Best filler for joint between two MDF sheets

[JamieB3009]

Hi,

I have built a bulkhead above a kitchen island for extractor etc. out of MDF on a timber frame. Due to the size of the bulkhead i have had to make it out of two sheets of MDF. What would be the best recommended filler for the joint between the two sheets to make it both unnoticeable when painted and prevent cracking? I've filled the screw holes with ronseal two part but inderstand it doesnt flex much. The joint is quite tight in places but i dont really want to start raking MDF out. Any recommendations? I do have some repaircare part A & B epoxy. Would this work? Pics attached.

Cheers.

 

[Wayners]

I filled all my MDF with repair care resin. Never cracked

 

[JamieB3009]

I filled all my MDF with repair care resin. Never cracked

Cheers. Does the MDF need raking out or will it take against a gap like that? Thanks,

 

[opps]

I am a decorator, and spent many years painting mdf installed by other tradesmen.

Had it been biscuit joined and glued, it may good for years. That is clearly not the case here. Too late to do anything about that now though.

I would use a filler knife to push in a PVA type glue. Wipe away the excess. Then when dry, fill with a soft filler such as Red Devil OneTime. 2 part (polyester) fillers will push away as the MDF expands and contracts. The gap is too thin for your RepairCare.

On the balance of probability, you will find that the screw holes that you filled, the filler will push outwards, very, very slightly (might take 2-3 years though). On the upside, when you need to sand them back, they behave and stay flat. I do not understand how or why. After sanding, you will have a tiny gap that may end up being paint fill, or use the aforementioned OneTime.

 

[Wayners]

Yes. I cut joint out a bit.
They make a resin filler that don't need a primer in mastic tube.

You could v joint it and apply some CT1 type mastic or put a cover strip over the joint.
All depends on what finish you want but its a difficult product to fill so it lasts tbh

 

[opps]

I don't understand, V joints, . Reverse v joints make more sense. You have a channel that is back filled.

I would never use CT1 to fill a gap.