Waterproofing cardboard
 

Do you guys know any way to make cardboard boards semi water resistant? I've looked high and low for some coroplast and can't find any, so I'm doing a grille block with cardboard... and I would prefer that it last more than a couple of rainstorms.

I stumbled across some water repellant stuff for work boots... could this work? lol.

Scotch guarding cardboard? Hmmmm... that's a first for me. From my own experience that stuff lasts as long as the material its applied to so it can vary with heat, light (UV) and friction... not to mention the amount and duration of the water.

Test a small piece and put it through the ringer of simulated rain and see how it lasts.

Another option is plastic wrap around the cardboard and using waterproof tape to seal the exposed edges. The problem with this is that some water can still get in. Check frequently to make sure the cardboard isn't rotting from trapped moisture.

You can also find coroplast online through some shops like this:
COROPLAST SHEET - COROPLAST - Order Online

I attached the grill block with duct tape, so I considered layering the entire thing with tape. I don't think I have quite enough tape for that though.

A layer of fiberglass resin might do it.

you could purchase a can of tent water proofing spray, they sell it at most camping stores, worked for my tent when the plastic froze (0 degree weather) and tried to put it away. I put it over masking tape and it worked perfectly, no leaking.

I'd use polyurethane ... you might even have some on hand.

With any product that will soak into the fibers, you run the risk of warping the cardboard into a new (probably undesirable) shape.

i used cardboard once to make small wheel dams, i build them up useing pva (white wood glue) and covered them with a layer of this glue, next i painted them black useing acrylic paint. they held up quite well.

i think some sort of varnish might work well, perhaps a can and brush would work better then spraying as it would soak the cardboard and than dry, creating something similar to glassfiber.

i'd avoid any sort of tape. it will effectively protect the carboard, but if there's a tiny leak somewhere it will trap the water on the inside and the carboard will act as a sponge.

since you're doing a grillblock the card might not have to be all that rigid so perhaps something like a cereal box or similar that already has a gloss coat is a good starting point.

also some sort of greece could repell water although its nor that practical and will get dirty.

Wax works well. Not expensive car polish wax, mold release wax. You can buy it in a bucket and polish it on with a paper towel. It will work for a little while.

Really though, I would find some coroplast.

here another thing that just crossed my mind: get a plastic bag, maybe a garbage bag or something, put the carboard inside, fold the bag as closely around the card as possible, tape it tightly together ... even an external block wouldn't look to bad if done carefully.

any kind of plastic would work by itself too so perhaps some squarish PE containers from distilled water or soap, could be cut up to from some rectangles that give you the right surface... you could weld the edges together, as glue (and paint won't bond to PE) or perhaps staple them together

Boiled Linseed Oil.............Available at any hardware store. If necessary thin out 20% with paint thinner. Downside is that tape will likely no longer stick to it until it cures which can take several days.