I have a lot of concrete in my yard that has several 2×4 6-10 foot wood expansions. The 2×4's are now between a 1/2" and a full inch above my concrete. What can I do to fix this? I thought about a hammer and chisel, but it would take me a year! Can I take the 2x4s out? I've had this concrete for about 15 years. No cracks anywhere just expanding wood!
Concrete – do about 2×4 wood expansion joints that are above the surface of the concrete
concretewood
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We had an almost identical situation in a former garage that we refinished to be an office. Our contractor suggested this and we liked the result: he installed a piece of wood about an inch out from the concrete, putting insulation between them and keeping the wood a consistent and level height - a little higher than the concrete. I can't remember if it was pink fluffy insulation or spray stuff. Then a shelf about 6 inches out from the wall - nice and level by being a bit up from the concrete and supported by the vertical wood, and there's insulation under the shelf too. The whole thing is a good looking clear pine and is well varnished.
Looking from the side gives an idea of the distance from the wall:
The shelf runs around the entire room and is remarkably useful for something so low. It hides all the lumpy bumpy aspects of the concrete and while it's not something you see everywhere, no-one has ever mentioned it so it can't be that unusual.
I have been caulking expansion joints in concrete for 15 years. This is what you do:
- Get the wood out
- Clean the top 3/4" of the interior walls of the joint with a wire brush
- Install "closed cell" backer rod into the joint. You want it to be about 1/8"-1/4" larger than the joint. Roll it down in from the side is easiest. The top of the rod should be about 3/4" below the top of the concrete.
- Blow the crack out with a leaf blower. (the backer rod should fit tight enough to stay in place as long as you dont blast it head on)
- Use professional grade urethane or silicone caulk for concrete. The best thing is probably Dow 888 silicone but its very expensive. Urethanes are cheaper and almost as good. Sika brand Sikaflex 1a or Sonneborn brand NP1 are great
- Caulk depth in the center of the joint should be 1/2 the width of the joint but no deeper than 1/2". People are tempted to think deeper is better but it will cause bubbling and premature failure. If it is too thick it will not stretch easily and therefore pull away from the concrete.
- Tooling the caulk is necessary. It will force the caulk into the pores of the concrete and it will smooth out lumpiness. Use a metal or rubber spatula or a tablespoon.
- Self levelling urethanes are available but the have the consistency of pancake batter so your joints have to be pretty level to use it. You'll also have to dam up the ends of your joints. Plus you will have to be on the lookout for rain, bugs, and blowing leaves for a couple of hours after you finish.
- 2x4s are a lousy choice for expansion joint because they are so wide. You are going to use a lot of caulk.
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Best Answer
Not knowing what you use this concrete pad for, you could take the plywood out and fill the gaps with polymeric sand. Once you water it in, the sand forms a locking pattern that resists weeds and is fairly easy to replace if it cracks.