C
cornish_crofter
Apologies for the length of this. I know it’s a bit on the long side but....
I may have backed myself into a corner with this small wetroom that I am undertaking. But I’m looking for your views on what I’ve typed below please.
The whole area is approximately 2.7m long and 1.3m wide. The former will sit at the far end meaning that the screeded area will be 1300m wide x 1800mm long. The back wall of the room isn’t square, hence the former is going to be cut to shape and will ‘fill’ the otherwise useless area at the back of the room.
Having poured the concrete yesterday (Friday) and learning today that Mapai recommend leaving 7 weeks before tiling onto concrete, I have had to consider my options.
My original plan was:
1) Pour the concrete leaving a channel for the wetroom former waste to travel until it goes under the concrete. This has now been done. The slab is 5 inches thick.
2) Fit the former using a good flexible fast setting adhesive directly onto the concrete. Use the same material to back fill the channel for the waste as illustrated in the former instructions.
3) Screed the remainder of the floor and apply a tanking solution – I was thinking of the Weber kit for £40 odd at CTD
4) Tile the former then the floor.
However
1) Mapai are adamant that before tiling onto concrete I should wait 7 weeks. This apparently is due to the thermal shock that concrete undergoes during the curing process from the end of week 1 to the end of week 7. Failure to comply with this risks cracking of tiles. However I have been told by Mapai that tiling onto concrete before the first 5 days are up after laying the slab would beat the start of the thermal shock, thereby allowing the adhesive to fully cure before and (so far as I understand) hence be immune to the thermal shock. My view is that it could work for the former.
2) Mapai were also concerned that laying the screed onto concrete before the 7 weeks are up could also cause me problems with the screed decoupling with the concrete. They also quoted about 1 day per mm of screed for complete curing and drying times. For a 3 inch screed that’s 75 days!
3) BAL on the other hand were excelling the virtues of their Greenscreed. This is apparently a slow setting flexible tile adhesive. Apparently this can be used on one week old concrete, or 24 hour old screed. The only issue that the BAL guy seemed to see was the potential movement between the concrete and the screed during the first few weeks.
4) Hanson, who supplied the concrete, don’t seem at all perturbed about laying a screed on new concrete, even when I raised the issue about the curing process of concrete. The technical rep was of the view that screed on top of concrete slab was the way to go, and it is best to do this before the concrete dries out too much, which to my mind goes against waiting 7 weeks for the concrete to dry before laying a cement based adhesive onto it (since screed is also cement based). When I raised the issue of movement between the screed and concrete he was of the view that applying the screed as early as possible (but not while the concrete is green) was the best way to go, and differential shrinkage shouldn’t be an issue over such a small area of screed. He also reckoned that wetting the concrete or adding a bonding agent before the screed went down would help if it were too dry.
Hence, having taken all this on board I reckon I have a few options
1) Stop the job and wait 7 weeks to lay the former, then screed and wait longer to tile. I think the customer will think I’m taking the mick!
2) Just carry on regardless, after all it’s only a small slab and the screed is only 2 m square or so.
3) Lay the former quickly, before the first 5 days are up to get in before the thermal shock using a good flexible tile adhesive, then concentrate on laying up the screed across the rest of the room, tank then tile. Again it’s a small area and I am unlikely to get any problems with the screed cracking. The use of a mesh in the screed would further reduce that likelihood.
4) Similar to above, but wait a week and use the Greenscreed for the former, backfilling the waste channel with ordinary fast setting tile adhesive to strengthen the floor under the former. Then screed the rest of the floor and use the Greenscreed to tile the whole floor a day later. As far as waterproofing the floor is concerned, I could
a. Use SBR in the screed mix, making it a waterproof screed
b. Apply the Weber tanking kit to the new screed
c. Use the Ditra matting. I can get it for £10.50 plus VAT a metre. I understand that it is a waterproof decoupling membrane
Finally, am I worrying about this too much? After all it is only a small area. It’s not like it’s a 5m x 5m room.
What do you think?
I may have backed myself into a corner with this small wetroom that I am undertaking. But I’m looking for your views on what I’ve typed below please.
The whole area is approximately 2.7m long and 1.3m wide. The former will sit at the far end meaning that the screeded area will be 1300m wide x 1800mm long. The back wall of the room isn’t square, hence the former is going to be cut to shape and will ‘fill’ the otherwise useless area at the back of the room.
Having poured the concrete yesterday (Friday) and learning today that Mapai recommend leaving 7 weeks before tiling onto concrete, I have had to consider my options.
My original plan was:
1) Pour the concrete leaving a channel for the wetroom former waste to travel until it goes under the concrete. This has now been done. The slab is 5 inches thick.
2) Fit the former using a good flexible fast setting adhesive directly onto the concrete. Use the same material to back fill the channel for the waste as illustrated in the former instructions.
3) Screed the remainder of the floor and apply a tanking solution – I was thinking of the Weber kit for £40 odd at CTD
4) Tile the former then the floor.
However
1) Mapai are adamant that before tiling onto concrete I should wait 7 weeks. This apparently is due to the thermal shock that concrete undergoes during the curing process from the end of week 1 to the end of week 7. Failure to comply with this risks cracking of tiles. However I have been told by Mapai that tiling onto concrete before the first 5 days are up after laying the slab would beat the start of the thermal shock, thereby allowing the adhesive to fully cure before and (so far as I understand) hence be immune to the thermal shock. My view is that it could work for the former.
2) Mapai were also concerned that laying the screed onto concrete before the 7 weeks are up could also cause me problems with the screed decoupling with the concrete. They also quoted about 1 day per mm of screed for complete curing and drying times. For a 3 inch screed that’s 75 days!
3) BAL on the other hand were excelling the virtues of their Greenscreed. This is apparently a slow setting flexible tile adhesive. Apparently this can be used on one week old concrete, or 24 hour old screed. The only issue that the BAL guy seemed to see was the potential movement between the concrete and the screed during the first few weeks.
4) Hanson, who supplied the concrete, don’t seem at all perturbed about laying a screed on new concrete, even when I raised the issue about the curing process of concrete. The technical rep was of the view that screed on top of concrete slab was the way to go, and it is best to do this before the concrete dries out too much, which to my mind goes against waiting 7 weeks for the concrete to dry before laying a cement based adhesive onto it (since screed is also cement based). When I raised the issue of movement between the screed and concrete he was of the view that applying the screed as early as possible (but not while the concrete is green) was the best way to go, and differential shrinkage shouldn’t be an issue over such a small area of screed. He also reckoned that wetting the concrete or adding a bonding agent before the screed went down would help if it were too dry.
Hence, having taken all this on board I reckon I have a few options
1) Stop the job and wait 7 weeks to lay the former, then screed and wait longer to tile. I think the customer will think I’m taking the mick!
2) Just carry on regardless, after all it’s only a small slab and the screed is only 2 m square or so.
3) Lay the former quickly, before the first 5 days are up to get in before the thermal shock using a good flexible tile adhesive, then concentrate on laying up the screed across the rest of the room, tank then tile. Again it’s a small area and I am unlikely to get any problems with the screed cracking. The use of a mesh in the screed would further reduce that likelihood.
4) Similar to above, but wait a week and use the Greenscreed for the former, backfilling the waste channel with ordinary fast setting tile adhesive to strengthen the floor under the former. Then screed the rest of the floor and use the Greenscreed to tile the whole floor a day later. As far as waterproofing the floor is concerned, I could
a. Use SBR in the screed mix, making it a waterproof screed
b. Apply the Weber tanking kit to the new screed
c. Use the Ditra matting. I can get it for £10.50 plus VAT a metre. I understand that it is a waterproof decoupling membrane
Finally, am I worrying about this too much? After all it is only a small area. It’s not like it’s a 5m x 5m room.
What do you think?
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