What Kind of Foam

[tomelenbaas]

I tore up the soft spots in the floor of my '88 Mariah last weekend. Fortunately the problem was confined to the flooring - the stringers are all good and the engine mount lags are solid. I did remove a significant amount of the foam in order to expose more of the structure. Would "Great Stuff" insulating foam (the kind you get at Home Depot) be OK to use as a replacement when I install the new floor? If not, what is the proper foam to use and where can it be purchased.? Thanks.

[Okie Boarder]

I wouldn't use the "Great Stuff". You want something that is dense and closed cell. Here's a good foam product (http://www.shopmaninc.com/foam.html).

One thing to also keep in mind is to seal the floor real good when you put it back. Make sure you clean and grind all seams and glass/epoxy them really good. The PO of my boat didn't do this well when he replaced the floor deck and it created another entry point for water to penetrate down into the sub-floor.

[tomelenbaas]

According to Dow's website, Great Stuff is closed cell, but I can't find anything that tells me its density. The foam product you recommend looks great but its short pot life (45 seconds) concerns me. I'm only replacing a portion of the floor - about 2 square feet on each side of the engine box. What I was planning to do was to patch the floor and then drill small holes to inject the foam. (It looks like that's the way Supra installed the foam originally - when I pulled the carpet up I saw holes about 1/2" in diameter where the foam appears to have been injected.) I'm not sure how practical it will be to pour the foam in given the short pot life. I guess if I drilled a larger hole that would work. (After the foam sets I will then glass over the area, overlapping the floor I left in place. I also plan to treat the marine plywood with CPES before installing it.)

Did you install your foam after your floor was in place, and if so, by what method.

[dbennett]

I own a boat repair shop in Tn. that specializes in the older MC and Supras.I have put floor and stringers in about 80 to 90 Supras.The foam I uses has a pot life of about 5 or 6 mins.I get it from north american composite(NAC).I don't have the name of it in front of me but if you want I can get it when I go back to my shop.Thanks,Bennett's Boat Repair

[Okie Boarder]

You might check to see how closed cell it is. From what I understand you want a high 90% closed cell and I'm not sure Great Stuff is like that. FWIW, the PO of my boat added some foam in spots that looked like Great Stuff and there was a big difference between it and the factory foam.

I haven't done foam and don't plan to, but a few others might be able to give you some pointers. I would guess you would just mix it up and quickly pour it in the holes you made. The expansion of that foam seems to be quite a lot from the specs.

Good move on overlapping and I think it is a great idea using CPES. I'm using that on all my wood in my rebuild. It sure seems to penetrate well and I'm sure it really protects the wood from rot.

[tomelenbaas]

dbennett - If you can post the name and where it can be purchased, that would be great.

I'm convinced that Great Stuff is not great stuff for what I need. I did find the following foam which looks like it will fit the bill.

http://www.jgreer.com/boat-foam.htm

Thanks for all the help and advice.

[dbennett]

I will look for the name of the foam tomorrow.Thanks,Bennett's boat repair

[87SunSportMikeyD]

Thanks for the foam links

So I have a couple small (silver dollar sized) soft spots alongside my engine box. Lets say I cut them out and wanted to patch the floor and then recarpet. Oakie you are saying I should scoop out that wet foam and then proceed to reglass the entire 'compartment' that is accessable through the hole I cut to remove the rotten topeck/floor wood? Thanks.

[Okie Boarder]

Thanks for the foam links

So I have a couple small (silver dollar sized) soft spots alongside my engine box. Lets say I cut them out and wanted to patch the floor and then recarpet. Oakie you are saying I should scoop out that wet foam and then proceed to reglass the entire 'compartment' that is accessable through the hole I cut to remove the rotten topeck/floor wood? Thanks.


For that small of spots, I'm not sure I'd mess with it at all. But, if you want to just replace a small section of the floor to correct the soft spot I'd probably just do the floor and not mess with the foam. If you want to get the wet foam out, plan to cut away a foot or two along a length of that area so you can chisel out all the foam in that section, see what things look like and make a decision from there. You may need to grind and lay a new layer of glass on any nearby stringer or cross braces, then put foam back in and replace the floor section and carpet.

Like I said, I'd almost just leave it alone for such small areas. As soon as you open things up, you just created a "seam" which allows the potential for water to get down in there.

[dbennett]

North American Composite is where I get the foam.The name of the foam is Isotec part A and part B.You mix equal amounts.Thanks,Donnie