I plan to finish my basement but I wanted to get some input on a few things. What are some options for sealing between the slab and wall? I don't have a water problem (knock on wood) and my radon levels were very low. I just want to seal it before I insulate and frame and don't have access to it. I have used hydraulic cement before and would like to avoid that if at all possible. I am real good at making way more than I can apply before it sets!

My plan is to follow the buildingscience.com recommendation of 2" foam board with framing. I don't plan to insluate between the studs. It is pretty comfortable now with just the foil backed insulation on the top half (which will be removed) of the wall. Question 2...What is the best way to install the foam board? Simply tape the seams (what kind of tape?) and let the mass hold itself together or glue it to the wall. I realize that the framing should hold it in place. When I install it between the floor joists at the outside wall to I caulk (what kind) the edges? I get the basic concept from buildingscience.com but its the little details that end up getting me.

Finally question 3. From reading I gather that a lot of moisture enters through the slab and walls. Before in****ing I was hoping to apply a sealer to minimize this, not as a waterproofer but just to limit humidity. I'm leaning towards something like radon seal since it "seams" easy to apply (no need to kill pilot lights and clear the family from the house )
Again this would be to limit normal moisture penetration. Any thoughts?


The house is only ~4 years old. The basement walls are 9' poured concrete walls and is entirely below ground. I have a few cracks on the floor that I have already cleaned and patched. I think they are just shrinkage cracks. There are few hairline verticle cracks on the walls but they are pretty small and don't seem to be moving. There is internal and external drainage around the foundation and under some under the slab with a sump pit and pump. When it rains the pump does runs but I have not had any water issues

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Originally posted by Mr. T:
I plan to finish my basement but I wanted to get some input on a few things. What are some options for sealing between the slab and wall? I don't have a water problem (knock on wood) and my radon levels were very low. I just want to seal it before I insulate and frame and don't have access to it. I have used hydraulic cement before and would like to avoid that if at all possible. I am real good at making way more than I can apply before it sets!

If you are going to seal that joint, the hydraulic cement would be your best choice, since that's what it's made for. Sounds like you've mixed up the fast drying cement before, there are others that doesn't dry as fast - either that or simply don't mix as much.

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My plan is to follow the buildingscience.com recommendation of 2" foam board with framing. I don't plan to insluate between the studs. It is pretty comfortable now with just the foil backed insulation on the top half (which will be removed) of the wall. Question 2...What is the best way to install the foam board? Simply tape the seams (what kind of tape?) and let the mass hold itself together or glue it to the wall. I realize that the framing should hold it in place. When I install it between the floor joists at the outside wall to I caulk (what kind) the edges? I get the basic concept from buildingscience.com but its the little details that end up getting me.

What I have done is to glue the 2" foam board directly to the concrete. Incidently I like to use foil faced because of the built in vapor barrier, it costs a little more but well worth it in my opinion. Make sure that you run the glue bead vertically, not horizontally. If any kind of vapor or moisture makes it way back there, it will be able to drain down the wall, instead of hanging up on an horizontal bead. The seams between the foam should be taped using house wrap tape. Any lumber yard or box store will have it, I like to use this stuff because it'll stick to anything and it is thick and durable.

Your question on the rim joists - caulking around the edges. I prefer to cut my foam insulation 1/2" short all around and instead of caulking, use a can of spray foam and fill this gap. If you try and caulk this, you will find after about 2 or 3 rim joist cavities that it is unpleasant work and it's going to take forever to do the whole house. Spray foam is easy and it will seal those gaps tight and insulate it at the same time. Caulking does not insulate and it will break down over time.

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Finally question 3. From reading I gather that a lot of moisture enters through the slab and walls. Before in****ing I was hoping to apply a sealer to minimize this, not as a waterproofer but just to limit humidity. I'm leaning towards something like radon seal since it "seams" easy to apply (no need to kill pilot lights and clear the family from the house )
Again this would be to limit normal moisture penetration. Any thoughts?

Again there are products out there for this application, drylok makes one and I'm sure that there are others as well, I've only heard of drylok. (Incidently they also make hydraulic cement)

Sounds like you have all your foundation drainage bases covered. As long as you have a good waterproofer on the outside, those small cracks on the wall shouldn't be an issue. Good luck

The floating floor along the wall can be sealed using closed cell backer rod and caulk. Do not use cement! Also any cement sealant may void warranty on floors and water intrusion if done by owner other then builder.

You must correct the humidty level and determine where the moisture is coming from on the walls before you proceed. Is the moisture from condenation or from seepage on the wall?

Place a large piece of plastic wrap on the floor and wall areas where you are seeing moisture. Tape this plastic tight to the cement with duct tape.
Wait a few days (the longer the better) and then check back. Is the condensate on the surface of the plastic or between it and the cement. The former is excessive humidity in the basement from an internal source. The latter is leakage from and through the cement. This MUST be fixed before you proceed with rebuilding. Otherwise you will end up with a very expensive petri dish full of mold.
Simply painting the walls with a water proofing paint will not solve the issue long term. Its a quick fix but the problem will not go away and only get worse over time.
Depending on where you live, you should have a new home warranty against moisture intrusion into the basement and home. In NJ the builder must supply a 10 year warranty for this. Check on this as your warranty may be diffrent. Have your lawyer review it if you do not understand it or before you go to your builder for repairs. Not doing so may void your rights to go ofter them if you end up agreeing to their fix without knowing if its right or not and you experiance a water loss before the warranty is up.

As far as the drainage. The internal pit should not have to work if they did the exterior water proofing correct. The idea of exterior water proofing is to prevent the water from getting past the foundation in the first place. What you have on the outside of the house is damp proofing NOT water proofing. If you did, no water in basement at all. But again if you have dampness and its the result of moisture getting through the cement. What ever they used failed and should be corrected.

Once you have this corrected you can glue the foam to the walls using contractor adhesive. Be sure however that the foam is tight as any gaps on edges will cause interior humidity to reach the cooler cement wall and condense. Another method would be to apply foam to all the walls and then fasten the studs over the foam rather then to fit each piece between the studs.
Also remember. No foam insulation can be left exposed to living areas. This is for fire safety. When foam burns it gives off toxic gasses that can kill in seconds. Personally I use fiberglass beween the studs for that very reason.
Good luck

Thanks for the replies, I appreciate the information. JayinMinnesota is there a certain type of foil tape to use? If have used several kinds before to seal duct work but my concern was how well it would stick to the foam sheets. I guessing one of the thinner more flexible types? I like your idea on the rim joist using the foam I think I will use that approach. The Home Care Club LLC I will use the backer rod on some areas. Others are quite narrow (< 1/16 ") so I quess I just use caulk alone.

Again thanks!

Any tape that is used specifically for taping house wrap, tyvek makes a good one - I think I used Dupont on my last one, either one is fine. Good luck.

Instead of taping these joints could a person intentionally leave a 1/4 to 1/2 inch gap and then use spray foam to seal the gap? My understanding is that it would make a water and air tight connection between all surfaces (wall and foam board on each side.

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Preping my basement.

Howdy how are you going to deal with the added moisture into the rest of the house?
Depending on what part of the country you are in moisture is more or less of an issue. Last basement pool system i saw was fiberglass steel studs 6 mill plastic They went the extra step ov caulking all the studs to plastic so screws did not breach the water proofing. They installed a timer for exhaust fan vented outside to expell the moisture.
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