Glasscrete system for a Victorian house

[Keymon]

Continuing my questions regarding floor structure. I had the option of timber or concrete.

But I learn about this other system: Glasscrete, with a lime based screed:

 

https://www.mikewye.co.uk/product/glasscrete-floor/#1511968619333-7006ff0e-6459

https://www.limecrete.net/wp-content/uploads/2019/06/Glasscrete-Installation-Guide-V1.pdf

In theory it checks all the boxes:

• Solves the issues with the damp as timber (they claim)
• It is energy efficient, I can get a 0.22 u-value with 150mm+100mm. this is great because we have a 450-500mm foundation.
• It has all the pros of concrete.
   

Cost wise, I got a quote for materials, almost 6k for 85sqm. I am not sure how it compares with concrete in terms of cost.

I see the caveat of the drying time. They say 7-14 days depending temperature. Also, if the builders will know how to install it or not (although it seems fairly simple)

What do you think about this system?

 

[Gus Potter]

11 minutes ago, Keymon said:

But I learn about this other system: Glasscrete, with a lime based screed:

Great approach Keymon.

 

Just before you embark on this what kind of soil are the base stones of the walls founded on. If clay you don't want to dry it out or it will shrink and cause you big trouble. At the other end if sand then you want keep some "ballast" to keep the sand confined around the founds.  They key here is to look hollistically at this and work to conserve / preserve what you have.. but improve using least risk options. Anything you do to alter the conditions of 100 year plus walls and their founds always carries some risk, just think it all through before acting.

 

The "glasscrete" concept is great. To go back in time. We think we have come up with something new but for thousands of years folk have been creating damp proof floors that are breathable. The concept is so simple. You use boulders, single size aggregate that is angular with a low contact surface area and top that off with smaller aggregate and maybe compacted clay. It's (aggregate) shape creates the maximum amount of air voids ( good insulator) while creating a layer that can breathe and so on.

 

Now glasscrete I think is a bit like the stuff you have in a living flame fire, bit more dense / better cemented so it can carry load. 40mm single size granite railway ballast is surprisingly similar? Granite aggregate is for all intents impervious, can't get damp rising through the granite stones.

 

I do wonder just how thick the glasscrete needs to be to achieve the same level of performance as say a layer of PIR insulation. The R value is starting point. That said on BH there are threads about insulating floor slabs and the effect of the perimeter area. See @saveasteadinget al. Glasscrete may have developed this idea where you can heat the soil dumpling in the middle and use perimeter insulation. Now that concept has potential when we come to look at old buildings and how we let them breath but make them warm enough and energy efficient for modern living.

 

Maybe you can extract some calcs / technical data from glass Crete that are applicable to your project?

 

Keep posting, maybe some more info on the walls and founds?

 

 

 

 

 

 

 

 

 

 

 

 

[Keymon]

I described my current situation here:

 

At the beginning the plan was to make all timber, then we considered concrete in the rear, keep timber in the front. But the architect says we won't pass building control with the current joists of 100mm, we need to replace all to get ticker insulation, and then we will need to dig more, etc. If we put concrete in all the floor, we would achieve a good u-value, but the recommendation then is to do DPC across all the perimeter.

 

29 minutes ago, Gus Potter said:

do wonder just how thick the glasscrete needs to be to achieve the same level of performance as say a layer of PIR insulation

I reached the company. They say that. U-value of 0.22W/(m2K), can be done with 150mm Compacted Geocell + 100mm Lime Screed

Price wise is ~6k, but 7.5k with the screed sand.

 

31 minutes ago, Gus Potter said:

what kind of soil are the base stones of the walls founded on. If clay you don't want to dry it out or it will shrink and cause you big trouble

 

The soil is mostly clay. How can it be dried out?

[Gus Potter]

26 minutes ago, Keymon said:

The soil is mostly clay. How can it be dried out?

Don't try and dry out the clay as it will shrink and probably result in a bad outcome.. the drying effect will continue outwards and could affect the founds. You have a lovely old house, be sympathetic. One aim is to continue to keep the moisure content of the clay as it has been for the last hundred years.

 

In terms of drying time, programme your works so buy as much time as possible. An old rule of thumb is that for things to really settle allow for 25mm thickness a month for a slab to settle down. In other words, give slabs time to bed in, settle a bit, cure properly and develop a few cracks before the final finish. Hard to do but try as best you can to go old school.

 

Post a few details and some photos and folk will give you good advise on BH, maybe save you some money and a bit of grief.

 

 

 

 

 

 

Edited July 20, 2022 by Gus Potter

[Keymon]

6 minutes ago, Gus Potter said:

Don't try and dry out the clay as it will shrink and probably result in a bad outcome

Sorry, I meant: I do not want to dry the soil. But I understood from your original comment "If clay you don't want to dry it out or it will shrink and cause you big trouble." that having glasscrete could cause the soil to dry.

 

 

8 minutes ago, Gus Potter said:

An old rule of thumb is that for things to really settle allow for 25mm thickness a month for a slab to settle down. In other words, give slabs time to bed in, settle a bit, cure properly and develop a few cracks before the final finish

You mean for the screed, in case if I go for glasscrete or similar with the lime screed?

Interesting. I am not doing the works myself, hiring some builders. Likely they will not be happy, but maybe they are OK?

[Gus Potter]

49 minutes ago, Keymon said:

Sorry, I meant: I do not want to dry the soil. But I understood from your original comment "If clay you don't want to dry it out or it will shrink and cause you big trouble." that having glasscrete could cause the soil to dry.

Confusion!! The glasscrete and lime screed should let the clay breathe similar to how it has done for the last hundred years.

 

Some folk may be inclined to dig out the ground, fill it with type one or a suspended floor, field drain round the outside and thus dry out the clay.  This invites the "big trouble". I think your approach is good and worth exploring.

 

Historically the clay would have been able to breathe a bit, say if there were old flag stones with wide joints. Each season the moisture content in the clay will change and from year to year too. The glasscrete, although a modern material should not be an issue as you have the lime screed on top. It's the lime screed that I think will dominate the rate of moisture loss. The key will be your floor finish? No point in doing it if you put down limestone flags say and then seal them with oil to stop staining as the sealant works both ways. same with slate.. we put it on roofs to stop the water getting in. If you really want a breathable floor then you need to fully embrace it all the way. Now that may not suit you.. you need to think this through.. before you spend your money.

 

As an SE with interest in old buildings the thing for me is to start with the ground.. what is outside.. trees, the natural and built landscape, then work your way up, enjoy old structures and appreciate what they are. Then explore options but always recognise that you will need to compromise and that you are just a custodian at this point in time. Then look to see where you can say uprate insulation elsewhere to "balance the books". I know it's hard to make the economic arguement but please try and design / alter your old house in a way that can be reversed later unless it is necessary for the long term life of the building.

 

For all on BH. Many want to design in an environmntally friendy way, preserve our heritage, but we also want to make some money. If we go for floor makeups ect that rely on it breathing how do we later sell the house, do we caveate it.. such as.. the floor is breathable so no lino tiles etc.. how do we ensure that this is in the title.. few will do this.. so while it may make you feel good while you own the house what about the future?

Edited July 21, 2022 by Gus Potter

[Keymon]

7 hours ago, Gus Potter said:

Some folk may be inclined to dig out the ground, fill it with type one or a suspended floor, field drain round the outside and thus dry out the clay

Interesting. We have a serious damp issue in the front of the cause, because they raised the ground levels outside above the DPC level, they partially blocked the airvents, and we had the roof gutter (mine and neighbours) just pouring water heavily by the wall and the air vent. Also the soil had rumble and was touching the wood and bridging the DPC. And a pair of poorly old chimney foundations with all the rumble left behind. This house seem to be a book example have all the damp problems 😄

Then I dig the soil in that corner to check the foundation depth (btw, 450-500mm) and it was actually very wet, no water, but muddy and soft.

Our damp surveyor advice was to extend the gutter to the main street (obviously). Restore ventilation and lower soil levels. Then either lower the front ground levels (break an bunch of concrete and tiles) or install a french trench at 400-500mm in the front perimeter. I was planning to install the french trench.

Do you think the french trench might dry the soil? And if I install glasscrete, does it make sense to still do the french trench?
 

 

7 hours ago, Gus Potter said:

The glasscrete and lime screed should let the clay breathe similar to how it has done for the last hundred years.

Yes, that is what I thought!

 

BTW, my neighbours have a concrete slab there. I think part of my damp issues, apart of all the other issues

7 hours ago, Gus Potter said:

The key will be your floor finish

We are still choosing. The previous owners had a solid oak of 15mm flooring in the lounge. It is very damaged, but it is good quality. We were thinking to reuse it, but it means giving up UFH there. Do you think soild oak would do the trick with this ground?

Then for the rear kitchen area, we didn't decide yet, but these tiles seem ok: https://www.stonesuperstore.co.uk/limestone-tiles

 

 

7 hours ago, Gus Potter said:

what is outside.. trees, the natural and built landscape

 

Nothing really, just a normal north London residential street with terraced houses. In the garden/patio there is a small fig tree 4m away.

This house is very basic and had been removed of any nice features, no chimney, nothing special. Had been heavily extended. There is not much to preserve.

So basically the options I have are:

• Timber: breathable and ventilated, but not so energy efficient. Might require digging.
• Concrete, energy efficient, not breathable and risk of damp, requires DPC, requires more depth (450mm) But quick and all builders are familiar with it.
• Glasscrete, breathable, but restricts on flooring options. Long time to dry. builders are not used to it.

Still, I think breathable and ecological are selling points.

 

[markc]

I would start with sorting the damp issue and allow the structure to dry out while doing other stuff.

remove the build up bridging the DPC and clear the air vents. Remove any damp/wet plaster inside to let the walls breath. Good time to check timbers etc.

Advice from Gus is spot on! Too many people (builders included) add drains without looking at the implications.

[Keymon]

19 minutes ago, markc said:

Too many people (builders included) add drains without looking at the implications.

So, do you reckon adding a French trench like this might be a bad idea?:

https://www.1stassociated.co.uk/french-drains.asp

https://www.ihbc.org.uk/guidance_notes/docs/tech_papers/French Drains.htm

 

It was recommended by my Damp surveyor, see below

 

[markc]

@Keymon a small drain like the one above is great and will definitely help.

french drains are often deep and large capacity and used for de-watering fields etc. 

around buildings, adding large deep drains can remove too much water destabilising clay, sand and silt etc.

[Keymon]

8 minutes ago, markc said:

a small drain like the one above is great and will definitely help

Thank you @markc. So basically something like this, not deeper than the foundations would be fine. It is a much cheaper approach than breaking all the front tiled ground floor and lowering it

[markc]

Yes that’s the idea, removes water from the wall but leaves the founds as they were.

[saveasteading]

8 hours ago, Keymon said:

So, do you reckon adding a French trench like this might be a bad idea?:

It is a very good idea. I must have looked at dozens of damp problems and this is the most usual solution  (apart from obvious overflowing gutters etc).

Make sure the pipe has somewhere to empty.

 

The problem is usually that successive owners have built up the ground around. Taking it all down to original level is better than the gravel trench, if possible.

Even without deliberate surfacing, buildings settle a little and ground builds up (otherwise why are all archaeological investigations called 'digs)

 

 

I don't often favour trendy ideas of breathing floors and walls. Any floor is going to move, and if it is concrete or lime it will crack.

I am equally cautious of your proposal too, unless you don't mind seeing cracks in the floor, and not being able to sell the house.

 

These doubts apply equally to hempcrete, living walls, straw bale construction, and more i will think of later.

There are very good reasons why these are trendy but not mainstream.

 

• Solves the issues with the damp as timber (they claim)    Ask for a guarantee, with insurance cover in case they aren't around.
• It is energy efficient, I can get a 0.22 u-value with 150mm+100mm. this is great because we have a 450-500mm foundation.  ok , but this is just the  effect of PIR. Lime above PIR will not breathe, or am i misunderstanding the problem?
• It has all the pros of concrete.   The pros of concrete are strength, crack control, hard surface, industry standard material.

 

As above, sort the damp problem first.