Cleaning and sealing a concrete driveway

Q.    About 10 years ago, I had a concrete driveway put in. The company put a concrete sealer on the driveway, then told me it was saturated and needed no more treatment for a few years. Since then, the driveway has become stained with organic things (mold, crab apples, leaves, etc.) and non-organic things (black tires marks, etc.)

Last summer, I power-washed the driveway using a concrete and driveway cleaner with little in the way of results. Later, I accidentally spilled some chlorine bleach on one section of the driveway and it looked great.

Dirty driveway
Concrete driveway with dirt and stains

Can I use a hand tank sprayer and spray a water/bleach solution on the rest of the driveway? Would it ruin the sealant? If not, what percentage water/bleach should I use? How often can I use this solution safely? Thank you for any help you can give me.

A.    The sealant applied was topical; it forms a film and needs to be re-applied every year or two. The other type of sealer is penetrating, which needs to be applied only once, as it seals the pores of the concrete.
Nature does a great job of cleaning concrete from organic matter stains, and of tire marks as well. Snow over the winter will bleach the concrete very effectively in your climate (Pennsylvania).

But if it doesn’t to your satisfaction, go ahead and spray the concrete with a mixture a water and bleach. Start with 1/3rd bleach to 2/3rd water, and increase the bleach proportion if it does not satisfactorily do the job. Once clean, rinse well with your garden hose or pressure washer.

Once clean, if you decide to apply a penetrating sealer, wet the concrete to see if water penetrates it or beads on its surface. If the water penetrates, a penetrating sealer should work.

Condensation leaks from new concrete porch

Q.  We added a room and porch to our house last summer. The porch is covered and the room beneath it is heated. The porch is cement and the problem is that it constantly leaks water. I have 2-inch thick Styrofoam insulation on the ceiling of the room, but as soon as you touch the boards, water runs off. Is there any way to prevent this water (condensation) leak?

Also, the outside walls are split-faced blocks, which were painted red and over the summer white has run over the painted surface. I am not sure if this is from the mortar or the blocks. Can anything be done to prevent this from happening again if we re-paint the split-face blocks?

A.    If the concrete porch floor was poured onto a ribbed steel form, the rigid Styrofoam insulation boards cannot prevent condensation from forming. To be effective at preventing condensation, the Styrofoam would have to be glued tightly to a smooth concrete surface. The best solution may be to replace the Styrofoam with sprayed-on, closed-cell polyurethane insulation, unless you have a way to inject canned foam into the open slots until you fill them completely.

If the white you mention on the red-painted, split-faced blocks is powdery, it is efflorescence, and it is caused by salts in the masonry leached out by moisture, which leaves the salts high and dry after the water evaporates. Remove it with a stiff bristle brush. Solving the condensation problem may also eliminate this one if the excess moisture in the room is absorbing the salts and moving to the outside.

Water forms on new basement walls

Q.   Our new house has water on some of the basement walls. The builder says it is condensation from humidity. It is on the above ground portion of the concrete basement walls. Is this common with new construction?

A.    Yes, it is. Concrete exudes a lot of water because it requires about twice as much water to pour it in place for it to cure properly.

It takes one to two heating seasons for the excess moisture generated by the entire construction process to dry. In your case, the moisture appears only at the top of the concrete walls because it is colder above grade than it is below.

Restoring the color to stained concrete

Q.  My patio is large and made of poured concrete that had a green tint added at the processing plant. That was long ago; the color has faded and the concrete surface has a dull, drab look to it. What suggestions can you offer to treat or recoat the surface without creating a slippery surface?

A.  The wisest thing to do is to have a concrete or experienced masonry contractor etch the surface and apply a concrete stain to it.

However, if you decide to tackle the job yourself, the concrete surface can be prepared for the application of a stain by grinding it lightly. Although this is a harder task than etching it with chemicals, it’s a lot safer.

If you choose to etch the concrete, make sure to clean the surface thoroughly, remove any contaminants such as leaf stains, grease or oil, etc. You may need to use a commercial degreaser and/or laundry detergent.

Wet the concrete evenly to prepare for the application of the acid solution and keep it damp, but with no standing water, until you are ready to apply the acid mix. Protect adjacent surfaces.

Try sulfamic acid; it’s a good choice for DIYs because it is much less caustic and dangerous than the other recommended acids – muriatic and phosphoric acids. You should be able to buy it at Home Depot or Lowe’s, or on eBay and some tile stores. But be sure to check the label of the product you are considering to make sure that it is suitable for etching concrete.

If you decide to use muriatic acid – the most commonly used acid by concrete and masonry workers, and easily available in hardware stores – start by mixing one part muriatic acid (extremely caustic!) to nine parts water. Use a plastic pail; never use metal with muriatic acid. Always pour the acid in the water, never the other way around, and do so gently to avoid any splashing.

Gently and very carefully apply the solution to the surface with a plastic sprayer or watering can. If you do not start seeing bubbles, the solution is not strong enough; add more acid to it.

Use a squeegee to spread it evenly. Keep in mind that the floor must remain wet during the entire operation, so if you see a spot drying out, immediately spray water on it with your garden hose.

Watch the floor. When the bubbling stops in about a few to 20 minutes, it’s time for the next step. Some acids do not require neutralizing, so check the label of your chosen acid. If it specifies that you need to neutralize the action of the acid, mix one cup of baking soda in a gallon of hot water and mix it thoroughly ahead of time. Spray the neutralizer on and use the squeegee to spread it evenly.

Now you are ready to rinse the surface with your garden hose. Use the squeegee to push the rinse solution in a corner, and use a wet vac to suck it up. Dispose of the solution according to the instructions on the package. If it is not possible to dump it down the drain, check your local regulations to dispose of it environmentally and legally.

Whichever acid you choose, take maximum precautions, especially for muriatic or phosphoric acid. Cover skin, wear old clothes, eye protection and heavy-duty rubber gloves.

You should be ready to apply the concrete stain of your choice, keeping in mind that concrete stains are a lot better than other coatings for a lasting job, unless you choose epoxy, which is not the best choice for a patio, as it could be slippery.

As you can see, it may be best to leave this job to experienced contractors who will be responsible for the final outcome.

Painting over mold stains

Q.    We had a new home built and after we closed, we noticed spotty areas of mold on the ceiling of our unfinished basement. Either the wood used already had the mold on it or it occurred during the construction process when they closed up the basement without adequately drying it out. The builder was pretty responsive and hired a mold remediation company to clean it up. After they completed their process we were left with “mold stains” on the wood. It is a year later and there is not further growth. Should we paint these areas? We do not want any problems selling the house in the future.

A.    The mold developed because of the high level of moisture exuding from the concrete and other components of the building process. You are fortunate in having had a responsible contractor who took care of the problem. You certainly can paint the basement ceiling to make it more attractive. Prime first with a stain blocker like B-I-N.

Concrete scaling on basement floor

Q.    I need help. I have had my house from new. After four years, I used a good industrial oil-based floor paint on my cement basement floor. It was down for 20 years. Then I used water-based paint and it lasted 20 years. I wanted to get back to oil-based paint.I used as heavy-duty floor sander and took off much of the old paint.

Now the problem. In a few spots on the floor, by the cinderblock wall, the cement is scaling. It bubbles up; I scrape it and a white powder comes up. What can I put on it to stop the white powder from coming back and to make the paint stick to the floor?

A.    By the cement scaling, do you mean that it is breaking up or simply that the white powder is developing? The white powder is undoubtedly efflorescence. Moisture is dissolving the salts in the concrete and bringing them up. The moisture then evaporates, leaving the salts behind. It sounds to me that after 44 years you are suddenly having a mild moisture problem at the base of the walls — just enough to cause this new problem.

Check the grade around the house to see if there have been any changes that lead the water from the roof or gutters to pool against the foundation. If you find any anomalies, take care of them, and see if that solves your problem.

Green spots on concrete patio

Q.    I live in a townhouse with a 10-foot by 10-foot concrete patio. The concrete has greenish-colored spots that appear to be moss or mold growing into its porous surface.

I’ve used a 2-to-1 mixture of hot water and bleach, and scrubbed the patio. This removed all the dirt but the greenish spots remained. What is this? Is there a simple and easy way to remove these spots? The patio faces west and does receive full afternoon sun.

A.    Try a mixture of equal parts water and fresh Clorox bleach (it contains chemicals other brands may not have). Pour it on and let it stand for a few minutes to see if it gets rid of the greenish spots. If it does not, increase the ratio of bleach to water and try it in one spot. Once you have succeeded, you’ll probably have to bleach the entire patio so it will have an even color.

Restoring a pitted garage floor

Q.    My garage floor has become pitted from road salt over the years. I’m considering using one of those epoxy coatings to fill in the pitting and smooth it out and/or first using concrete restorer to fill in the pits and then the coating. What do you think of the possible outcome (looking decent) from this approach?

A.    Why not simply using a polymer-modified product such as Thorocrete or vinyl-reinforced TOP’N BOND? They are both one-step processes for repairing damaged concrete surfaces and should be easily available in building supply stores.

Just be sure that you remove all loose particles with a strong jet of water before applying the new mix and that you follow the instructions on the containers.