Thread: Techniques everyone knows (except me)

Originally Posted by antiphile

After nearly 30 hours, I unveiled my repaired and now glorious piece of wood! And then watched it all pour out onto the workbench. It had well and truly set not at all. Actually, I'm sure it was less viscous than when I mixed it and put it in.

A big blob of PVA would take most likely 30 days to cure rather than the 30 hours. Hence the use of epoxy.


Peter.

PVA also tends to not sand as nicely as epoxy (it can turn into a horrible gummy mess all over the sandpaper due to heat)

Epoxy essentially turns into a rigid plastic when it sets, making it much more sandpaper friendly...and I'd hate to think how much shrinkage you'd get in a big lump of PVC as it dries out.

Epoxy is best for the bigger holes, but shellac sticks are excellent and instantaneous for smaller repairs and you can get water-clear sticks which are excellent for filling a surface blemish.

PVA is one of those products that is both over and under estimated.

Common or garden white PVA is great stuff if used within its designed purpose, but may people try using it in place of techniques that worked with the glues that it replaced.

For example, mixing sawdust ( or other matter) with hide glue, U.F. glue, or shelac works quite well as a filler...and it translates with epoxy and any of the harder crisper resins......but using PVA as an edge sealer or a filler is very pedestrian at best.

PVA is a soft plastic...that is its advantage and its drawback.

PVA never sets hard, and large volumes of it will take ages to dry and will shrink considerably.

Remember too that these days there are many types of PVA and related glues that are better in their uses than plain old 101 white glue.

OH a warning about storing PVA.....it does not like the cold, let it freeze and its buggered, it degrades variably below 15C.....the colder the more and quicker it degrades.

SO, store your PVA off the ground and away from cold places...AND buy from places where it is stored likewise.

For filling holes & voids in timber, ya best two suspects are epoxy and polyester resins.

the domestic epoxies like araldite bothe 24 hour and 5 minute are tollerable, but the higher order epoxies like West system, system 3 and Boat Coat, go off a bit harder and crisper, thus the sand better.....the preceeding 3 are also unfilled raw resins, so you can taylor you filler from runny to stiff by adding more filler.


As for filling holes and it leaking out....yeh somtimes masking tape on the other side works....but many of the resins and epoxies will disolve the glue on the tape or eak out thru very fine holes.

I have found the best option is to seal the oposite side will the same or similar glue and either thin card or heavy paper.......like paste it on like wall paper.

ya then proceed to fll the other side and sande the paper off later.

cheers