicting posts! I'm reckoning the field is wide open. Follow your heart's path and know that you have supporters either way!

Peerie Maa
03-29-2015, 04:51 AM
Well, concurrent and conflicting posts! I'm reckoning the field is wide open. Follow your heart's path and know that you have supporters either way!

Some, like Shades, build/rebuild boats for their living.

Mikey Floyd
03-29-2015, 04:55 AM
Some, like Shades, build/rebuild boats for their living.

Although I have moved on now, I have 20+ years in the trade professionally. Gluing a ply deck to the beams is a perfectly acceptable solution. Neither option is 'right' over the other, they offer advantages and disadvantages either way.

Mikey Floyd
03-29-2015, 05:14 AM
I actually don't see the use of glue or bedding as a terribly big deal as far as the beams are concerned. What I would be far more particular about is how the deck edge and openings are dealt with and whether the slight flexibility and movement due to a deck sitting on bedding will be accommodated in a way that won't cause future issues.

Peerie Maa
03-29-2015, 08:15 AM
Although I have moved on now, I have 20+ years in the trade professionally. Gluing a ply deck to the beams is a perfectly acceptable solution. Neither option is 'right' over the other, they offer advantages and disadvantages either way.

OK, although I see that you are now in the delicate no hammers end of wood working. I think the difference is if you want to be able to repair the boat easily in the future, or sell it to someone that you don't like.:D

I actually don't see the use of glue or bedding as a terribly big deal as far as the beams are concerned. What I would be far more particular about is how the deck edge and openings are dealt with and whether the slight flexibility and movement due to a deck sitting on bedding will be accommodated in a way that won't cause future issues.
If the screws are adequate for gauge and number, there should be no movement even if bedded in thick paint or nothing at all.

David G
03-29-2015, 08:16 AM
Yes... I wouldn't be too fussed about how that first layer of ply went down. My own inclination would be to bed it in something (old paint, thick shellac, dolphinite, etc.) or glue it down with something a bit flexible (g-flex, PL Premium). And yes... the more likely cause of future problems is around the edge. Strategies there are way too boat-specific to begin to delineate. And since he hasn't asked about that detail, I'm guessing Ron is comfortable with a strategy there.

ron ll
03-29-2015, 10:16 AM
My concern about epoxy is the old issue of thinking about the next guy. But as the old deck lasted 70 years, I'm pretty sure the next guy won't be me. :) Seriously tho, someone on a previous thread said that when an epoxied deck has to be removed a clever use of a router and maybe a heat gun make that not such a big deal. And by the time this needs to be replaced, Fein or Festool will probably be marketing a special tool to do so. The plywood edges will all get ample coats of CPES and will be detailed carefully.

Yes, the beams are purple heart. A friend was rebuilding a deck on his 55' seiner and gave me his crown cutoffs which were big enough to make my beams. Here is a pic of the beams and carlins around my "troller hole" hatch.

http://i1171.photobucket.com/albums/r560/ron_ll/9CAFB8C4-97F5-4AB9-BC9F-5DBADE09080D_zpskchgmbca.jpg

slug
03-29-2015, 10:33 AM
A ply deck is very stiff. Loads concentrate around the perimeter...the sheer clamp, cabin, ......These edges are important....engineer these bonds correctly

varadero
03-29-2015, 12:05 PM
I made a a rebate in the sheer plank f or the first layer of ply bedde with micro fibres and fastened to the sheer and beams with anchor fast copper nails, the second layer of ply staggered the first, again with the nails. Countersunk bronze screws finished the job into the beams, and the covering board finished the job. Just a squiggle of 5200 down the beam centre to quieten the creaks. 30 years later, 75 foot boat, all is still good. All plys are not equal.

David G
03-29-2015, 12:36 PM
I would screw them down and use some form of caulk, or thick old paint to bed them. The screws are the structural strength, so the bedding only needs to prevent damp condensing in there. Dunno why slug mentioned counter sinking, there is no need to countersink the screws because the second layer of ply will cover the heads, just don't use round head screws ;)

Pardon me while I get fussy about nomenclature.

Countersinking is what one does to get a screw's head flush with the surface (or just barely below). Typically used with a flathead screw, and requiring a chamfered (conical) hole. I think you're thinking of counterboring... which allows you to embed a screw deeper than that. That counterbore has straight sides. The counterbored screw is then oftimes covered with a bung of a matching species.

One WOULD want to countersink the fasteners in that first layer of plywood. And probably the second, as well... but one might choose to counterbore the top layer.

https://s.yimg.com/fz/api/res/1.2/m8O55ndo4kmLd5rZm7dgsA--/YXBwaWQ9c3JjaGRkO2g9MzQwO3E9OTU7dz00MDA-/http://images.meredith.com/wood/images/p_wood_words6.jpg

Peerie Maa
03-29-2015, 12:47 PM
Yah..complety prepare and paint all interior pieces before assembly . You will save very much time.

as for the bonding to frames. Dont know.

Caulking like Sika or 3m will work but iits messy to use ,cleanup and requires substanial clamping pressure to create the bond . Countersunk screws and plywood are not friends

i don't see any reason why you cant epoxy to the frames.

if scarfing the joints is not possible, use butt joints , hollow out the joint on the top, visable layer , then lay a layer of eglass tape across. This will prevent print thru of the joint.


Pardon me while I get fussy about nomenclature.

Countersinking is what one does to get a screw's head flush with the surface (or just barely below). Typically used with a flathead screw, and requiring a chamfered (conical) hole. I think you're thinking of counterboring... which allows you to embed a screw deeper than that. That counterbore has straight sides. The counterbored screw is then oftimes covered with a bung of a matching species.

One WOULD want to countersink the fasteners in that first layer of plywood. And probably the second, as well... but one might choose to counterbore the top layer.

https://s.yimg.com/fz/api/res/1.2/m8O55ndo4kmLd5rZm7dgsA--/YXBwaWQ9c3JjaGRkO2g9MzQwO3E9OTU7dz00MDA-/http://images.meredith.com/wood/images/p_wood_words6.jpg

talk to the slug, 'cos the Nick 'aint bovvered. :D

David G
03-29-2015, 12:51 PM
talk to the slug, 'cos the Nick 'aint bovvered. :D

Bovvered... that's one of those danged Brit words that means something weird, ain't it? Like strapped spread-eagle and naked to the bonnet of a lorry with ones tongue sprattled to the windscreen. Nevermind... I'm just being a prat and blowing the wind up your skirt... or somesuch <G>

Yeah... I don't know what slug had in mind, neither.

Peerie Maa
03-29-2015, 12:55 PM
Bovvered... that's one of those danged Brit words that means something weird, ain't it? Like strapped spread-eagle and naked to the bonnet of a lorry with ones tongue sprattled to the windscreen. Nevermind... I'm just being a prat and blowing the wind up your skirt... or somesuch <G>

Yeah... I don't know what slug had in mind, neither.


https://www.youtube.com/watch?v=zV1zK8zRCPo

ron ll
03-29-2015, 12:59 PM
Counterbore 3/8" plywood? That is fussy. Plus it's creating a whole lot of edges into the plywood interior. Unless someone tells me it's crazy, I'm starting to think epoxy the first layer to the beams and fasten with an air stapler with galv. staples.

As you alluded to above David, every boat is different. This boat is built so hellishly stout that this little bit of plywood deck isn't really holding it together. Most of this little aft deck is a large hatch opening. The plywood just surrounds that. I'm pretty sure BOTH layers can be gotten out of one 4x8 sheet.

David G
03-29-2015, 01:21 PM
Counterbore 3/8" plywood? That is fussy. Plus it's creating a whole lot of edges into the plywood interior. Unless someone tells me it's crazy, I'm starting to think epoxy the first layer to the beams and fasten with an air stapler with galv. staples.

As you alluded to above David, every boat is different. This boat is built so hellishly stout that this little bit of plywood deck isn't really holding it together. Most of this little aft deck is a large hatch opening. The plywood just surrounds that. I'm pretty sure BOTH layers can be gotten out of one 4x8 sheet.

The staples will simply serve as clamps until the epoxy cures. I'd lean toward ss... only so there's a good bit less chance in the future that someone will experience rusty drips. OTOH... those rust drips can be a useful alert. Have fun!

Bob Cleek
03-29-2015, 01:28 PM
I wish I had the answer to that question. If I was to use epoxy between layers I might consider the sealing of the first layer carefully. Why not just one layer of 3/4", or less? / Jim

If you don't have the answer, why post? Save the bandwidth.

Bob Cleek
03-29-2015, 01:32 PM
I would screw them down and use some form of caulk, or thick old paint to bed them. The screws are the structural strength, so the bedding only needs to prevent damp condensing in there. Dunno why slug mentioned counter sinking, there is no need to countersink the screws because the second layer of ply will cover the heads, just don't use round head screws ;)

Best answer so far.

Bob Cleek
03-29-2015, 01:33 PM
Well, concurrent and conflicting posts! I'm reckoning the field is wide open. Follow your heart's path and know that you have supporters either way!

This is helpful how? The field isn't wide open. It's just cluttered with people who don't know what they are talking about.

Bob Cleek
03-29-2015, 01:35 PM
OK, although I see that you are now in the delicate no hammers end of wood working. I think the difference is if you want to be able to repair the boat easily in the future, or sell it to someone that you don't like.:D

If the screws are adequate for gauge and number, there should be no movement even if bedded in thick paint or nothing at all.

Another good answer. Peerie get's extra credit for this one.

Bob Cleek
03-29-2015, 01:37 PM
A ply deck is very stiff. Loads concentrate around the perimeter...the sheer clamp, cabin, ......These edges are important....engineer these bonds correctly

Correct!

Bob Cleek
03-29-2015, 01:39 PM
I made a a rebate in the sheer plank f or the first layer of ply bedde with micro fibres and fastened to the sheer and beams with anchor fast copper nails, the second layer of ply staggered the first, again with the nails. Countersunk bronze screws finished the job into the beams, and the covering board finished the job. Just a squiggle of 5200 down the beam centre to quieten the creaks. 30 years later, 75 foot boat, all is still good. All plys are not equal.

It may last longer than you do, but the next guy that encounters your "solution" in the course of a repair is going to piss on your grave.

TR
03-29-2015, 01:52 PM
In my experience Purpleheart does not get along reliably with epoxy. You might paint the tops (or the whole thing) of the beams with red lead but I've never bedded plywood decks. Ring nails through both layers of ply is pretty traditional.

Bob Cleek
03-29-2015, 02:05 PM
Pardon me while I get fussy about nomenclature.

Countersinking is what one does to get a screw's head flush with the surface (or just barely below). Typically used with a flathead screw, and requiring a chamfered (conical) hole. I think you're thinking of counterboring... which allows you to embed a screw deeper than that. That counterbore has straight sides. The counterbored screw is then oftimes covered with a bung of a matching species.

One WOULD want to countersink the fasteners in that first layer of plywood. And probably the second, as well... but one might choose to counterbore the top layer.

https://s.yimg.com/fz/api/res/1.2/m8O55ndo4kmLd5rZm7dgsA--/YXBwaWQ9c3JjaGRkO2g9MzQwO3E9OTU7dz00MDA-/http://images.meredith.com/wood/images/p_wood_words6.jpg

If you want to get really picky about nomenclature, a bung is a truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel.

https://swittersb.files.wordpress.com/2011/01/barrel-bung-hold-bung1.jpg

http://i279.photobucket.com/albums/kk158/magicalibur/bunghole.jpg

Given it's similar function, if not exact appearance, in most animals, including humans, the hole into which a bung would be placed, a so-called "bung hole" has another meaning. In culinary nomenclature, a "bung (hole)" is the rectum and large intestine of the pig. In the West it is commonly used as a large sausage casing. In East and Southeast Asia it is a popular street food. They are also prepared similarly in Mexico. If sold for cooking it's called "Pork Bung", if sold for making sausages it's called "Hog Bung".

http://www.randomassaultpodcast.com/storage/post-images/photo0000012.jpg?__SQUARESPACE_CACHEVERSION=139682 1886117

Some also colloquially apply the term "bung hole" to the same part of the human anatomy.

http://www.troll.me/images/beavis-and-butthead-lol/he-said-bunghole.jpg


What is placed in a counterbore is a plug.

http://www.snappytools.com/wp-content/uploads/2014/09/TAPEREDCROSS-SECTION.jpg


(Sorry, David, I just couldn't resist.)

David G
03-29-2015, 02:53 PM
Cleekster, you old fraud. You've got some lobbying work to do to get the rest of the world to adhere to the uniformity of terminology you describe.

http://store.hamiltonmarine.com/browse.cfm/bung-teak-1-4-100-per-pkg-114874-/4,515.html

BUNG TEAK 1/4" 100 PER PKG 114874
BOATBUILDING (http://store.hamiltonmarine.com/browse.cfm/boatbuilding/2,265.html) / BUNGS (http://store.hamiltonmarine.com/browse.cfm/bungs/2,291.html)






http://www.jamestowndistributors.com/userportal/show_product.do?pid=1939



SA Mahogany Wood Bungs / Plugs






Chamfered South American mahogany wood plugs are perfect for when the finished appearance is important. The flat grained orientation of these plugs will allow you to match the grain and disguise the unwanted screw hole.

BUNG14MH 1/4 in BUNG516MH 5/16 in BUNG38MH 3/8 in BUNG716MH 7/16 in BUNG12MH 1/2 in BUNG916MH 9/16 in BUNG58MH 5/8 in BUNG34MH 3/4 in BUNG78MH 7/8 in BUNG1MH 1 in
1 bx and more


(1 bx contains 100 ea) IN STOCK - Available for pickup



$16.55 / bx

qty.

Bob Cleek
03-29-2015, 03:05 PM
Cleekster, you old fraud. You've got some lobbying work to do to get the rest of the world to adhere to the uniformity of terminology you describe.

http://store.hamiltonmarine.com/browse.cfm/bung-teak-1-4-100-per-pkg-114874-/4,515.html

BUNG TEAK 1/4" 100 PER PKG 114874
BOATBUILDING (http://store.hamiltonmarine.com/browse.cfm/boatbuilding/2,265.html) / BUNGS (http://store.hamiltonmarine.com/browse.cfm/bungs/2,291.html)






http://www.jamestowndistributors.com/userportal/show_product.do?pid=1939



SA Mahogany Wood Bungs / Plugs






Chamfered South American mahogany wood plugs are perfect for when the finished appearance is important. The flat grained orientation of these plugs will allow you to match the grain and disguise the unwanted screw hole.

BUNG14MH 1/4 in BUNG516MH 5/16 in BUNG38MH 3/8 in BUNG716MH 7/16 in BUNG12MH 1/2 in BUNG916MH 9/16 in BUNG58MH 5/8 in BUNG34MH 3/4 in BUNG78MH 7/8 in BUNG1MH 1 in
1 bx and more


(1 bx contains 100 ea) IN STOCK - Available for pickup



$16.55 / bx

qty.






Hey, you're the self-described nomenclature Nazi. We can't go by what those Right Coast catalogs say. They have to sell their stuff to the same fools who call plugs bungs, so they've sold out to make a profit. If they call a plug a bung, do they call a bung a plug? They'd be in a world of hurt looking for a "plug" to "bung" their busted through-hull spud in a hurry, wouldn't they?

http://images.jamestowndistributors.com/woeimages/250_250/00002774.jpg

Jamestown Distributors calls these things "wood throughhull plugs," too. What a bunch of bungholes!

http://www.jamestowndistributors.com/userportal/show_product.do?pid=4055

Peerie Maa
03-29-2015, 03:19 PM
Hey, you're the self-described nomenclature Nazi. We can't go by what those Right Coast catalogs say. They have to sell their stuff to the same fools who call plugs bungs, so they've sold out to make a profit. If they call a plug a bung, do they call a bung a plug? They'd be in a world of hurt looking for a "plug" to "bung" their busted through-hull spud in a hurry, wouldn't they?

http://images.jamestowndistributors.com/woeimages/250_250/00002774.jpg

Jamestown Distributors calls these things "wood throughhull plugs," too. What a bunch of bungholes!

http://www.jamestowndistributors.com/userportal/show_product.do?pid=4055

Are they not snottle dogs?

David G
03-29-2015, 03:21 PM
Please send street address... I want to contribute to your Campaign Of Terminology Rationalization!!! Don't worry.... I don't expect much by way of results... but you and your campaign will provide much entertainment. Have you chosen a Sancho yet?

Hmmm... upon consideration... I don't think the traditional PR campaign is gonna work. Maybe you should aggregate your resources toward a campaign contribution to the presidential candidate of your choice... with the understanding that they'll appoint you Marine Terminology Czar. You could then impose your version of ALL ambiguous maritime terminology, by the wave of your scepter!!! Yeah... THAT could work.

ron ll
03-29-2015, 03:31 PM
In my experience Purpleheart does not get along reliably with epoxy. You might paint the tops (or the whole thing) of the beams with red lead but I've never bedded plywood decks. Ring nails through both layers of ply is pretty traditional.

Bronze ring nails, even better. Don't have to lug a compressor down to the boat. Been a while since I've used a hammer for its intended purpose, hope I remember to keep my thumbs clear. Thanks for the tip on epoxy and Purple Heart. Makes sense, it's a pretty dense wood.

So you suggest setting the plywood on the beams dry? How about a layer of building paper?

David G
03-29-2015, 03:37 PM
Bronze ring nails, even better. Don't have to lug a compressor down to the boat. Been a while since I've used a hammer for its intended purpose, hope I remember to keep my thumbs clear. Thanks for the tip on epoxy and Purple Heart. Makes sense, it's a pretty dense wood.

So you suggest setting the plywood on the beams dry? How about a layer of building paper?

P'heart IS dense wood. Probably 10-15 % over even white oak. Maybe 40-50% more than mahogany. If you're gonna bang in a bunch of nails, you might consider the possibility that it will require predrilling each hole.

ron ll
03-29-2015, 03:51 PM
Predrilling holes isn't a problem once the correct bit and depth are established.

TR
03-29-2015, 03:56 PM
You're going to cut out all the ply pieces, then seal the ply with the cpes (three coats on the edge grain). Then finish paint the underside of the deck. If the fit (ply on the beams) is good I wouldn't put anything in there(low cost solution). If the fit is not so great a bit of 3M 4200 will go a long way(more expensive solution). Get under there with thinner right away and clean up any 4200 dribbles. Absolutely drill for the nails, proper size and depth (test in scrap). Putty the nail heads with thickened epoxy before fairing and sheathing.

Mikey Floyd
03-29-2015, 04:41 PM
This is helpful how? The field isn't wide open. It's just cluttered with people who don't know what they are talking about.

Thanks for that input Bob. I'm really not sure how to respond intelligently and respectfully at the same time. I could counter your short offering on so many levels... but then again, maybe I won't get involved with that.

slug
03-29-2015, 04:51 PM
Thanks for that input Bob. I'm really not sure how to respond intelligently and respectfully at the same time. I could counter your short offering on so many levels... but then again, maybe I won't get involved with that.


Yah, best avoid responding to that guy until he gets back on his medication .

As for ring nails...they work well with ply. Its common that after the first layer of ply is layed , a batten is worked on deck to spot any high, low spots . They are dealt with , filling or fairing , before the top layer of ply is added. Be sure the nail heads are below the surface .