Undercoating and Wood Weights…Questions and Answers

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Undercoating and Wood Weights…Questions and Answers

Postby cracker39 » Mon Feb 13, 2006 5:54 pm

First, the questions:

I went to HD today to buy flooring, framing, and template lumber, and while there, I looked at roof coatings. They have so many that I came away unsure of what is being used to coat the underside of the floors. I saw several types, including:

Gardner Fibered Roof Coat, $5.99 per gal.
Wet R Dri All Weather Ruberized Cement, $5.89 per gal.
Perectrex Rubberized Roof Patch, $8.47 per gal.
Kool Seal Elastomeric Roof Coating, $14.94 per gal.

Who has used any of these and how well does it seal? The first 3 are troweled on, and the last looks like it can be rolled. I used Elastomeric paint on my block walls of my house, and it is fantastic. I still plan on putting an application of eurothane varnish on the bottom and edges of the floor before the undercoating anyway. AFter construction, I'll varnish the interior side of it before putting down vinly flooring.

Now, the answers:

I have charts for wood weights, and the ¾” plywood says 75 lbs per sheet. I weighed a sheet of ¾” B/C that I bought, and it weighs 87 lbs. I weighed 3 sheets of 5mm moisture resistant luan and they weighed 56 lbs, or 18.66 lbs per sheet. I weighed three 1x10s (spruce) and they computed to about 1.5 lbs per sq ft. This may be of interest to anyone estimating their trailer cabin weight before or while building. I had the luan and ¾” framing lumber estimated heavier and the ¾” lighter. Over all, these actual weights put in to my spreadsheet reduced my estimated weight a little, mostly by the reduction in weight of the framing as the plywood differences almost canceled each other out.
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Postby derekxcole » Mon Feb 13, 2006 6:00 pm

I built a basic utility trailer and coated the underside with 2 coats of roof tar and its worked great.
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Postby cracker39 » Mon Feb 13, 2006 6:10 pm

I think that the first 3 products I listed are considered "roof tar". Did yours just say roof tar on the can?
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Postby mikeschn » Mon Feb 13, 2006 6:19 pm

This is what I used...

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Postby sid » Mon Feb 13, 2006 6:40 pm

The Kuffel Creek plans call for Asphalt Emulsion which I purchased at HD. It's made by Henry and I brushed it on. I put on 2 coats because I had plenty of time, and it seemed to cover good.

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Postby critter » Mon Feb 13, 2006 7:18 pm

hey cracker,
i can tell you what not to use,thats auto undercoating,i coverd the bottom of mine with fiberglass resign witch worked out great then with undercoatin and it scraches off real easy.it works ok just easy to nock off.i will put the same stuff your going to use on for final coat just to make extra double shure on no mosture getting in. :thumbsup:
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Postby Jim Marshall » Mon Feb 13, 2006 7:31 pm

We used the liquid asphalt with fiber on ours. We coated it really heavy, installed our styrofoam insulation while it was still wet and put a coat over the insulation. I don't think it will let any water in at all. I wouldn't use the Kool Seal Roof Coating. I have used it before and after a while it will peel off, especially if it gets any moisture under it at all, at least it did on our 24 foot camper.

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Postby Ira » Mon Feb 13, 2006 8:10 pm

The Gardners is the one I (and Tom) used. Don't know about the others, but the Gardners is exactly the kind of "product" that the Kuffel plans are calling for here.

Not saying it's the best, but it's dang cheap, and I thought it was a pleasure to apply.

And yes, others have called me nuts for this, but the smell didn't bother me one lttile bit either.
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Postby Steve_Cox » Mon Feb 13, 2006 8:27 pm

Ira wrote:The Gardners is the one I (and Tom) used. Don't know about the others, but the Gardners is exactly the kind of "product" that the Kuffel plans are calling for here.

Not saying it's the best, but it's dang cheap, and I thought it was a pleasure to apply.

And yes, others have called me nuts for this, but the smell didn't bother me one lttile bit either.


Dale,

I used Gardners too. Cause the other guys did. I too didn't mind the smell, wife hated the smell. I had it in the garage so she could smell it for about 3 days. Cured out pretty good won't come off easily.

Steve 8)
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Postby derekxcole » Mon Feb 13, 2006 10:06 pm

cracker39 wrote:I think that the first 3 products I listed are considered "roof tar". Did yours just say roof tar on the can?

It was just some old stuff that I had in the garage. Me and my dad found it in his old house. Quite old but it did the job.
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Postby cracker39 » Mon Feb 13, 2006 10:11 pm

The Gardner Fibered Roof Coat is cheap at $5.99 per gallon. If I remember correctly, it said to trowel it on. I thought all of you brushed on your asphalt coating. I'll ask of they have any other asphalt emulsion in another section.
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Postby doug hodder » Mon Feb 13, 2006 10:18 pm

Good work on putting the numbers together on the wood...I tried to do some of that, but found that the moisture content on some of the materials made it hard....It's not uncommon to pick up a piece of plywood and the moisture content is way up in it...at least out here in Ca....same thing for 2x material...on this tear..I ripped up all the cross members and put them into pipe clamps and stickered them all and set them in front of the wood stove for a couple of days first...hopefully that will stop any distortion on them once I start putting them into the ceiling...Doug
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Postby cracker39 » Mon Feb 13, 2006 10:58 pm

I don't know if my 3/4" plywood has high moisture content that makes it so heavy. I do know that I've picked up 2x4s that felt like they weighed as much as a half a pound different due to moisture in the wood. That's especially true of treated wood. I hate to think what my 5' x 9' floor will weigh and how I'm going to turn it over for coating by myself (that floor will weigh about 125 lbs before it gets coated). Oh well...where there's a will, there's a way, and I'll find it.
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Postby Tim Greiner » Fri Feb 17, 2006 1:28 am

Dale-

Wood weights differences are more than just moisture content- species is a big factor. The density of your spruce is right where my book says is correct for Eastern spruce. You didn't say what the ply is made from but Southern yellow pine is a good guess. It tends to be denser than say Doug Fir that we have out here in the west. Think of how light balsa is, going up through cedar, cottonwood, hemlock, most softwoods, most hardwoods, then oak and ending with ironwood(doesn't float). Southern yellow pine when freshly cut sometimes sinks if the moisture content is high. Lots of other properties vary, too- strength, rot resistance, etc. If you're confused, find a good lumberman and pick his brain for the application you have in mind.

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Postby cracker39 » Fri Feb 17, 2006 5:35 am

Tim, you're right about our plywood. Most of the building plywood we buy here is yellow pine. For my trailer sides and top, I had a choice of Luan (moisture resistant), cabinet grade oak or poplar, or an inported hardwood plywood called Sanderply. The Sanderply didn't have as smooth a finish as the others and cost more than the Luan. I picked up 8 sheets of 1/4 or 5mm oak ply being cleared out at about $9 per sheet, cheaper than the luan, and will use 6 of them for my sides. I'll get the moisture resistant luan for the rest of the exterior.
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