Smooth with rough patches.

by Steve M
(Surrey)

Hi, I am getting the wall really flat and smooth. The walls look great whilst plaster is still setting and even feels like glass. However, once it has dried totally I find the wall is really smooth then suddenly rough in patches, like sand paper.

Do you know what is causing this?

Answer
Sorry for the delay - it sounds like a lack of pressure in the earlier stages of troweling up. If you push really firmly then your trowel will be in contact with all parts of the wall - by pushing the highs into the lows. If you don't push hard enough then your trowel will just be in contact with the highs.

So plenty of pressure but at the correct angle - otherwise you'll scrape plaster off. As a rough guide the leading edge of your trowel will be about 15mm off the wall. This gap can be increased as the plaster firms up.

Paul

Comments for Smooth with rough patches.

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Oct 22, 2016
 I've had this problem as well
by: Rick

I have not figured the cause of this yet, but I experience this routinely. I have a few clues though. The hosts reply is of course a possibility we should all work to eliminate. For when you're sure that's not the case, mindful of your technique, and having only our eyes and hands to judge a surface, and when everything is smooth as glass and flat, butt doesn't remain so after drying, safe to presume that one of these areas which seemed felt and looked both flat and glass-smooth was filled (as intended), with material which did not retain the same properties as the material in the surrounding surface, after drying. I've noticed a pattern; these rough patches tend to appear only in areas where I'd done a lot of troweling! one possible cause i think is over-troweling, or over watering, where you've stripped too much fat from the surface in an area, leaving a flat, (AND smooth-when-wet) surface but which dries with micro-pores, feeling like "open cement."
Alternatively, in my case these areas could also have been where I had worked extra hard to fill a low spot with excess fat,which would explain the extra troweling in that area. Being of a slightly different composition, perhaps the fat used was too wet or too sparse, or shrunk slightly during drying leaving that rough texture. For me, either of these possible causes can be avoided by getting on a wall at the right time. I find I only over trowel when either I'm so early that an area or two still too fresh to have made a good bond is pulling off under the trowel and then needs special attention to both correct, then pull again on an adjacent stroke, correct again, etc (which, I also often cause from too much pressure, which would be an appropriate pressure at the right time, as leaving the wall go a tad longer affords you tolerance to more pressure, as I've noticed) OR, when I've let the wall go to the point that one spot or two no longer retains the water content within I need for it to remain pliable, (not just what I add to the surface), no big deal until I notice a flaw or holiday and need to muscle some fat from the surrounding material in order to fill it.
Just a consideration based on my experiences. Keep in mind however, I do use a different product/series of products, however they are still all gypsum plasters and the procedure is largely the same for most applications, as are the "common problems" and their recommended corrections or preventions.
Hope his helps somebody or somebody helps me if I'm way off!
Huge fan of the site, much appreciated!
Oct 03, 2014
 painting plaster
by: Paul

It will paint ok - but a quick rub with sand paper first will help. Not to make it smoother but to make the ares that are like glass- slightly rougher - so that they are a bit more porous. This will make it easier to get an even finish with the paint
Sep 29, 2014
 Same problem. can I paint?
by: Anonymous

Will it paint ok or does this need redoing?

90% of my wall is like glass 10% rough patches.

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