Easier way for balsa core deck replacement?

Discussion in 'Boatbuilding' started by pago cruiser, May 19, 2005.

  1. pago cruiser
    Joined: May 2005
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    pago cruiser New Member

    To: any experts out there with some advice,

    I have a 25 year old Tayana 37 cruising sailboat (aka lead sled) that has had major water ingress into the deck balsa core.

    I am planning to replace the rotted 1/2" balsa with Airex/kledgecel/whatever (also looking for recommendations on this), but I am trying to find an easier way to replace the "top" fiberglass skin. Due to rotten weather here (lots of rain), I can only work on sections about 4 feet in length at a time. If I am careful when I cut the top skin with my circular saw, is there any reason that I cannot re-use that SAME panel, and fiberglass it back in where it was? Obviously the joints would be well tapered, and filled with glass/epoxy. It would seem to me that it would save a lot of faining and "sloping" work (trying to match the existing deck countours), which would be the case if I were to lay-up a new top skin on top of the Airex/kledgecell/whatever. It would also be critical to ensure a 100% bond od the "old" top skin to the new core.

    Any comments appreciated.

  2. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Why don't you work from below? Remove the inner skin and the balsa, prep the bottom of the outer skin, attach the core, re-laminate the inner skin. Don't cut the outer skin at all, spread a tarp over everything and you should be able to work in almost any weather. Sam
  3. RThompson
    Joined: Nov 2004
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    Location: New Zealand

    RThompson Senior Member

    Working upside down with anything (especially FRP/Bog/Glue) is much harder than the right way up. Especially FRP. did I mention that?
    If you are working in a rainy place then you would do well to erect a cover for the whole job. A $100 or so and some old timber would do it, and you could re-use the tarp after for something else. If you have dropped the rig then you could support that on something and stretch a tarp over it.
    I imagine you would have more grief trying to re-use the removed laminate than simply laminating a new skin.
    Using the old panels you may also have trouble ensuring there are no voids between the core and the laminate. (core bond is a sensitive part of laminates) Once you had glued down (vacumn bag?) the old panels you would probably have just as much fairing to do anyway.

    enjoy yourself :)
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It's a rather common method to cut the whole of the repair area, in your case the top skin of the deck, off, set it aside, hack out the rotted balsa, clean up the inside skin, install the new core then re-bond the deck skin. Working overhead from below is an option, but you'll be using your bald spot as a laminate roller and as has been noted, a much more difficult process.

    The skin can be reattached and a good bond made, if your methods and techniques are sound. Laminating a new skin will be a lot more difficult, consume a bunch more material, effort and money then bonding the old skin back down and filling the well tapered seams. Also noted is the requirement for a good bond to the core, sandwich structures rely on this bond to work properly.

    The tarp idea is typically what would be used in a case like yours. A tent can be rigged up reasonably easily in an afternoon's effort. This will keep the 4:00 PM rain off the work, which I'm sure you get pretty regularly in the warmer months. You could do it in sections, if you like, but why wait or have to fit a bunch of smaller panels in when you can just cut the whole thing off. A number of well placed concrete blocks or sand bags will provide enough pressure to hold your deck skin down as the goo kicks off. If you tape off the seams carefully, you can give yourself a leg up on cleaning up the seam areas from the squeeze out.

    So to answer you questions directly, yes, you can work in smaller sections, if this makes you more comfortable in the effort. Yes, you can (and should, in my opinion) reuse the outer deck skin. If you can vacuum bag the deck skin, it would be great, but there are other ways, less costly and easier to do, though bagging it would be the ideal way to go. Personally, I'd remove the whole of the effected areas (sure will make cleaning out the balsa and the inner skin a lot easier) The single piece idea will have much less seam to be filled and faired. If the area is just too big for you to handle (working alone of short handed) then keep the section as big as possible, but still manageable.

  5. lcheatherly
    Joined: Jun 2005
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    Location: slidell, LA

    lcheatherly New Member

    Replacing deck balsa core

    I have done exactly what you are addressing on my 1972 Allied Chance 30-30. The deck alongside the cabin trunk was very springy and you could almost hear the water squish in the core when you walked there. This repair was done 11 years ago and is still doing fine. Since I was repainting the entire boat, it was no problem with doing the rework since I did not have to "match" any deck skid pattern or paint. By the way, trying to do this job from underneath/inside would be impossible.

    I marked off an area on the deck between the toe rail and the cabin trunk radius at the deck, approximately 16 inches wide by 60 inches long. This provided about a 2" strip along the toe rail and about 2" strip along the cabin top radius. The 60" measuremment was based on what felt like the length of core "sponge" and a couple of inches on each end of the length which felt solid. It doesn't make too much difference because when you open the deck up, you can always extend the cut length. It is important to leave the 2" wide edges along the toe rail and the cabin trunk radius because you will taper these edges in thickness when you reinstall the deck panel which you will cut out. Also, the 2" stip alongside the cabin trunk radius should be the "flat" - it is difficult to fair the radius when you button this repair up.

    With the magic marker lines in place, take a 4" angle grinder with a metal grinder disc and turn it on edge to cut through the deck layer. Take only a small bite with the grinder disc edge and follow your mark lines. The deck layer will only be 3/16" to 1/4" thick so don't go much deeper. The balsa core is about 1/2" thick beneath the deck layer and the disc can go into that thickness since you will be replacing the core. Do not go completely through the core or you will damage the headliner beneath the core. The grinder cut does not have to be all that neat since you will be fairing the cuts when you re-apply the deck panel - just be careful with the depth of the cut and do not go through the core thickness.

    Pry off the deck panel cutout - it doesn't matter if you damage the old core in doing this but you do want the panel to be whole and structurally undamaged. With the panel removed, determine the extent of the core damage and remove any balsa that is damp,wet or delaminated from the headliner underneath. If any of the core is damaged underneath the edges of the cutout, dig the core out as far as you can reach with the 4" grinder disc. Allow the area to dry if it is damp or wet. When dry, sand the cutout area which will be the top of the headliner. Sand underneath the edges of the cutout as far as you can reach with the sanding disc. The angle grinder with a 36 or 60 grit sanding disc is the tool of choice for this operation.

    At this point you may use the sanding disc to taper the top/upper edges of the deck panel cutout and along the deck edges - you want about a 1 1/4" to 1 1/2" long taper along all of the edges and approximately 1/2 of the thickness of those edges.

    I used 3"x 3" tiles of marine plywood to replace the balsa core. I installed these tiles on top of the headliner inside the cutout area by painting the headliner surface with epoxy and then laying in a bed of filled epoxy on top of the rich epoxy. Paint the epoxy and spread the filled epoxy up underneath the edges of the deck cutout as far as you can reach. Place the tiles in a pattern and approximately 1/16" to 1/8" between the tiles into the bedding and pressed firmly down onto the underneath headliner. The pattern should allow tiles along the edges to go up underneath the deck cutout edges. Spread the filled epoxy across the top of the tiles and press the epoxy into the spaces between the tiles. Smooth any epoxy on top of the tiles to minimum thickness. You should layout the tiles and establish your pattern before you start with the epoxy because you will probaly have to trim/cut some of the tiles along some of the edges. Try to limit any gaps filled with epoxy to 3/16" or less. The tile thickness will have to be determined after you have removed the cutout panel - my balsa core was only 1/2" thick so I used 3/8" thick plywood which, with the filled epoxy bedding, provided the exact composite deck thickness when the repair was completed.

    Sand the top of the tile and epoxy fill in the deck cutout and the underside of the removed deck panel cutout. Fit check the panel cutout noting how flush is the panel compared to the deck edges. Hopefully the panel is somewhat recessed as the panel is going to be bedded into a filled epoxy bed atop the tiles. This fit check will tell you about how thick the bed should be. Paint pure epoxy across the top of the tiles and spread a layer of filled epoxy across the tops of the tiles. Make sure the filler is pushed into any voids along the edges of the cutout and the tops of the tiles. Paint pure epoxy on the underside of the deck panel cutout and spread a thin even layer of the filled epoxy on the underside of the panel cutout. Place the panel in the deck cutout atop the tile layer and place some evenly distributed weights (bricks) on the top of the panel. Check the flush of the in-place panel with the cutout edges. Tap the in place panel to determine if there are any voids beneath - if so, remove the panel and spread more bedding where indicated. Some bedding should be squeezed out along the edges of the cutout and the panel should follow the intended contour of the deck.

    After the panel has setup, sand the tapered edges around the deck cutout and paint the tapered surfaces with epoxy. Prepare a thin filled epoxy mix and paint onto the tapered surfaces. Place fiberglas tape (3") along and across the cutout edge joints and press the tape into the filled layer. After the fill sets, paint the joints with pure epoxy and apply a layer of filled epoxy across the joint and fair to the finished surface.
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