Fir plywood question

[win_wood]

I have completed planking the bottom of my 9' speed boat with marine fir. I fastened it on with about 200 S.S. screws and thickened epoxy. I am now filling the c'bores with West's and 407 fairing compound. I had to fill twice because the epoxy mixture sagged out of the holes on the vertical sides of the hull. now I am in the process of sanding the filler and am finding that the plywood is not sanding evenly. I know that the soft and hard areas of the grain will sand at different rates and this is giving me some subtle waves that follow the grain of the ply. My question is how will this subtle waviness come out in the end when I add a layer of fiberglass cloth. The waviness is only apparent to the touch but I am worried about what will happen when I apply a gloss finish. Should I use another type of ply on my next project or is there a better method of filling screw holes? I also plan to coat the bottom of the hull with unthickened West's and turn it over to finish the deck and interior before flipping it over to apply the glass. Is this a good idea? I thought that it would protect and seal it while I finish the topsides. Thanks for the input.

[JohnDory]

Hello,
I had the same problem very recently. I just finished my glass job on doug fir marine ply with 7.5 oz cloth. I glassed over the waves that were created from sanding too much. It has been recommended that I fair the valleys with compound post glass job since I am going to paint the hull anyhow. I just am unsure if I should fair it before adding more coats of epoxy or after.
Good Luck,
Chris

[Russ]

If you are going to glass the bottom then stop sanding the fir plywood. Getting a paintable surface under the glass is a lot of extra work and as you have found out can cause waves. At this point I would think about applying a slightly heavier glass cloth to help mask some of the waves if they aren't too pronounced.

Second thing. If you are going to coat the hull with unthickened epoxy then continue the process with glass and epoxy coats before you stop and flip the boat. This way you will get the chemical bond between coats instead of just the mechanical bond. After the last coat of epoxy then give the boat a week or two to let it cure fully.

Counterbores can be trimmed with a very sharp putty knife or even an old wood chisel if you get to it before the epoxy has completely gone off. Simply slice it as close as you can to the surface and when cured give a little hand sand.

[NormMessinger]

Right. Do not sand fir plywood. Glass it then fare. You can start troweling on filler at the same time you are filling the weave. Use a knotched spreader to spread epoxy thickened with glass beads. When sandable, sand with a long board. Using the knotched spreader leaves ridges to sand off so you don'd have to sand off as much googue. When you have all the low places even with the high places go back with more micro and sqeeegy and fill the valleys between the ridges. Long board again and you've got it. Micro should never be more than 1/8" thick or it might flake off later. Top coat with raw epoxy and proceed to finish in a way Wild Wassa would be proud of.

We all have our tried and true way of doing this. All work. More or less. Naturally, my way is right.

--Norm

[Bruce Hooke]

What I would do at this point to fair the filler you have applied to the screw holes is either use a plane, chisel, or cabinet scraper to trim the extra googe off, or roll on the first coat of regular epoxy on the bottom and then sand the filler smooth. With a coat of epoxy on the bottom you should have much less problem with creating waves.

The other thing to do in this situation is to make sure your sandpaper is backed by a firm sanding block so that the sandpaper does not try to follow the waves.

[Bill Berrisford]

Win-
The use of MDO reduces the fir-grain bleed-through and MDO with a tropical hardwood veneer layer under the paper will stay smooth as glass. smile.gif As suggested, the use of fairing or glazing will help.
-Bill

[JimD]

Like others have said, stop sanding the wood, get some epoxy, glass, balloon thicked epoxy on, and fair