painted plasterboard

[grumpygrouter]

Softening adhesive with a steamer is relevant to dispersion adhesive and it is only to soften the adhesive to aid scraping it off. The same caution needs to be applied so the paper coating of the board isn't damaged. I personally abrade any painted plasterboard back to the paper surface and no further. I can agree that scoring will give a "key" but if you penetrate the paper surface you are weakening the board as that is what gives it it's strength. Wheather it has been done that way or not for years doesn't make it "right"imo.......pva has been used as a primer for years too....

Oh, and i wasn't "challenging" your advice nor was I suggesting your were incompetent and I don't know why you mentioned that. I was giving an opinion to your response as that is what the forums are about...help, advice and debate. If you think what I said is wrong then that is fine, but at least the readers have now been given a different opinion to consider if the situation arises for someone else.

 

[White Room]

Personally I would use a course abrasive oxide paper to break the surface of the paint on the board, scoring with a knife would weaken the board.

The paper is what give's it it's strength

 

[tfs]

If I had the choice I would do neither the tiling on to paint (I would resheat the area being tiled) and I would not choose to use a steamer on plasterboard to remove adhesive (I would again choose to resheat) applying hot steam to a substrate like plaster board would do more damage than scoring the paint. Plaster board is not designed to be resistant to any kind of moisture especialy at a heat that will weaken and strip the paper face of it.

and to be honest scoring paint is not comparable to using pva as a primer.

 

[Stan001]

Why has nobody mentioned 1. The tape test? (a recognised test) and 2. Asked what tile he is intending on installing (ref weight limit) ?


If the painted wall passes the tape test (in several locations to be safe) and the tiles are lighter than the holding weight then the paint is doing the job of the primer.


If it fails the tape test or the weight is higher than the holding surface then replace the plasterboards (cheap and easy job – and very much cheaper than replacing tiles falling off in 6 months)

 

[grumpygrouter]

If I had the choice I would do neither the tiling on to paint (I would resheat the area being tiled) and I would not choose to use a steamer on plasterboard to remove adhesive (I would again choose to resheat) applying hot steam to a substrate like plaster board would do more damage than scoring the paint. Plaster board is not designed to be resistant to any kind of moisture especialy at a heat that will weaken and strip the paper face of it.

and to be honest scoring paint is not comparable to using pva as a primer.

I never said it was, it was an anolgy I used to illustrate that just because it had "been done that way for years" that it doesn't necessarily make it right. Everyone has their own way of doing things and that is what the forums are for, to allow people to read the advice given by contributors on here, compare that advice, contradictory or not, and then make their own informed decision from that information. I think we both agree though that it would be better to re-sheet than waste time removing adhesive or paint if possible. It isn't always possible though!

 

[grumpygrouter]

Why has nobody mentioned 1. The tape test? (a recognised test) and 2. Asked what tile he is intending on installing (ref weight limit) ?


If the painted wall passes the tape test (in several locations to be safe) and the tiles are lighter than the holding weight then the paint is doing the job of the primer.


If it fails the tape test or the weight is higher than the holding surface then replace the plasterboards (cheap and easy job – and very much cheaper than replacing tiles falling off in 6 months)

It depends if the painted surface is gloss or emulsion. Elmusion paint should never be tiled on really as it can go soft on contact with moisture and affect the bond of the adhesive.

 

[Stan001]

grumpy - 100% agree ref emulsion - i forgot to add that, thx for adding that

 

[Gazebo]

Never known anyone to put gloss on walls, so the whole debate was a bit ott if emulsion is in place. which i'm sure is nearly always the case on walls.

 

[Stan001]

Never known anyone to put gloss on walls, so the whole debate was a bit ott if emulsion is in place. which i'm sure is nearly always the case on walls.

I have seen plenty of non emulsion (especially in bathrooms), normally that semi matt or sometimes quite high gloss bathroom eggshell type paint - some of it (the paint) is firm, some patchy, some flakey. Tape test will tell you if its good to tile or not.

 

[The Legend; Phil Hobson RIP]

I would prefer where poss to remove by sanding just the paint. I believe scoring can not only damage the board, But even if you score diagonal criss cross at 20mm intervals then prime. You are only getting a good bond on a tiny percentage of the wall.