What Your Foundation Is Made Of
Five minutes with a torch tells you which of three completely different problems you have - and rules out about half the products you will be offered.
How to identify it
- Look at an unfinished section of wall with a torch held close and at an angle.
- Regular rectangular units with visible mortar lines every 8 by 16 inches: concrete block, almost certainly hollow.
- Irregular, larger stone units with wide mortar joints and a warm sandy colour: sandstone. Common in Akron's oldest stock.
- A continuous grey surface with occasional form-tie marks and no unit lines: poured concrete, generally post-war.
- Tap it. Hollow block sounds hollow. Sandstone and poured do not.
Knowing this before any contractor visits is worth real money, because it lets you immediately discount anyone who proposes the wrong product for the wall you have.
Crack injection on hollow block or sandstone is the clearest example. It is a legitimate product on poured concrete and close to useless on the other two, because there is no discrete crack carrying the water.
Hollow block: the reservoir problem
A hollow block wall has vertical cavities running through it. Water entering through the mortar joints collects in those cavities and sits there. The wall becomes a tank, and the water finds its way out at the weakest point - usually the joint between the wall and the floor slab.
The correct treatment involves drilling weep holes at the base of the cores so the trapped water can drain into the new drainage system rather than sitting inside the wall. If a quote for a block basement does not mention relieving the cores, ask about it directly - it is the difference between a system that works and one that manages the symptom.
Sandstone: the mortar problem
Sandstone blocks themselves are durable. The lime mortar between them is not, after a century of freeze-thaw. Water passes through the joints across the whole wall rather than at any single point.
Repointing - raking out failed mortar and replacing it - is skilled masonry work and is priced accordingly. It is also worth doing properly, with a mortar mix appropriate to old soft stone. A hard modern cement mortar against soft sandstone causes the stone to spall instead of the mortar, which trades a repairable problem for an unrepairable one.
Common questions
Is a bowing block wall an emergency?
It depends on how much and whether it is moving. Deflection under about an inch is commonly monitored and reinforced with carbon fibre. More than that, or visible horizontal cracking with displacement, warrants a structural engineer rather than a waterproofing salesperson.
Can I repoint sandstone myself?
Small areas, yes, with the right mortar mix - and the mix matters more than the technique. Use a soft lime-based mortar, not standard modern cement. Getting that wrong causes damage that is much more expensive than the repointing would have been.
Will an interior system work on sandstone?
Yes. Interior drainage does not care what the wall is made of - it collects water at the footing regardless. What differs is whether you also need to address the wall itself, which on sandstone often means repointing to slow the deterioration.
Not sure what you have?
Describe what the wall looks like, or tell us the age of the house, and a local contractor can usually tell you immediately. No charge, no obligation.
Or call (877) 701-2518