Flagstones

[Mollieb001]

Hello! Myself and my partner have recently bought a 1800s cottage. We realised the old owners had carpeted the original flagstone flooring in the living room. We took this up to find half of them were concrete replacements! So dug those out and replaced them. We laid them with waterproof sand and cement and grouted them with a waterproofer.

We have now had them laid for about a week, and the old flagstones seem to be looking very damp, they are laid directly on the earth, no DPM.

The new flagstones look absolutely fine, which is strange as they were soaking wet when we picked them up.

We have been lighting our fire every night and now installed a dehumidifier into the room to try and dry them out.

We had the floor sandblasted as the old tiles were covered in glue and concrete residue, we really need to seal the floor before we can use the room (I.e add our sofas and Christmas tree!) but we are really reluctant to do so while the floor looks damp?

Can we seal this or should we continue to try and dry it as much as we can?

We notice when the fire is on and dehumidifier on, the floors seem to look bone dry, but as soon as the fire dies down and looses heat, they go back very dark.

TIA

 

[Mollieb001]

Also this was the photo of how dark the stones were before we lit the fire / added the dehumidifier. So In 3 days there is a big difference. We are hoping to seal the floor tomorrow - but not sure whether to wait a bit longer!

 

[Cubist]

I'm afraid that you have created a problem for yourselves by just replacing the concrete slabs with new stone slabs laid over a cement bedding. The cement will be operating as an almost impermeable barrier to moisture rising from the earth below and therefore largely preventing it from reaching the new slabs. However, the old slabs are directly exposed to the moisture rising from the earth over which they are laid. As a consequence the new slabs will dry faster and more effectively than the old ones as their moisture content is not being constantly renewed from the earth below. This latter point also explains why the old slabs appear to become dry when the heating/de-humidifier has been in operation but return to looking damp later.

Sadly, if you want to achieve a thoroughly consistent appearance and performance from the floor simply sealing it will not do the trick. Unfortunately I believe that you need to do one or other of the following: -

• Lift the new slabs, get rid of the cement mortar and so-called water-proof grout and relay the slabs directly over the earth.
  • This approach returns the floor to its original intended state in which it can effectively breathe and allow the escape of water into the atmosphere.
• Lift the old slabs and re-lay them on a bed of the same cement mortar and grout as the new ones.
  • This traps damp rising from the earth and forces it migrate towards the walls of the house to have any chance of escape to atmosphere.

Sorry to be the bearer of sad tidings, particularly at this time of year, but in my opinion the first option would be best for the house.

 

[Mollieb001]

I'm afraid that you have created a problem for yourselves by just replacing the concrete slabs with new stone slabs laid over a cement bedding. The cement will be operating as an almost impermeable barrier to moisture rising from the earth below and therefore largely preventing it from reaching the new slabs. However, the old slabs are directly exposed to the moisture rising from the earth over which they are laid. As a consequence the new slabs will dry faster and more effectively than the old ones as their moisture content is not being constantly renewed from the earth below. This latter point also explains why the old slabs appear to become dry when the heating/de-humidifier has been in operation but return to looking damp later.

Sadly, if you want to achieve a thoroughly consistent appearance and performance from the floor simply sealing it will not do the trick. Unfortunately I believe that you need to do one or other of the following: -

• Lift the new slabs, get rid of the cement mortar and so-called water-proof grout and relay the slabs directly over the earth.
  • This approach returns the floor to its original intended state in which it can effectively breathe and allow the escape of water into the atmosphere.
• Lift the old slabs and re-lay them on a bed of the same cement mortar and grout as the new ones.
  • This traps damp rising from the earth and forces it migrate towards the walls of the house to have any chance of escape to atmosphere.

Sorry to be the bearer of sad tidings, particularly at this time of year, but in my opinion the first option would be best for the house.

Thanks for your response. What would happen if we seal it as it is? Will we just be pushing a much larger problem down the line? Thanks

 

[Mollieb001]

Thanks for your response. What would happen if we seal it as it is? Will we just be pushing a much larger problem down the line? Thanks

Or is it fine to leave the stones breathing in different ways and accepting the different colour slabs? It’s hard to know if we need to take the floor up or if we can seal it now. Thanks again

 

[Cubist]

Based on what I've learned most, if not all, the sealants out there are fairly ineffective and cannot/do not penetrate far into the stone. They may inhibit/reduce the risk of staining from foot traffic and spills but this is entirely temporary as the sealant will soon wear away with surface abrasion. On balance though the impact of its use would be limited to the fact that damp rising through the slabs directly over the earth will still darken their appearance and thus become a lasting contrast to the newer slabs.

In you shoes I would be tempted to leave them alone to see if I became more comfortable with the contrasting shades before making a final decision. As to applying the sealant, personally I wouldn't bother except perhaps in heavy foot traffic areas.

 

[Mollieb001]

Based on what I've learned most, if not all, the sealants out there are fairly ineffective and cannot/do not penetrate far into the stone. They may inhibit/reduce the risk of staining from foot traffic and spills but this is entirely temporary as the sealant will soon wear away with surface abrasion. On balance though the impact of its use would be limited to the fact that damp rising through the slabs directly over the earth will still darken their appearance and thus become a lasting contrast to the newer slabs.

In you shoes I would be tempted to leave them alone to see if I became more comfortable with the contrasting shades before making a final decision. As to applying the sealant, personally I wouldn't bother except perhaps in heavy foot traffic areas.

Thanks so much. It’s our living room so the whole thing is quite heavy traffic! We were told because we’d had it sandblasted that we need to seal it as at the moment you cannot even wear shoes in the room without it marking the stones!

We do not mind the colours, as long as the floor can still breathe as it should we will leave it as it is for now, or until we can get some more money to fix it properly.

Thanks again for your help