My basement (currently unfinished) is mostly dry. It doesn't smell musty at all and there is no visible moisture coming in through the CMU walls. In the two years I have owned the house, there have been a couple times where a small amount of water has come in at the bottom of the wall at one corner. Because I want to finish the basement, I had a company come give me a quote for one of those interior trenches at the foundation that drains to a sump pump. They basically said it would do no good because there is so little water coming in that it would never even reach the pump. Since then, I have done significant regrading, added clay at the exterior and replaced the gutters. I haven't had any water come in since doing this work (about 8 months). Still, it would make me feel better to have a bit of protection on the inside of the basement just in case. I realize that basement waterproofing needs to happen on the exterior, but the problem is so minimal I can't justify the cost to dig out and waterproof or add drain tile. So, I figure something on the inside can't hurt. Are there any waterproofing products recommended for this use? I'm picturing something you would put on the exterior like an adhered membrane. There are products that are more of a coating (like DryLok) but most require a clean surface and my walls have multiple layers of paint. Any product recommendations would be very helpful!
It does sound like you don't have much of a problem. Especially if during the last 8 months since your outside work if there has been rains that normally would have let that trickle of water in that now do not.
Interior waterproofing IS the last thing to do and would be a good idea for the basement like yours that doesn't really leak but you want to make sure. The problem in your case is the paint that is already on the inside of the block walls. A good interior waterproofer works by being drawn into the voids of the block wall and making the wall 'waterproof". Any coating on the surface of the wall (like the paint that is already there) will not hold back any water for long as it will be on the surface of a water soaked block. Because of that, anything that you add on top of the paint will do nothing to keep water out.
About the only thing that would do any good will be to add an interior water seal to the joint where the block wall meets the floor. And/or use a sealing caulk for any cracks in this area.
Finally, even though the interior waterproof guys say that there is not enough water for an interior drain system, you could still install a simple sump - especially if this small potential leak is confined to one area. Other that spending a little money, there would be nothing wrong with cutting in a sump in the suspect area and installing a small pump with a float switch. It will not hurt it if it's never used but will give you the peace of mind to know that if any water gets in via the most likely spot, that it will get pumped out.
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