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Forum topic by RussellAP posted 11-19-2012 07:35 PM 778 views 0 times favorited 4 replies Add to Favorites Watch
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3104 posts in 2287 days

11-19-2012 07:35 PM

I have a steam kit and I’m making a box for it. The box measures 47.5”x18” x8” and is made with a couple of half inch panels from an old nicely made entertainment center 1/2 inch particle board with rosewood veneer and the sides and ends with 4/4 oak.

The box needs to be absolutely sealed against moisture infiltration to the wood.

I am using Spar now on all interior surfaces.

Question. Is spar okay to use, and if so how many coats should I use?

I know some of you are going to suggest marine sealer, but is that really needed as long as you account for water drainage and don’t let it sit with water in it?

-- A positive attitude will take you much further than positive thinking ever will.

4 replies so far

View mbs's profile


1656 posts in 2940 days

#1 posted 11-20-2012 01:10 AM

I’m not sure but I probably wouldn’t use particle board regardless of the finish because the pressure of the steam MAY penetrate the finish and turn the particle board into mush. However, there is a rubberized coating that supposedly will seal a cardboard box to hold water. I can’t remember what it’s called though. I remember it being used to seal basements and dog runs too.

-- Sorry the reply is so long. I didn't have time to write a short reply.

View a1Jim's profile (online now)


117095 posts in 3577 days

#2 posted 11-20-2012 01:35 AM

Again I would not use particle board.

-- wood crafting & woodworking classes

View RussellAP's profile


3104 posts in 2287 days

#3 posted 11-20-2012 01:38 AM

I think I’ll get some PVC tomorrow and use that Jim. Easier all the way around.

-- A positive attitude will take you much further than positive thinking ever will.

View JAAune's profile


1799 posts in 2317 days

#4 posted 11-20-2012 02:56 AM

I don’t seal my steam boxes nor do the others I know who do steam bending. As MBS indicates, wood finishes won’t hold up under the harsh conditions the box will be subjected to. Also (in case you don’t already know), don’t pressurize the box. Steam pressure is dangerous and doesn’t help the bending process any (unless you’re at high altitudes and need pressure to reach temperature). You just need a heat source around 200-212 degrees fahrenhiet that won’t dry out the wood. Steam does that job well.

There may be some coatings such as epoxy finishes that will completely sealing the wood but I wouldn’t count on that. Even if the coating is completely water-proof it may develop cracks at some point that will admit moisture. The downside to applying finish to the wood is that finish acts as a moisture barrier both ways. Once the finished wood gets wet it will take forever to dry out.

I suggest a cheap, exterior grade plywood without any caulk, sealer or finish of any type. Assemble it with some deck screws. When the steaming operation is done, open the box and let everything air dry before storing. Not only is such a box fast and cheap to make, but it will hold up for years before it needs replacing.

47.5”x18”x8” is a very large box. Hopefully your steam source is up to task. If you really need one that big then build it but otherwise, keep it as small as possible. Having two or three boxes of different sizes for different jobs is also a good idea.

-- See my work at and

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