Hi All,

I recently painted finished mudded drywall and found one nasty thing - I can clearly see joints under natural light (not necessarily under direct sunlight). Drywall was put vertically (after the job has been done I read that it's recommended to lay it horizontally because of this very reason). I put only one coat of primer before painting with 2 coats of dark paint.

I had a bit of reading and some people point to a different absorption rate of plasterboard and mud and even suggest to use oil based primer for the very first coat. Some suggest that it can be caused by uneven mud, but I don't think it's an issue as I can't feel this - the wall seems very flat. However it seems to have a bit different texture.

I was wondering whether you experienced this in your practice and know a solution?

Thanks!

I suggest you post a picture so we can better understand what the problem is. I am sure there is a way to fix the problem. My way of avoiding any kind of problem is to skim coat the entire wall. Its not for everyone because it is time consuming 2,3, or even 4 coats are needed for that. Vertically or not if the mudding was done right you wont see any joints. They say that installing drywall horizontal with the studs gives a much stronger structure, but that's nothing major if you are building in basement and assuming these are not load bearing walls.

Did you roll on the primer? that usually leaves a slight texture that blends the drywall surface to the mud. You could take one wall and apply some more primer with a roller that leaves a slight texture then paint and see what happens.

Thank you for your replies.

I'll upload a picture tonight, I took one using my mobile but quality is too bad to see anything, so I'll take another one with a real camera.

Yes, I used a texture roller - the same one for both priming and painting. It seems to be that texture is slightly different and that's causing the problem.

I'd like to try applying more primer and paint on a small area to see how it goes.

By the way what's the optimal sand paper for sanding? This guy used 120 - may be it's not fine enough for this job?

Thanks.

I used sanding screens made for drywall. I think they came in 120 and 160-180.

They worked very well. Sand until you can't feel a ridge any longer.

CJ

Thanks carboranadum,

I couldn't feel any ridges, and still can't feel it after I painted the wall... At this moment I tend to believe that this happened because I put only one coat of primer, but can be wrong in my assumption.

Something similar happened to me.

On my ceiling, you can clearly see where the tape is on the joints of the drywall-- and the edges are sharp, almost as if I didn't use any mud. Similar to what you have, it would almost seem like a change in texture where the tape is, buit I can't feel anything-- it is smooth.

This is through one coat of white primer (Kilz), a coat of tinted primer (Behr) and two coats of black paint (Behr)!

I've decided to live with it, and maybe attempt a repaint in the future sometime.

Consider paint sheen. Flat will hide allot of blemished, the glossier it gets the more the blemishes show.

On the flip side, flat really can't be cleaned and show smudges and dirt real easily, where glossy can easily be wiped down.

If youre really sure you cant feel a ridge or bump it sounds like a texture problem to me. Some guys will use 220 to finish, 120 will work too though. Its possible that seam just didnt get a good final sanding.

The only time ive come across needing to use an oil based primer is for bare plasterwalls, to help keep them from chaulking off. I can understand why you might want to use oil over mud...but im pretty sure you arent supposed to use oil on new drywall...so priming just seems with oil and then the drywall with latex seems a bit of a waste to me.

as far as vertical or horizontal orientation to me its 6 of one and half a dozen of the other, I woudlnt lose any sleep over it. if your walls are ceilings are taller or longer than 8 feet, you are going to have a butted seam somewhere.

what length nap roller did you use? It might be possible to fade out the textural difference with another good heavy coat of primer and paint. at least make it a little less noticable. Its unlikely you would be able to sand out what you are seeing, considering there are already 3 coats of paint on it.

the other options is to close your eyes and pretend its not there. :-)

Ive had my wife help me on some drywalling jobs....and thats what I do.

you could always bite the bullent, and add a layer of green glue and a new layer of dry wall, this would solve your problem and help with sound isolation issues.

Consider paint sheen. Flat will hide allot of blemished, the glossier it gets the more the blemishes show.

On the flip side, flat really can't be cleaned and show smudges and dirt real easily, where glossy can easily be wiped down.

I'm with Chiahead, try a flat paint and see if that hides it. Another thing to consider is that every piece of lumber has a crown to it. If the crown is facing out on each wall when you run the drywall vertical to the stud it will tend to exaggerate the crown somewhat. If paint doesn't solve it then I would double the width of my mud over the seams to lessen the effect.

Thank you very much.

I visited the local hardware store I bought my paint and primer from. A guy from painting section has around 30 years experience, and recommended a few things.

First of all, it's too late to do something rather than repainting with flat paint as Chiahead and yaj123 said. Luckily it's washable. It doesn't hide the joints completely but dramatically reduces their visibility, so will just live with this :( :cool:

He also said to use oil based primer for the very first coat to avoid this in the first place - hopefully it will help me for other walls in the house.

Wanted to upload a picture, but it doesn't show much so there was no point in this.

Thank you all again!

In order to avoid the problem that you describe, here is what I did with the ceiling in my theater, which was subsequently painted flat black and would show any imperfections.

I skim coated the entire ceiling with a thinned mud. I put it on and then troweled it off which left very little mud but just enough to even out the finish. Finally sanding of the entire surface and then primer and paint left a very nice, even finish.

I wish I had done that with the 100 sheets of drywall that I hung in the rest of the basement.

Best of Luck.

Thanks budk,

I thought about this option, but the two remaining walls are to be painted white, so no real reason to do this there. However, I would like to use oil-based primer just to minimise impact from all possible imperfections.

Just because its smooth doesnt mean it was floated correctly. Sounds like the mudding was not floated out enough and you are able to view the different thickness from where the joints are.

What is the claim of oil based primer? How is it supposed to make a difference?

It looks really flat, may be there is some difference of 0.2mm or even less, I tried to place ruler across the joints - it doesn't show any difference.

The reason behind oil-based primer is it seals whole surface the same way, so all subsequent coats of water-based primer or paint are not absorbed into the wall, so absorption rate is the same everywhere. This seems to be a valid point as in my case not only edges of joints but whole area of joints had different colour. Not sure however if 2 coats of water-based primer could have brought the same result. I haven't tried it yet, so not sure whether this theory will prove right or not...