Greeetings fellow Vikings! At last comes the build back of the side decks and with great excitement we realize that we are nearing the end of the balsa core replacement on the deck!!!! After the side decks there is only one small foredeck area left!!!
Fitting the Balsa Core
For whatever reason I cannot now fathom, I felt as though I HAD to cut out 2 foot lengths of core and fit them into the side decks. After a lot of scrap, and no success, I finally realized that it didn't make any difference if I put the blocks in one at a time, or a whole sheet. Every 1" x 2" block had to be covered in epoxy on all six sides anyway and pressed against its neighbor. When I finally had this mental breakthrough, I started fitting in much much smaller pieces of balsa core sheet with great success.
The pictures below nicely shows the layout of the balsa core pieces on the side deck. It took 50 individual pieces per side deck. After a few hours, I had the process down smoothly and working efficiently:
- First cut a piece of balsa core about 6-8" wide, and a little longer than the distance from the cabin sides to the deck sides, or toerail.
- Lay the balsa core down over the side deck where you want to fit it, then take a pencil and mark a line on the sub layer of fiberglass parallel to the beam of the boat (Port to Starboard / Cabin to Toerail). This becomes your first reference line. In the picture below you will see what I mean, there are lots of these lines as I moved from one pieces to the next.
- Move the balsa core piece aside, and then measure the depth of the fiberglass deck overhang with a ruler, or hold the pencil under it and your thumb on the pencil, then mark it on the deck. Do this in several places and connect the marks with a line. This will show you how much bigger you have to cut the balsa core to fit under the overhang, and show you the hidden curve under the overhang. Do it on both sides, the cabin overhang and the toerail side overhang.
- Place the balsa core piece back in place and in line with your reference mark. Transfer the depth lines to the balsa core so it matches the curvature of the deck sides. Close is fine as you will be using filler under the overhangs as well anyway.
- Cut the balsa core piece on both sides to the curve.
- Lay back down on the deck aligned with your reference mark. It should now be one piece of balsa core, 6"-8" wide, with the ends curved to match the cabin and toerail and the right size to fit under the overhangs.
- Cut the piece into three equal pieces. Make sure the middle piece is smaller than the opening you cut in the deck.
- Fit the piece next to the cabin under the overhang (You may have to sand the thickness some to get it to fit). Mark all around it with a pencil and number it.
- Fit the piece next to the toerail under the overhang (You may have to sand the thickness some to get it to fit). Mark all around it with a pencil and number it.
- Fit the middle piece in, it should fit nicely into the space between the other two pieces. Number it.
- Move to the spot next to this and start all over with a new piece and a new reference line.
Note: Sometimes a piece of balsa block will pop off of the backing. Just save it and push it in when you fit the bigger sheet. No big deal. You can see in piece number one in the picture below one of the pieces on the top popped off where the angle on the top is.
Mixing Resin For Installation
Next comes the mixing of epoxy into three batches which I place in the fridge to keep cool until all three are mixed and I am ready to go.
- First batch is just plain epoxy mixed.
- The 2nd batch is a filling mixture to fill in voids under the overhangs in places where there will be NO through bolts. I mix 16 ounces of epoxy, then add about a 1/2 cup of milled fiberglass for strength. Then I add wood flour for thickener until it is like oatmeal. Pasty but still gooey and wet. This makes a really strong filler material to take care of the gaps where the balsa blocks do not fit perfectly under the ledges and around odd shapes.
- The third batch is also a filling mixture, but for where I will have through bolts. Here I want solid fiberglass and epoxy so this is a mixture of cut up fiberglass scrap, milled fiberglass, and epoxy. Mixed until it looks like fine spaggetti in thick sauce. I push it up under the overhangs where the T-Track bolts, or deck cleats may go.
Epoxying Down the Balsa Core
Once I have my mixtures, I start epoxying down the balsa core. I follow a process here as well, and it goes pretty easily and smoothly.
- Starting with balsa core piece number 1 and using a brush paint all 6 sides of every individual balsa block in the sheet. Yep, every side of every block, well coated. Then I coat the sublayer and brush epoxy all up under the overhangs to wet it out really well.
- Take a scoop of thickened epoxy and push it up under the sublayer all along where the balsa block will fit. Depending if there will be a through bolt here or not, use the wood flour mixture or the scrap fiberglass mixture.
- Take your well soaked piece of balsa core and push it up under the overhang. You should see thickened epoxy ooze out from all the sides, and it should push in kinda tight given that you have to push out the excess thickened epoxy. Otherwise, pull it out and add some more thickened epoxy.
- Repeat process with the next piece. Remember that on the middle pieces you shouldn't need to use a lot of thickened epoxy, but be liberal with the straight epoxy so it is well soaked and bonds.
- As you go, you will get extra thickened epoxy and straight epoxy oozing out. I just brush it towards the next overhang or piece and use it there.
When you are done, you will have all the blocks epoxied into place. This looks messy, and it kinda is, but you can see the brown thickened epoxy well in the picture below and how well soaked the blocks are in epoxy. And of course, this is a real picture...... from a real amateur..... in all of its ugly mess
Don't try and clean it up, just let it harden and you will sand it smooth later.
Sand the Balsa Core and Overhangs
Key in this step is to smoothly transition from the full thickness original deck, down to the balsa core. And then to make sure the balsa core is level and smooth. Trust me here, anything that is uneven or not level just transmits right through to the finished surface. So sand and fill it nice and smooth. Just don't sand down all of the balsa core, only the high spots in the core. I found that a half sheet sander with a nice flat bottom worked very well for me here. The bright sections of epoxy are where I sanded down the high spots.
Note that I have also prepped with tape to keep off excess epoxy. Also note the cutout section left where the chain plates come through the deck. That square will be filled with solid fiberglass mat.
Lay Fiberglass Matt and Sand
This part was again a bit more tricky than the other spots because I needed to cut 13 pieces of 24 ounce fiberglass stitch mat per side, each one cut to the curve of the cabin and toerail. I also needed to stagger the seams so that they did not land in the same place. Once again I followed a process to keep it going smoothly:
First Layer:
- Start by cutting a rectangular section of stitch mat the full width of the roll, and only 10" - 15" wide depending on where you are working on the side decks. The pieces should be just a little wider than the deck is.
- Lay that rectangular piece in place on the deck, smooth it out, and use a pencil to mark the outline of the cabin and the toerail.
- Remove the piece and cut it out to the marked shape.
Second Layer: Repeat the process back at the beginning by cutting out another rectangular piece but this time come in 1/3 the distance of your 12:1 taper width when you mark the outline of the cabin and toerail. So for instance, if your ground tapers are 3" wide, come in one inch from the edge of the cabin and toerail. This makes the second layer slightly smaller and saves you a lot of sanding later since you do not need the full thickness of new fiberglass at the thinner part of the taper, but at the bottom of the taper where it meets the balsa core blocks you need the full thickness of all three layer.
Next Layers: Just repeat again but come in 2/3 the distance of the 12:1 tapers. Repeat, repeat, repeat, repeat.
The last steps are just to remove all the number pieces of fiberglass mat, mix up epoxy and start applying it to the deck.
This is also pretty easy, taking our time to soak the mat side very well, and using the laminating roller in between each layer. A week later we sanded it flat and it looked great! Only a few spots were a little high and easily sanded down. Later on we will use fairing compound to smooth out the edges and corners but we are waiting until we are fairing much more of the boat before doing that.
You can see the one small section of original deck left on the foredeck!!!!
John Olsen
Ericson 25CB "Nordic Thunder"
