Expert: Bruce E. Johnson - 5/18/2009

Question
QUESTION: Hi Bruce,

My house was built in 1915. The basement walls are very thick concrete, but porous, crumbly, and sometimes damp. I have to run a dehumidifier. The basement is roughly 26 by 22 feet. Two extensions were built in front and back of house each 8 by 16 feet. They were built on cinder blocks over crawl spaces. I encapsulated the crawl spaces with 9 mil plastic and that slightly helped, it prevented moisture from the earth evaporating into the basement. (About 8 inches of the top of the basement walls is open extending into the crawl spaces. The crawl spaces as I said are now encapsulated.
The moisture in basement seems to come through the wall through penetration. The basement floor does not get wet.  

How do you recommend safely:

1. Cleaning off the walls. Do I need a pressure washer? If so is electric sufficient. Gas ones are much more powerful, but I am concerned about using one indoors. Maybe there is a cheaper simpler way to clean the walls which as I said contains failed attempts at cement coatings, masonry paint and even tar in some places. Basically I am writing to do as I want to do it right this time.

2. I need to apply a resurfacing cement to smooth the walls. I tried Sacrete Top and
Bond. It is very hard and adheres well. But under one window there is efflorescence occurring, How do I clean off the efflorescence? Which resurfacing cement do you recommend that resists hydrostatic pressure.

3. Sealers. What sealer ((s)) do you recommend that truly bonds into the cement and stops hydrostatic pressure? Note I will probably have to apply a sealer on the adjacent side walk which is old and porous. VSeal sounds good but I don't like the fact that I must reapply it every three years. every company bad mouths the other companies so I need a professional like yourself to make a recommendation I can trust.

Lastly, I have mostly worked on the obvious, gutters and leaders, and sloping the soil away from the house or if there is cement next to the house to place a polyurethane caulk between the house and driveway.

ANSWER: Hi Kenneth, I prefer to use a sandblaster for cleaning walls like yours.  Home Depot, Lowes and other tool places have inexpensive sand blasting guns however you do need a compressor to provide the air power.  I just use cheap bagged play sand for the media.  It does what a pressure washer does without the excess water.  Some rental companies have shot blasting equipment that will also accomplish the same thing, faster using metal beads.  When doing large commercial block buildings that develop efflorescence during construction the sand blaster cleans it off quite well. Protect your window during the process and yourself, a welding shield and gloves are a must..Any good topping mix, sacrete works good, vinylpatch, or just a plain mortar/stucco mix will suffice with a little latex bonding agent added..It is important to let whatever you use to cure completely, up to a month!  before you paint on any coatings.  Dry-lok is a good product and can be found locally..It takes several good coats and they need to dry completely between coats following all the manufacturer's recommendations.  To be honest with you, nothing really resists hydrostatic pressure completely on the inside of a wall.  The true location for vapor barriers is the exterior of the wall..Which, in your case, it would pose a problem to dig out your walls and properly waterproof them and then provide footing drains to carry any water away from the foundation.  So although you may be able to stop a lot of the moisture, you will have to continue the good fight and keep up with your maintenance over the years. And keep the humidifier..you will notice a decrease in moisture accumulation..but don't overdo it..keep the moisture content in the air at around 45-50%.    I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Hi Bruce,

Excellent answer. I would have never thought of sand blasting the interior. It seems so obvious when you think of it but you are the only one who came up with the idea. Thank you for the advice on protective gear for myself and windows. Sounds like you have years of experience doing this.

You think I should buy or rent the compressor? If so what do you recommend?

Copper pipes run along the walls, near the washing machine. I'm afraid the sand blasting could possibly break the weld in the pipes and cause a leak. If you think I should be concerned, any thoughts on how to protect the copper pipes.

I know you answered this part of my question but I was really hoping that Concrete
Sealer X-2 or Radon Seal Plus could get deep into the walls and stop the hydrostatic pressure from the inside. It appears you disagree with their claims. There is some dampness on the walls but not a lot of hydrostatic pressure as far as I can see. Nevertheless, you're probably right. It is just that I have read so many complaints about Dry lock not adhering and flaking off eventually, that I was hoping one of these other products might adhere better and prevent moisture from coming through. The complaints about the dry lock not adhering could well be that no one sand blasted the walls. Anyway between Dry-Lock, ThoroSeal, Concrete Sealer X-2 and Radon Seal Plus, I am tending towards the Concrete Sealer X-2. Any preference for you?

Lastly, you raise an important point that I agree totally with you, about stopping the outside moisture. If I seal the porous sidewalk with something like concrete Sealer X2 I would hope that there would be less moisture coming through at least one of the walls. After everything is finally done and the walls resurfaced and after waiting another 30 days I plan to use a waterproof masonary paint by Behr.
Bruce Thanks again. You have a 1000 more knowledge about this subject than anyone else I have spoken to.

Ken  

Answer
Hi again Ken, sorry I haven't gotten back sooner but I have been away..still am actually..anyhow: Any of the above products will probably work for a while but you will need to redo some of it over time.  Picture a screen with a piece of notebook paper slapped up against it.  Put a hose on the paper and it will keep the water from going through the screen.  Now put a hose on the other side of the screen.  How long does it take to blow the paper off the screen? No time at all.  Your paint/sealer coating is that paper and the screen is your wall.  A penetrating sealer can only penetrate so far, an elastomeric coating can only hold on for so long..etc.  You will have to maintain all of the above coatings you have listed.  As far as protecting other surfaces just throw a drop cloth or old sheet or towel over the object.  When sandblasting you will be able to see where the sand is going so it will be easy to isolate any sensitive objects..Yes buy a compressor for your house!  I have a small five gallon single tank compressor and I use it for everything.  Get a long hose and put it on a rack or a hose reel and you can probably reach every point in your house in case you need to use a nail gun or other air powered tool. Read the directions on your tools and adjust the air pressure accordingly. I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com