I'd like to seal and prime my previously painted (but now peeling) basement floor before painting it again. Any suggestions on a sealer, primer, or waterproofer material, or waterproof paint, I can use? There is no water intrusion, but occasional very, very, slight dampness coming from an old floor crack repair. I can barely feel it. I've refilled the crack with hydraulic cement and now need to finish the floor. I don't really care if it's paint over primer or a waterprrof paint. Any suggestions?

You cannot successfully paint over old floor paint and expect it to stick.
In order to do this right you need to do one of two things.
If your planning to use an epoxy paint system the manufacture will normally provide a acid in which to dilute and to put on the floor. This will chemically etch the floor and provide the bonding required for the paint to stick.

The other method is to use a scarifyer which is a machine that looks like a floor buffer, its heavy and it grinds the surface of the cement down to fresh surface. This is the best way to do this but it sometimes can be a little daunting for those who have not used this type of machine in the past.

As far as dampness and sealing.
Unless the floor is dry all the time, the paint will eventually peel off the surface. Epoxy paints will last the longest providing you prep the surface. But it to will eventually begin to chip and peel where ever water/dampness occurs.
I know of no method of prepping the floor to prevent the dampness from coming thru.

I've seen a number of products that can be applied over previously painted floors that are properly prepared with just deglossing or sanding. I have belt sanded the floor with #40 paper and used TSP, which chemically deglossed what he sander didn't get. It even lifed much of the bad paint and I power sprayed it away. Why wouldn't regular latex floor paint now stick to this surface? Are the steps and product you suggested really needed?

Wouldn't water proof paints like Behr Basement & Masonry WaterProof Paint prevent very light dampness from coming through?

Home care is right about not applying over the old. If you do, you are relying on the bond of the old coating.

Epoxy with proper preparation can be very good.

If you have moisture under the slab, you always have to face the the possibility of peeling. One things is that epoxy will adhere longer and will usually come off in larger pieces, unless it is damaged.

Epoxies have very low permiability, meaning that moisture does not pass through them easily. If you already have some dampness, the epoxy could trap the moisture under it allowing the vapor pressure build to a point where it will blow the finish off of the concrete. This will even occur where multiple layers of non epoxy floor coatings are used. If your existing coating is peeling, it could be telling you something. You need to remove all of the original coating and then recoat. After removing the old finish, I would tape a 3'x3' piece of 6 mil plastic to the floor in the most suspect area. After about a week, lift it and see whether any moisturte has accumulated under it. If so, forego the epoxy and apply a latex coating. If you decide on an epoxy, be careful to provide plenty of ventilation as many produce some nasty fumes until cured.

Water proofing paints such as the brands your discribing as well as all others will not work for a few reasons.

one being they are very thick not a good type of material on a floor as it will not look very good even if it did work.

The second issue is this type of paint is a band-aid type of material. Yes it will hold back some dampness and even water. But if you read the directions carefully it says it must be put on cement that has not had any other paint applied. These products work by seeping into the pores of the surface of the concrete. This provides a bond that prevents the water from entering and causing peeling. The surface needs to be perfectly clean and prepped as well. Very difficult if not impossible to do.

The issue you have with damp floors and walls as well is that vapor pressure builds up behind the paint and even if the paint is properly applied will end up causing the surface of the cement to fail as the pressure and corrosiveness of the water eats away on the cement below the paint. The end result is spalling surface. Sure the water proof paint held but the cement ended up failing.

You should address the cause of the dampness. It can be simple as lowering the float on the sump pump if you have one, or the need to properly water-proof or the install of a interior water deversion system. Water proof is done on outside. But be careful on the interior ones as all the warranties from the companies that I have seen in the past only cover seepage from floor out about four feet from the repair.

AS far as the prep you did. Good work! Your on track to doing it correct, but the vapor pressure below the floor will still cause the paint to blister and come up. It will not happen right away may even take a few years. But it will happen again. You now understand how much work it was to prep the floor, do you want to do that work again? I think not. So you need to be sure that the hard work you have done will last.

My suggestion is to address the moisture from the source if at all possible then paint with an apoxy paint. Google this type of material and purchase on line. The HD brands although good, only offer two or three colors for the homeowner to apply all other colors they have need to be applied by their professional contractors. I have used epoxy coat in the past and have had great luck with it. They offer many colors and chips. Their prices are very reasonable as well. Go to their web site at http://www.epoxy-coat.com/index.php

Keep us posted on how you make out.

A good point!

Getting rid of the moisture around and under a basement gives you far more latitude and long term solutions since the "band-aid" on either the interior or exterior are not as critical.

Remeber, your basement is built inside the same type of hole a swimming pool is. If you can divert or drain the water away, you will not have a lot of the common problems.

quote:

Remember, your basement is built inside the same type of hole a swimming pool is

The difference is that most basements are not built like swimming pools. Swimming pools are built to keep the water in, by means of either a waterproof membrane, or an impervious material. The vast majority of basements are not built with such materials, and that number includes some which should have been.

If a basement were built exactly like a swimming pool, it would keep every bit of water out, just as a swimming pool keeps every bit of water in. Unfortunately, some basements allow water in where it doesn't belong, and that is inside the house. That is why we recommend taking measures to (a) diagnose the cause of the water entry, and (b) cure the problem by dealing with it outside, where the water is coming from.

Oh sure, they'll tell you there is hydrostatic pressure under the floor, but think about it...were you just so unlucky that the hydrostatic pressure exists precisely under your floor but does not affect even one inch of the walls? Does that make any sense? Of course not.

The water issue has been addressed as much as possible given that I live on the bottom of a hill with bedrock 2 feet under the soil. Any water getting under the floor can be coming from a hundred feet away. I'm very fortunate that I don't have a major water problem. For 5 years the floor remained exactly as it was when first painted. Not even a hint of moisture. Then came the rains this spring, you know, the ones in the news that are flooding the entire Iowa/Missouri/Illinois river area. The volume of water was so big for so long that it super saturated the soil. With this water sitting under the floor it was only natural for vapor to begin to come up where there was an old crack repair. That's all it took. The paint peeled within a few months all along the repaired area. Hence the current repair. I've been told to just cover that area with a skim coat of Drylock pourable masonry crack repair over the hydraulic cement I already used to actually fill the crack. It can be painted in 7 days with a latex paint that lets moisture come through instead of popping the paint. Seems reasonable. If I need tp repaint just this area every few years when we get extreme rain I'm OK with that. It's an unfinished basement that during the normal seasons never gets wet. Looks mean nothing to me.

Sagebuilder -

I had a similar situation. At one time I owned a unique home (possibly a very early Frank Lloyd Wright masonry home with a flat roof)that had a similar problem. Probably like your area, I had a basement only a foot or so above solid limestone that was as level as a pool table. I was at the bottom of a 6 block long slope of a hill of a glacial sand deposit. When the spring melt came or there was a very rapid increase of the ground water that was concentrated at the bottom where I lived and the water was flowing through the soil and was forced upward. Fortunately, the architec was smart enough to require drain tile to remove as much water from the soil as possile, so the only minor leakage was during the one week of the spring thaw when there was just too much water in the 4 sumps and about 5 feet of ground water against the walls. - The pumps ran continuously for about two days just like clockwork every spring. I tried several coatings on the floor, but due to the extremely high concrete strength and density most of the coatings used would not hold sitting on my private buried swimming pool. Even though the basement was dry, there was enough moisture in the soil during the year to create the vapor pressure (not measured in psi, but still a disruptive force.

Your situation is similar, but maybe not as sudden or predictable. From what you describe. you probably have a very intermitant and not a once or twice a year situation.

Some people are mislead/misinformed to think that the cause is hydrostatic pressure causing the peeling. It is actually the vapor pressure from the concrete fed by the underlaying soil and the property of concrete to absorb a certain amount of moisture. With my geology, there was always moisture in the soil under the slab. If your coating does not have the permeability (due to the wrong type or too many coats/thinckness), the vapor pressure can cause peeling. Even "breathing" paints if applied thickly (especially on horizontal surfaces)becomes a sufficient vapor barriers to cause peeling. The moisture (not fluid water) in the soil is the cause and that is why wood in contact should be pressure treated.

If you do apply a coating, make sure you clean and/or etch the surface to eliminate the effects and reduced permeability causing the the existing failing paint. If you use a coating, do not use a paint type coating. You might want to consider a clear pentrating sealer oe even a cement based coating. I had reasonably good luck with Thoroseal, but it was a sloppy mess to apply and did not look "pretty".

As long as you recognize that you could be faced with limited problems and do not anticipate finishing the area, it makes little sense to go into major waterproofing expedition. It seems just like you want to clean things up and make the floor reasonably clean and not powdery, so a breathing coating that can be be a solution for you. - Epoxy does not breathe enough even though it is a reasonably good waterproofer.