Concrete base uneven for garden workshop

I cant see it being a problem, maybe use plenty of SBR in the mix.

Itll be well cured by the time we get frosty weather and it will be protected from wet and most frost anyway.

Im surprised your friend was handmixing the concrete and laying on his own 13sq m of concrete, thats 3 to 4 bags of ballast. He shouldve done a thickish mix then he couldve tamped as he laid and then go over at the end. 1 person cant tamp flowing concrete on his own. Anyway what is done is done, it can be sorted......

Final update:

The solution was to get it screeded. There were 2 options, each added a different amount of height from the highest point:

(A) 50mm. Screed had fibres added for strength
or
(B) 10mm. Screed had both SBR and fibres in it (they called it polymer modified sand cement screed)


We went with (B), but it got sub-contracted and they went 20mm instead. (not sure why)

But they screwed it up and it wasn't level in the corners!!!

So the main contractor came back and added a hard wearing layer just a few mm thick of a self levelling product called Tekcem 375 Fiber.

It's now rock-hard and near perfectly level. Done! (even if looks like a 3 layer cake! )




Top Tips if you're rescuing a bad concrete base:

1. Ensure the screeder has experience with outdoor screeds (there are various off the shelf products like Sika 30 which may be great, but you don't want to be the guinea pig!)

2. Agree the finish - screed can be quite sandy depending on the mix

3. Ensure your base is really clean and dry before the screed goes on (you want a good bond!)


Top tips for having any concrete shed base poured:

- Agree the tolerance in advance -- that is, how level it will be corner-to-corner measured in mm, whether there will be waves/dips.
-- Everyone has a different idea of what is acceptable! Beware!!!

- Ensure they have the tools to measure the level: An acoustic level or a green laser level are must-haves! If they show up with a red laser level that they can't see in the sun, send them away!

- Agree the finish in advance -- can it be bumpy with bits of gravel sticking up?

- Don't pay until it's dried and you're happy with it.

- Ask them what quality checks they will do and ensure they do them -- beware people who say "trust me it'll be fine " Everyone thinks they can do a concrete base, but very few can do a large base that is perfectly level and smooth

- Look at screed companies that also do concrete. The screeders are more serious about a quality finish

- If your base is large (anything over 3m by 2m) then
- don't hire anyone hand mixing - it should arrive in a lorry or mixed with a large petrol pump towed behind their van
- ensure they have at least 2 people on the job (ideally 3 or 4!) it's exhausting work and once exhausted mistakes are made


Good luck!

p.s. the above is only my opinion based on my recent experience!

How big is the kiln?

A place I work at had to relocate a kiln because it was too close to a wall and the service engineer wouldn't certify it. He neeeded at least one Metre all round and no timber within one metre - is the floor wood?

Hi @Tigercubrider,

Thank you for the heads up on the Kiln - thankfully we were warned and have met the manufacturers clearance guidelines (we found each kiln had different guidelines). The floor is wood, but we are putting concrete blocks down to the necessary thickness (I think they are 50mm). For the walls we are using fire retardant plasterboard and added the necessary ventilation. We've divided the shed into two rooms so that we can isolate the kiln completely. No small job having a Kiln and trying to remain fire safe.... it's hilarious that some people just have them sat in their kitchen!