Glues, Screws and Sealnt questions.

[mufb]

I've got my sidewalls cut out and ready to begin framing for a sandwich wall. I've got questions I can't find answers to with the search function. I understand that walls should be sealed inside and out. I'm using titebond III. I read that sealant should be applied everywhere except where it will be glued. However, I also read that the 3/4" insulation I'm using should be glued to the wood so as to become part of the stuctural element. So how do I reconcile these two opinions? Should I cover everything with the Titebond? Use a particular sealer? Also, when gluing the bracing, should I screw thru the outside of the wall into it for a stronger structural unit or just trust the glue? Thanks for any advice.

[Ira]

If you're doing sandwich walls, you don't have to glue the insulation in. Just wedge it in there.

If you're using 3/4 insulation, you'll be using 1 by 2s for your framing, which when positioned right, actually measures 3/4" deep--perfect for your insulation to go in there, and then to place your interior wall/skin.

Also, what dimension material are you using for your interior wall? You don't have to go overboard here--1/4" is more than enough. You can probably get away with 1/8". (Note that some people don't even PUT an interior wall in; they just frame, no insulation.)

Also, I just sealed my exterior walls with Thompson's deck sealer. (I just edited this post because I just REMEMBERED that I did this. It's been so LONG!)

[cablerunners]

Hi mufb,

I'm at the same point in my construction...

I wasn't planning to seal my plywood inside the sandwich.

But now that you've brought it up, I too want to know what most do.

-phil

[mufb]

I'm using 1/4" birch for interior and exterior wall with 1x2 and 1x3 for framing with the 3/4" foam board for insulation.

[Ira]

See my edit above. I just remembered that I used Thompsons deck sealer for my ply, since I was covering with a wood skin anyway.

Your materials sound fine, but I think I used 3/8" or 1/2" for the exterior, but I don't remember what the stuff actually measured. (My inside walls are just thin wall paneling.) Also, since I was skinning mine with WOOD, not aluminum which would show screw heads if not recessed and filled, I was able to screw from the outside into the framing.

And here's the other thing:

Remember that your side walls, in the galley part, WON'T be sandwhich walls. And that you'll need to install channel molding on those edges. ANyone listening here--what's that standard channel molding size that 99% of us used?

Are you doing a woody, or skinning with aluminum?

[CHUCKLEHEAD69]

i used 1/2 inch outer walls and screwed it from the inside (through the 1x4s into the outer wall )so i didn't have no screw holes to fill but the ones from the spars around the edge. with 1/4 or 1/8 inch outer walls i don't think the screws will hold enough the way i did mine

[Miriam C.]

Good morning,
I used 3/8 outside and 1/8 inside. I covered my ply inside the walls with floor finish after I glued the frame to it. The tightbond stuck the insulation to it just fine. I didn't put sealer where the glue was structural.

I glued my frame to the sides before putting them up. Screwing them into the floor was harder but this can be fixed by putting your bottom frame member on the floor and screw the sides to it after sealing. You need to fasten the side framing also to the floor frame someway. Pocket screws might be easiest.

I have screws through the sides to the spars. I also have screws down the side where my panels meet and at the door. I don't think it is going to fall apart.

The galley area is built up with luan so it is thicker. There are others who framed this area in also. You just need it thick enough to put the seal and trim on.

Good luck

[mufb]

Thanks for the replies folks. I'll be using Poly floor finish for sealer. And I'll be painting the outside, probably with Rot Doc. I'll let you know how this turns out.

[Ira]

Thanks for the replies folks. I'll be using Poly floor finish for sealer. And I'll be painting the outside, probably with Rot Doc. I'll let you know how this turns out.

The Rot Doctor/Uniflex is good stuff.

But as Tom Swenson can attest, watch out for moths and other insects in the area.

Think fossils.

[Esteban]

I'm thinking of building a teardrop, so at this point I'm a backseat sawdust maker. Here's how I intend to seal the frame and insides of the sandwich construction walls and roof of my (future) teardrop. There will be unsealed wood to wood areas to hold glue between the frame and the skins with this method. (edited 10/31/06)

Short Version:

1. Before you attach inner and outer wall skins to the wall frameworks draw an outline of the framework on the inside of the inner skin and seal only the areas not within the framework outline.

2. Attach outside wall skin to framework then seal inside of outer skin and the framwork *Except* the side of the framework that the inner skin will be glued to.

3. Complete inside the sandwich wall wiring and insulation, attach the frameworks and outer wall to floor then glue and attach the inner wall skin to the frameworks.


Longer Step By Step Version:

1. Build side frameworks.

2. Cut out outside skins.

3. Cut out inside skins.

4. Lay inside skin on table or sawhorses inside (framework side) facing up.

5. Lay appropriate framework (left side framework on left skin... right side frameworks on right skin) in it's correct position on top of the inner skin and trace around the framework with a pencil. After you lift off framework you've got a cartoon (drawing) of the framework on the skin.

6. Mask off areas inside the penciled framework cartoon so these areas don't get sealed.

7. Seal exposed areas of skin. Remove masking tape. Let sealer dry.

8. Attach frame to outside skin.

9. Seal inside of outer skin and sides of framework. Leave inner (cabin) side of framework unsealed to better hold glue...use masking tape as necessary.

10. Attach frame and outer skin to floor.

11. Install wiring and insulation inside wall area.

12. Stain and finish cabin side of inner skin.

13. Attach inner skin to frame. The inner skin's frame work cartoon previously covered in masking tape in step 6 above is unsealed so it will glue well to the raw wood side of the framework.

14. Drink your favorite beverage.


Backseat TearDropper, aka Steve

[Miriam C.]

Good plan Steve
I used panel nails on my inside skin and sealed the frame. Just in case I wanted to get past the inner panel or change it.

Welcome to the playpen.

[mufb]

Just for kicks, I emailed both the makers of Titebond and Minwax. These were the replies:

Thank you for your inquiry. I do not recommend sealing your wood before
bonding with Titebond III. Like all of our traditional wood glues,
Titebond III is designed to bond bare wood to bare wood. Applying any
type of sealer before bonding will prohibit the glue from penetrating
into the pores. A strong bond can not be achieved if our wood glue can
not flow into the wood's pores when pressure is applied. For sealed or
finished wood, you may want to consider using a polyurethane glue or
epoxy. I hope this information is helpful to you.

------------------------------------------------------------
Thank you for your inquiry with the Minwax website. We appreciate you
taking the time to contact us.

Unfortunately I have no way of telling if a certain glue is going to bond
well to any of the finishes we offer, so the best thing I can recommend is
to contact the manufacturer and find out from them as to how well their
product will adhere to different surfaces/finishes. None of the finishes we
offer are intended to be painted over, so that would not be recommended.

[cracker39]

If you're doing sandwich walls, you don't have to glue the insulation in. Just wedge it in there.

If you're using 3/4 insulation, you'll be using 1 by 2s for your framing, which when positioned right, actually measures 3/4" deep--perfect for your insulation to go in there, and then to place your interior wall/skin.

I have to say that my experience proves otherwise, at least in my case. I didn't cement my foam to the walls and I got some warpage in my paneling. It wouldn't have warped if I had cemented the foam to the exterior skin, then cemented the paneling to the foam with zig-zag beads of construction cement.

I sealed with varnish. If I had to do it again, I'd use epoxy like most people told me to. I'm having to resand and repaint spots where the varnish sealant wasn't heavy enough to seal properly. I may end up having to redo the entire exterior, but I hope not.