A question that I am asked often concerns tar coating foundations. Is this process recommended? Will it keep the groundwater out of the basement?
Many contractors make a business out of this simple treatment, but does it really do any good? Let’s examine this subject. I have a few opinions from my experience, and I will share them with you in hopes that you will make an informed decision when confronted by this technique as a possible way to keep groundwater out the basement or crawlspace.
The coating of exterior foundation walls with tar is not required if the foundation grade can be raised with compacted dirt and clay, and hand excavated french drains are installed and vented in the correct areas around the exterior foundation walls in the proper way.
I am a mason as well as a home drainage contractor, although I do not bid standard masonry jobs, and only work on foundations that have suffered groundwater damage. I occasionally will do a post beam foundation reconstruction or a basement concrete wall reconstruction.
If I am working on a foundation that has significant concrete foundation cracks in the wall that needs to be chiseled out and filled with an expandable concrete made for this purpose, I will tar the exterior foundation wall after the masonry work is completed, but I do not advocate tar placed on the foundation unless crack repair is needed and has been completed first.
I would not dig a foundation back just to tar the wall. The soil will never get compacted as tight as it was prior to the area being excavated, and subsequently groundwater saturates the soil on the foundation wall easier even if hand excavated french drains are installed after the area is compacted. Hand excavated french drains will work to prevent groundwater saturation if the foundation area is well compacted in lifts of about 6 inches when the soil is backfilled against the foundation wall, but it is not necessary to achieve results and therefore I do not charge homeowners for this procedure as I believe they do not need to spend the money on it unless the foundation needs to be repaired, in which case they have already paid for the foundation excavation. The only additional cost to them at that point is the tar.
The exterior foundation wall must be cleaned with a wire brush prior to the chisel work and the crack sealing. After this is accomplished, the exterior foundation wall should be tar coated, back filled with dirt and hand compacted in lifts of about 6 inches to the dirt grade, with the tar below the grade dirt level to the depth that the work was done or a bit lower.
Tar coating by itself will most often not solve a groundwater drainage problem without crack repair work being completed if the structure has significant foundation cracks.
Hand excavated french drains are installed after the grade is raised and compacted as a splash block against and away from the foundation is completed, and in a huge majority of cases this stops the groundwater without adding tar at all.
Another lesson to remember is that the painting of interior basement walls white with dry lock paint may look nice, but from a home groundwater drainage perspective that alone will not prevent groundwater from entering a basement without removing the groundwater on the outside of the foundation with a compacted splash block and hand excavated french drains.
In addition when you paint the interior basement walls with dry lock paint you will never be able to completely finish and skim coat the basement walls to reconditioned like new standard without the costly removable of this paint by chipping it off with a roto-hammer waffle bit, also removing lots of concrete chips with the paint.
This procedure must be done prior to the chiseling of cracks, patching and sealing of cracks, and stripping of the soft exterior of the bare concrete itself.
The new concrete skim coating with a masonry adhesive will not stick to the dry lock paint. You must start with bare concrete to do this work. The process of getting basement walls ready for reconditioning is time consuming and expensive, so don’t paint that rotten basement wall and expect a bid to restore the basement to be cheap. The cost is not cheap to begin with. Putting a new coat of lipstick on that pig will cost you in the end even more.