Layup multiple pieces of ply in limited space

Discussion in 'Wooden Boat Building and Restoration' started by Brentmctigue, Mar 1, 2021.

  1. Brentmctigue
    Joined: Apr 2015
    Posts: 36
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Newcastle

    Brentmctigue Junior Member

    I have 13 sheets of 12mm ply that I need to glass both sides. In my limited space it will take quite a long time to do them individually. Can I stack them with plastic between the faces so that I can glass one side of all the sheets, one over the other?
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 1,075
    Likes: 228, Points: 63
    Location: Colorado

    Blueknarr Senior Member

    Depends on the resin, the plastic used and the desired surface texture.
     
  3. gonzo
    Joined: Aug 2002
    Posts: 15,148
    Likes: 910, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    If you stack them before the resin is cured, it will take two people to lay them on top without making the fiberglass slide or bunch up. I would make some guides with wood so there is no danger of the plywood sliding around.
     
  4. Blueknarr
    Joined: Aug 2017
    Posts: 1,075
    Likes: 228, Points: 63
    Location: Colorado

    Blueknarr Senior Member

    First
    Test to see if your plastic will release and what texture it leaves.

    I would then limit the stack to three or four sheet because a heavier stack may squeeze the resin out of the bottom layer.
     
  5. Brentmctigue
    Joined: Apr 2015
    Posts: 36
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Newcastle

    Brentmctigue Junior Member

    Thanks Guys.
    Gonzo, I hadn't thought of that. Thank you.

    I'm using an epoxy resin and HDPE plastic drop sheets. The finish will be sanded and painted over with high build non-slip deck paint, so I'm not too concerned with small imperfections in the finish texture.
     
  6. philSweet
    Joined: May 2008
    Posts: 2,410
    Likes: 237, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    What is the laminate schedule? If it is a couple layers of 1708 with a decently high resin content, there will be considerable heat associated with the cure, and no place for the outgassing to go. You will need to start with warm plywood and less warm resin and then transfer the laminated ply to an area that is at least 20 degrees cooler for about 30 minutes before placing the poly and stacking the next piece. I'd use long sheetrock screws and screw the edges of each new sheet every foot to make damn sure nothing scooched. Then plan on sawing an inch off all around because the poly is not going to release on the edges very well.

    So start with ply soaked at 90 degrees for a day. Mix resin at 80 degrees, and transfer to 70 degree area to cure.

    If the ply is AB, do the B side first so the bare A-side is on the plastic. It probably won't have an acceptable finish with anything other than an A surface veneer on the poly. If the inside of the deck is visible, you want the A side down anyway, and you can build a crowned base mold and build some crown into the deck as you go. Crown helps with rolling the next sheet down on the previous one. You'll need at least 6mil poly, preferably heavier. And even A-side fir ply is iffy from a print-through standpoint.

    This suggests you haven't done this before. You need a flat surface. Otherwise dirt and water finds pockets on the deck. Don't pass on any chance to get a better smoother flatter finish on the laminate. It is way easier and cheaper to build it flat than to try to flatten it later. You'll have $300-$400 per sheet into this by the time you are done, so maybe just take the time to do it in a way you know will work.
     
    bajansailor likes this.
  7. Blueknarr
    Joined: Aug 2017
    Posts: 1,075
    Likes: 228, Points: 63
    Location: Colorado

    Blueknarr Senior Member

    You could skip the plastic and use a whole lot of five foot 2x4s.
    Glass the first sheet
    Place a 2x4 on edge next to the long sides.
    Span across with flat 2x4s
    Stack on the next sheet and glass it.
    More 2 by bridging
    . . .
    Pray that there isn't an earthquake
     
  8. cracked_ribs
    Joined: Nov 2018
    Posts: 94
    Likes: 78, Points: 18
    Location: Republic of Vancouver Island

    cracked_ribs Junior Member

    I've done stacks of scarf joints with wax paper between and had it work out really well. The surface texture was excellent.

    I'd definitely attempt this. I do think that spacers between layers is a good idea so you aren't cooking the inner sheets and making them outgas. I'd just make sure that the areas between the spacers are small enough that there's no chance you're laminating in a bit of curvature.
     
  9. Brentmctigue
    Joined: Apr 2015
    Posts: 36
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Newcastle

    Brentmctigue Junior Member

    Excellent idea, however it would cost in the order of $75AU for the timber per layer. On this project budget wins over speed of production.

    Thanks philSweet. Correct, never done this before. It is going on the aft deck of a houseboat. Ive allowed a 1:50 fall outboard to ensure water will not pond.

    FAST CATALYST
    I've been testing a fast catalyst from my supplier today. Only a small penalty in strength. Goes off quite quickly so small batches and fast work. It took about 2.5 - 3 hours to gel. I think I can work with those times without stacking. As you say better to play it safe and take my time.
     
  10. Brentmctigue
    Joined: Apr 2015
    Posts: 36
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Newcastle

    Brentmctigue Junior Member

    Using 400g double bias both sides. Skim coat of fairing compound over glass to avoid print through. Framing under the deck is at 400mm (16") centres.
     
  11. gonzo
    Joined: Aug 2002
    Posts: 15,148
    Likes: 910, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Fibreglassing the underside of the deck is rather unusual. Epoxy resin thickened with a bit of silica is enough for waterproofing. You could simply laminate the top surface of the deck.
     
  12. philSweet
    Joined: May 2008
    Posts: 2,410
    Likes: 237, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    So transverse frames on 16" centers with sheeting fore-aft—correct? Any carlins between frames or other ply edge support? I redecked a couple of 40' rental houseboats down in the Everglades. The framing was pretty crude, like 2 x 12's across a 14' beam. Half-inch ply cores will need to land on support on all edges.

    Pro tip. Before you do any painting. Place the panels and locate every single last thing that fastens to these sheets and add a patch of glass to build up a little boss there. Then feather it out with smooch. This way, your hardware won't suck down little pockets that hold water on a flat deck. I also had to redo the deck on a 100 pax tour boat because every seat leg held water in a pocket and the deck got washed 3 times a day. The patch only needs to fit the footprint of the stanchion or bench leg. And don't non-skid these patched areas. Mask them off for the nonskid application—they'll dry better and stay cleaner looking and you'll know where stuff goes.

    And I agree with Gonzo. I always try to provide a controlled way for wood to breath. Preferably a way that doesn't involve exposed end grain. If you epoxy the topsides of the deck, I would use polyester resin on the underside because it has a much greater moisture permeability. Of particular concern is any air conditioned spaces where moisture would be attracted to the inner ply/skin boundary making a biosoup. I'd go with a very permeable coating there, like shellac or tung oil.
     
    Last edited: Mar 2, 2021

  13. Brentmctigue
    Joined: Apr 2015
    Posts: 36
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Newcastle

    Brentmctigue Junior Member

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.