"Clay master" in building foundations. What are th

[Corrado]

Does anyone know what Clay Master is on a building's foundations? We are having building work done at home and the builders have dug their holes and filled them with concrete mix. Looking at the plans, though, it shows the concrete foundations and then a "75mm Clay Master" - I dont actually know what this bit could be. Does anyone know?

I know I could wait until tomorrow and ask the architect, but I wanted to find out before Monday so that I am all clued up.

The builders are planning to start building on the footings tomorrow and I am nervous that the foundations are incomplete as I cannot see this "Clay Master".

Greatful for any help - I have done a web search but can find nothing!

 

[Nige F]

Allegedly .expanded polystyrene foam @ the sides of the trench....I think In case the builders sue me Best ask the architect

 

[tawelfryn]

I have worked with claymaster, its compressible polystyrene, usually fitted to the internal of strip foundations and pile ground beam foundations to help alleviate ground movement stress. Different thicknesses for different assumed ground movements. Clay heave is the primary cause of ground movement on residential sites.
I think its usually pink in colour.

 

[Corrado]

Well, the foundations have now been filled with concrete mix and there is no Claymaster anywhere. Just did a google and found that it is not two separate words, hence being unable to find it before.

So, gven that they did not insert Claymaster at the time of digging the trench - is it now too late to put it in now?

Is it necessary (ie if they say they didn't need it, should I say, "yes you did"?)

Is there another way of getting round it? Perhaps by digging the earth between the concrete strips and filling it with hardcore and concrete again instead of using this Claymaster?

My architect's plans show a ventilated void with a suspended block and beam floor.

Foundation strips are 1.7metres deep by the way!

 

[tawelfryn]

Well the point is, if claymaster is scheduled on your plans then it must be adhered to, after all these are the plans that have been passed for the commencement of works.

So, gven that they did not insert Claymaster at the time of digging the trench - is it now too late to put it in now?

Well its more difficult, means it has to be excavated at the side of the foundation, normally if the foundation is deep strip, it doesn't have to go the full depth, this should informed on your plans.

Is it necessary (ie if they say they didn't need it, should I say, "yes you did"?)

Yes it is if its on the plans

Is there another way of getting round it? Perhaps by digging the earth between the concrete strips and filling it with hardcore and concrete again instead of using this Claymaster?

No thats not doing anything, claymaster is there to contract under clayheave to stop the stress going onto the foundations

My architect's plans show a ventilated void with a suspended block and beam floor.

Yes they have that, with air bricks on your top course below dpc. Sometimes with a radon barrier to stop gases rising through the floor

 

[Corrado]

Thanks for that, as long as it can still be done, I guess we are safe.

One thing I should say, is that when the plans were passed, the foundations were to be 2.9m deep at the rear and tapering to 1.5m deep at the front because of some Leylandii to the rear of the property. This was the architects reason for using Claymaster and a block and beam floor.

When the building inspector came, he said that they only had to dig to 1.7m at the rear and that was fine, so they were 1.2metres shallower than intended in the end.

The foundations have been filled to 1.7m all round, now, so this is different from the plans, does this, in effect, mean that the foundations no longer need Claymaster?

Really appreciate all of the help!

 

[tawelfryn]

Plans are often superseded when work is progressing ,as after all they are drawn up without really "seeing" the job, and are done to the regs.
As work progresses "RFI's" (requests for information) are always submitted from contractors, if things which are originally planned cannot be adhered too etc.
Building Inspectors have the power to supersede plans, to what they see fit with their site visits, and, he is the one to talk too, to see if the claymaster has been removed from the schedule. But not to get off on the wrong foot with your builder, its worth having an "informal" chat about it, as he may well have been told this by the inspector and hasn't told you. Thats why I always involve the customer on decisions like this as, thats when customers may think something untoward is happening. Always communicate with the customer is rule number one, get them "involved" they are always interested, after all it is their job.

 

[Corrado]

Thanks very much, that is great. Hopefully Claymaster has been removed from the schedule. Is Claymaster normally only used when foundations are very deep, then?

From experience, do you have any idea what they would do with the ground in-between the concrete strip foundations? Would they just leave unmade ground (earth) beneath the void and the suspended floor?

Or, perhaps they have abandoned the Block and beam idea and are just having screeded concrete floors, but it would be good to know that if they were planning that, eh!?

 

[tawelfryn]

No claymaster is used at any depth foundations, if when the architect and engineer surveys, think that it is needed from clayheave. If there has been movement of clay in your area before etc.
Unmade ground is below the "void" on block and beam, yes. T beams are laid across the footings, filled in with thermalite block, then your dpm, with then concrete poured, sometimes a radon barrier, if there is a risk of gasses in the ground rising into the dwelling, air bricks on your top course of footings, (one below dpc) ventilate the void underneath. These airbricks are normally connected to plastic housings which channel the air through the footing.

Or, perhaps they have abandoned the Block and beam idea and are just having screeded concrete floors, but it would be good to know that if they were planning that, eh!?

You still have concrete floors with block and beam as I said above, I think you mean if its been changed to "traditional" with solid hardcore floors.
Only you can find out this with your builder.

 

[Corrado]

You still have concrete floors with block and beam as I said above, I think you mean if its been changed to "traditional" with solid hardcore floors.
Only you can find out this with your builder.

Yes, I do mean "if" they have moved to traditional hardcore floors. Admittedly, the architect did not take a soil sample and decided that we needed Claymaster, after we said that we were not going to remove the Leylandii from our garden.

His original plans showed 1.5m foundations with no claymaster and a traditional hardcore floor. When we said we were keeping the leylandii, he decided to go to 2.9m and have claymaster and the said suspended floor!

Maybe he just got in a mood, eh!? As long as Claymaster is not normally used, then I am probably fine. It is not a pre-requisite of block and beam flooring then?

Thanks for all of your help, I really do appreciate it.

 

[Static]

Ok,
Claymaster is a compressible material for clay heave due to trees. IF your footings need to be more than 1.5m below existing or proposed ground level you will require a compressible material on the inner face of footings. As your footings are 1.7m deep near the tree then they should have put in the claymaster and were probably saving costs. Get in contact with your Engineer and see if hes happy with this.
How close is the tree? from a guess i would say 2-3m away from footing. You have suspended floors where you have clay soils with potential to heave from trees, claymaster is very common.
The Architect would have made assumptions on what footings etc were going in, the engineer would have corrected these assumptions after some investigation.
What exactly are these building works? an extension? new house? garage?
Oh and claymaster can be placed after footings have been cast by sliding it behind the footing.. what you are risking is seasonal cracking to the corner footing area with no heave protection..

 

[Corrado]

Hi Static

I just spoke to the architect who said that as we are now only at 1.7m in places, building control would have tested the soil and may have passed it without claymaster.

I phoned building control and they confirmed that as we were not going too low and that they were happy with the soil, I no longer needed Claymaster.

Sorry = this is a 2 storey extension onto the side of the existing 1930s house (which I am sure has shallow foundations and no Claymaster!

I hope I am okay, I guess the Building Inspector's decision is a safe one.

 

[Static]

How close is the tree to the footing?
It sounds like at least someones thinking about it so i wouldnt worry too much, but i would get something in writing just in case as it can take years for these problems to show themself.

 

[Corrado]

neareast tree is about 5 metres away. Okay, I think I will email Building Control and have them confirm it in writing.

 

[Static]

Ok cool, looks like you have Low shrinkability soil thus need only 1.77m deep footing at 5m from tree and NO claymaster
But still get the letter confirming this.