Note: The tip is for those of us who don’t own a biscuit joiner.
Here’s how I deal with a butt joint that won’t stay flush to the surface I’m trying to even it out with.
In this example I’m installing the vertical style that makes up the wall panels in our half bathroom. I’m not using biscuits to align the joint because I don’t own a biscuit joiner any more.
Besides, the Liquid Nails between the joints and on the back of the flat-stock mdf will be more than sufficient to hold the joint together. But if the finished joint is going to look good, then the two surfaces must match.
This problem is especially common when working in corners like this one. Corners are rarely flat — they are usually full of bulges caused by unfeathered joint compound, stucco and warped 2×4 framing.
Step 1 Pry then Pound
I slipped a putty knife behind the flat stock and pried it out proud (above) of the mating surface. Then I tapped it back in with a mallet until it was flush.
This usually works, but in this case it did not. It kept dropping below the mating surface on the right side.
Step 2 Shim
Now I slip my putty knife behind the molding and tap in it until the mating surfaces are flush.
I’m using the putty knife as a wedge-shaped shim. Sometimes I make small shims on my miter saw from scrap material, but I’ll save that for another Quick Tip post.
Step 3 Let the Glue Dry
Behind this piece of flat stock is a liberal amount of Liquid Nails. I applied enough so that when it cures it acts not just as adhesive but as a spacer as well.
When this “glue spacer” cures, this intersection of flat-stock moldings will become rock-solid. But until that happens, the joint must be held in place and not move.
Crown Molding Example
The picture below shows how I used the same technique while installing the cornice flat-stock for Paul and Sarah’s kitchen crown molding here in Tucson.
Biscuit Joiner Solution
Of course, using a biscuit joiner would eliminate this issue. But not everyone is ready to commit to that next level of expertise or spend the money to buy a good one.
So until you decide to make that leap, this technique works just fine.