Hey guys. I have a couple of cracks in the firewall of my 76. The longest runs about 7 inches, up the transmission tunnel. I recently bought some epoxy for SMC and some fiberglass mat material. My plan was to cut some of the material out from around the cracks, put some duct tape on the engine compartment side and then fill in with mat and epoxy. That is the proper procedure from what I have read on this forum. I wanted to know if anyone had any pics of cracks being repaired. If so, could you please email them to me at sabrooks@bellsouth.net. Also, if you can direct me to any good threads with pics, I would appreciate it. I have done a lot of research, but want to see some more pics before I start. Any other suggestions would be greatly appreciated. Thanks a lot for your time.

Shaun

 

I would need to see what you have for a crack. But this type of repair is pretty much "cut and dry" especially if the crack is still allowing the two sides to stay flush/level with one another.

Depending on the amount of contamination from the engine side ( oil and what have you) that may have soaking into teh SMC. Just grind it back on BOTH sides of your crack about 2". When grinding...grind it at an angle so where the two sides of your crack meet...it will be very thin. And then taper it back. This is so your can apply a piece of fiberglass about 1" wide...then the next layer can be about 2" wide...then the next layer will be about 3" wide and then the final layer be 4" wide. These layers will fill in your taper and make it so when the job is done...the repair patch is basically level and not be a big lump. So care and attention to the anlge of your taper is kinda important...but is not "rocket science". DO NOT taper gind it to a sharpe angle like the letter "V"...but make the taper more flatter than that but yet in the shape of a "V". The wider out you go onto your GOOD fiberglass firewall area ...the better it is for strength.

ONE TIP: IF when you grind, you get the crack so wide (missing fiberglass) that your backing tape can not successfully hold up your lamination...and it wants to buckle and flex. JUST APPLY ONE LAYER of fiberglass and resin and let it dry. Then the next day...lightly grind it so you get good adhesion and then apply your other layers.

"DUB"

Sorry, no photo's...and those I have do not apply.

 

Thanks a lot, DUB. Just to confirm, I am going to to grind a 4 inch hole in the firewall and then fill with minimal overlapping over the existing firewall? Thanks again.

 

Unless this area is highly stressed I would keep the patch narrower so I'd have to do less grinding/finishing. About 2" should be enough.

Dunno about duct tape as a backing. Sounds like a gooey mess. I use yellow bondo spreaders as resin won't stick to them and just tape them to the back of the panel with painters tape (3M, Green).

Put 2 layers of green tape on each side of the repair. After the resin sets you grind down until you hit the tape . Makes it much, much easier.

This pic shows adding to the front of the door. The piece of cardboard holds a bondo spreader behind the patch. As it's not a stressed area the contact patch is fairly narrow, only 1/2-3/4".

 

Thanks a lot for all the replies, guys. Unfortunately, after further inspection, it appears that the crack has gotten worse. In addition, there is a shorter crack approx 1 inch away from the original crack. Both of them have now spread up and around the area that holds the wiper motor... I put in new floor pans last week and I guess all the banging and manipulating caused them to get worse. I drilled some holes to try and stop further cracking. I am going to try to add a link to some photos. Please let me know what you think. I would like to try and tackle this myself, instead of sending it out for repair; however, it may be too difficult now.


Here are the pics


If the link doesn't work, here is the unlinked version:
http://s577.photobucket.com/albums/ss218/sabrooks005/

 

WRONG!!!!!!!!!

If the split/crack between the two parts of your firewall area is ...lets say 1/8" wide. TRY NOT to widen it, if at all possible. Widen it only for prep for laminating and to determine that while you are grinding the SMC away and creating your taper...that the SMC is solid and NOT flaking away when you grind.

The idea is to try to maintain as much GOOD SMC as possible and thus trying to make sure that your two sections are level and flush with one another.

NOW...with your area prepped and you tapered the area back on both sides about 2"...thus making the prepped area about 4" wide.....and NOT a 4" missing piece of SMC...that you would ahve to fill in.. You will then be ready for your laminatinig. So the further back you go from the crack...the less you have to grind away.

You want MORE fiberglass on your GOOD SMC and a less of a visible crack if at all possible....when prep is done. The more fiberlgass you apply to your GOOD SMC the better it is for strength. NOT the other way around as you stated>

"DUB"

 

Okay, that makes sense. The idea of widening the hole scared me... I am simply going to start tapering for an area to lay the new material. I'll take some pics and post. I may start on it today.

 

I looked at your photo's and I do not see a big issue here. Just prep the area and laminate it. The crack is so tight that you may be able to reduce the width of your prepped are down to 2" total width...one inch on each side of the crack. You can go wider if you choose. JUST get your taper right so you do not have any sharp edges or steps that make the fiberglass not want to lay down smooth.

"DUB"

 

Just be careful on how much fiberglass you apply at one time...IF you are laminating the crack that is up-side down...thus causing GRAVITY to cause the weighted fiberglass patch material to release and fall away from your repair. IF you have to laminate something the is UP-SIDE down. do only one or two layers and let it cure.

Vertical is not a problem...but up-side down horizontal is another.
"DUB"

 

i used cloth instead of mat. it will conform to the curves of the existing glass better than the stiffer mat, so the ends of the patch will not lift before the epoxy sets. also, do as dub suggested, and place one layer and let it set so that it acts as a form. cut several pieces of cloth and dry fit them, then paint the body with epoxy. lay the patch on a piece of plastic (like heavy drop cloth) that has been taped to the floor so it won't move, and paint the patch piece with epoxy. then lift the patch and place into position(use gloves !). it will stick even in an up-side down position. then if you want , add a layer of mat so that the surface is smoth. my current project had an engine fire and i had to repair very large sections of the firewall and the cowl area, and this technique worked well for me.

 

Just to follow up, I have started the repair. Unfortunately, I made the crack quite a bit larger than I should have. I should have stuck with the dremmel... Anyway, after "prepping" the area, I laid my initial layer of mat and then went back a few days later and sanded and added three more progressively larger layers. The repair looks great. I am going to add two layer of mat on the inside of the car to add some more strength, but I wanted to see what the experts had to say about what I have done thus far. The final pic of the exterior isn't that great, but you can tell that the layers have been added. At this point it looks like it will clean up very well. Please let me know what you think. Thanks!!!!

http://s577.photobucket.com/albums/ss218/sabrooks005/

 

sabrooks,
From your photo's of your prep and to completion, everything appeared to look fine. Personally I am glad that the crack area got a bit larger than you first though. Because adding resin and matt to it to recreate it is really not that big of a deal. AND with working room...which makes applying the resin and matt not that hard.....the repair is not going to suffer in structural integrity. GOOD JOB.

"DUB"

 

Thanks a lot DUB... as well as everyone else. There is no way I would have attempted this without the info I have gotten from this forum. You guys rock! And fiberglassing really isn't that bad!

 

Glass it on the backside, then grind out the front and glass it shut...




















All fiberglass matte and epoxy resin.