Replacing 2X4's Used as Expansion Joints in Patio

by John Wurl
(Renton, Wa USA)

concrete expansion joint grass

Q: I have a 30' X 18', aggregate finish patio which is divided into 5' squares separated by 2X4's. Or rather, WAS separated by 2X4's as they were rotted and I removed them a couple years ago.

Gaps are now filled with grasses, weeds etc. I would like to permanently fill the gaps with cement.

I believe I will certainly need to allow for expansion when doing this.

Can you please advise what type of cement to use, what type of expansion material to use etc etc?

I have some experience working with cement on a small scale and have trowels, edgers and a tub to mix.

Thank you in advance.
John Wurl
Renton, Washington

A: Hi John,

I'm sorry to hear about your grassy joints. I know people that enjoy grassy joints - but I think they are indulging in a different type, haha. The 2 X 4s were definitely not a good idea, but you can take care of this.

Thanks for the pics! They are very helpful and hopefully other visitors will start submitting them more often.

Your best bet is to use large diameter closed cell backer rod to fill in the gaps.

Once you have cleaned out the gaps, choose backer rod in a diameter that is about 25% bigger than the width of the gap you want to fill.

You'll need to make the grooves deep enough to compress the backer rod in place between the patio squares. Press the backer rod in so that it's between 1/2 and 1/4 inches below the level of the patio squares.

Then, use self-leveling concrete joint sealant over top of the backer rod. It comes in tubes that you use with caulking guns. It should flatten out by itself and will contract and expand to accommodate any expansion or contraction of the patio blocks.

Best of luck!

Alan
Meet-Mr-Concrete.com
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