The best approach to seal a basement from moisture is to do it from the outside.
- This will keep all moisture from setting in concrete blocks which will lead to futher degredation of the concrete blocks.
- Sealing it from the inside is just covering up the problem.
As for the cracks, if the cracks are in the mortar joint you can have this tuck pointed.
- If you are experiancing cracks through the center of the blocks, this is a sign of larger problems possible consisting of movement within the structure or freeze and thaw cycles over winter months due to moisture trapped in the block.
- If you are concerned about the condition, I would contact a structural engineer to do a field visit and assess the situation regarding teh cracks.
Also dig around the outside of the home to visually inspect the condition of the waterproofing. If it appears to be in poor condition, contact a reputable water proofing contractor to do a field assessment and make recomendations.
For more information:
Read "How would you preserve a turn-of-the-century rock wall in a moist basement?" a Q&A answered by Tim Montgomery.