Subfloor replacement in a 1979 Dodge Brougham

[Randy Mancuso]

Well, I'm not only a newbie to Good Old RVs, but also to the world of RV restoration. I own a 1979 Dodge Brougham in great mechanical shape as well as good external condition. As I'm sure many of you are painfully aware of, sometimes the deeper you get into the restoration, the more damage you find, ie water damage to be exact. I pulled up eh carpeting and much to my surprise was a decaying floor at the edges extensive enough where as I chipped away at it, I was left with big holes. Well I knew very well that I would need to replace the plywood. The thing is that this is the only thing between the interior and outside (frame). I mean you look down at the driveway. Is this the way they made them? I mean with no metal sheet panels beneath the plywood? Not knowing, this seems rather odd to me. If this is normal, can I protect the new wood somehow. My reading has discovered that you use 3/4" treated plywood but can I do anything else to protect the wood. I was thinking of sealing the outside surface with Proflex brushable sealant and possibly even stapling galvanized metal to the undersurface and sealing that. In short, #1 is this the way they manufactured these things and #2 what can I do to protect it and maybe even insulate it? Thank you so much for any suggestions. I could provide pictures if you think this would be helpful. 

[Lakota Wolf]

A good all weather seal on the wood,, inside and out... and yes you can insulate below the flooring from the under side elements, and affixing galvanized sheets to protect the under side. I loosened my *belly pan and added an additional 3 inches of insulation, (after I did an inspection of my wood flooring from the outside). Made a world of difference as far as heat loss.

[Randy Mancuso]

Thanks Lakota! What type of insulation would you use and how would I affix it to the wood? Also, is Proflex brushable a good sealant?

[Lakota Wolf]

I used a stryofoam based insulation,,,, It wont collect mold and fungus, Most of the heat loss is due to wind cooling everything down and wind does blow underneath. I used a construction adhesive (mainly for foam board and pourus materail.. Im not that familiar with Proflex.. I will have to look at my records and see what I used,, I do know it was a good sealant that cured well and is somewhat pliable with temp changes.

[Rich Thomas]

My old travelcraft has a full cover of sheet aluminum underneath; you could do something like that or  something you my look into is an under coating you spray on. one in particular and the name escapes me is a compound impregnated with ceramic beads. it is a sound deaden-er and insulator you can find it on auto restoration sites. I'm thinking of doing this my self to get rid of some of the road noise. unless you plan on winter camping. IMHO insulating the underside is a costly thing to do and unless you are extremely diligent about the installation you can cause more and more serious problems down the road. The KISS method is the way to go. I will say that if you decide to insulate you can't go wrong following Lakota's  advice. His 5er has been around a long time and there's a reason for that.       

[Lakota Wolf]

I have a full belly pan on my 5th wheel..

[Randy Mancuso]

I'm going to seal the treated plywood tomorrow with West System epoxy, top, bottom, end grain, and then apply a noise dampener after the epoxy cures. Any other suggestions? Thanks.

[Rich Thomas]

Sounds like you have a plan Randy. Have fun with it and good luck with your project..

[Matthew Tritt]

Beside using the West epoxy system, saturating the plywood with 3 coats of polyurethane works as well, but is a lot less expensive. This is a method commonly used in the marine field as a cure for the lousy plywood being sold these days that's sold as marine grade. You might also consider using polyurethane foam as your insulation as styrene (stryofoam) products tend to compact with time and vibration, which diminishes the R value. Your question about what the delivered cab and chassis should have come with from the factory is interesting. My 73 Hall GTC did come with a sheet of aluminum from the factory, the 2" of foam and plywood floor being added at the coachworks.

[Erik Anderson]

Good Morning All !,  I Know I'm A Newby ?, But I Have To Suggest Sheet Aluminum As A Road & Elements Protector, Steel Rusts, Galvanized Steel Corrodes over time.  Even quicker if you Nest where Salt is used in the winter. As Far as coatings. I'll Just say this, ( I Would only use something that has a very LOW fire fuel making Potential). As Far as insulation is concerned, Go with making a system to keep the wind from under it when parked camping. ie., weighted heavy canvas with snaps (just an example, from my pop-up days).