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cfsully 04-01-2010 12:32 AM

Basement Project - Grafton, MA
I wanted to share the progress, approaches and experiences as I go through my basement finishing project. My basement is about 1700 sq ft with 7.5 foot foundation walls. It has a few small basement windows and a bulkhead. there is not a lot of light and given the amount of concrete I was concerned about moisture and dampness. This moisture concern was made greater by the fact that the dehumidifier had to run non stop and was not keeping up.

To help with the moisture I wanted to use a concrete sealant. After doing a bunch of research I decided to go with Radon Seal because of the potential for both radon and moisture sealing. I had had an issue in a past house with Radon and I wanted to mitigate this if I was creating a living space even though the tested levels were below threshold at the home inspection, that had the potential to change as I seal up the place.

The Radon Seal was applied by spraying on water followed by spraying on the Radon Seal. I will say that I think it works well but I wish they added some tint to it. After it is sprayed on it is invisible and you are left wondering if you just paid $1000 for snake oil. I have seen the humidifier load decrease with just half the basement treated so far. The Radon Seal was sprayed up to the level where the grade level is and not up to the top of the foundation.

cfsully 04-01-2010 12:46 AM

Insulating the floor
2 Attachment(s)
To insulate the floor I am going with a 1 inch 2' x 8' tongue & grooved XPS. I am squirting great stuff into the joints of the Styrofoam and taping the joints using Tyvek House Wrap vinyl tape to complete the moisture barrier.

The great stuff is terrible to work with as it gives you no control over the amount dispensed and it results in a lot of mess and waste. I have ordered a foam gun and some foam from and I can not wait until it arrives. The gun has a knob that allows the foam dispensed to be controlled and it has a closed tip to allow it to remain fresh.

The technique I am using I learned from the article, "The Stay-Dry, No-Mold Finished Basement" written by Andy Engel for Fine Homebuilding. I have some slight modifications to the technique described in that article that I will discuss as I get to those phases of the project.

I am attaching a couple of images from the start of the flooring insulation.

ccarlisle 04-01-2010 06:25 AM

'RadonSeal' is a straight chemical called a silicate; it reacts with the concrete and the salts inside it to create a barrier against penetrating water. Chemical and physical barrier...however as good as it is, it must go hand in hand with measures to prevent water penetrating in the first place and that means channeling runoffs away from the foundation.

$1000 should have gotten you about 3 pails; silicates are cheap as they come from sand, I think, but sell industrially for a few bucks a pound. But a good choice. Not a final solution - but part of a plan. Good choice of reference material too.

Scuba_Dave 04-01-2010 07:27 AM

I'm guessing with all the recent rain you found out if your basement stays dry 1st :laughing:
I'm next to a small stream under normal conditions
That's a weird shaped wall - window bump out above ?
Good luck & post pics as you go along

cfsully 04-01-2010 10:23 AM

3 Attachment(s)
Thanks Scuba Dave! I saw you on the Fireblocking Thread started by TheKCTermite. I was actually researching the fireblocking approaches when Termite's thread inspired me to document this ordeal.

This corner is above a group of 3 windows on the right side of my house. I am attaching a photo. It is a poor man's semi circle. The space I hope to use as an office.

I was going to wait for the foam gun from but I had some great stuff and I wanted to get some of my techniques down in a small section of the basement before I go wild. My basement is also not empty so I will likely be building it in stages clockwise around my foundation up to the level of subfloor and studding.

Yes that was a heck of a rain storm we just received and I was blessed to get some water in at some crack points. I am glad it happened now and not after I sealed up the walls. attached is a photo of the leak at a crack near my HVAC unit. A second photo shows the water pooling on my plastic decking (no gaps) and running to a spot just to the left of the door where it looks like it was guessed it, right down to that crack.

cfsully 04-01-2010 10:34 AM


Originally Posted by ccarlisle (Post 422546)
$1000 should have gotten you about 3 pails; silicates are cheap as they come from sand, I think, but sell industrially for a few bucks a pound. But a good choice. Not a final solution - but part of a plan. Good choice of reference material too.

Thanks for your input Carlisle. I had bought the RadonSeal a year or more ago because I had wanted to be sure my basement was sealed. I think I got 6 pails for about $1100. I just checked their site and the dropped the price from $170 to $150 per 5 gal since when I bought it. They also send it by freight as opposed to standard shipping.

I used to work in liquid silicone molding and I think this stuff is just a very low viscosity RTV. Like an RTV, it uses the moisture to cure up. You apply water via sprayer to the concrete first, it soaks into the pores and then you apply the RadonSeal and it soaks into the pores as well in a moisture rich environment to lock it in place before it can flow vertically.

On the Finishing the Basement article by Andy Engel, it was the best basement article I had read in my two months of research. The illustrations were awesome as well. I got the good fortune of meeting Andy at the JLC Live show in Providence last weekend, he is a great guy! After watching his live demonstration and how he stood on the foam I have decided to not anchor my subfloor to the concrete but to leave it floating. I can get away with this because it is a good flat pour.

downrightart 04-02-2010 08:49 AM

Ohmygosh! That's awful Chris!:(

I came here to see if you had any more pics of your progress. Man, the outside of your home is lovely!:yes:

Gary in WA 04-02-2010 11:07 PM

A few small windows.......... I hope you get a permit for the finishing- if required. If only for egress:

That's great you will be finishing it here- I see someone framed a short wall with the end of the stud on the concrete (to help suck up the water leak) instead of on a treated bottom plate. And used a tiny L-bracket for a connector. It's good you'll be finishing it!

Be safe, Gary

Tomco 06-09-2010 06:48 PM

CFSully - I am finishing my basement floor the same way - foam with a plywood subfloor (but plan to just use a single 5/8" sheet vs. two 1/2"sheets). Just curious if how many tapcons you used to hold the plywood down? Given their expense, I want to minimize how many I do.

seavlad 02-04-2011 06:00 PM

any update or photos of your project?? wanting to model my plans off your real life experience

cfsully 01-14-2012 11:35 PM

Hi everyone, I am sorry for the lack of replies. I dropped this project because my work schedule got busy. So I am just now ramping it up again.

Tomco, I think it is a bad idea to use one layer of subfloor for possible stability issues at the cracks. I am using 2 layers of the 1/2 plywood 90 degrees opposed so the seems never line up. At the recommendation of Andy Engel, I decided not to screw the subfloor to the concrete. I have a relatively new home and the poured floor is fairly flat. I decided the extra time and cost of locking the subfloor down was not worth it. I have seen some articles about floating subfloors as well. If at some point it seems like I need some stability (before I lay the flooring), I will put some in at that point.

Trucon01 05-30-2012 12:51 PM

Is it wise to use Radon Seal and then go over top of it with Drylok Extreme?

cfsully 05-30-2012 12:59 PM

When I was researching it, I had looked at Drylock (not sure if it was extreme) and the Radon Seal. For me it was an either or decision, but things may have changed or you may be dealing with a different situation. I chose the Radon Seal because it talked about all the benefits of a moisture barrier and the radon protection. To me, anything that inhibits moisture vapor should also inhibit radon since they are both gases. (Not taking into account molecule size and diffusion rates)

Trucon01 05-30-2012 01:08 PM

Thanks for writing back...

I already have 5 gal buckets of drylok extreme and liked what I heard about Radon Seal as well. On the Radon Seal site, it says the surface is paintable after Radon Seal, but Drylok is more than just a paint as it expands in the gaps as well.

I'd be wondering if Radon Seal seals "deep" as they say and then Drylok would seal in behind that?

In theory, it sounds good :)

cfsully 05-30-2012 01:22 PM

In theory it does sound good, I do not see any harm that comes from it. In practice, it may be overkill and a needless expense of hundreds of dollars. I know that when I spray on the Radon Seal, it soaks into the concrete and you can not tell it is even there. I wish it had some tinting as it would make it easier to know when it is applied. In spots that I "over applied" it on the floor, it made it shinny and had a milky appearance. It seems like the Drylok Extreme would be great for applications where you are looking to paint over the moisture barrier.

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