walkway concrete form question

[Guest]

I need to replace the concrete 38" wide walkway on one end of our Lanai. It abuts the aluminum on the wall.
I believe I need to leave a gap, between the concrete and aluminum, and then caulk the joint.
What is the way to establish the gap? How wide should it be?

Being the concrete will go very close to the wall, there is no room to put a form to use to screed the concrete. Would a 1/4" form set along the wall work to run the screed, then remove and caulk the joint when cured a bit.

The lanai is on a slab, and walk is 20' long.

Any help would be helpful. Thanks

[fishhh4]

something like this

Looks like you can pull off that 1/4 top and caulk . Never used it myself .
They make a black creosote type board as well . Cut to width , glue up , couple nails ... pour concrete to top .

[rlnguy]

I hired a guy to pour a slab against the existing foundation for an addition. He snapped a chalk line on the old foundation and screeded to the line, without any guide board. All that was left was run the caulk.
Dunno if you are planning to do this yourself, or hire it, but here is my experience.
I hired a small contractor. He brought his crew, did the job, and all in one day-17'x42'
The cost to have him do the pour, after I set the forms, was almost the same as just the cost of the concrete, had I bought it myself, because he got a discount on the concrete.
The redi-mix company gave me his name when I was talking to them about what I was doing.
They did a very professional job, better than I could have done.
Even after 20 years, there are no cracks.
That allowed me to focus on the parts of the build I was good at.
My 2 cents

[ez-duzit]

I wouldn't hesitate to use the 1/4" form.

[fixtureman]

We always used expansion joint material

[mike4244]

I have used foam board 1/4" thick that is used for siding backing. When the concrete is dry you can pour a small amount of gas on the foam to dissolve it instead of scraping it out. Black Celotex board is used often but all you need is a small piece. Probably easier to get a scrap of foam board.
mike

[EdL]

Using Celotex for concrete expansion joints should be outlawed. It's garbage! Rots away, dirt & debris fill in, you have a place for weeds to grow forever.......

They make a foam expansion joint material, just a little bit more $, but the cheap contractors won't use it, might cost them an extra 20...

It's no different than fibermesh in the slump, quick & easy for the contractor, a nightmare for you when the concrete cracks and starts to move.

Ed