Screed - water based, chipping/lifting, not stuck ? - help !

[carpetpaul]

I'm a carpet fitter, who's been talked into doing a bit of screeding for someone. I've used a water based screed a few times in the past, and usually for floor repairs where there's not much thickness involved or where I wasn't doing the whole of the floor.
I've just been to do a screed job where they're going to be having some lino fitted in a couple of weeks, half of the gents floor has sunk a few millimetres and a small crack has appeared. My intention was to screen over the crack and then blend out the screed to nothing over about a foot.
When I do screed jobs, I always call back 24 hours later and use a bolster chisel to gently remove any bits or float marks, and to 'shape' the finished result by sort of 'sanding' it with the chisel, if I didn't do this, the quality of the finshed result would not be quite good enough for vinyl.
Basically, all the screed I put down, with the exception of a thicker bit which was over some existing rough screed has come flaking off, none is stuck, it's all powdery and when I shoved by bolster under it, I could just run the bolster along and the screed very easily came flying off everywhere ! - a total loss, I'm now back to square one !



1, The screed was still soft in the bag but was about 2 months old (looked ok, and I figured that since it was soft it would be ok)

2, I didn't seal the floor first, mainly because it looked nice and clean, think this was a mistake !

3, The floor 'could' have been slightly damp, maybe the customer had mopped it that day, I'm not sure and I didn't ask, but it did cross my mind

4, Could the screed have not been fully set ?, it did look a slightly different colour when I was scraping the top to shape it, and it was more powdery underneath.

5, Am I trying to work this screed thinner than intended, all the bits that came flaking off were around 2mm or slightly less.

6, I have to have an 'edge' to the screed as I can't screed the whole area, are water based screeds suitable for sanding from 3mm down to nothing ?



Conclusion:-

My thoughts were, buy a new bag of screed, seal/prime the floor first, screed as before, allow 3 days to dry, sand carefully. What do you think ?


Paul.

 

[noseall]

you do need to stabilize the substrate first whatever happens. if you try and use floor levelling compound on a perished or flaking floor then you will pay the price.

have you thought about chiselling the entire thickness of screed up and re-laying it whole sale, rather than trying to over coat a rather poor surface?

or try stabilizing the surface with several coats of diluted pva. also, wet the area prior to applying the floor levelling compound.

 

[carpetpaul]

thanks for the edvice. I may not have been clear in my post, there's only a tiny bit of original screed and this infact is the only bit where my screed actually stuck (it's also the only bit of my screed thats 5mm plus)

I will certainly put several coats of pva this time........ but I thought that water based screeds don't like moisture ( I realise they're containing moisure themselves)....... oh, I'm confused now ! - - - I read on this very site that water based screeds are not suitable where moisutre is present in the floor ?!


help !!! --- AAAArrrrrrrhrhhhhh !!!


cheers- Paul.



P.S - to quote this site :- "waterbased - This is also very good. Flows very well and is really hard when dry. Downside is that it does not like moisture in subfloor base. "

 

[noseall]

cement loves water, but not some of the chemicals or salts that sometimes mix with it. damping down is a good way of removing dust and helps prolong the setting time of cement based products thus ensuring a good cure and a good key.

 

[carpetpaul]

Ok, I'm keen to get on to this problem, I've just found some pva sealer. I'm gonna nip back round to the guys house, mix this stuff up like thick milk and paint in onto the areas that I'm going to be screeding.
Do you think that the problem is my preparation of the existing surface (lack of primer/sealer) and not the fact that the bag of screed has been open for a couple of months. (the bag was tightly closed) ?


Paul

 

[noseall]

[quote="carpetpaul"

mix this stuff up like thick milk

don't mix it too thick, about 5:1 should be ok. apply two or three coats.

Do you think that the problem is my preparation of the existing surface (lack of primer/sealer) and not the fact that the bag of screed has been open for a couple of months. (the bag was tightly closed) ?

Paul[/quote]

could be both, although i seem to think it may be the former.