How to Create Chamfer on Concrete Base for Garage??

[SteFairy]

Hey all,

Long time lurker first time poster. Never had the need to post really as I've managed to find everything i need via search, until now lol.

Basically I'm laying a concrete slab for my soon to be erected sectional concrete garage. I've read a lot about the dreaded water ingress under the panels. I'm trying to design a solution into the slab instead of trying to fix once I get leaks.

If i can get the exact measurements of the garage, and i mean exact, would i be able to put a chamfer on the bases edge? Just like in my crap drawing below?

I'm thinking of just nailing some 4" wedges to the edge of the shuttering but I'm afraid they wont stay square and level once i start to level off the concrete. I intend to use the traditional method of a straight piece of wood across the edges of the shuttering to level it all off.

Am i over thinking this??

Cheers guys

Steve

Untitled

• SteFairy
• 6 Dec 2014
• 1

 

[Burnerman]

You could trowel a sloping edge on the concrete before it goes fully off - i.e when it's still green, but I think a better way is to lower the garage panels onto a thick layer of silicone......the weight of the panels squeezes the silicone out and should give you a good seal.
Your idea, fine though it is, won't stop water from running down the panels and seeping under them......although it should help the panels from standing in water.
John

 

[SteFairy]

Cheers John,

Sounds like a good idea with the silicone sealant.

I suppose if i do both the sealant AND chamfer then the water will run down the panel and away once it reaches the chamfer, reducing it's time to be able to seep through?

I know that most of these sectional garages have some form of leak but like i said if i think about it before it's installed it will reduce them to a minimum.

I had intended on building my own block garage on strip foundations but the neighbours forest 1 meter away from where i want to build will mean 3 meter deep footings! Economically unviable for what i want to achieve.

Cheers again.

Steve

 

[Burnerman]

Sure Steve, the more water that's cast away the better.
Good luck with the project!
John

 

[theprinceofdarkness]

If you are attempting to trowel of the concrete while its green, Then I think you need a runner. .i.e. a jig that you can slide along the inner edge of your forming to to remove some material AND to give some reference to your troweling. I personally do not think it will work as you hit pebbles which when removed will give rough depressions. A variation on the theme would be to make a runner that WILL remove too much material. Then make good the "missing" area with a 3:1 sand cement and a proper runner. The finer sand should give you a smoother finish to your bevel.
I would not worry, I have built two pre-cast garages (one second hand) and with a proper 3:1 cement/sharp sand fillet and have had no problems with either, the last one lasted for over 25 years without leaking. I sold the house and moved on.
The silicone sounds good in theory, but in practice, I wonder, what with sliding the posts around and the general rough treatment until all the posts are held by the bottom course of panels. Also the crack between the posts and the panels, when the rain blows in here, with the fillet any water in this area will not pool and flow inwards, I am not so sure with silicone.
Frank

 

[Hugh Jaleak]

http://www.denso.net/densostrip/index.htm Is another option, used it on plenty of occasions when building manholes. Would be better than silicone I would think.

 

[Andyc84]

The angle of wood you will use should be fine, place it so the top is slightly lower than your shuttering, then you can level off on the shuttering and not this angle.

Whilst it is green you can then remove the angle and any concrete that has gone to high, leaving you with the shape you desire whilst not affecting the form work while you level off.

Also while levelling you will be, at worst, pushing the wood down into the concrete and the concrete should resist this movement meaning the form shouldnt move.

 

[SteFairy]

Cheers for the advice guys.

Next question, how do i know when it's green? I'm thinking crumbly but not too hard, enough to hold its form but still obviously not set. Or is there a set time against temperature one can get a rough guess from?

Cheers again.

 

[Burnerman]

That's about right really......just soft enough to work, but obviously not collapse.
You can tidy things up after with an angle grinder if need be - shuttering away of course.
The setting time can depend on ambient temperature and the cement content so there's no hard and fast rule.
Hugh's proposal with the mastic strip is better than my silicone idea, but you must use something.....personally I find moisture getting in through the panel vertical joins not an issue.
John