Underwater Cement

[User]

 

[Fnaar]

If this is about a pond, my friend Miss Goodbody reports that one should always wait till it's hard, especially if it's an inch or so thick. Rubbery can be good, but refilling within 5 mins is desirable.

 

[slowmotion]

Days not hours. I would go for 4:1 sand cement and wait at least two weeks. If you are adding a pore-blocker like Sika No.1 you can cut down on the time, but it costs a bit.

Edit: Sika No1 is used with sharp sand not soft sand so if you are laying blocks my advice was rubbish! Sorry.

 

[TissoT]

Week + in this damp weather

 

[subaqua]

http://www.cement.org/cement-concrete-basics/faqs

 

[User6179]

Add some Cement hardener to the mix .

 

[User6179]

[QUOTE 3391015, member: 9609"]Cement hardens perfectly well underwater, infact in some cases it may well end up stronger being allowed to set underwater) My question really is at what stage can it be submerged, I'm sort of thinking hours ?[/QUOTE]

I would of thought cement needs air to fully set though , stick some in an air tight tub and it takes ages.

 

[subaqua]

I would of thought cement needs air to fully set though , stick some in an air tight tub and it takes ages.

it is a chemical reaction that requires moisture. air tight also seals out moisture .

it can be poured and submerged almost immediately. and yes the water does help with the curing as it helps remove the heat generated by the curing process.

Lime Mortar however is not able to set under water

 

[slowmotion]

I would be a bit worried about the the mortar being washed away before it hardens up.

 

[User6179]

it is a chemical reaction that requires moisture. air tight also seals out moisture .

it can be poured and submerged almost immediately. and yes the water does help with the curing as it helps remove the heat generated by the curing process.

Lime Mortar however is not able to set under water

I take it though that if it cures under water then like you say ,it does not bond? , I say this as building the under building of a house one day then came back the next day to find the block work floating after a few inches of rain.

 

[Richard A Thackeray]

Joseph Bazalgette specified Portland Cement for his work on the London Sewers in he 1850's, & the vast majority are still used (he designed with very excess capacity!)

 

[slowmotion]

Joseph Bazalgette specified Portland Cement for his work on the London Sewers in he 1850's, & the vast majority are still used (he designed with very excess capacity!)

Have you got his email address? We could ask him how long he left the brickwork before sluicing it down with sewage.BTW, did you know that the sewers are egg-shaped in cross section so that when there is little flow, the stuff runs faster and helps prevent blockages?

 

[User6179]

Joseph Bazalgette specified Portland Cement for his work on the London Sewers in he 1850's, & the vast majority are still used (he designed with very excess capacity!)

Did they use sand in the mix or granite dust ?

 

[User6179]

[QUOTE 3391442, member: 9609"]I guess you were using Thermalite blocks ? just seems odd when using something so light for foundations that they float - but they do use them for that, apparently, or so have been told, they have a greater crush resistance than normal dense concrete blocks.

Anyway what I have put into place wont be floating, ffs it was heavy I reckon about 18 stone, got it balanced then built up underneath it so it wont topple. Will fill the pond back up the morn and hopefully it should look like a little island with just the top 6" poking out

[/QUOTE]
Yep was trench block , the ones that you don't joint , looks like you don't have the same problem

 

[Richard A Thackeray]

Have you got his email address? We could ask him how long he left the brickwork before sluicing it down with sewage.BTW, did you know that the sewers are egg-shaped in cross section so that when there is little flow, the stuff runs faster and helps prevent blockages?

Yes, ovoid, with the narrower section to the lower point, so, yes, it was self-scouring

Did they use sand in the mix or granite dust ?

I'll have a flick through my book, as I've got this on my shelves;
http://www.amazon.co.uk/The-Great-Stink-London-Bazalgette/dp/0750925809