Subfloor material and foundations in high watertable area plus a question re render

[Grace]

Hello,

This is my first post on here but I have been reading for months and have already gleaned so much info so thank you. I have looked through the forum for an answer to my quandary though cant seem to find one but sorry if I missed it.

We have just moved into a 17th century chalk cob thatched cottage in Hants. Dont currently have WIFI but will post pictures when it is installed. We love the house however as a surveyor cheerfully told us we had committed ourselfs to a money pit! It has issues with concrete render, gypson plaster, and a concrete sub floor plus lots of damp, mould and wet rot. We are planing to take all the render and plaster off and put lime on to hopefully help this.

We are also planning to extend with a green oak timber frame, straw bale infill and green seedum roof.

First question is: Initially we really wanted to dig out the concrete floor and install limecrete, however we are in an area with a high water-table and in the recent past the house has flooded a few times from groundwater flooding. I spoke to Mike Wye and Ty-Mawr and they both suggested that limecrete might not be the best solution as if it flooded then it could get contaminated and we would have to re-do it. Most builders have said we need to have a concrete sub floor but we really don’t want this. Can anybody suggest an alternative to concrete or limecrete in this situation? I should mention when it floods the water is crystal clear, and we are planning on installing french drains, a swale and also a pond in the garden to help draw flood water away from the house.

Secondly with the foundations for the extension we are looking at a free draining flexible foundation like rubble filled wire cages or old tires filled with rubble. Does anybody have any experience with these and do you think they will work in our watery situation?

Finally if we start taking the external render off now but don’t plan to re-render with lime until next spring do you think the cob wall will be okay over winter exposed?

We are taking to surveyors, building regs and our architect as well but I thought somebody on here might have had experience of a similar scenario. Thank you for taking the time to read my massive post.

Kind regards,

Grace

 

[MatthewC]

Hello Grace, welcome to the forum. It seems from the silence that you have asked a difficult question, which I don't recall being asked here before.

I installed a limecrete floor here but we are pretty well drained (once I got rid of the high ground against one wall). I am puzzled as to exactly what would happen to a limecrete floor in a flood - what do Mike Wye and Ty-Mawr mean by "contaminated"? I would have hoped that, done with NHL, it would survive the flood and then dry out as designed when the flood recedes, whereas a concrete floor will retain any water underneath...

I think the other questions are how often does it flood and how high? I cannot see a French drain working if you have a really high water table, as it needs somewhere to soak away. In the same way your proposed foundations might have the same trouble.

Matthew

 

[TheRoost]

Hi Grace, welcome to the forum

It sounds like an interesting house. I can't really help much other than say that I think rubble filled tyres would be a bad idea for your extension foundation - tyres rot after a few years when permanently wet underground.

I guess what they mean by a limecrete floor becoming contaminated after a flood, is concern that foul water/sewage would get into the structure of the floor - but then any sort of 'waterproof' floor is not going to be suitable either.

Don't forget to post some pics!

 

[livias]

Soakaway crates? They come in different strengths depending on what will be on top of them, we had to have some which will take the weight of a fire engine

 

[plasticpigeon]

Hello, welcome to the forum.

It does sound like you have taken on a house with some unusual issues. I concur with Matthew that I can't see why a limecrete floor shouldn't withstand a flood. As far as I know lime is not particularly affected by water and the foamed glass sub base will also not be affected so perhaps Mike Wye and Ty Mawr are being cautious. One thing I can think of is that the foamed glass is very lightweight, and I'm pretty sure it is less dense than water, so if totally submerged there would be an upthrust on the floor. I wonder if there is a denser alternative that might work. I'm sure even broken bricks with a lime slab would have advatages in allowing some evaporation from the surface, but it wouldn't be well insulated so probably wouldn't pass building regs.

As far as taking the render off, cob is mud and straw isn't it? I am absolutely no expert, but I would imagine that under the render the walls may be damp and the integrity might be a bit compromised because if this. It could be that the cement is doing a good job of helping to keep the house standing. You will need to talk to a proper historic building expert really, not just a local surveyor, but I can imagine that it might be best to remove the render in sections, to allow one part to dry out without risking movement or weakness while this happens.

 

[Grace]

Thank you everybody for your responses, that is all good advice that I will look into more. I forgot to mention as well the house isn't listed.

Yes I am trying to find a surveyor who I knowledgeable about chalk cob, but it is proving a bit difficult. And it is quite urgent as there is one wall we are really worried about. Does anybody have any suggestions in hants area?

I am trying to post pics but it keeps saying file to large. I will keep trying.

Thanks again.

 

[plasticpigeon]

I am trying to post pics but it keeps saying file to large. I will keep trying.

Yes you will have to reduce the size of the picture using paint or some other graphics program. Usually 800 pixels on the long side of the picture is about right. Alternatively you can add a link to photos stored online, for example on photobucket or flickr

 

[Flyfisher]

Secondly with the foundations for the extension we are looking at a free draining flexible foundation like rubble filled wire cages or old tires filled with rubble.

Is 'flexible foundation' an oxymoron or am I thinking of the wrong kind of 'flexible'?

 

[MatthewC]

It could be that the cement is doing a good job of helping to keep the house standing.

I saw that several times in Uganda - they have houses which are basically a eucalyptus frame with mud/straw infill which dries pretty hard. Then they fill the cracks and when it's really dry they render it with cement. In time the wood rots at the base and the thin render is the sole structural component!

 

[GPHouse]

Hi

re the comments on the cob covered in concrete.... if as damp as it sounds, the advice is always apply some caution. I've seen some interesting photos of damp Cob collapsing post 'structural' render being removed!


Sound amazing. Good luck!

 

[MatthewC]

Finally if we start taking the external render off now but don’t plan to re-render with lime until next spring do you think the cob wall will be okay over winter exposed?

Why do you not intend to render until next spring? If the render is so bad that you must remove now, then you really should render it again as soon as possible.

 

[steveb]

we had a timber framed house that had structural render - none of the timber reached the ground anymore and the whole place was being held up by various decorative coatings. Word you never want to hear from a builder are "we're going to need more acrows" so be careful....