cracked!

[stevegreen]

Hi, hope someone can help, I have tiled three quarters of my kitchen floor which has wet underfloor heating and sand and cement screed. The room size is approx 8m x 5m and has an expansion joint splitting the screed into two bays. I have been using mapei makeper tiling adhesive. Prior to plastering the room I covered the whole area with cardboard to protect the screed, and have been uncovering as I go. My problem is - when uncovering the last area to be tiled, I have found a crack in the screed which goes across the width of the room (but not in a straight line) the width of the crack at most is only 0.5mm wide.
I can't use an isolating matting in this area as i won't be able to maintain the correct levels. Has anybody got any suggestions about tiling over this area that would help in preventing the crack affecting the new tiles.
Thanks.

[nybor62]

how long as the screed be down for and how thick is the screed

[Sir Ramic]

Has the heating been commisioned ?

[stevegreen]

Screed has been down approx 12 month and is 65mm thick.

[shaney2000000]

You can get matting thats only 1-2 mm thick

[stevegreen]

Yes the heating system has been commisioned.

[stevegreen]

Who makes this, and how much adhesive above and below would I need. Thanks

[Rich]

How much height do you have to play with? Most matting is only 3mm thick and you can lay it with a very thin bed of adhesive and then tile over the top of it with a solid bed trowel as you would do normally.

[stevegreen]

I've got 6mm max!

[Saltire69]

Mapeker is unsuitable for underfloor heating.

[Daz]

Mapeker is unsuitable for underfloor heating.

What makes you say that Saltire???

Here's the spec sheet direct from Mapei website that states it is suitable to UFH installations....

http://www.mapei.com/public/GB/produ...lex_uk.pdf.PDF

[stevegreen]

I don't think i will have enough depth to install matting - would Keraquick mixed with latex plus help?

[Ajax123]

Why not resin stich and overlay the crack with a fibre glass mesh scrim to stabilise it.

Here are a some of products you could use

UZIN: Product Search[productsubgroup]=2&tx_ddproductmatrix_pi1[productgroup]=3&tx_ddproductmatrix_pi1[cmd]=search&cHash=df13d483b315bef867be8d03109d9d87

go to Product Overview and Substrate repairs page

[Saltire69]

I stand corrected. Didnt think the old Mapeker was flexiable.

[chrisroe]

half right they upgraded the spec on mapeker as they found it is flexible but not a fexible as kerraquick

[Dave]

Mapeker is now flexible enough to tile on timber (min15mm overlay)... it has been this way for around a year now..

[pjc]

i use pci pecilastic less than 1mm thick
PCI Pecilastic®

[Rich]

i use pci pecilastic less than 1mm thick
PCI Pecilastic®

I havnt come across this before, ta

[stevegreen]

How would I resin stitch crack?

[Ajax123]

How would I resin stitch crack?

take a disc cutter and turn the blade on its side so the corner of the blade is in contact with the top of the crack. Run it along the crack to create a "funnel" shape at the top of the crack. vaccuum out any dust or debris that is created. check for vertical movement either side of the crack (stand with one foot either side of the crack and put your weight as heavily on one fot as you can and see if the screed moves. If it does this needs to be stabilised (no uncoupling mat will do this) to stabilise the screed you cut small slots at right angles to the crack running from one side to the other. Repeat for the length of the crack at roughly 1m intervals taking great care to ensure that you do not cut too deeply. You then drop into each slot a peice of stainless steel or plastic bar. If there is no movement then this part can be omitted.

Once you have done this you simply mix up your resin and pour it into the crack. It will settle so allow it to do so then top it up. Scrape any excess off the top of the screed and then leave it to set (24 hours)

If you want to over lay the crack with reinforcing fibreglass mesh then you pour the resin so that it over flows the top of the crack and then place the mesh into the resin.

Sounds complicated but really if you think about it it is really simple. The only issue I see with this is if the screed has cracked because it needs a joint at that point then no repair will help you because it will simply crack somewhere else nearby. However given the age of the screed I would think it has done any movement it needs to do.

[Mike]

take a disc cutter and turn the blade on its side so the corner of the blade is in contact with the top of the crack. Run it along the crack to create a "funnel" shape at the top of the crack. vaccuum out any dust or debris that is created. check for vertical movement either side of the crack (stand with one foot either side of the crack and put your weight as heavily on one fot as you can and see if the screed moves. If it does this needs to be stabilised (no uncoupling mat will do this) to stabilise the screed you cut small slots at right angles to the crack running from one side to the other. Repeat for the length of the crack at roughly 1m intervals taking great care to ensure that you do not cut too deeply. You then drop into each slot a peice of stainless steel or plastic bar. If there is no movement then this part can be omitted.

Once you have done this you simply mix up your resin and pour it into the crack. It will settle so allow it to do so then top it up. Scrape any excess off the top of the screed and then leave it to set (24 hours)

If you want to over lay the crack with reinforcing fibreglass mesh then you pour the resin so that it over flows the top of the crack and then place the mesh into the resin.

Sounds complicated but really if you think about it it is really simple. The only issue I see with this is if the screed has cracked because it needs a joint at that point then no repair will help you because it will simply crack somewhere else nearby. However given the age of the screed I would think it has done any movement it needs to do.

sounds a good way alan but i guess you'd have to be careful if there's ufh pipes in the screed? i know they should be clipped down but i've seen some near or on the surface a few times when they've lifted as the screed is poured

[stevegreen]

Thanks for reply - there is no vertical movement, but how does the resin tie the screed together without ties , or is the resin just to fill the crack?
Where can I get the resin from?
Thanks

[Ajax123]

Thanks for reply - there is no vertical movement, but how does the resin tie the screed together without ties , or is the resin just to fill the crack?
Where can I get the resin from?
Thanks

If there is no vertical movement the resin basically stitches the screed by soaking into it on either side of the crack and knitting it back together. Esetially you turn the area around the crack into an epoxy or PU screed rather than a cement screed. . Epoxy and Polyurethane resins are very significantly stronger than the screed itself. You need to make sure it is a resin specifically designed for such a purpose. If you contact Uzin or Bostik directly they will be able to point you to the right products. If you need contact numbers PM me and I will be happy to supply.

[whitebeam]

I have in the past used a single tube with a special nozzle which contains a 2 part resin and mixes in the nozzle as it flows out.

[Ajax123]

I have in the past used a single tube with a special nozzle which contains a 2 part resin and mixes in the nozzle as it flows out.

Same as the resin idea but in a tube. Probably cheaper too