Invisible join?

joanna3293

We have joined together two pieces of MDF to create a desk, would love any suggestions to minimise the join?  I tried filling and sanding but it didnt really help... thanks!

Emmia

joanna3293 said:

We have joined together two pieces of MDF to create a desk, would love any suggestions to minimise the join?  I tried filling and sanding but it didnt really help... thanks!

A photo of what you're trying to hide would help

FreeBear

Done this once with a surface made up from two layers of 18mm MDF. Bottom layer had keyhole slots routed to take worktop connecting bolts. Top layer glued to the bottom piece. It is possible to get a near invisible join, but the edges need to be accurately cut and pulled up tight when glued together.

joanna3293

sorry, thought I already uploaded a photo, here it is

FreeBear

If you don't mind pulling it apart, a couple of things you could try. Fix a couple of wood blocks (or modesty blocks with short screws) on the underside. Use some clamps across the blocks to pull the joint together (do a dummy run or two). Once happy with the fit, apply a thin bead of Gorilla Glue to one side, and then clamp up again. Come back the following day, and scrape off any excess glue with a sharp stanley blade.

rob7475

You'll never get an invisible join on that. I'd try and redo with a single sheet.

If that's not an option, you could try adding a bevel to the two edges, then once they are glued / fixed together, use some filler to fill the bevel. After several coats of primer and paint, it will be less noticeable. 

daivid

Redo with a single sheet seems to be the best option. Or you could try a thin single sheet on top, 6mm ply perhaps, though with that you have the horizontal joins to mask (if you care) and need a means to accurately cut to the size and shape of what is already there.

ThisIsWeird

joanna3293 said:

Hi Joanna.

Q - how are these two joined? I presume the edges are at least glued - PVA'd - together, but is there also a joining strip of MDF underneath the two ends, spanning that join?

If so, ie if there is no movement, and no cracks open up, then that can simply be filled, sanded, and made invisible.

(If the two panels are simply butted, with no reinforcement, then an additional strip of MDF, say 50+mm wide, will need to be firmly PVA'd to its underside, spanning the two, and ideally screwed up into the worktop.

Once the joint is secured from movement, then you need 120 grit paper and a flat sanding block. With gentle pressure only, sand over the joint area until all the high spots have been brought down to 'worktop' level. Give the whole painted top a light going over too, to make it all the same level of smoothness. You may break through to the actual MDF at some points, but that's not a problem, but ease off the sanding pressure so you still have a smooooth finish.

Then you apply a smear of 'fine surface filler', using an application blade that spans over the joint area. Press it down, and apply at a low angle - force it into every nook.

Allow to dry.

Lightly sand again until it's perfectly smooth. Check for any 'holidays' - if there are any, then apply another thin smear, and repeat.

This should work. It should be perfectly smooth and level.

What paint did you use on the MDF top? Ideally use an MDF (or wood) primer, water-based ('quick-dry') so's it's easier for a novice (no offence...   ). Apply using a mini foam roller to get an even finish. Apply a second coat when dry.

Then very lightly go over it again with the 120 and the flat block. It should now be ready for the top coat, but check for any trace of the joint showing through.

I'd use water-based satinwood, again applied using the mini foam roller for an even finish. Don't over load the roller, roll it out evenly, and ease off the pressure as you finish it off.

If this doesn't appear to be working, then show us some close-up photos so we can work out why. It should work.

You don't need a bead along the front lip, although that's what would normally be done. Again, sand it perfectly flat, take the sharpness off the corners - lightly hold the block at 45o - and apply 2 or 3 coats of the primer, lightly sanding between coats. You should be able to get the end finish nicely smooth too.