Decorating / masking tape - what went wrong?

[Lobster]

Am decorating a replastered room. Since the ceiling meets the external wall on a curve rather than the usual 90-deg corner, I had to decide arbitrarily where to delineate the wall and ceiling for decorating purposes (which I'm doing using different-coloured Leyland-brand matt vinyl emulsions.)

So - I painted the whole lot with a sealing piss-coat (the emulsion thinned down by 20-30%), then 3-4 days ago gave the ceiling one coat of brilliant white. This morning I painted the walls in apricot white (OK, that's magnolia to you and me!), having run a line of 1" masking tape (3M brand) across the top of the wall to make a nice sharp edge to the wall colour. So far so good.

This afternoon everything was at least touch dry (it's been damned hot here all day) so I peeled off the masking tape. Beautiful sharp edge did indeed result - but unfortunately the tape removed nearly all the underlying brilliant white, leaving bare plaster. Bollocks, bollocks and bollocks.

So WTF went wrong? Was the plaster not properly sealed - did I use the wrong stuff? Or was it not properly 'set' even after a few days; ie should I have waited longer before applying masking tape? Would be interested to know for next time.

Thanks David

[Mogga]

How long has your plaster been drying? A builder (reitred after some

40+ years) has said today that we should be waiting 6-8 weeks minimum before thinking about decorating. Fine with me as its too darn hot to paint.

[Lobster]

Just over 3 months, actually! (Didn't wait that long on purpose...)

David

[Andy Hall]

Tape too agressive? there are different stickinesses....

[meow2222]

I notice 2 things: a) diluting paint dilutes the glue component b) any dampness in the plaster will reduce the paint strength in the short term. c) plaster doesnt need sealing.

NT

[diypaint]

There are two reason for diluting your first coat of paint over new (but dry) plaster -

(1) So that it doesn't dry too quickly. The plaster absorbs water - so water is being sucked out of the paint from underneath at the same time as it is evaporating from the top. This is bad news for getting good film formation & a good finish. (2) If it is thinner, it can sink in to the surface a bit better

However! Matt paint does not have much binder in it. Especially the lower cost matt paints. So, it isn't very effective at binding the powdery surface of plaster. (NB. I wouldnt recommend silk either!).

This is why I would *always* recommend plaster sealer (not PVA). It sinks in, binds the powdery surface and helps seal the surface ready for the paint.Plus it removes the need to dilute your first coat.

Run your finger along the reverse side of the stuff that has peeled off. You'll have a dusty finger. No wonder it came off! It was "stuck" to a layer of dust. This is why plaster should always be sealed with plaster sealer - if you want a long lasting durable finish.

NB. Always use low tack masking tape & remove it gently - as soon as possible after painting. The shorter the time it is up there, the less time it has to really get a grip on the surface.

[Tim S]

B&Q Pro(IIRC) range (blue tape) turned out to be very good when I used it. Not too sticky and left a clean edge.

Tim

[Dave]

That is the way I have done it in the past. The longer you leave the masking tape the worse the line. (the paint dries to some extent and sticks to both the wall and the tape) I would rather get paint all over my hands than rip the straight paint line.

Dave

[Weatherlawyer]

I'm not too sure but I think that the paint that masking tape was designed for is not water based. It is used primarily in situations where a sprayer is used.

I don't know anything about the above tape but if the stuff is removed immediately there is less chance of the white stuff removing the paint it is stuck to.

But if I were going to use it I'd make damn sure the paint it was going on was not freshly applied, overly thinned down stuff. Not on plaster at least.

[Andrew Gabriel]

Emulsion paint takes weeks to reach final strength. I wouldn't dare use masking tape on it during this period.

[meow2222]

The water coat method avoids the downsides of the piss coat approach.

[Peter Ashby]

Well for one thing 1 inch tape is wider than you need. For another masking tape is rated by time. I have found even the 24hr stuff should be removed well within that time. If you are at all uncertain then try the delicate surfaces tape, only problem: getting the stuff to stick in the first place.

I've just oiled our bannisters as the last step in our hallway redecoration (an afterthought, unfortunately) and the tape I applied to the painted wall has removed the paint down to plaster in one small section, otherwise fine though. So I have concluded the paint in that place was probably not secure. I was a bit sloppy with the stain rag and the prep meant I need to touch up the paint anyway so no big problem.

So, wait before taping new paint. Use the least sticky tape you can get away with. Remove it when the paint is just tacky. The point when you can remove the tape but the paint won't flow over the line. Don't wait until the paint is absolutely dry.

Peter

[Lobster]

Thanks for all the replies.

Well, this has been an education! I hadn't actually realised that there were different types of masking tape; I've rarely had occasion to use the stuff before and simply picked up a roll I found in the cupboard. I've just checked its reference number on the 3M site and found it's a general purpose automotive masking tape... presumably that must be really sticky compared with stuff intended for plaster walls - so that's a big OOPS I think.

FWIW I also happened across the following 'masking tape selector' chart which describes which of several types to use in different circumstances, which others might find useful: (or )

David