Jump to content

Level tolerance for hardcore under a concrete slab.


epsilonGreedy

Recommended Posts

I am getting ready for my garage floor concrete pour and have done many circuits with a compactor. Think I am ready for the sand blinding layer but I can still see a few shallows under a 4m staight edge. The concrete will be 150mm deep and I assume will flow to mask out any undulations in the compacted hardcore finish.

 

How level is level enough? +/- 5mm or +/- 10mm?

Link to comment
Share on other sites

The concretes not going to care it will be levelled regardless, the question would be how much lee-way have you in your estimated concrete order in order to take into account any dips

though in your case, 4mm etc I very much doubt itll make a difference

Link to comment
Share on other sites

29 minutes ago, epsilonGreedy said:

I am getting ready for my garage floor concrete pour and have done many circuits with a compactor. Think I am ready for the sand blinding layer but I can still see a few shallows under a 4m staight edge. The concrete will be 150mm deep and I assume will flow to mask out any undulations in the compacted hardcore finish.

 

How level is level enough? +/- 5mm or +/- 10mm?

After my hardcore looked pretty level with about 1000 passes with a compactor I think it had some bits that were probably up to 30mm lower in areas. Concrete cares not, you may end up with an extra barrow of concrete going in but it will sure take care of any undulations - no need to worry. I also intentionally left the sides lower so the slab edges were thicker. 

 

Just make sure your forms are bang on and everything just literally falls into place!

Edited by Carrerahill
  • Like 1
Link to comment
Share on other sites

33 minutes ago, Tin Soldier said:

 the question would be how much lee-way have you in your estimated concrete order in order to take into account any dips

though in your case, 4mm etc I very much doubt itll make a difference

 

 

I will have some side projects ready to take any surplus if I have a few barrow loads left over. Experience of earlier concrete delivery has refinforce the point there is no time to say to the wagon operator "hang on while I have a think". 

Link to comment
Share on other sites

18 minutes ago, Carrerahill said:

 I also intentionally left the sides lower so the slab edges were thicker. 

 

 

I had a similar thought this morning i.e. create a slight hint of a peripheral ring beam in the poured shape though I am finding it difficult to compact the outer edges because I don't want the compactor to collide with the containing blocks.

Link to comment
Share on other sites

20 minutes ago, epsilonGreedy said:

 

I had a similar thought this morning i.e. create a slight hint of a peripheral ring beam in the poured shape though I am finding it difficult to compact the outer edges because I don't want the compactor to collide with the containing blocks.

Are the containing blocks on a solid foundation with the intention of building up from them? If so then there is no benefit to thickening the edges much as they will not be load bearing.

 

I formed my slab with 8x2's and then thickened the edges as the block walls were then built on the edges of the slab (50mm setback). 

 

 

Link to comment
Share on other sites

21 minutes ago, Carrerahill said:

Are the containing blocks on a solid foundation with the intention of building up from them?

 

 

Yes. I was thinking the thickened edge would help if the slab is subject to heave from the subsoil below. I have been out re measuring the hardcore level and found the edges were generally lower by up to 20mm which equates to 6" deep in the centre of the main slab 5m x 4m and upto nearly 7" around the outer 400mm boundary. I need to recalc my order because at this stage of body fatigue an extra £50 of concrete is a bargain compared to shifting more hardcore into the garage footings.  

Link to comment
Share on other sites

1 hour ago, epsilonGreedy said:

 

Yes. I was thinking the thickened edge would help if the slab is subject to heave from the subsoil below. I have been out re measuring the hardcore level and found the edges were generally lower by up to 20mm which equates to 6" deep in the centre of the main slab 5m x 4m and upto nearly 7" around the outer 400mm boundary. I need to recalc my order because at this stage of body fatigue an extra £50 of concrete is a bargain compared to shifting more hardcore into the garage footings.  

 

Sounds fine. Have some big pieces of clean concrete or slabs handy - can be a saviour if your order runs a bit short. 

 

If you were close I would come and help you on pour day, I love concreting!

 

You know, with all this concrete talk, I think I will order a 750Kg bag of all in one sand/ballast next week with my next materials order so I can do some little pours around my new garage for the slab at the side door etc.

 

 

Link to comment
Share on other sites

Real bodgers add empty 2L Coke bottles if a bit short on the mix...or Coke cans placed upside down...empty beer bottles with the lids whacked back on or lumps of eps, pir etc. 

 

I've come across all the above. Lucky none of it was structural...oh hang on, it WAS!

 

Pump up the volume!

 

?

Link to comment
Share on other sites

1 hour ago, Carrerahill said:

Sounds fine. Have some big pieces of clean concrete or slabs handy - can be a saviour if your order runs a bit short. 

 

 

I have 100 blocks to hand should I underestimate, never thought of throwing things in to raise the finish concrete level.

 

1 hour ago, Carrerahill said:

If you were close I would come and help you on pour day, I love concreting!

 

 

My self build neighbour has offered to help though think I will play safe and find an extra 3rd team member.

Link to comment
Share on other sites

Since starting this thread I have spread 1/2 m3 of blinding sand over the surface which should equate to a 20mm layer on top of the hardcore. Running the compactor over the blinding sand was a far smoother ride than the hardcore, most of it wriggled between the hardcore as I don't have a 20mm layer left on top.

 

The local building pro advised me not to lay the membrane until a few hours before the concrete delivery to avoid puddles or tears due to foot traffic.

Link to comment
Share on other sites

4 minutes ago, Mr Punter said:

Get someone to help. It is hard work for 1 person.

 

 

One of my self build neighbours is helping plus one other hired help because I only have 1.5 effective arms at the moment.

 

On local advice we are doing a rough tampdown to be followed by "latex" layer once the roof is on. I hope a rough tamped finish will provide a good mechanical key for the final few mm of hi-tech leveling compound.

Link to comment
Share on other sites

4 hours ago, Mr Punter said:

Cover the concrete with plastic as soon as you are able, so that it cures properly and you do not get surface dusting.

 

 

Presumably I would wait until the surface is no longer wet and tacky? Or alternatively I could arrange some wooden battens standing 8" above the surface then lift the plastic over these, but then would I ask creating a greenhouse heating effect?

 

Weather tomorrow is sunny after lunch.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...