Concrete base

[Bk456]

I put down a 100mm deep concrete base, 800x800m last week. It is to hold an outdoor boiler. I will be moving the boiler onto the base in the coming days but having pressure washed the base today and some bits to chip out of it I'm worried I've made it too weak...

Is there anything i can do to check strength of base, or should i just put the boiler on and keep an eye for cracks etc...

40kg of cement went into the base along with 50/50 sand gravel. There probably was a bit too much water in though....

But perhaps a boiler weighing id say approx 150kg and being stationary should it be fine??

 

[AJT]

Ideal mix would have been 3-2-1. 3 x sand 2 x gravel 1 x cement.
Can not say as I don’t know your mix..
So was it like 3 buckets of sand/gravel mix and 3 buckets of cement.? If yes then you have used way to much cement but would still be strong enough did you put in any rebar.?..I would suggest making another mix this time at 3-2-1 and laying another inch on top..soak base before laying new layer on top and smooth off on the top when new layer done..
If it’s in a area that can be rained on put bin bag or something over until cured..

 

[willin]

I put down a 100mm deep concrete base, 800x800m last week. It is to hold an outdoor boiler. I will be moving the boiler onto the base in the coming days but having pressure washed the base today and some bits to chip out of it I'm worried I've made it too weak...

Is there anything i can do to check strength of base, or should i just put the boiler on and keep an eye for cracks etc...

40kg of cement went into the base along with 50/50 sand gravel. There probably was a bit too much water in though....

But perhaps a boiler weighing id say approx 150kg and being stationary should it be fine??

The mix AJT suggests is easily strong enough, 40kg of cement is nearly 2 bags (25kg bags) + the same sand/gravel (I think that’s what you’re saying) is overkill IE 1-1 mix, that is also around the amount to do 800mm (80cm) X 800mm.
Putting in more water would actually make it stronger, so long as it is not like say pea soup or wetter.
7-day-old concrete would only be at about 60% strength, why do you need to jet wash it?
Let us know if I’ve misread anything, if you’ve done as above it should be easily strong enough.

 

[Mick]

150KG is not that much weight to be fair especially if stationary weight is applied to it.

What was the sub floor comprised off.

Personally I think it will be fine, those jetwash machines can be very strong and would chip allot of just dried concrete mixes.

But as others mentioned, the mix is a lilttle off, where did you get the values from to make that?

I think it will be fine!

Mick

 

[HappyH]

Pressure washer too early for me too. Should be fine though.
Can you & a mate jump on it simultaneously to test it
HH.

 

[lescantle]

Get a trowel or scraper and scratch the surface of the base when dry,If its digs and chips easy then its to weak

 

[dooohhhh]

Frost can also damage a concrete base. Do not concrete if there will be an overnight frost. There are products available to protect fromf rost to put into concrete if it must be done in the winter

 

[cappuccino99]

Too much cement can make mortar or concrete weaker

I think you'll be OK though. Just let it go off for a lot longer .. mortar and concrete does take a lot longer to go off & a pressure washer would rip the surface up

You could get a trowel out and just put a thin screed over it.. I say wet with a pva / water solution and add to the mix of the screed too (read up on recommemded quantities for those 2 too and ideally use waterproof pva .. will make it a nice job.. just cover for rain / protect for Frost atm and leave it longer)

What's this outdoor boiler and what does it run on

 

[silverdale]

On bases make sure your mix is correct and I always put chicken mesh in to give it strength