Clamping down newly laid skin

[doug hodder]

JLaman....it may be that your ply sub surface is not a completely flat curved surface....any bubbles in the 1/8" laminates will make problems in the top aluminum coat...I laid down 1/4" ply. (luan bends fine) and then used a straight edge checking for high spots in the ply...sanded any down, filled any low spots..within reason...the adhesieve will take care of a lot of that especially using carpet adheseive....plugged the screw holes at the outer edge....but any bubble in the ply will not allow the aluminum to lay down flat...you're bending the aluminum in 1 direction...anything that is not flat on that plane will throw another curve into the aluminum roughly 90 degrees to what you are trying to achieve, (compound curve) causing problems like you have....just my thoughts on it....sorry you had a problem with it.... doug

[JLaman]

Thanks all for your interest in this aluminum skin flatness problem.

I took exceptional care in making certain the sides were plump and that the spars were perpendicular and true. I even waited a couple of weeks after installing the spars to make sure that they did not warp. One warped, so I removed it and replaced it with a straight spar before adding plywood. I layed a straight edge across each one and belt sanded any uneveness to get all spar surfaces horizontal with no irregularities. The 1/8 plywood did seem to have a slight buldge at the edges after I installed it, particularly the 2nd sheet. Plywood is more forgiving than aluminum (0.040), however, and it drew down without a problem. I am thinking now that maybe the 2 layers of 3/4 rigid insulation did not quite lay flat in the 1.5" spaces between the spars and caused the center sections to push up some. That would cause the edges of the aluminum to be above the plywood if the plywood was pushed up in the middle section. I am really hoping that the 1" x 1/2" molding with screws at 4" oc will pull the aluminum down enough to close the gap from water. I plan to do that tomorrow........ Otherwise, all is well and everything on the trailer is falling into place perfectly. After this aluminum disaster, I finished up the galley, looking for some success to end the day. The drawer fits nicely and cooler and water jug slide in just as planned. Thanks again.

[toypusher]

Make sure that you use ample 'caulk' under the trim piece. I used PL type caulk or polyurethene. A real good bead and let it squeeze out. After about 8 hours you can run a razor blade along the edge of the trim piece and then peel the excess off. You can also clean it up as you go with paint thinner and paper towels, but that seemed like alot of extra work to me at the time. Just a matter of choice, i guess. I can not vouch for it, but lots of folks use silicone cauld too.

[JLaman]

Thanks again all for suggestions. I have dry fit the 1'"x1/2" trim on both joints between the roof and sides. Remember that the 2 layers of 1/8 ply and about 1/4" gap between aluminum and plywood were exposed leaving 1/2" to be covered by the 1/2" trim. After gradually tightened down the screws for the trim in a sequencial pattern so as not to force one spot down and have another pop up and a little persuasion from the rubber mallet, it looks like I have at least 1/8" to 3/16 coverage by the trim in all places with a very tight fit. Tomorrow I will caulk and replace the trim, hoping to limit the amount of caulk that will squeeze out..... I still can't find the source of this problem even after remeasuring everything. Found a few other unconnected flaws, but nothing serious. I still suspect the insulation buldging is the culprit.

Jeff L.