BobS

Yes, more concerned these cracks will grow in the future, especially once we put the heating on. It seems like the oval part in the centre of the doorway is now fully seperated from the rest but probably held in place by the UFH for now. We are planning to put Karndean down so thinking the tiles could start to seperate and lift over time.

Longfloor has an integral curing agent to stop cracking rather than one which is sprayed on later. As far as I can tell it is relatively new on the market so unsure how tried and tested it is. The fact Cemfloor said the cracks indicate a problem with the installation or material when they thought it was their own product makes it difficult to accept this as an equivelent. The UFH had not been turned on at this point. We have a temporary willis heater connected up which is warming it very slowly but yet to reach 20 degrees. As @saveasteading says, crack inducers would seem to be the key. It makes no sense to me that they didn't use them.

After my original post I contacted Cemfloor directly with photos. They told me these cracks are not normal for their product and indicate either a problem with the installation or material. However, they also asked some questions about the company who poured this and it eventually emerged that it was not Cemfloor Therm, as we were sold, but a different product called Longfloor. At no point was this product discussed and we were repeatedly told this was Cemfloor up until the point Cemfloor themselves confirmed they do not supply the company. The cracks have got worse since my original post and curled. We have not even used the UFH yet. Our builder is now claiming Longfloor is just a different brand name of the same product and these cracks are normal. Clearly it is not the same as it has cracked badly so I wanted to correct my post saying this is Cemfloor as it potentially damages their reputation unfairly.

Thanks all for the replies. Controlled cracking sounds like it would have been a good idea. I am wondering if there is an issue with both sides of the door cracking and creating a small island in the centre that could become loose over time. Or are they only surface cracks?

Our Cemfloor screed was poured on Friday over UFH (75mm screed, UFH, 100mm PIR, concrete slab). Went to check it today and there are a number of large cracks, about 1.5mm wide. The main ones of concern are around the doorways as they are ovals that look like the threshold of the door is now separated from either side. Would this be considered normal shrinkage cracking?

Pour went well and done very quickly (once the mixers arrived). It's the first time our builder has used it and he seemed really happy with how it went, certainly a lot less work than wheelbarrowing it in. Not sure of the exact cost as the floor was included in our builder's quote but he said it worked out about the same as standard concrete due to the time saving.

We are having our slab poured today, 100mm Topflow Horizontal self-compacting concrete. The supplier has been out to prep the area. Because we dug out the previous slab the plan was to run a new DPM up the walls from beneath the slab and lap over the DPC. However, the concrete supplier has cut the DPM they laid off just above where the slab will be. They apparently intend to lay another DPM over the concrete - beneath the insulation, UFH and top screed. When I questioned it they said this is just how they always do it. It seems a bit strange not to run the DPM up the wall in a continuious piece so I wondered if there are any pros or cons to doing it this way?

To match our new door and window openings with the existing building we are placing bricks end-on over the patio door lintels. Our builder is using lightweight engineering bricks with large perforations. We have two sliding doors meeting at a corner meaning there will be an 8m continuous run of these around the corner of the building and supporting the first floor masonry and gable end. Will this type of brick be strong enough for such a long run around the corner of the building, or should we insist on solid bricks?

Thanks for getting back to me. Could damp still travel up the mortar that covers the DPC, behind the black jack and come out further up the wall? I realise lots of old houses don't have proper damp proofing so not sure if this should be a real concern. Just don't want to spend all the money on finishing walls and floors if there is a chance of a damp problem.

We are a couple of months into a renovation and extension of a 1980s house that feels closer to a complete rebuild. Currently we are digging out the concrete floor slab, ready to install a new one with UFH continuing into the extension. Because of the intention to pour a new slab in one, our builder has already begun building the extension walls without any damp proof membrane lapped in. They have used a DPC but pointed over most of it on the inside wall, thus there is nothing to attach a new membrane to. Their logic is that because the original membrane is broken it wasn’t worth putting one into the new walls. However, the old house not only has the remains of DPM in the walls but the DPC hangs out about 30mm, which seems better than nothing. The new walls have little visible DPC and no overhang, so my concern is the new extension is now worse than the existing house. I am wondering how important the joint between DPC and DPM is or can the new DPM just continue up the wall past DPC level? Also, is pointing over the DPC on the inside wall a problem that needs correcting? Thanks