Caulking the bottom plate of walls

Q.    I think our house leaks – both cold air in and warm air out — at the area where the structure and siding sit on the concrete slab (no basement). I believe there is nothing to seal the exchange of air at the 200 feet of this contact. Is there a product like a putty to build up an insulation barrier? I realize I would have to work with my head on the ground to install whatever product is recommended.

A.    It does sound as if there is no sill sealer under the bottom plate of the walls. You can try to caulk the perimeter from outside, but it may be a lot easier to caulk the joint between the concrete slab and the wall plates from inside, if you have access to it.

Use polyurethane caulking, which you can buy in construction specialty houses like A.H. Harris:

Synthetic stucco causes problems if improperly installed

Q.  I plan on moving to North Carolina from New Jersey. There is a house that I am interested in but the exterior is synthetic stucco. I have heard horror stories about this kind of material and wonder if you could enlighten me regarding the pros and cons.

The house is between 10 and 15 years old. The seller has advised that every year and a half, he would have it inspected. He says that if you carefully watch the caulking around the windows, there won’t be any problem. I have inquired as to the cost to have it replaced and was told that it would be approximately $40,000. Quite a lot of money!

A.    The problems associated with synthetic stucco, known as EIFS, are in the installation. Although the installation instructions are very clear, unfortunately, many builders do not read or follow them, according to an architect who has been called to check many such installations.

If not properly flashed and caulked, water will get behind the panels, and serious deterioration problems will develop in the substrate. If not caught in time, the repairs may be extensive and very costly. The  best advice I can give you is to find someone who is very familiar with this product and have him or her check the siding thoroughly.

This person might be an experienced and thoroughly trained certified home inspector. You can find a certified member of the American Society of Home Inspectors — ASHI —  by looking in your Yellow Pages under “Home & Building Inspection Services” or similar listing, or online at, or a professional engineer or architect familiar with this type of stucco. If you can find out the name of the manufacturer, you may also have their local or regional representative come and inspect the siding.

Keep in mind that, if properly installed and maintained, this is a satisfactory material that can last a long time. But if it is not, you may be in for a very expensive fix.

Polyurethane caulk needs to cure for a week

Q.  I know that you are a fan of polyurethane caulk for its performance, and I have used it for some time. I had a curious experience recently, and wonder if you might have any insight.

My shower stall was in need of some caulking, both inside and out. Unfortunately, several hours after I completed the job, my son used the shower. I noticed several days later that while the caulk on the outside of the shower stall retained its white color, the inside caulking, which had been exposed to running water, developed what appear to be small rust stains.

There is not an overabundance of them, but enough to be somewhat annoying. They have not changed or grown since I first noticed them, which has been about two weeks now. I can only assume that the water had a reaction with the caulk before it had sufficient time to cure. Are you familiar with this phenomenon?

A.    Polyurethane caulking needs to be allowed to cure without getting wet for seven days. Otherwise, it turns somewhat pink. Unfortunately, you will have to remove it (which is not easy to do) and put new caulking if you cannot live with the change.

Or try to apply a thin film of the same caulking over the stained one after making sure it is thoroughly dry, and be sure not to let it get wet for a week, if that is possible. Otherwise, choose a different brand such as DAP Kwik Seal Plus Premium Kitchen & Bath Adhesive Caulk w/MICROBAN, a mildew retarder.

I have used it as well to see how it would hold up, but was disappointed over time as it separated from the tiles. But it did remain sparkling white. It has some silicone in it, and my experiences with silicone products have not been too successful, which is why I prefer polyurethane caulking compounds.

Recommended caulk for use in bathrooms

Q.  I would like your recommendation for a caulk for bathroom applications: shower enclosures, sinks, base of the toilet, etc. A few years ago, I used Phenoseal, because that is what a plumber used. I had previously used silicone caulk and found it difficult to apply cleanly.

The advantage of Phenoseal is that you can smooth it out with a damp finger (or similar shaped rod) to get a clean bead. If you make too much of a mess, you can clean it up with a wet sponge and start over. You can’t do that with silicone.

Now the downside: After a year or so, a slight amount of black mold started growing in the caulk, mainly in the shower enclosure (not surprising since it’s a wet environment). Note that I had bleached the area before applying the caulk, and I tried bleaching it when the mold first appeared. This helped some, but now 5 yrs later, the caulk in the shower enclosure is heavily overgrown with mold, and I need to replace it.

Should I still use Phenoseal, perhaps with an anti-mold additive? I assume that Phenoseal is susceptible to mold because it is a water-based (latex?) compound. Or should I switch back to a silicone caulk and practice, practice, practice laying down a clean bead?

A.    In my experience, silicone is the worst thing to use at the joint of a tub and tiles. I have seen so many failures in my nearly 60 years in the residential construction field. It will eventually peel and allow water to get behind it, leading to serious problems.

I have used polyurethane caulking for bathrooms for many years. But you need to allow the caulking seven days air-curing before you can get it wet or it will turn yellowish-pink. Even then, the white caulk will turn slightly greyer over time.

You can find polyurethane caulking in building supply houses that specialize in masonry and waterproofing products. A.H. Harris, with stores throughout the east coast, carries Sikaflex 1-a, my favorite and a product I have used for 50 plus years. Their website is

You may want to try Dap Kwik Seal Plus Premium Kitchen & Bath Adhesive Caulk with Microban. The manufacturer says that Microban fights mold and mildew and the growth of stains and odor-causing bacteria. Although it is a siliconized latex caulk, it has much better adhesion than pure silicone caulking. It is guaranteed crack-proof.

Unfortunately, although the caulk remained white, I have also experienced separation between tub and tiled walls in year-long tests on the same tub, half of which was caulked with it and half with Sikaflex-1a.

Beam is rotting on exterior of house

Q.    I have a post-and-beam house built in 1980. The ends of the main beam extend outside the house and are exposed to the elements. These ends are flat on top and one of them is rotting from the top.

I am wondering what you might suggest I should do on this end (the rotting one) and to head off the possibility of rot on the other end. Thanks you in advance for your advice.

A.    The treatment of the rotten end on one beam depends on how advanced the rot is. If the rot is minor, you can gouge it out, pour a wood preservative in the gouge and, when the preservative has dried thoroughly, fill the gouge with an epoxy wood filler (buy in paint or hardware stores, or in home centers). If the rot is extensive, an experienced contractor should look at it and advise you on what to do.

To protect the beam ends, paint them and cover the exposed tops with metal. Have a contractor do so or, if you want to do the job yourself, you can buy coil aluminum in building supply stores. It is available in mill finish, or black or brown on one side and white on the other side.  Rent a metal break to bend the metal so it looks professional.

Be sure to caulk the joint of the beams where they project from the house and the metal. Do not use silicone as it will eventually peel off; use polyurethane caulking you can buy in specialty building products stores such as A.H. Harris.

Sealing a cracked concrete fountain

Q.    I have a concrete fountain, approximately 24 inches in diameter, which has several cracks and will not hold water. What product can I use to seal the fountain, so that it will hold water.

A.    The easiest fix is to find a polyurethane caulking, available at a masonry supply house. My favorite is Sikaflex 1-a, which I have used for over 50 years. It comes in several colors, including one that very much resembles concrete. It can also be painted after it has cured. You did not mention where you live but you may find an A.H. Harris store near you; they carry either Sikaflex. You can find the store closest to you on their Web site:

It is absolutely essential that you clean and dry the fountain and, once you have applied the caulking to the cracks, that you let it air-cure for a minimum of seven days, so be sure that you cover it to keep it dry but in such a way as to allow for ventilation. Once properly cured, polyurethane caulking can be immersed in water.

Ridding cabin of cluster flies and other pests

Q.  We have a cabin in Upper Michigan that was built in the mid 1960s. Cluster flies drive us crazy, as well as mosquitoes getting in, along with mice, sometimes bats and we even had a red squirrel.

We have caulked everything we can think of, to no avail. Also, we would like to add some insulation (there is none behind the wood “panel” walls). Any thoughts on the most effective and efficient ways to tackle these matters?

A.    Unfortunately, the answer to these intrusions is always the same: Seal all possible points of entry. This will require a thorough inspection of every inch of the outside of your cabin — walls, floor, roof.

Bats will usually get inside around the joint where walls and roof meet, and they don’t need a big hole. Cabins, camps and similar rustic buildings. often have rafters extending through the walls to provide some overhang. Check around every rafter projection for the smallest crack where the wildlife that is disturbing you can get in. Seal small cracks with polyurethane caulking in a tube.

A red squirrel needs a bigger hole than a bat, possibly requiring him to chew an existing hole so he could get in. For larger cracks, you may need to use low-expansion canned foam but you will have to protect the foam with fine-mesh hardware cloth to keep animals from chewing through it.
Another and perhaps simpler system is to seal the overhangs with boards or plywood. If ventilation of an attic is desired in conjunction with a ridge vent, use off-the-shelf perforated metal soffit vents.

Be sure to check the joints of floor and walls, particularly if the cabin is on piers or stilts, as opposed to a full foundation.

If the cabin is unheated and strictly used in mild weather, you can have cellulose blown into the walls but stay away from wet-spray; it is unlikely to ever dry. The inability to provide a vapor retarder on the inside of the walls will not be a problem if the cabin is not used regularly in winter. I assume you have insulation in the ceiling, otherwise there would be no point in insulating the walls.

Bathtub Caulk

Q.  What is the best brand of caulk to use around a shower or bathtub?

A.    There are two issues to consider. A bathroom caulk that is mildew-resistant and one that I consider the best. Here is a repeat of an answer to another reader last April:

Some time ago, I tried  DAP KWIK SEAL PLUS Premium Kitchen & Bath Adhesive Caulk with Microban because of its claim that it is mildew-proof. I caulked half of our tub with it and the other half with Sikaflex-1a polyurethane caulking/sealant, which I have used for over 50 years in all types of construction applications.

I decided to give DAP’s product a try because some of my readers had reported that Sikaflex-1a had turned pink after a while, or simply did not remain as white as when first applied, which does happen if Sikaflex-1a is not allowed to air-cure without being repeatedly wet for a week (hard to do if your tub or shower is the only one in the house).

Although the DAP caulk remained sparkling white and did not mildew, I found out that it began to peel off the wall in about a year, typical of siliconized products, whereas Sikaflex-1a was still firmly stuck to both the tub and the wall. Sikaflex-1a tubes sell for around $5 in A.H. Harris stores ( found throughout the Northeast. You can also buy it from DHC Supplies, Home Depot stores do not carry Sikaflex-1a, but Sika Construction Sealant, which looks quite the same to me.

Sikaflex-1a has not mildewed in my experience, but that does not mean that it won’t under different conditions. Which one to use is a personal choice. For me, after the “test”, the choice is Sikaflex-1a every time.