Have I made a boo boo

[DIY-oh-why!]

Dear Forum

ive just joined up to ask for some advice.

I'm refitting and modernising our under stairs toilet. New units, new everything.

The room (1.5x1m squared floor area) has had wallpaper stripped, walls washed, sugar soaped, all very clean. top half has been painted as bottom half to have tiles coming one tile above the little corner sink. Tiles are ceramic 450x250x9mm.

Under the old removed wallpaper was a coat of paint, probably painted in 80s. Seems quite tough so did a gaffer tape test and only a little came off. To be safe I've scored the walls quite a lot, score marks about an inch apart and criss cross over the whole tile area.

This exposed a bit of plaster in the score marks etc. So to seal the wall and prime the exposed plaster I used some SBR I had. My concern is I may have used the wrong thing. I had some Cementone SBR Admixture. Only afterwards did I wonder if this has different properties to a normal SBR Primer. I had mixed it 1 part water 1 part SBR. It's all dried now and feels a tiny bit tacky.

question is, was it ok to use this? I scored the wall again in one area and was able to just raise a little of the dried SBR skin off the wall. Only a very very little. But is this enough to mean the tile adhesive won't be any stronger than the SBR's bond? Adhesive I've been sold is 'norcros one part flexible white adhesive'. Is the skin element of the SBR on my wall normal SBR behaviour or is the fact this is an admixture mean it's not the same as a SBR primer?

Have I made a boo boo?

thanks for any feedback, greatly appreciated.

 

[Dave]

Morning .

First off you should never score plaster/plasterboard as this weakens the integrity of the substrate and could result in a failure.

The SBR mix ratio was to strong , ideally 4:1 water to SBR .. If it's skinned and can peel , then sand it off ..

 

[DIY-oh-why!]

Dear DavidHoweTiling

thanks for taking the time to give me advise on this. I will give it all a sand as there does seem to be a very fine skin. Although near impossible to get off by hand I guess a heavy tile can't be trusted. It's not the sort of skin you get if you let pva dry on your hand (if you know what I mean).

After sanding, should I apply 4:1 water:SBR again?

Regards the plaster, I didn't know this and have scored into it, as that's how I interpreted the advice all over the net regards scoring painted walls before tiling. However the plaster feels so solid (it wasn't easy to score in the first place) I'm gonna have to hope it's ok. It's not like scored plasterboard that I imagine becomes all crumbly.

Lesson learnt I guess!

Thanks again.

 

[Dash J]

Morning .

First off you should never score plaster/plasterboard as this weakens the integrity of the substrate and could result in a failure.

The SBR mix ratio was to strong , ideally 4:1 water to SBR .. If it's skinned and can peel , then sand it off ..[/QUOT
E]


Is is that correct re never score walls?i have honestly never heard of that one

 

[White Room]

Morning .

First off you should never score plaster/plasterboard as this weakens the integrity of the substrate and could result in a failure.

The SBR mix ratio was to strong , ideally 4:1 water to SBR .. If it's skinned and can peel , then sand it off ..[/QUOT
E]


Is is that correct re never score walls?i have honestly never heard of that one

Especially plasterboard as it's only the paper which gives it it's strength...

 

[Dave]

Morning .

First off you should never score plaster/plasterboard as this weakens the integrity of the substrate and could result in a failure.

The SBR mix ratio was to strong , ideally 4:1 water to SBR .. If it's skinned and can peel , then sand it off ..[/QUOT
E]


Is is that correct re never score walls?i have honestly never heard of that one

plasterskim is a finish coat , so scoring into it with a knife does what ? Apart from break down its integrity with its base coat , not rocket science really.

Its a DIY myth to score painted surfaces and not a trade tip. IMHO anyway.