Vol.1 No.2
6 March 2002



Using Foam Core to Construct a Room Box, Part II
--Questions and Answers

George Hoffman

Q: How do you attach Foam core walls, floor, and ceilings to each other?

A: Using Gator Board for 3/4" base, glue wood strip flooring to the Gator Board using tinted vinyl glue –Elmer’s or equivalent. To glue the 1/4" Foam Core walls we suggest using a combination of Elmer's (plain white) and Zap A Gap (cyanoacrylate). The cyanoacrylate will dry fast and will hold the wall in position until the vinyl glue is dry.  Repeat this process when gluing ceiling to tops of walls.

Q: We use 1/2" MDO plywood for rooms and screw everything together, rather than using glue. I assume you use glue, what type?

A: The same procedure as above

Q: When you use glue is their any problem with everything staying square, etc ?

A: Use a square and Mark a pencil line of the room layout on the base of either 3/4" Gator Board or 3/4" Plywood (your choice).  Clamp straight pieces of 1/8" X 2" wood to outer edge of base following the marked lines.  Place the first flooring strip even with the 1/8” X 2” guide.  Continue until all flooring is in place.  Weight down the flooring strips with something fairly heavy as you glue.  For example we use 1 lb lead ingots. Leave weights in place a minimum of 8 to 24 hrs. If you marked your lines carefully, the flooring should be square. The next step is to glue walls against flooring edge as shown on the diagram in last week’s forum.

Q: How and what do you use to finish over the rough Foam Core and studs to complete the room box?

A: After walls are in place glue and clamp all pine studs flush with outer edge of base. Once this is done glue black construction paper to the Foam Core between the studs.  This will prevent light from passing through the Foam Core from the room interior. To finish the exterior of the room box use 1/4" Birch plywood cut to size.  Glue using a tinted  vinyl Elmer's or equivalent.  Using a tinted glue here will allow you to see any messy glue spots that will need to be cleaned so you can stain or paint your exterior.  Clamp with furniture type clamps to secure this exterior shell until dry.

 



© 2002 George Hoffman, courtesy IGMA Forum

 

Staining

The following question on staining from Anne H. is answered below by Julian Biggers and Sally Hoffman


Q: Do you recommend staining furniture before gluing or staining after gluing? - Anne H.


Julian's response--
 Stain AFTER gluing for the strongest possible bond of the joints of the piece you are making. Many ingredients in stains inhibit the glue from doing its best job. That may not be so important on parts that do not have any stress placed on them, and the weakness may not show up for some years.

The proponents of stain before gluing are concerned about the lighter blemishes or "ghosts" that may appear upon staining after a messy glue job. The blemish is caused by glue soaking into the wood grain and keeping the stain from penetrating the same as on surrounding raw wood. The problem can be eliminated by using a tinted glue such as distributed by Houseworks, Inc. With tinted glue, you can see the excess or smudge and remove it by scraping or sanding. Even when all the glue cannot be removed, it will blend in with the color of the dark stain.

Short answer: Glue before staining and use a tinted glue.

A note from the Frugal Woodworker: You can purchase tinted glue or make your own by adding a few drops of very dark brown acrylic paint to white wood glue. Test on scrap before using.

Sally's response--
When to apply stain is a matter of personal preference and...the style of the piece you are working on plays a big role. I agree with Julian that glue should be tinted so you can see the places you need to clean up before staining.
I personally find that if a case piece or cupboard is being constructed pre-staining or painting the interior sections is better. This allows free access and smoother brush work when applying the stain or paint. Take great care to keep the stain out of any joinery grooves as this will weaken the glue's bonding ability. Steps would be as follow.

1. Sand the wood lightly
2. Wipe the wood with a tack cloth or non-lint cloth (panty hose work well) to remove sanding dust.
3. Apply stain with a small brush ( I have always liked a #7 water color sable) or a small sponge brush. Apply the stain in one direction.
4. Wipe away excess stain with the non-lint cloth --panty hose. I prefer the panty hose here as it does not remove too much stain.
5. Check to be sure the areas that are to glued are free of stain, if necessary clean them lightly.
6. Allow stain to dry before gluing pieces together. This may take overnight if you have used an oil base stain. Follow the manufacturer's suggested drying times.