What is the best procedure for painting over latex paint? The walls in my dining room were not properly preped before the old owner pained on the walls with latex paint. I want to re paint the walls, but I wanted to get some tips on the best way to go about doing this....
IMHO, 220 sandpaper is too fine to knock down the ridges of old paint and lint left from cheap roller covers used on the walls of past paint jobs. Even 100 grit tends to get clog rapidly because of the gummy nature of latex paints. Even when sanding new drywall, the most common grits available for sanding blocks are between 100 and 150.
For super-fine smoothwall drywall jobs, the final "sanding" is actually done with a dampened block sponge.
220 would be suitable for dulling down an oil enamel on kitchen or bath walls, or scuff sanding furniture or woodwork prior to painting. Here, a course 100 grit could make scratches that might possible show through the new coat of paint.
When smoothing patches out in the middle of textured walls, I sand first with 100 grit paper, followed by wiping the edges of the patch with a dampened sponge, so as to blend the edge into the surrounding texture. Even texture spray will not hide a ridge left by a spackle knife. My preferred patching material is either "hot mud" such as DuraBond Easy Sand 20, or regular drywall compound. Unlike the premixed patching compounds, drywall muds will re-dissolve and blend in. My main reason for avoiding the pre-mixed compounds is that I lived in a very cold climate. The pre-mix compounds would freeze overnight in the work truck and then be ruined. I always carried DuraBond in a 2 gallon bucket and would mix it is needed.
After the patch looks pretty good in its own right, the texture can then be sprayed on and allowed to dry. It should then be, at a minimum, spot primed. It is sometimes advisable to prime the entire wall to assure that the patch will not show through as a dull or shinier spot or, in the case of a strong color change, show a color difference.
If I read your question correctly, your main concern is how to prep the wall before repainting ... your concern rises from the appearance created when the walls were painted by the prior owner.
Based upon your description, I have two conclusions:
1) The existing imperfections can be smoothed, but be very careful not to cause more wall damage by using a low number sandpaper. I commonly recommend 220-grit to my customers ... it is labeled "Finishing" and "Very Fine."
Sandpaper with more grit than this can tear the paper facing on your wallboard and create secondary repairs that simply are not necessary. Once these tears are made, your only recourse is skim-coating the entire wall, sanding again, priming, and painting.
2) The imperfections on the walls were probably created by a dirty wall or a roller cover that dropped nap/fuzz.
The solution for this ... use TSP mixed into warm water to wash the walls after sanding, but before painting.
And, use the best roller cover available to apply your paint.
I believe is was my buddy Forrest Gump who said, "Cheap is as cheap does."
He was soo right! My customers regularly complain that the least expensive roller covers drop nap.
A three-eighths nap roller cover is recommended for smooth walls and the TSP will remove the remaining sanding dust, dirt, lint, and other debris ... lightly rinse with fresh, clean water and allow the walls to completely dry before painting.
So, no matter what else you do, stay away from low number sandpaper and use the best roller cover available.
NOTE: After your walls are smooth, but before you wash with TSP, use a wet/dry Shop-Vac to remove the sanding dust. Be certain to check proper fit of the cannister filter to ensure that dust is not blown around the room/house.
FINALLY: The words Latex and Water-base are synonymous ... meaning you can repaint using any water-base paint. Lower sheens like Flat or Eggshell will show the fewest imperfections because they reflect light the least.
You don't state the nature of the bad preparation by the last owner. so I will make general comments:
It is always good to wash any dirt or oils from the wall and woodwork. If the past painter got a lot of junk or roller lint in the paint, a general sanding of the walls with about a 100 grit sandpaper is advisable. Check over the walls for any holes or cracks which need patching. After the patches are dried and sanded smooth, you should spot prime them. If you have textured walls, the texture should be applied before the spot priming.
You have your choice of using a general wall primer and then a finish coat of paint or, using one of the new generation self-priming paints. These include: the new generation of Behr Premium Plus which is just now being introduced into the Home Depots around the country, Behr's Ultra Premium Plus, or Glidden's new DUO paint.
The sheen of the paint you choose is to some degree personal taste. In general, higher sheens are more washable. Lower sheens are more forgiving about hiding wall imperfections and are less glarey.
I am assuming that you are only re-doing your walls. However, if you intend to do the entire room, including ceilings and woodwork, the order I follow is: ceilings, then woodwork, then walls. Some people prefer to do the woodwork last. I do the woodwork first because it is much easier to cut in a nice straight line to the woodwork, rather than the woodwork to the walls.
After the woodwork paint is thoroughly dry, I like to tape the baseboards with painter's "Delicate"blue tape or "FROG" tape.. Taping the baseboard assures that roller speckles will not get all over them. It also gives a nice straight line when the tape is pulled. If I am sure that the paint has covered well, I pull the tape immediately after I have finished rolling a wall, rather then wait until it has dried. This assures that the paint will not peel away from the edge. It also allows you to easily clean up any paint which might have crawled under the edge of the tape.
Preparation of woodwork is not unlike the walls: clean, patch, scuff sand, paint. The new self-priming paints can go directly to the woodwork, unlike conventional paints. Scuff sanding is important though. I really like the Behr Ultra for woodwork. One secret of good results with acrylic/latex paints is to not over brush them. Acrylic paints set in a much shorter time than oil paints. You should brush the paint on quickly, using a good brush, and then leave it alone to level itself out. Over brushing will result in brush marks!
Hope this has been helpful. Good luck!