Consequences of using Rapid Set

I was just thinking :eek: ,

There are thousands of low level decks etc out there that have used rapid set for the post/stirrup holes (you see it all the time on the DIY shows), before I knew any better I have done it.

Now every time someone mentions it, you get the usual, "dont use that crap", "it aint good enough", "it shouldnt be used for structural applications, even low decks", etc etc...

Assuming all the post spacing, footing depth, timber sizes etc are correct.... I am just curious if anyone has actually seen a deck (or similar) fail from using rapid set instead of structural concrete? I have helped with and built a few decks in the past using rapid set for post holes, AFAIK all are still standing..... ;)

Just curious.....

Jdub, I think the reason rapid set has got such a bad rap is because somehow people think you can pour it into a post hole dry and then add water over the top.

Common sense will tell you that you can not create concrete with structural integrity that way.

In my experience if you mix it up wet in a barrow before you place it, it will harden almost as strong as any other premixed product. OK you have to be quick but you can generally mix it wetter than normal concrete.

I've watched people using Rapid Set for deck post holes and fence posts. The major problem is that they usually have a hose close by and just squirt water into the hole until they think it looks right. Mixing dry mix and water is a chemical process. Its crucial to add the right amount of water to get the optimum result. If you add to much milk to a cake mix it will not be a cake at the end of the cooking process. It will be mush which falls apart. Just like too much water in Rapid Set. From memory, a standard size bag of Rapid Set specifies 2.4 litres of water (per bag) added to the dry mix AFTER the mix has been put into the hole. if the hole is in very porous soil the hole should be thoroughly dampened (not so water pools in the bottom) before putting the dry mix in.
Its also important that the mix is not disturbed for at least 24 hours (48 hours is better - no adjusting, no nailing and no sawing) and there is no need to agitate the dry mix and water. Just pour the 2.4 litres (per bag) onto the mix and let the chemical reaction do the work.
Its good stuff and I've been building fences with it for quite a few years and never had a failure even in the face of very strong westerly winds.

Just read your post BT. Sorry to disagree but the method I describe works for me with nno problems.
Cheers

Hi Shedhand,

If you are aware about getting a good mix insitu then your ok.

As I like to leave these chores to labourers, I get them to wet mix in a barrow prior to placeing that way I can have a quick look and give the go ahead - or abuse the hell out of them for pretending to know what their doing.

I have found that rapid set clumps up and won't mix in a mixer, real PIA, and that fencing contractors mix the rapid set (dry) with the dirt they have extracted from the hole then push it back in to give a bit more rigidity as the moisture will eventually set it off.

IF you mix out of the hole DO NOT leave the mixing tool in the mud while answering the phone. 'Tis funny but can be expensive.:D

I have used rapid set on a deck and it was fine. I guess one thing to note is that there is a major difference between the loads from a deck and the loads from a full house and roof etc. Yet often decks are built with similar materials, footings and spans to that found for a full sub-floor.